Ways To Travel Faster Than Light Without Violating Relativity

StartsWithABang writes: It's one of the cardinal laws of physics and the underlying principle of Einstein's relativity itself: the fact that there's a universal speed limit to the motion of anything through space and time, the speed of light, or c. Light itself will always move at this speed (as well as certain other phenomena, like the force of gravity), while anything with mass — like all known particles of matter and antimatter — will always move slower than that. But if you want something to travel faster-than-light, you aren't, as you might think, relegated to the realm of science fiction. There are real, physical phenomena that do exactly this, and yet are perfectly consistent with relativity.

Comments

faster than light never violates Relativity

[catmistake]

Nothing can go as fast as light. Slower or faster, sure, but not c.

Re:faster than light never violates Relativity

[catmistake]

Relativity requires that nothing can move through space faster than light.

Relativity requres that nothing can move through space as fast as light (c). Nothing with mass moving slower than c can reach c by moving faster, due to increase in mass and infinite energy required to reach c, and nothing moving faster than light can slow down to c, for the same reasons. The quote from teh article is at best misleading and at worst, false.

Re:faster than light never violates Relativity

[circletimessquare]

we have no technology remotely capable of this, but:

1. a quantum entangled version of yourself moves away from you (at "normal" speed, less than c)

2. say... many light years away (i know, i said we have no technology remotely capable of this, bear with me here, just a thought experiment)

3. the "copy" of you can't violate c, but at the last moment, one version of you interacts with its surroundings, collapsing you to that single copy. such that you have achieved instantaneous transportation across light years of distances

doesn't that happen faster than c?

Re:faster than light never violates Relativity

[Anonymous Coward]

Try reading the article, numbnuts, you might learn something. It gives several real and concrete examples of things that travel faster than light.

Re:faster than light never violates Relativity

[Anonymous Coward]

gravity called ...

Re:faster than light never violates Relativity

[catmistake]

You're at a very straight, very long beach. Imagine parallel waves striking the shore at a vanishingly slight angle. The point that the wave meets the shore moves along as the intersection of wave and beach occurs. As the waves get closer and closer to parallel with the beach, but not quite parallel, eventually that intersection point will be moving much faster than c.

But the interesection point between waves and shore doesn't have mass, isn't really a "thing" that's moving.

Re:faster than light never violates Relativity

[Anonymous Coward]

No, because it also collapses your frame of reference to a single frame. You haven't moved at all. Photons don't know they are moving at the speed of light.

Re:faster than light never violates Relativity

[Guildor]

Well, when you consider black holes, that even light can't escape, it's possible the light on the event horizon could take an almost infinite time to reach us. So light is not exempt, as the article states in a way. But let's consider the opposite, if light enters the event horizon and sling-shots around the black hole, would it escape at no more than the speed of light?

It's all nonsense really. Einstein postulated something that's feels right to most people, but isn't actually correct, but holds true enough for most everyday physics. Some decent radio / electrical engineers who are on to Nikola Tesla's real works, as described in more detail through people like Steinberg, and nowadays (supposedly) crack-pot Eric Dollard, question what's possible, and we begin to see how reality isn't what we think it is, and neither is electricity. We learn that it makes more sense to think of two sides to space/time - time/space, that when we see energy appearing and disappearing in our reality, where there is zero time between the distances between the point the energy comes into and then out of existence in our reality, we should pause to consider! At least, that's how I remember it. I could be completely wrong, and no doubt most would think so.

Yet still, the mentioned phenomena has been demonstrated and documented, and to this day, still not explained by Einstein's relativity.
We live in a world ready to break new grounds, in research, yet too afraid to do so, for fear of failure as a minimum.

One last thing, I remember listening to a discussion about gravity, and how this can't act at the speed of light, but needs to be much closer to instantaneous for the distances it has effect. If we knew what gravity is, and how it's formed (current theories don't satisfy) then we'd really begin to move forwards on the FTL discussion.

Re:faster than light never violates Relativity

[Anonymous Coward]

I once saw a picture of Famke Janssen from an 86 Vogue editorial that made me ejaculate fast than c.

Does that count?

Re:faster than light never violates Relativity

[circletimessquare]

that's an excellent analogy, thank you

and you are correct, there's no real movement, only a collapse to a single frame of reference

however, for the intents and purposes of outside human observers, haven't you instantly blinked across light years?

Re:faster than light never violates Relativity

[towermac]

Height, width, depth, time, ... and gravity. Gravity is not a force, it's a dimension. It might be more accurate to say it is an attribute of dimensions.

In any case, it travels nowhere; it was already there. So there is no speed of light, or speed of anything concerning gravity.

That doesn't violate relativity in any way. If they find a gravitational quanta, then I'm wrong. They won't.

Re:faster than light never violates Relativity

[Antique Geekmeister]

Except that according to general relativity, gravitational _waves_ also are limited to C. As long as people confuse the current state of the system and what are basically "phase velocity" of changes in that state with the limitations of the "group veolocity", which is limited to C, we'll continue to see this sort of confusion.

Re:faster than light never violates Relativity

[circletimessquare]

yes, only a collapse to a single frame of reference according to physics

but, for the intents and purposes of outside human observers, haven't you instantly blinked across light years?

it's a legalistic, semantic cheat, but... it "works"?

Re:faster than light never violates Relativity

[Maritz]

You can only transmit random information with this method. You can 'instantly' know the state of the entangled partner, many light years away, but their spin will be 50% one way and 50% the other. So yes you can transmit random noise faster than light. ;)

Re:faster than light never violates Relativity

[Anonymous Coward]

Completely untrue.

Re:faster than light never violates Relativity

[Anonymous Coward]

Away with your sophistry! Your angles, and parallels and intersections! When will you geeks come into the 21st century and present your ideas as sensible powerpoint presentations!

-- Yours, Management.

Re:faster than light never violates Relativity

[Anonymous Coward]

It's also wrong in certain aspects, e.g. light always moves always at c, no matter through which medium it travels. It just takes a longer path sometimes than we would naively think.

Re:faster than light never violates Relativity

[circletimessquare]

isn't quantum entanglement a burgeoning field in quantum cryptography?

http://en.wikipedia.org/wiki/Q...

quantum key distribution would not be researched if what you say is true

Re:faster than light never violates Relativity

[sycodon]

What it really forbids is the transfer of information or objects through space at a speed greater than that of light in a vacuum.

What was the point of all this? Did anyone ever express an interest in FTL that did not include information or objects?

I want the last 5 minutes back please.

Re:faster than light never violates Relativity

[Roger W Moore]

Relativity requres that nothing can move through space as fast as light (c).

Not correct - light moves through space as fast as light. Nothing can move faster.

nothing moving faster than light can slow down to c

Actually it is stronger than that - nothing moving faster than 'c' should exist because of causality. If something moving faster that 'c' exists then then some inertial frames it will be propagating backwards in time. We could then use whatever it is to communicate with the past and set up all sorts of nasty temporal paradoxes.

Re:faster than light never violates Relativity

[bobbied]

I want the last 5 minutes back please.

Not until you violate the cosmic speed limit and go back in time..

Re:faster than light never violates Relativity

[bobbied]

Relativity requres that nothing can move through space as fast as light (c).

Not correct - light moves through space as fast as light. Nothing can move faster.

I've seen rumors that did....

Re:faster than light never violates Relativity

[NotDrWho]

"Yeah, but WORMHOLES!!"--which to me sounds an awful lot like the secular version of "Yeah, but MAGIC!!"

Re:faster than light never violates Relativity

[Immerman]

Actually, correlated random noise is extremely useful for cryptography. At its simplest, Alice takes their noise as received, Bob takes the inverse of their received noise, and since the noise source is entangled they are then guaranteed to have the same noise, which can be used as an encryption key, or even a one-time pad.

Re:faster than light never violates Relativity

[circletimessquare]

i get it: they are guaranteed the same white noise, which is fine for encryption purposes (and know if someone snooped, because that would render their white noise dissimilar)

but there is no preserving the integrity of a particle/ wave for transportation purposes

thank you, i learned something

Re:faster than light never violates Relativity

[Anonymous Coward]

Meh, thats really not true.
Having no mass light travels at infinite speed.
Knowing this is as simple as understanding the basic principal of opposite reactions.
If a known force pushes two objects away from each other those objects will travel based upon the force divided by the mass. The mass of light being 0 means any force causes light to travel at speed infinite.

Light instead travels at infinite speed limited by the progression of time. Time only allows information to spreed at the speed of C.

Re:faster than light never violates Relativity

[ultranova]

Nothing can go as fast as light. Slower or faster, sure, but not c.

Every massless thing not only can, but must, go at c. That's the very reason light does.

Re:faster than light never violates Relativity

[fahrbot-bot]

You're at a very straight, very long beach.

But, I'm in a maze of twisty little passages, all alike so I think I'm screwed.

Re:faster than light never violates Relativity

[Anonymous Coward]

It is pitch black. You are likely to be eaten by a grue.

Re:faster than light never violates Relativity

[Just Some Guy]

Similarly, open and close a pair of scissors. Notice that the point where the blades meet moves a lot faster than the blades themselves.

Re:faster than light never violates Relativity

[towermac]

Wow, you sort of got that all wrong.

First off, light does have mass. Everything that exists has mass. How would a solar sail work if light has no mass?

You might have meant rest mass, but even so, you're still fairly wrong.

Good thing you posted AC.

Re:faster than light never violates Relativity

[Anonymous Coward]

Yeah but the only other massless particles than the photon are gluons, and they're always confined inside hadrons, so photons are the only thing you can ever actually observe going at light speed.

Re:faster than light never violates Relativity

[Anonymous Coward]

the truth is probably simple, some string attaches to both and goes into a dimension that is CRUNCHED into a much much smaller space.....thus it can appear to go thorugh this to the other entagled particle and APPEAR to do as you say....its not violating anything jsut the way things prolly are. WE JUST have as yet been able to see this dimension or prove beyond my example that it exists....it might also explain dark matter and energy as well...if you let your mind fly with the idea.

Re:faster than light never violates Relativity

[UnknownSoldier]

> Relativity requres (sic) that nothing can move through space as fast as light (c)

That is not entirely accurate.

Worm holes allow you to travel between points A and B; the Euclidian distance which means your effective velocity was/is significantly faster then 'c'.

--
First Contact is coming 2024. Are you ready for a new paradigm?

Re:faster than light never violates Relativity

[TopherC]

I think you've stated the main argument about stuff moving faster than c. But more abstractly, consider two events that are separated in both space and time, A and B. Let's say A happens first and "causes" B. Maybe A is "someone throws a ball" and B is "someone catches it." Or perhaps A and B could be sending and receiving a communication. In any case if B is outside of the light cone of A, meaning that light or anything slower could not travel from event A to event B, then there is a reference frame in which events A and B happen at the same place. But when you "boost" into this frame of reference, you'll find that B happens before A. Faster-than-light communication implies that effect can precede cause. Maybe that could be true, but regardless that's what we're up against. Part of this is a conceptual difficulty: the nature of space-time is slightly more complex than our intuition allows for. A better intuition might involve a different definition of "now" that is dependent on where you are in space. Your "now" is a little behind mine, and vice-versa. Or something like that.

Re:faster than light never violates Relativity

[david_thornley]

This would appear to run into the problem that quantum entanglement can't transfer anything FTL.

Also, when two particles are quantum entangled, they need to be kept from undergoing any changes that would break entanglement. Make another human body, quantum entangle it somehow, and how long is that entanglement going to last during normal living? I'm not real happy about being kept in stasis for five hundred years so the quantum entanglement doesn't collapse earlier.

Re:faster than light never violates Relativity

[david_thornley]

Light has energy and momentum. It does not have rest mass, and physicists usually use "mass" to mean rest mass nowadays.

If light had positive rest mass, it's fairly easy to show that, to travel at the speed of light, it would require infinite energy.

Re:faster than light never violates Relativity

[micahraleigh]

Space can move faster than light.

(Not a joke: it's different than nothing)

Re:faster than light never violates Relativity

[Pikoro]

I realize that this is a very simplistic explanation, but think of quantum entanglement like this:

You have 2 cubes. Each cube can be only either blue or green. You have no idea what color each cube is as you packed them into boxes for mailing across the galaxy in a completely dark room. They are then mailed.

Now, you open your box. Turns out that your cube is green. You instantly know that the other cube is blue, even if it's on the other side of the galaxy, however, you have no way of communicating your discovery to the other party.

You now have instant knowledge of what color the remote cube is, but no information has been transferred.

Simple enough?

Re:faster than light never violates Relativity

[Anonymous Coward]

Photons have mass

Re:faster than light never violates Relativity

[circletimessquare]

yes, agreed. the idea of keeping anything larger than an atom entangled for anything longer than a second over any distance over an inch seems like a colossal almost impossible task with today's technology

i was only doing a thought experiment

in the realm of way out there then: i wonder if you could entangle a number of "copies" of yourself: dozens, hundreds, millions

you just sort of disperse throughout the universe (not interacting with anything, i know, basically impossible by today's standards)

but in an instant, if you, or someone outside, decides one "copy" of you should be the one that coheres at a given place: boom, you're there

just an interesting thought with interesting ramifications- you (or someone else) doesn't have to decide out of dozens or maybe thousands of destinations... until the very last moment. that's a pretty exotic form of "travel"

Re:faster than light never violates Relativity

[dak664]

Yes, the direction of the time axis is as observer-dependent as is the rotation of spatial axes. In Cartesian geometry the distance (dx, dy, dz) between points depends on the choice of coordinate system, but the length of that 3-vector is always the same (compared to the distance between some reference pair of points)

Similarly in space-time it is only the length of the 4-vector between events A and B that can have any physical meaning. This length can be positive, negative, or zero. A positive length means the events are outside each other's light cones ("space-like"), thus have no causal influence on each other. A negative length ("time-like") means each could have participated in the events leading up to the other.

A zero-length ("light-like") means there is no event separation between the two, i.e. they are the SAME EVENT (this might be understood as length contraction in the direction of motion going to zero when v=c). All the points on A's light cone (which includes B) are the same event as A. All the points on B's light cone (which includes A) are the same event as B. So far there is nothing to determine the direction of time, and indeed the physics describing the transfer of action when v=c is symmetric with time.

But there are points Z on A's cone not on B's cone and these are also part of the same event AB even if they also have space- or time-like separation from B. Even if nothing can interrupt the ZAB event, the direct ZB distance could be time-like and thus set a direction of time, B before A. If B was a causal factor for A, it is difficult to see how ZAB could not be affected by the the direct BA interaction. It seems to me, here is the collapsing wavefunction. The only way I can reconcile it, is to introduce some time average long enough to allow all these paths to interact.

Re:faster than light never violates Relativity

[schlachter]

must I do it with a pair if scissors, or can I just use one?

Re:faster than light never violates Relativity

[circletimessquare]

i get it

so "he went to alpha centauri"/ "he didn't leave at all" isn't known until you interact

there's no guaranteeing you go anywhere

schrodinger's rocket ship

Re:faster than light never violates Relativity

[Just Some Guy]

It would be hard to do it with just one, but scissor blades almost always come in pairs, hence "pair of scissors".

Re:faster than light never violates Relativity

[Anonymous Coward]

Relativity requires that nothing can move through space faster than light.

Actually, light moves through space as fast as light ;)

Re:faster than light never violates Relativity

[Anonymous Coward]

You're at a very straight, very long beach. Imagine parallel waves striking the shore at a vanishingly slight angle. The point that the wave meets the shore moves along as the intersection of wave and beach occurs. As the waves get closer and closer to parallel with the beach, but not quite parallel, eventually that intersection point will be moving much faster than c.

But the interesection point between waves and shore doesn't have mass, isn't really a "thing" that's moving.

It's similar to the old riddle that shadows can move faster than light. Imagine a bird flying along the equator at noon, its shadow moving over the ground. Then the bird flies over a wall that is almost, but not quite completely vertical. The shadow of the bird will 'move' over the wall faster than the speed of light.

Re:faster than light never violates Relativity

[MrBigInThePants]

This is a gross oversimplification and has been misleading people for decades.

When communicating velocity for practical purposes we always do so in terms of relative velocity with a common frame of reference. We do this because to do otherwise is utterly ridiculous.

It is perfectly "legal" to travel at relative velocities faster than C - even if your starting relative velocities were zero. Now I understand and I assume you know: as you accelerate towards C, wierd things happen to the frames of reference of the traveller and external observer. But this really is irrelevant for practical purposes.

The important point is that to YOUR OWN measurements as taken BEFORE the trip, you travelled faster than the speed of light. This is the common and practical frame of reference that we would use to communicate our velocity. i.e. This was 100 LY away and I covered it in this amount of my time so I travelled at...

THAT, my friend, is what counts here for practical purposes of travel - as opposed to the esoteric world of the theory.

What many here are suggesting (practically speaking) is metaphorically akin to taking a velocity reading of your own body while sprinting on a supersonic jet and concluding you are travelling 6 km/hr as relative to the jet.

And it is a stupid thing to tell the average person because they fail to see the value in jet travel (durrr...I could never run to Paris!). (which is what has happened with space travel)

Re:faster than light never violates Relativity

[Anonymous Coward]

No. That's not quite how quantum entanglement works.

It's a bit more like a pair of boxes that contain the same book. If you open both of them at once, you're not blinking the book across instantly. The book exists in both locations at once, but cannot be seen until the box is opened.

As far as we are aware, quantum entanglement is like a pair of dice that are guaranteed to have the same result after you roll them once. We don't actually know for sure if the roll is random, because cannot break the mechanics of the dice into separate components (which is why the mechanics are "quantum").

Re: faster than light never violates Relativity

[Anonymous Coward]

You've now posted this same thing about jet travel twice in this conversation. What in the name of Dog are you talking about?

Oh and continuing to state that FTL is easily possible doesn't make it so.

Re: faster than light never violates Relativity

[MrBigInThePants]

I never said it was easy at all. I said that it was not theoretically impossible at all in practical terms. Also that the the above simplification leads people who don't understand the theory to assume it is impossible.

This is a huge difference which you are wilfully ignoring in your desperation to construct a straw man to burn at the stake.

Just because you cannot understand something, does not mean it is rubbish.

Re:faster than light never violates Relativity

[Mal-2]

Even simpler, you point a laser pointer at the sky, and sweep it manually over a very distant target (bigger than the moon, but further away as well). Clearly your hand is not going to move faster than light, but the point where the beam finally hits something very well might. Again, this intersection is not a "thing", and cannot be used to communicate faster than the speed of light.

Re:faster than light never violates Relativity

[Anonymous Coward]

On that subject, we (Swedish , archaic) call the bladed (iron age / Viking age) weapon with one edge and a primitive point a "scissor" ("Sax"). And a "scissor" (the weapon) has roughly the same shape as one of the blades of a pair of scissors.

My question is, is this weapon I'm describing also called "a scissor" in English (archaic)?

Re:faster than light never violates Relativity

[Anonymous Coward]

Darkness goes as fast as the light.

Re:faster than light never violates Relativity

[david_thornley]

If you make lots of copies of me, and distribute them around a large chunk of the Universe, then why do I care which one was the original (figure that the me on a given planet owns my stuff that happens to be on the planet), or which one somebody specifically wanted to instantiate? This doesn't carry any FTL information, and frankly I'm not sure what you want here.

Re:faster than light never violates Relativity

[CanEHdian]

But more abstractly, consider two events that are separated in both space and time, A and B. Let's say A happens first and "causes" B. Maybe A is "someone throws a ball" and B is "someone catches it." In any case if B is outside of the light cone of A, meaning that light or anything slower could not travel from event A to event B, then there is a reference frame in which events A and B happen at the same place. But when you "boost" into this frame of reference, you'll find that B happens before A. Faster-than-light communication implies that effect can precede cause.

Suppose there's a game of FTL baseball. I'm sitting in the audience, and in my peripheral vision the guy next to me get hits by a ball literally coming out of nowhere, while I'm looking at the bat swinging towards that same ball on the other side of the field... it hits and the ball vanishes (say enters Hyperspace). That doesn't mean the impact of the ball happened before the hit, I just saw it happen before the hit because photons coming from the ball next to me reach my eye faster than the ones from the ball being in play across the field. So I know the result of the hit before I see it happen. There's nothing wrong with that.

Now also suppose we can "rewind" the entire universe, and replay the entire event, while you can be a ghost present at any location in Realspace and experience events like you've always been there. Say there's a "ghost" of me sitting right at the other side of the field. Looking through the ghosts eyes, the bat hits the ball, the ball vanishes, then rematerializes hitting the guy -- a lot sooner than expected but not before it vanishes. The ghost can see it no sooner than a photon hits the ball and travels back to the ghost eye. Rewind and put the ghost smack dab in the middle, the ball vanishes and appears hitting the guy at almost the same time.

Finally, you can be the ball... you're actually a 360 degree camera that can take Realspace snapshots. That bat swings towards you, then bang! Looking back, you can see yourself, in the past. The bat is just about to hit you. And the next snapshot is a little bit further in the past as you're farther away from the bat about to hit you. It looks like time is going in reverse. Then you pop out of Hyperspace, hit the guy, but looking back time reverses again and is back in forward. You see the bat swing, hit you and see yourself vanish. Then you can see yourself, just a few times and for minute fractions of seconds, as you get closer and closer when you took those Realspace snapshots.

Re:faster than light never violates Relativity

[Agripa]

Even simpler, you point a laser pointer at the sky, and sweep it manually over a very distant target (bigger than the moon, but further away as well). Clearly your hand is not going to move faster than light, but the point where the beam finally hits something very well might. Again, this intersection is not a "thing", and cannot be used to communicate faster than the speed of light.

A Tektronix 7104 oscilloscope can sweep its electron beam across the CRT faster than the speed of light:

https://web.archive.org/web/20...

The Soviets made some oscilloscopes which could do this also but they used very long CRTs.

Re:faster than light never violates Relativity

[Anonymous Coward]

The Poincaré group, the symmetry group of Minkowski space, has one free variable, the speed of a massless particle.

Photons are expected by particle people like you to be massless, and that holds up pretty well under experiment. They should therefore move at c. Despite the history of relativity, for many modern relativists photons moving at c have in some sense been demoted from postulate to (useful! happy! desirable!) coincidence.

In curved spacetime (i.e., not Minkowski space), the Poincare symmetries are exact only in the limit as spacetime regions go to zero. There are extra global degrees of freedom in curved spacetime. (Additionally, comparing speeds in the GR limit outside the local section of the fibre bundle is somewhere between fraught and pointless).

So in GR we test for local violations of Poincare (or more restrictively Lorentz) invariance, since the invariances are ENORMOUSLY violated at cosmological scales by, for example, the metric expansion of space (i.e., we are actually in a very strongly curved spacetime, although curvature close to us is small, and in particluar small enough to be negligible for many experiments involving approximations of test particles, but not for experiments in, say, (missile) ballistics, where one is likely to think in terms of Newtonian gravity rather than geodesics through actually curved spacetime).

Unlike the Minkowski tensor, the Einstein tensor (along with its close relatives) is fine with a democracy of causal cones that are wider or narrower than the null one in SR. SR is maybe deformable, or there may be room for a dual under the Klein Erlanger programme, or perhaps a Wilsonian fix as we have in semiclassical gravity.

Finally, we can already show in numerical GR that many "nasty temporal paradoxes" are simply initial values surface problems; some types of backtracking-timelike curves are becoming less frightening in practice (they get studied for a variety of reasons).

Re:faster than light never violates Relativity

[Anonymous Coward]

Every massless thing not only can, but must, go at c.

... in a spacetime region where the Minkowski tensor describes every point.

(We don't really live in such a spacetime especially not at cosmological scales, and we usually ignore the fact that massless things are much easier to boost onto less curved geodesics than massive things. Go outside right now and you can "throw" photons to infinity from your fingertips, but you won't be able to throw a baseball from your fingertips onto a geodesic that will not curve back to Earth's surface somewhere within a few billion nanoseconds and a few metres. The reason is not dominated by the atmosphere...)

Medium.com Alert!

[weilawei]

Danger Will Robinson, Danger! This article doesn't actually provide what its title claims. Clickbait, pure and unadulterated. Plus, it's not even that informative. All stuff we see in Slashdot comments any time anyone mentions FTL travel.

Re:Medium.com Alert!

[sectokia]

Terrible click bait, doesn't mention a single way to go faster than light. Most nerds would already know all of this.

Re:Medium.com Alert!

[Intrepid imaginaut]

Yeah by the standards of this article sound waves travel faster than light, at least if you're talking about their speed when passing through a sheet of tin.

Re:Medium.com Alert!

[DigiShaman]

Well, in that case, this article proves that least bullshit can be accessed at the speed of light.

Re:Medium.com Alert!

[Jason Levine]

This means we've already got a plentiful source of fuel to go faster than light: Politicians! I *knew* there had to be some reason we have them.

Re:Medium.com Alert!

[Anonymous Coward]

That's not fuel! Get enough politicians together, and the universe goes supercritical. Do you want to invoke a cosmic rebirth? None of us will live through the process.

Re:Medium.com Alert!

[Skarjak]

Since when do we get all these medium.com articles? Nowadays I just skip the story when I see it's from their website. Did an editor cofound it or something?

Re:Medium.com Alert!

[ortholattice]

Much better is the KentuckyFC guy who scours arxiv.org for interesting NEW physics ideas, discoveries, and speculations. https://medium.com/the-physics... Some of his stories were posted on slashdot in the past, but it seems this StartsWithABang guy has replaced him. So now I just go there directly.

Re:Medium.com Alert!

[ortholattice]

It seems he also has more general (including non-physics) arxiv.org highlights that seem to be updated more frequently: http://www.technologyreview.co...

Re:Medium.com Alert!

[dmatos]

With a bit of creative interpretation, it does. For example, you could mimic the beta-decay electrons in nuclear piles:

1. Start out traveling at almost c.
2. Slam into a medium with a refractive index > 1.

For a brief period of time, while your body is being vaporized by the impact, and before Cherenkov radiation robs you of your kinetic energy, you will be traveling faster than light.

Re: Medium.com Alert!

[AvitarX]

I don't have htth you insensitive clod

Re:Medium.com Alert!

[Anonymous Coward]

phase velocity of light != speed of light

Re:Medium.com Alert!

[slashmydots]

Wait, are you saying you didn't like when they said, and I quote, "When those electrons travel through the coolant (water) surrounding the reactor they travel faster than light can travel through the water, thus breaking the light barrier."

Re:Medium.com Alert!

[Anonymous Coward]

Quantum suicide my friend. Quantum suicide. Don't let the madness grip you.

Re:Medium.com Alert!

[Anonymous Coward]

you will be traveling faster than light.

Light, the particle, always travels at c. Light, the particle, will impact with other particles in a non-vacuum, and be absorbed, delay a bit, and then a new particle will be emitted. Light, the wave, behaves as if it is traveling at something less than c, as the particles constituting it are repeatedly absorbed and emitted by the medium it is traveling through. Light, the wave, behaves as if it is being turned, as the delayed emission of its constituent particles interferes to produce a wave front at a different angle.

So no, you're not traveling faster than light. You're traveling faster than one peculiar characteristic of light.

With a very bad definition of travel

[Anonymous Coward]

Yes. And it's very possible to create a perpetuum mobile. Just charge your phone all the time. It doesn't generate energy and it doesn't run forever though.

Easy!

[Anonymous Coward]

Make the Law of Relativity Obamas fault, then the Republicans will repeal it, Pandora here we come!

Re:Easy!

[bobbied]

Whish that would work for the 2nd law of thermodynamics.... No THAT would be something...

thanks. On to the next article

[Anonymous Coward]

Nm

Light speed

[ArcadeMan]

The fact that there's a universal speed limit to the motion of anything through space and time, the speed of light, or c. Light itself will always move at this speed.

Except, you know, cases where we slowed down light itself. By a lot.

Re:Light speed

[ArcadeMan]

One way is to note that the immutable speed of light only applies to light in a vacuum. When light travels through a material, its effective speed is reduced.

Burn! /Michael Kelso

Re:Light speed

[Anonymous Coward]

When you say the speed of light as "c" usually you mean the speed of light in a vacuum...
Also when we measure "speed" we aren't measuring average speed in a particular direction (or velocity), we are usually measuring instantaneous speed...

Two things the article doesn't seem to care about and chooses to be pedantic assholes instead.

Might as well post the "Ask Slashdot: Have you stopped beating your wife?"

Re:Light speed

[Anonymous Coward]

We slowed down the propagation of light quite a bit, but light always travels at c over the entire duration from emission to absorption.

TL;DR

[Lord Duran]

You can go faster than light goes in certain materials because then it travels slower than c. If you do that, badass things happen.

That said, the article is pretty well written IMHO, so if you've never heard of this before, go ahead and read it.

Re: TL;DR

[Anonymous Coward]

I disagree. With the exception of the radiation, all the examples are complete bullshit, like the recent gnashing of teeth recently experienced on /. about a laser spot moving across the face of the moon faster than light. That shit don't count, either.

At least he could have brought up the neutrino experiment where we /thought/ they had exceeded the speed of light, but then found out they hadn't. It would have been better than these mental masturbation exercises about non-things moving faster than light (come ON: sound waves inside stars? The author even specifically states that the sound wave isn't a thing - "not a material").

Re: TL;DR

[Anonymous Coward]

I liked the part that everyone skipped over like it was no big thang: the corrected measurements had the neutrinos traveling at the speed of light. Neutrinos, otherwise known as particles with a measurable mass.
Mass that was traveling at the speed of light.

Also, in an experiment where light was slowed to an insanely low speed by passing it through argon also found that the light accelerated back to the speed of light pretty much instantly. It should have taken almost a second at the speeds they had it down to, but the slowed light hit light speed again instantly.

Re: TL;DR

[Anonymous Coward]

Also, in an experiment where light was slowed to an insanely low speed by passing it through argon also found that the light accelerated back to the speed of light pretty much instantly. It should have taken almost a second at the speeds they had it down to, but the slowed light hit light speed again instantly.

Photons travel at c, always. Light is propagated through photons. When light travels through a medium with a high refractive index, those photons are repeatedly absorbed and emitted by that medium, slowing the propagation of that light. The photons are still traveling at c. When the light exits that medium, the photons continue to travel at c. Nothing has decelerated or accelerated.

What a load

[koan]

"You can travel faster than the speed of light" If you slow light down....

Re:What a load

[idontgno]

A perfect example of "solving the wrong problem".

"Astronaut: We want to travel faster than light."
"Scientist: Easily done! I'll just slow down light!"
"Astronaut: You missed the point."

Article's summary

[m.alessandrini]

Light goes slower than c in any medium different from vacuum. Some objects can go faster than light in that medium (but not faster than c of course).

Re:Article's summary

[Anonymous Coward]

And even then, light in a vacuum goes slower than the actual speed of light.

The truest speed of light can't be attained in nature due to the fact that the vacuum is not, in fact, a true vacuum. There are virtual particles popping in and out of existence constantly, which light interacts with.
Creating 2 casimir plates to create a true vacuum would give you the true speed. What that speed may be is not known since, as far as I know, nobody has made such an experiment. But it is theorized to not be that big of a change.

Nobody knows what effect the quantum vacuum has on EM radiation for sure.
Hell, for all we know, it could be stealing energy off said photons, making a larger universe considerably smaller, and surely breaking some "laws" while we are at it, but since we are all about breaking the laws of physics recently, everything is up for grabs, all laws must go before 6pm!
It is already a possible culprit for the expansion of the universe, next to dark energy.
And given that weird ass EM Drive, that seemingly is able to bounce energy OFF of "space itself" (the vacuum), it appears that it is possible to directly interact with it, and it also gives even more momentum to Hawking Radiation being capable of stealing mass from blackholes.
The distinction between virtual and ordinary particles just got weirder, if it holds that is. (I believe NASA is preparing a further test for next month, sometime this summer at least, to figure out what the hell that thing is doing)

Science is going to be a very interesting topic over the rest of this century.
Get in while you can kids. What's that, we're all old? Oh yeah. Sorta screwed that one up.

Re:Article's summary

[Anonymous Coward]

Whoa, boyo...
"The truest speed of light can't be attained in nature due to the fact that the vacuum is not, in fact, a true vacuum."
There is subtlety here, but not in the way that you think, as so:

  "There are virtual particles popping in and out of existence constantly, which light interacts with."
This is a Theory, which the Standard Model fully backs up, but has _never_ been experimentally proven.
Walter Meyerhof, near the end of his life, tried. He was trying to disprove the existence of the "Axion", by looking closely at the production and absorption of Electron/Positron pairs in very Heavy Ion Nuclear Reactions. If Virtual Particle production existed, it would have been seen in the noise, but it wasn't. Neither were Axions.
Walter was an incredibly decent man, maybe because of his background. He didn't remember at first that I was in one of his Freshman Physics courses, but he was gracious enough to sign a copy of his "Elements Of Nuclear Physics" book anyway, and give it to me. (There is a pun in the title, and if you can find a copy, you'll find that he was as good as a writer as Feynman was. Maybe better.)

(Another Good Guy? Bernie Harvey. He gave me, years later, a good chunk of his Library, with all books signed, and with copious notes in the margins. Glen Seaborg left me nothing but advise, but the delightful Al Ghiorso gave me a few momentos, and a Career. Early on, I found and gave Al a menu card from his Father's Cafe. Al was proud of his Workingman's Heritage. A few years later, I was made Operations Group Leader.)

Like several really good Physicists that I've known, Walter took many Owl Shifts for himself at the HILAC, so that his students could get a good night's sleep.

As to the rest of your post, well, this was an article from Medium.com after all, so some laxity is permitted.

Re:Article's summary

[Anonymous Coward]

Light goes slower than c in any medium different from vacuum. Some objects can go faster than light in that medium (but not faster than c of course).

I was under the impression that the light was still moving at c, it is just bouncing around inside the medium and takes longer to actually travel through it than light would without obstruction.

Re:Article's summary

[david_thornley]

We know the conversion factor between space and time (c) very accurately: it's the asymptotic speed as we pump more and more energy into acceleration. The particles in the LHC are going really, really close to c.

Don't bother reading

[gsslay]

The whole thing hinges on the phrase in the first paragraph; "depending on what you mean by a "thing", "faster-than-light", and "travel""

If you want to play around with semantics and definitions, then you've got an article. Otherwise, nothing new here. Speed of light unchallenged.

Re:Don't bother reading

[Anonymous Coward]

Speed of light unchallenged

Obviously. The question is who would start reading that article thinking the speed of light was actually going to be challenged in it?

Re:Don't bother reading

[sootman]

In that case, I've banged a lot of chicks, depending on what you mean by "banged", "a lot", and "chicks".

Light itself will always move at this speed- false

[schleprock63]

not true. light moves at c in a vacuum. light can be slowed down, even stopped. so no, light does not always move at c...

Poorly written

[prisoner-of-enigma]

Poorly written article and misleading summary. Basically the article says you can "travel faster than the speed of light" without violating relativity...but neglects to mention which "speed of light" you're beating. Light speed is different in depending upon what medium -- or lack thereof -- it's traveling through. It's possible to slow light down to the point where you can walk faster than that speed of light. But you're not violating relativity by doing so because you're moving through a different medium.

So, hyperdrives...not so much.

Re:Poorly written

[Anonymous Coward]

This. It is speaking about the wrong kind of light-speed here.

The truest actual speed of light is always c. (whether it is the vacuum measurement, or the possible slightly faster true vacuum measurement we haven't measured yet, or even other oddities)

The speed they are talking about is the slowdown caused by light being bounced around between atoms inside a material.
This absorption and emission is a fairly slow process (still stupidly fast) compared to light, and it varies with all these different atomic arrangements, and atoms themselves. The noisier the atomic arrangement, generally the slower it travels through.

It is sadly an all too common mistake when it comes to the media.
Every speed of light experiment should be accompanied by this link to explain the very simple but significant difference in a fairly easy to understand way.
The front velocity is one that is commonly misunderstood at that, even by people interested in the industry.
The best way to describe it is like being at traffic lights, you look to your oncoming traffic obscured by a building, you see what looks like a train, but then suddenly, it is a van.
You cannot determine the entire structure of a wave until the whole unit has come in to "view".

You don't have to go faster

[koan]

Just as close as possible to C
https://www.fourmilab.ch/cship...

Time dilation allows for interstellar travel, of course speeding up and slowing down throws off the numbers.

How far can one travel from the Earth?

Since one might not travel faster than light, one might conclude that a human can never travel further from the earth than 40 light-years if the traveler is active between the age of 20 and 60. A traveler would then never be able to reach more than the very few star systems which exist within the limit of 20-40 light-years from the Earth. This is a mistaken conclusion: because of time dilation, the traveler can travel thousands of light-years during their 40 active years.

https://en.wikipedia.org/wiki/...

Re:You don't have to go faster

[Bengie]

Information cannot move through space faster than c, but space itself is not limited to this. This is why we can already see galaxies moving away from us much faster than c and we'll never interact with them again.

Re:You don't have to go faster

[XxtraLarGe]

I hear this all the time, but it doesn't seem to make sense to me. How exactly is space expanding, and what exactly is expanding into? For instance, a hot air balloon's surface expands by blowing air into it, and it expands into the surrounding atmosphere. But space itself is not a substance. It is not matter or energy, it's just the gaps between everything else. Likewise the area outside the expansion of matter in the universe should be space as well. Not trolling, just trying to gain a better understanding.

Re:You don't have to go faster

[prisoner-of-enigma]

How exactly is space expanding, and what exactly is expanding into?

This is difficult to answer without getting into a long discourse on spacetime. However, you have to get away from the notion that there is some kind of "edge" to the universe and space is somehow expanding that edge into infinite nothingness. There is no "edge" to the universe anymore than there is a definable "edge" to our planet (i.e. a flat earth).

Re:You don't have to go faster

[Anonymous Coward]

Geez, the amount of ignorance this one article inseminated is astonishing.

"This is why we can already see galaxies moving away from us much faster than c..."
No. Stop getting your Physics from "Idiotology Today".

Please, think of the Cosmologists. They are constantly exploited, and thoroughly misunderstood. Poor, poor, Cosmologists.
They are generally poorly paid, compared to the Slushdots who whine about GPU speeds, as if they even dimly understood the concept of a distributed Velocity Factor.
I know a couple of Cosmologists. Do you know what they want these days? Neutrino Spectrometers. Big honking Spectrometers filled with twenty Tonnes of 3He, and without the resumption of the production of Tritium, they'll never get anywhere near twenty Tonnes.
Unlike Photons, Neutrinos don't give much of a damn about Velocity Factor. However, no matter how little mass the little buggers have, they still respect Gravity. It's the Law.
Which means, maybe five decades from now, we will have a rough Neutrino Map of the Universe... if we make enough 3He from Tritium.
And the Gamers and Miners and Overclockers will have as much relevance five decades from now, as those that preened themselves with Vitalis five decades back.

Re:You don't have to go faster

[Bengie]

Just remember, the Universe are roughly 0 total energy in it. The entire Universe is literally made of nothing.

Light speed also depends on time

[ArcadeMan]

And time itself is also quite complex. Here's a quote from someone who explains time:

"People assume that time is a strict progression of cause to effect, but *actually* from a non-linear, non-subjective viewpoint - it's more like a big ball of wibbly wobbly... time-y wimey... stuff." - The Doctor.

Re:Light speed also depends on time

[Anonymous Coward]

I'm still waiting to see his academic transcripts.

Quantum Entanglement is already debunked

[Anonymous Coward]

Quantum entanglement is already well debunked,

This entanglement experiment simply uses a coincidence detector to select the photon at the slits that passes successfully the filter at the other detector.
https://en.wikipedia.org/wiki/Quantum_eraser_experiment

No special magic.

Bells theorem, they claims rules out hidden variables (that the photon has a hidden property that is shared between both and 'revealed' not 'set' by the detector), but you can understand that the variable is time, and its not hidden, the photon is simply selected by the time of emission and from that you know the other photon has the corresponding property, because it came from the photon emitted at that time..i.e Bells does not prove 'hidden variables' are impossible, so all entanglement theory that requires Bells be true, is not true. No time traveling, no reverse causality, no spooky distance effects, just filtering.

Re:Quantum Entanglement is already debunked

[Anonymous Coward]

I really do wish that you had put some more thought into the presentation, but you are nearly right.
If I was still teaching, I would give you an "A" for Thinking, and a "See Me" for the other stuff.
What you call "Filtering" has not only a time aspect, but a granularity aspect as well; it's intrinsic to the Quantum concept.

Oh, that Wikipedia article has a few problems. I think that Homer Conzett could have done a better job, but he's dead.

Really Though, DO NOT Bother Reading

[Anonymous Coward]

The whole thing hinges on the phrase in the first paragraph; "depending on what you mean by a "thing", "faster-than-light", and "travel""

If you want to play around with semantics and definitions, then you've got an article. Otherwise, nothing new here. Speed of light unchallenged.

Yeah ... came here, read the article, want my money back.

What a complete waste of time this article was!

Did you know that if you try to send a photon through a solid wooden door, it won't ever make it ... however if you shout at the door, the sounds will be heard softly on the other side? In this case of "breaking the light speed barrier" our calculations show that not only are your vocal sound waves traveling faster than the speed of light but since light never got through the door and time still marches on, you are approaching a speed infinitely faster than the speed of light!

Mind blown? Or are you just angry that I got you to read that horseshit?

Re:Really Though, DO NOT Bother Reading

[rastos1]

What a complete waste of time this article was!

Ha! That will teach you breaking the time honored slashdot tradition and reading TFA!

Tubes

[coofercat]

It's easy to go faster than light. All you do is construct a magic tube that's really really long. You fly that tube at (say) 0.75c. Inside the tube, you fly down its length at 0.75c and before you know it - you're going faster than light.Of course, no one can see you doing it, so you're not breaking any laws.

It's sort of how Warp drives work, only I've dumbed it down for the level of brains in TFA.

Re:Tubes

[Anonymous Coward]

What if you had a magic tube inside another magic tube?

A series of tubes?

Re:Tubes

[PvtVoid]

No.

https://en.wikipedia.org/wiki/Velocity-addition_formula

Re:Tubes

[Jason Levine]

You fly that tube at (say) 0.75c. Inside the tube, you fly down its length at 0.75c and before you know it - you're going faster than light.

Unfortunately, that's not how it works. You can't just add up the tube's velocity (0.75c) and your velocity (0.75c) and get 1.5c. To put it another way, if you somehow got a spaceship to move at the speed of light (c) and then turned on the ship's headlights, the light coming out of them wouldn't be travelling at 2c, it would be travelling at c.

Re:Tubes

[Godwin O'Hitler]

Well I realize the OP wasn't attempting to be serious, but I'll ask a serious question anyway.
A long, 3m diameter tube is moving at c. You set out to propel yourself from the aft of the tube to the fore, maybe with a power winch. What happens?
Does the tube disintegrate?
Does some physical phenomenon prevent you moving forward?
If you can move forward, by what magic are you still not travelling any faster than the tube?
Or are you indeed travelling faster then the tube but somehow not faster than light? If so please explain.

Re:Tubes

[aaaaaaargh!]

You (and the tube) can't move at c, because you have mass.

Re:Tubes

[Anonymous Coward]

"the light coming out of them wouldn't be travelling at 2c, it would be travelling at c."

Why? Without directly observed evidence I'm a bit dubious as to the accuracy of this statement. Its like saying that a baseball thrown in trailer of a semi driving down the highway is going to either accelerate or decelerate the second it leaves the pitchers hand, it doesn't make a whole lot of sense. You're suggesting that a theoretical craft moving at 1c with a light running is going to have light going nowhere out of one side of the bulb and shooting out at 2c from the other side in relation to the source to maintain its "correct" speed of 1c in all directions from an observer at 0c as the spacecraft zooms buy.

Re:Tubes

[SuiteSisterMary]

Your mass prevents it from happening. As you get closer and closer to c, your mass increases, requiring more energy to accelerate you further.

To actually move at c, you'd require infinite energy. You don't have infinite energy, hence you can't hit c.

Now, the trick with the tube would be this:
Take, say, a six foot by six foot square of material. Lets say light can move 3 feet/second, and you can move 1 foot/second, and you want to get a dinky car, represnting you, from the middle of the left edge to the middle of the right edge.

Light will do that in two seconds. The dinky car will do it in six seconds.

Now, pick up the cloth, and hang it over a clothes line. Hook a dinky-car sized flexible tube from point A to point B on the two edges. They'll be an inch or two apart. Light still travels along the surface, and takes two seconds to get there. Your dinky car, however, gets there virtually instantly.

Your car didn't move any faster, you just warped space to decrease the distance you had to travel.

Re:Tubes

[Anonymous Coward]

Because it's been observed, literally thousands of times, in a variety of experiments. And no, he isn't suggesting that, because even a "theoretical craft" can't move at c. Any craft will see light travelling at c, no matter how fast it's travelling. You don't have to like it, but it's been verified repeatedly.

Re:Tubes

[Godwin O'Hitler]

OK so the correct answer to my question, which imposes a tube moving at the speed of light whether there be a means of getting it there or not, is b) some physical phenomenon prevents me moving forward, that physical phenomenon being my outrageous mass, since to move anywhere at all I would have to accelerate or decelerate that mass.
Thank you.

Re:Tubes

[holmstar]

The tube couldn't travel at c, only very close to c. If you were in the tube, and propelled yourself within the tube by whatever means, you wouldn't notice anything particularly odd. To you, it might take 5 minutes to traverse the length of the tube. But to an outside observer, it would take **FAR** longer. Say, a thousand years, for the same action (the closer to c, the longer it it would take from the viewpoint of an outside observer). The faster you tried to move in the tube, the more time dilation you would experience.

Re:Tubes

[kenaaker]

And one of the things that is observed is that the energy of the emitted photon is observed by an external observer to be altered by the kinetic energy of the moving origin. In the direction of travel the photon will be observed to have been blue-shifted, in the opposite direction it will be observed to have been red-shifted.

Re:Tubes

[Anonymous Coward]

In fact, you can travel as fast as you like.

Pick a star, say Alpha Centauri (4.4 light years).

Go towards it really fast.

Arrive on Alpha Centauri one year later, having travelled 4.4 light years. Marvel that 4.4 light years divided by 1 year is 4.4 times the speed of light. Pat yourself on the back and burn all your physics textbooks.

Return home, another year older. Note how everyone else is 10 years older now. Scratch your head in puzzlement.

You can subjectively go as fast as you like. It's only from an external-observer point of view that nothing can travel faster than light.

Re:Tubes

[Anonymous Coward]

"Because it's been observed"

No, it hasn't. I believe there have been plenty of experiments regarding time dilation done by putting super accurate clocks on a spacecraft and a "fixed" (earthbound) location and trying to measure the infinitesimally small difference between the two and attempting to extrapolate what the difference would be at much higher rates of speed which is one part of the concept. But I can't recall of any spacecraft which have been accelerated to even a percent of the speed of light so that they could measure the speed difference between a light source aimed in the direction of travel and the opposite direction. There may have been some round about ways to attempt to confirm it (gravitational lensing maybe?), and I suppose it may even be correct, but it has not been directly observed.

Re:Tubes

[david_thornley]

Moreover, if you're at the speed of light, time is stopped for you. You can't move without taking time to do so. This, I believe, is how we know neutrinos don't go at the speed of light: they can change neutrino type as they move, and so they have to be experiencing time, and therefore they can't be going exactly c. (They go really close to it. In a supernova, the neutrino burst will leave the core immediately, while the light takes a few hours to get out of the star, so the neutrinos have a head start of a few hours - and we notice these few hours while watching supernovae from other galaxies.)

Re:Tubes

[rubycodez]

wrong, you are not even subjectively going faster than C, rather you observe a different shorter distance to Alpha C. Nice try.

Re:Tubes

[Anonymous Coward]

have you never heard of a fucking michelson-morley experiment? jesus wept

HEY i know

[Anonymous Coward]

ill post an article and never say anything aobu tit other then send you to my site advertising it here

Your listening to slashdot fm

[Anonymous Coward]

"All Ethan, all the time. Now lets go to Ethan for the forecast"

"Thank you Ethan, today will be mostly medium.com with some light links to other sites"

"Well that's the weather, now over to Ethan for the business"

"Well Ethan, Dice Holding have announced a shocking drop in profits after letting once popular Slashdot.com devolve into a medium.com link aggregator. Sharholders are angry, but DHI spokesperson Ethan Siegel insists the firm is making all the right moves, and it's purely market forces outside there control that have lead to this huge decline in readership. Now back to you Ethan"

"We will have more on that, and other stories on the hour, but now Ethan Turner Overdrive, and 'you ain't seen nothing yet'"

Mexican Wave: is not movement.

[MessyBlob]

Many entities that seem to exceed light speed, are in fact multiple entities exhibiting a change in measurable state, in sequence, which looks like a single object. Take the example of a Mexican Wave: we can set up a large one, that seems to move faster than the speed of light along the crowd, but no single person exceeds light speed. Likewise, one may take the interference pattern between two combs, and make the highlights and shadows move faster than light speed. None of these examples break causality rules.

Did you really think

[Anonymous Coward]

Did you really think that the place you will learn about speed of light just having been broken will be slashdot? I assure you THAT kind of news perhaps even travels faster than light.

Re:Did you really think

[Whiteox]

That's not hard to do. FTL is not only possible but exists as anyone who discounts Einstein's theory would attest.

To sum this up:

[tomxor]

1. Nothing can travel faster than light in a vacuum.

2. Some things can travel faster than light in a medium (when it is always slower by some factor).

Unfortunately the later is just an exploration of a pedantic nature and would never lead to any meaningful definition of FTL travel. it's like saying an ant is faster than a car but only when the car is stationary or moving extremely slowly (duh).

What was interesting about the article however was the part about cosmic expansion, even though again it does not produce any meaningful FTL phenomenon, it outlines the fact that under the laws of relativity it's impossible to travel to anything further than 16 billion light years away, because that is essentially a moving target (moving away from you at the speed of light due to cosmic expansion).

Really?

[Anonymous Coward]

What a shit article.

There's already a way to do it.

[Anonymous Coward]

As Cubert Farnsworth put it, "The engines don't move the ship at all. The ship stays where it is and the engines move the universe around it."

Light?

[Anonymous Coward]

I know absolutely nothing about physics but always wondered... is c the speed of "light" or actually a number slightly larger than a photon can travel through space? I thought the the closer you get to C, the less your mass can be because of some effect or other. Doesn't photons' mass mean they'd have to travel just a little bit slower than the actual maximum speed limit, which could just be possible for something with a mass of 0 (which of course is impossible)

Re:Light?

[Anonymous Coward]

If they had mass, yes. However, your assertion that a mass of 0 is impossible is, in fact, wrong. Photons are massless. They have energy, and they have momentum, but they do not have (rest) mass. You're probably thinking of E=mc^2, but that's a misleading equation at best. What we actually have is E^2=p^2c^2+m_0^2c^4, where m_0 is the *rest* mass, that is the mass of something measured in a frame moving alongside it. Photons have zero rest mass, so they have a momentum p=E/c.

[If you reverse the argument, and start from the assumption that photons have to propagate at the speed of light (which can be interpreted as a consequence of general relativity), you immediately see you can't have a rest mass because nothing can be in a comoving frame.]

Not scientific

[ITRambo]

This article is more of an opinion piece than anything else, lacking any evidence of faster than light travel in a vacuum. Light that moves through expanding space is not moving faster than c. It's simply being moved with space itself. The article reads like it was written by someone that normally covers the police beat and now is appearing amazed by science. Click-bait headlines bring in ad dollars though.

faster than light = time travel

[Geoffrey.landis]

Nothing can go as fast as light. Slower or faster, sure, but not c.

Light goes as fast as light.

More specifically, you can't send MATTER, ENERGY, or INFORMATION faster than the speed of light IN VACUUM.

The fact that there are "things" that travel faster than light (such as phase velocities) is well known; in these neither the matter nor the energy travels faster than light, and they don't carry information.

If you could, either relativity is wrong, or you can use this to make a time machine to access the past.

Re:faster than light = time travel

[towermac]

"If you could, either relativity is wrong, or you can use this to make a time machine to access the past."

Well, relativity is most certainly 'wrong', in the sense that there is more to the universe that it does not cover. Of course, that's not really wrong, any more than Newton was wrong. Newton was not attempting to model relativistic effects, and Einstein was not attempting to model string theory.

And luckily, we are not made out of light, so the speed of light has little to do with a machine designed to alter a local region's gravitational constant, that can travel at arbitrary speeds relative to the destination because it carries it's own engine with it. Relativity does not forbid a starship.

But none of that would ever allow you to travel back in time. That would be akin to traveling in a negative direction.

Re:faster than light = time travel

[david_thornley]

Sorry; if special relativity holds, FTL travel is equivalent to time travel.

Let's assume two spaceships pass each other at a speed giving a contraction factor of 2, and attune their ansibles. You're on one spaceship, and I'm on another.

Now, I knock my water glass into the main computer an hour later. This is bad. I send you a message saying that I did that, and ask you to repeat it. You receive it at the same time as I send it - but how is that measured? If I perceive you as receiving it at the same time I sent it, then I see you getting it when you've traveled half an hour from our meeting. You repeat it back to me. If you perceive me as receiving it at the same you sent it, then you see me getting it when I've traveled fifteen minutes, forty-five minutes before I sent it.

According to special relativity, there is no one privileged reference frame, so we have to measure things like simultaneity in a reference frame that varies with the observer. If there is any such thing as an absolute time that doesn't allow time travel, then special relativity is completely wrong.

Re:faster than light = time travel

[Geoffrey.landis]

"If you could, either relativity is wrong, or you can use this to make a time machine to access the past."

Well, relativity is most certainly 'wrong', in the sense that there is more to the universe that it does not cover.

Saying "there are things it doesn't cover" is not the same as saying "it's wrong."

Of course, that's not really wrong, any more than Newton was wrong. Newton was not attempting to model relativistic effects, and Einstein was not attempting to model string theory. And luckily, we are not made out of light, so the speed of light has little to do with

The phrase "speed of light" is historical usage. An equally accurate phrase would be the universal conversion factor from units of space (meters) to units of time (seconds). It doesn't apply just to light, it is a universal constant that applies to pretty much everything in the universe, not just light. Most particularly, it applies to gravity.

a machine designed to alter a local region's gravitational constant,

If you alter the gravitational potential, the gravitational time dilation will mean that external observers will observe your speed of light as having changed. If you're in a gravity well, your clocks have slowed down, so it looks (from the outside) as if light has slowed down. But, inside the region of altered gravitational potential, if you measure the speed of light, it's still moving at the speed of light. You can't travel faster than the speed of light where you are.

that can travel at arbitrary speeds relative to the destination because it carries it's own engine with it. Relativity does not forbid a starship.

If you could travel at arbitrary speed (in any direction, in any reference frame), relativity says you could make a time machine. Space is time. If you can travel faster than the speed of light you can travel backwards or forward in time.

But none of that would ever allow you to travel back in time. That would be akin to traveling in a negative direction.

Right. If you can travel faster than the speed of light, but only one direction, then you can't make a time machine.

Re:faster than light = time travel

[towermac]

"ansibles"

Hey, I love thought experiments and speculation as much as the next guy, but that is a fictional device without even an idea as to how it would work.

I'm also not sure what a contraction factor of 2 means, I assume you mean Lorentz contraction, but I don't know what 'speed' that would be. It really doesn't matter though, for the thought experiment of 2 FTL ships passing; anything over c will do. And I assure you I would never try to dis' special relativity.

Two ships pass each other, let's say each is going twice the speed of light relative to a nearby, relatively stationary 3rd observer. They are going to pass each other at 4c, although neither would be aware of the other of course.

No message can viably be sent between the two, at least not using EM radiation, or anything else I can think of.

But I suppose, if ship 1 knew where ship 2 was going to be ahead of time, they could broadcast their message to that empty space, knowing ship 2 would run into it. That would be a damned difficult message to both receive and decode, but let's say it is broadcast in such a way that a simple message could be decoded.

But you still didn't receive my message until after I sent it, and even after I passed you. You would not have seen me pass you, although you may have seen disrupted incident radiation as my 'light wake'. And if we stopped to talk, then you would get my message long after you saw me.

If you stick to real world science, with the exception of a machine that carries itself and occupants within a local bubble of spacetime, then you won't come up with any causality issues.

And time travel is certainly allowed; we are travelling through time right now. It can even be sped up or slowed down, but travelling backwards through time would be the same as travelling backwards through space. I can't even wrap my head around that.

Re:faster than light = time travel

[towermac]

People seem to think that an FTL drive would mean that relativity was wrong. It's false dichotomy. That's all I was getting at.

"You can't travel faster than the speed of light where you are."

No. Nor reasonably even approach it. Obviously the trick would be to travel faster than light from the reference of your destination.

I'm taking 'time machine' to mean traveling backwards in time. Building a time machine to travel 'forward' through time would be trivial. My truck actually does that. If I were to take it near a black hole that would boost the time travel quite a bit.

Space is not time, time is not gravity, gravity is not space. They are 'made out of' the same thing, but they are not the same.

You're getting caught up in causality in thinking that travel faster than c could take you back in time. There's no such thing as negative distance, time, or gravity. (Oh I know I should never say 'no such thing' but within this conversation, there is no such thing.)

Re:faster than light = time travel

[UltraOne]

There are a few ways (completely hypothetical) ways to salvage this situation, by imposing another limitation that allow FTL travel, but prevents the set up that allows causality violation. A (probably incomplete) list:

1. Preferred FTL reference frame - The "default" proposition for an FTL jump-type drive is that you move across space in no time (or a very short time) as measured in the reference frame of the drive when you engage it. The fact that those reference frames can be different for two FTL drives moving at relativistic normal space velocities (or for one drive making successive jumps after a relativistic-scale velocity change) is what allows you to turn FTL travel into causality-violating time travel. If instead, all FTL travel takes place in a single, preferred reference frame (for example, the frame in which the cosmic microwave background radiation has no dipole component) regardless of the velocity of the drive when engaged, it is impossible to create those causality-violating paths.
2. Virtual particle censorship of wormholes - A similar causality violation can occur with wormhole FTL if you have two wormholes (each with two ends), where the ends are moving at relativistic speeds relative to each other. The limitation that could prevent this is caused by virtual particles in vacuum (which are responsible for things like the Casimir effect). Simplifying greatly, you can "borrow" energy from vacuum to create a virtual particle pair (usually a particle and its antiparticle) as long as the virtual particle lifetime is short enough that the product of the that time and the "borrowed" energy is less than the Plank constant. Since the Plank constant is so small, that means that macroscopically observable virtual particle effects are typically secondary. However, as two wormholes move closer and closer to a condition in which you can loop through both of them and arrive at your start point in zero time, ever greater numbers of virtual particles will make that round trip, which increases the mass moving through the wormholes enough to collapse them before you get to a configuration that allows a zero or negative travel time (and thus leads to a causality violation).

Re:faster than light = time travel

[david_thornley]

Faster than light communication cannot be done by any means we know of, so I borrowed an instantaneous communicator from some of Ursula K. LeGuin's books. Making it instantaneous simplifies the exposition.

The purpose here is to show that FTL is the same as time travel if Special Relativity holds. To show this, I need to hypothesize something FTL. I can show it with FTL spaceships as well, although it is more complicated. If ships can go at 2C, relative to arbitrary reference frames, they can go back in time and meet themselves.

And, yes, "time travel" is ambiguous. Would you prefer it if I called it a closed causality loop?

Re:faster than light = time travel

[david_thornley]

You're right, it's not a dichotomy. It's a trichotomy.

We cannot have a Universe that allows FTL travel or communication and where Special Relativity holds that still preserves causality as we know it. If you can go FTL, you can go backwards in time.

There really isn't any such thing as space or time, since from different reference frames different amounts of separation are space and time.

Re:faster than light = time travel

[Noah Haders]

what is an ansible?

Re:faster than light = time travel

[towermac]

You can't meet yourself. There are ships going 2c right now, relative to our reference frame. I'm talking about automobiles on the surface of a planet about 20 billion light years from Earth. (And if there are no cars there then is a boulder moving away from us at 2c.)

If you actually make a ship or particle go 1c or faster, then the causality thing is academic in any case, because you used infinite power to get to infinite mass and are literally everywhere at once, thus destroying the universe.

There's no speed limit on space (or gravity or time for that matter). In this context, space has nothing to do with distance. If (big if), you could artificially expand and contract space and carry yourself around within it, relativity would be still be satisfied from all reference frames. Another term for a 'warp drive' would be a dimensional drive.

Outrunning and then intercepting your own reflected light or radio messages from the past is no big deal. That's how we are going to get all the lost Dr. Who episodes back; fly out enough light years, tune in, and then press record on the starship's dvr. :)

Re:faster than light = time travel

[towermac]

I see we are going to disagree on the subject.

You have a nice day, and I hope to speak with you again.

Re:faster than light = time travel

[SgtAaron]

Faster than light communication cannot be done by any means we know of, so I borrowed an instantaneous communicator from some of Ursula K. LeGuin's books.

Huh. I have never heard of her. Honestly I thought your use of "ansible" came from Orson Scott Card's books. So did he pick up the term himself from one of her books?

Re:faster than light = time travel

[SgtAaron]

what is an ansible?

In some science fiction stories such as the Ender's Game novels, an ansible is a method of communicating over great distances FTL. Two quantum-entangled particles transmit information between each other. And apparently, from a previous post I just replied to, another author Ursula LeGuin has used the term. And checking wikipedia it seems she coined the term, in 1966. Card must have borrowed the term for Ender's Game.

A fascinating thought. Who knows if such a thing will ever exist.

Re:faster than light = time travel

[Noah Haders]

I think of an ansible more as a device that can generate images, like the Ouija board was back in the occult movement of the late 1800's and early 1900's. it wasn't really a communication device, unless you count talking to somebody on the other side as communication. not on the other side of the universe, if you catch my drift...

Re:faster than light = time travel

[david_thornley]

The problem with simply disagreeing is that there is a right answer here.

Re:faster than light = time travel

[david_thornley]

Apparently LeGuin coined the term, and it became popular from there. It doesn't seem to be the sort of word that would get coined independently.

Re:faster than light = time travel

[david_thornley]

You need two reference frames to do the time travel trick with FTL, and you need to be able to meet. Anything that is receding that fast due to space expansion will never interact with us ever again.

TL;DR

[Tyrannosaur]

The article says that things don't actually go faster than c. It is possible in a certain medium (example of water) for things (like electrons) to go faster than light does, but not faster than c.

Not even information can go faster than c, because we haven't discovered quantum entanglement to work that way.

The end. A dumb article; not worth reading.

No interaction means you don't know

[Roger W Moore]

but, for the intents and purposes of outside human observers, haven't you instantly blinked across light years?

If you entangle two states such that the position is the only thing different between the two states then there can be no interaction with either 'copy' which differentiates between the two possible positions. The instant that there is an interaction which determines which state you are in (position A or B) that is the position you are in. It is no more mysterious than putting some one at the centre of a (very large) box and have them move away from that centre at almost the speed of light in an unknown direction. The person in the box does not know which direction they are moving in because there is nothing surrounding them and the people outside do not know until they open the box.

Re:No interaction means you don't know

[circletimessquare]

i understand that

but if there were some way to make sure the two "copies" do not interact with anything. i didn't say that was remotely possible today, or perhaps ever. just a way out there thought experiment

Re:No interaction means you don't know

[Roger W Moore]

..but if there were some way to make sure the two "copies" do not interact with anything.

That's my entire point! If you assume that you can make a system where there is no interaction then there is absolutely no difference whatsoever for all concerned between position A or position B. Hence there is absolutely no way to know whether you are in position A or B until you interact so there is no magical "teleportation". It's the same as Schrodinger's cat: the cat is either alive or dead and you find out which when you open the box and there is no undetermined state as per the common misconception.

To get the EPR paradox you need an entangled state for two particles. What you have is a single, unknown state of one particle (or person). These are not the same.

C is not what people think it means

[goombah99]

It's very easy to travel 100 light years in less than 100 years. Thus for all intents and purposes, one can travel distances at faster than the speed of light. The theory of relativity does not prevent this. You can without violating any laws accelerate a rocket ship at a comfortable 1g for as long as your fuel holds out. You will not get more massive. It will not take increasing amounts of fuel to maintain the 1g acceleration. If you accelerate for 1 year at 1g then you will know that you covering the distance to your destination at faster than the speed of light.

What is true about relativity is this: and OUTSIDE observer will see you traveling at less than the speed of light. But from your perspective you can travel across galaxies in your lifespan with ease. So for all intents and purposes, you can go faster than the speed of light provided we everything from your point of view (which is all that matters). We define speed as the distance to your destination measured in an inertia frame, divided by the time it takes you to get there, all measurements from your perspective.

the way reletivity is taught totally confuses people on this point: A HUMAN COULD EASILY TRAVEL ANYPLACE IN THE MILYWAY WITHIN THEIR LIFETIME WITH EXISTING TECHNOLOGY, except for the part about bringing your own fuel. we just don't know how to bring enough fuel to maintain a 1g acceleration for 50 years. This is why these new reactionless EM drives that NASA and others are toying with are really interesting. No doubt they are bullshit since they seem to defy newtons laws, but if it turns out they work.... see you on on the other side of the galaxy baby.

Re:C is not what people think it means

[Lumpy]

Or the pesky part that at relativistic speeds hydrogen atoms rip through the ship as if it was tinfoil.

Re:C is not what people think it means

[goombah99]

Or the pesky part that at relativistic speeds hydrogen atoms rip through the ship as if it was tinfoil.

well yes that too.

Re:C is not what people think it means

[firewrought]

except for the part about bringing your own fuel

And the part about obliterating your spacecraft by colliding with interstellar dust at super-high relative velocities. The speed limit for arriving in one piece is way lower than c.

Re:C is not what people think it means

[Anonymous Coward]

Not necessarily. After all velocity is relative, and there's a chance that some hyper speed dust is heading your way right now. When you are in your space ship and are not accelerating then you might as well be going zero since everything is relative.

Re:C is not what people think it means

[PPH]

Thus for all intents and purposes, one can travel distances at faster than the speed of light. The theory of relativity does not prevent this.

Except for the little problem of Lorentz contraction. As you move faster and faster, to a fixed observer you are getting shorter and shorter in the direction of travel. The other side of this is that to you, fixed distances get longer and longer. So that star that was 100 ly away when you were on earth starts to get farther and farther away as you accelerate toward it.

Re:C is not what people think it means

[sconeu]

Bzzzt!!! Thank you for playing. Here's your lovely parting gift.

Let's rephrase... as an outside observer sees you go faster you get compressed to THEM.

From your frame of reference, the outside world is going faster and is compressed, so the distance to the star that is 100 ly away gets compressed by the gamma coefficient.

Re: C is not what people think it means

[Anonymous Coward]

You have this wrong. You will observe the universe as having become contracted.

Re:C is not what people think it means

[goombah99]

Wrong. But you illustrate perfectly what I meant when I said the way relativity is taught confuses people. You are actually a member of the vast majority of people that think you can't travel to a destination in less time than it would take light. You can!

Re:C is not what people think it means

[PPH]

so the distance to the star that is 100 ly away gets compressed by the gamma coefficient.

So, at .99c, what I saw as 100 ly standing still becomes 10 ly and I cover that in 10.1 years (my time). I just traveled at 9.9c (as I measure it).

I just traveled faster than light. Not the light coming out of my headlights. But in terms of distance divided by time (my time).

Re:C is not what people think it means

[cyberchondriac]

That's why you use a magnetic ramscoop, plus the hydrogen solves the fuel shortage problem.

Re:C is not what people think it means

[kqs]

In your terms, you travelled 10 ly in 10.1 years.

In terms of someone else (not moving that fast), you moved 100 ly in 101 years.

So you only moved faster than light if you use your time with someone else's distance. I mean, you can divide anything by anything else, but that doesn't mean the resulting number means anything. :-)

Re:C is not what people think it means

[goombah99]

sure it does: you can travel 100 light years in less than 100 years. that's the only thing that is meaningful. Arguing about whether you can go faster than light is not meaningful.

Re:C is not what people think it means

[Anonymous Coward]

When reflects off an object, it's imparting a momentum change. In relativity, the fast one moves, the more outside reference frame objects tend to get bunched up into a single point. And the light we're approaching towards gets blue shifted. So at higher relativistic speeds, light starts to act as a retardant as the reflected momentum becomes larger.

Re:C is not what people think it means

[firewrought]

After all velocity is relative, and there's a chance that some hyper speed dust is heading your way right now.

Yeah, obviously you can't do anything about that piece of dust except hope it misses you. However, there's a much greater amount of dust simply drifting with the stars around the galactic center. If you move thru the interstellar medium at 0.7c, you're going to have a bad day. Creep thru at a much slower speed and you have a chance, especially if you stay within the Local Bubble.

Re:C is not what people think it means

[Anonymous Coward]

we just don't know how to bring enough fuel to maintain a 1g acceleration for 50 years

At a constant 1g accelleration you will reach c in just under a year. That's from the frame of reference of the outside observer. For the traveller it would seem shorter, although I don't know exactly how much.

Re:C is not what people think it means

[Anonymous Coward]

No. You're mixing reference frames... from yours you traveled 10ly in 10.1 years (or whatever) and from Earth's you traveled 100 ly in over 100 years. No one claims you went faster than light.

If we get to mix reference frames the way you just did, I'll stick my watch in the LHC and use that to time my walk to the corner store. Look at that! I can now walk faster than light!

Re:C is not what people think it means

[MrBigInThePants]

And likewise you can make anything relative to anything else and make it seem like that comparison is somehow more important.

The important point is that to an independent "observer" and to YOUR OWN measurements as taken BEFORE the trip, you travelled faster than the speed of light.

THAT, my friend, is what counts here for practical purposes.

What you are suggesting (practically speaking) is metaphorically akin to taking a velocity reading of your own body while seated on a supersonic jet and concluding you are travelling 0 km/hr because you are not moving relative to the jet.

And it is a stupid thing to tell the average person because they fail to see the value in jet travel. (which is what has happened with space travel)

Re:C is not what people think it means

[Anonymous Coward]

Wouldn't it be more like using your watch to estimate what the time at your destination will be, without resetting your clock, when travelling against the rotation of the planet?

Re:C is not what people think it means

[david_thornley]

From the outside frame of reference, you never hit c, but rather come close.

The easiest way to calculate how long the trip would take from your point of view is to forget about relativity and use Newtonian physics to calculate the time it would take. It's not going to produce many usable results, but that one should work.

We leave it as an exercise for the reader to figure out how to accelerate at 1 G that long.

Re:C is not what people think it means

[MrBigInThePants]

There is no need to complicate the scenario. This is what typically happens when people describe this stuff which is great for explaining the theory but they sometimes forget to mention what happens in practice.

Here is what they often forget to mention:
1) I want to make a journey I measure as 100LY. I accelerate then decelerate at 1g for equal amounts of time to stop at my destination.
2) A bunch strange perceptual shit happens..
3) The journey takes less than 100 Y for me.

QED.

Re:C is not what people think it means

[Anonymous Coward]

Wrong. But you illustrate perfectly what I meant when I said the way relativity is taught confuses people. You are actually a member of the vast majority of people that think you can't travel to a destination in less time than it would take light. You can!

No, you can't. The truth of the matter is that light arrives at its destination (from its point of view) the moment it is created. Each particle has 2 velocities, the sum of which is c. Each particle is traveling through both time and space. Light is moving through space, at a velocity of c, it has nothing to give in the time direction. If a particle is not traveling through space at c, some of that velocity is going through time. You'll always lose that race.

Re:C is not what people think it means

[the_other_chewey]

Wrong. But you illustrate perfectly what I meant when I said the way relativity is taught confuses people. You are actually a member of the vast majority of people that think you can't travel to a destination in less time than it would take light. You can!

No you can't.

If a light ray and your super rocket start from the same point towards the
same destination, the light will always be there first.

The effect of slowed down "clock time" in the rocket doesn't do anything
that would permit you to overtake the light.

Re:C is not what people think it means

[Anonymous Coward]

If you are traveling faster than light, then how will you see the light in your eyes? What will you see when you're moving faster than light particles?

Re:C is not what people think it means

[kqs]

Oh, in that case, I regularly fly in airplanes that are faster than military fighter jets. I board, fall asleep, the plane flies across the country, I wake up. Using my own subjective time and the objective distance the plane has travelled, I've moved at about mach 10.

Re:C is not what people think it means

[eriqk]

I thought the caveat was "with existing technology".

Re:C is not what people think it means

[Anonymous Coward]

No, on a spacetime diagram (x axis being the straightline spatial distance, y axis being time) you will have travelled on a curve inside the light cone. Any set of lines of simultaneity you draw will favour light departing from Earth along the same (or very very extremely parallel) spatial path; the light will have travelled along a null geodesic, your geodesic will have been timelike.

Your proper time is only privileged to you; nobody at source or destination would agree that your wristwatch is showing the "real" date and time. Additionally, if Earth and the destination are both using the same date conventions (e.g, a compatible localization of UT) their calendar when you arrive will not read earlier than 2115.

If you insist that your calendar showing, say, 2025, is completely accurate and an indication that you have travelled faster than light (since after all their telescopes will show images of Earth calendars of 2015), people at the destination will be perfectly justified in arguing that your shipboard clocks just ran so fast that you changed calendars too early, and have no external reason to justify having done so (e.g. by predicting the behaviours of distant astronomical objects, including having knowledge of events on Earth in 2020).

(Sure, you appear to expect them to say that your clocks ran so slow that you didn't advance your calendar to 2115 in time but BOTH objections are valid, and the one above is more clearly relevant when determining whether you outraced light from Earth).

Re:C is not what people think it means

[MrBigInThePants]

Thank you for giving yet another example why people confuse this issue and end up not understanding that you can travel distances of 1000's of light years in much shorter than those years without making Einstein sad.

I understand the theory. I don't need yet another reinterpretation or metaphor.

If you think that is what was required then you missed my point entirely.

But then that may have been the point...

Re:C is not what people think it means

[Anonymous Coward]

Well, except that you had written a couple articles above:

The important point is that to an independent "observer" and to YOUR OWN measurements as taken BEFORE the trip, you travelled faster than the speed of light.

There are relatively few possible observers that will agree that your proper time is the correct time. Observers like us, not moving relativistically compared to Earth and your destination, will do the GR line integral with x^1,x^2,x^3=const and thus $\Delta \tau =\int _{P}d\tau =\int _{P}{\frac {1}{c}}{\sqrt {g_{{00}}}}dx^{0}$ which is considerably longer than the beam of light you are racing. In fact, you should do the same calculation, and would have to arrive at the same conclusion: you did not outrun the beam of light.

If the destination knew (in UT, say) what time you were scheduled to leave Earth, they would expect you no sooner than 100 years later by their clocks. Your proper time at arrival will be considerably earlier than 100 years, but the conclusion to draw from that is not that you've at any infinitesimal time been on a spacelike geodesic.

So, yes, you can travel even billions of light-years within your proper time lifetime in principle, but wherever you wind up, billions of calendar years will have gone by during your ultrarelativstic trip. Kinda hard for sending postcards or facebook updates of the cool distant galaxies you've visited...

Law vs Theory

[Anonymous Coward]

"It's one of the cardinal laws of physics and the underlying principle of Einstein's relativity itself: the fact that there's a universal speed limit to the motion of anything through space and time, the speed of light, or c."

The speed of light and the idea that nothing can travel faster than light are theories, not laws in physics.

But I like how you associated the adjective cardinal to this erroneous statement.

The Earth is still not the center of the universe on a related note.

So if we fill space with water...

[Dareth]

So if we fill space with water... we can have fast space travel.

Missed an example

[GlobalEcho]

Just-in-time optimized code goes faster than c.

:-)

I am surprised that it did not mention tachyons

[Kaptain Kruton]

They are just hypothetical at right now... but if they do exist, they will have mass and travel faster than the speed of light. They do not violate the theory of relativity because they always travel faster than c.... they do not start at speeds less than c and accelerate to or beyond the speed of light.

Re:I am surprised that it did not mention tachyons

[Pro-feet]

Tachyons are nasty negative mass states; really just weird mathematical solutions. You would expect the Spanish inquisition more than the observation of a tachyon anytime soon.

Re:I am surprised that it did not mention tachyons

[Anonymous Coward]

Tachyons in one theory are not the only possible definition of tachyon, just like the electron in classical electrodynamics is not the electron in QED is not the electron in SM.

To a relativist a tachyon is any object freely falling along a spacelike geodesic, or equivalently, any object whose causal cone is wider than that of light's.

Any spacetime described by the Einstein tensor admits a democracy of causal cones, not just the light cone. For historical and practical reasons we focus on solutions to the Einstein Field Equations where the light cone is the causal cone; there's no *strong* reason to do so, and we probably could not continue to do so if we found, for example, superluminal neutrinos.

In fact, even spacetimes described by the Minkowski tensor can probably cope with superluminal causal cones, as Geroch notes in section 3 of http://arxiv.org/abs/1005.1614

Tachyons in that sense will have varying solutions that *may* require some sort of negative mass-energy (e.g. under the FLRW cosmology) or may not (e.g., under the inside Kerr metric). The mathematical solutions for tachyons can even be straightforward and obvious, which most people take to mean that the metric is probably unphysical because pretty much everyone agrees with you about expecting the Spanish Inquisition.

Bad news

[Anonymous Coward]

Bad news travels faster than light.

/fail

[uslurper]

This article was a total dissapointment. So things can technically go faster than light when light is slowed through a medium. BFD. This has nothing to do with FTL travel.

we all are already doing this

[Anonymous Coward]

Relative to the original particles from the big bang or whatever, we are moving faster than the speed of light relative to them.

There may be a way

[PPH]

But I'm not sure TFA deals with it. Nothing can travel faster than c in a vacuum. Light travels at c (in a vacuum). However, light cannot escape from inside a black hole. This isn't due to classical speed limits, but the way space time curves near the black hole's event horizon.

However, gravity can escape a black hole. Otherwise, how would they exist and grow? So gravity is not constrained by the same space-time curvature as light. Therefore, over long distances, the curvature of space time (even a slight effect caused by the masses of nearby galaxies) would cause the vacuum velocities of gravity to excced that of light. Or, to put another way, the path through space time for light is slightly longer than that for gravity. So gravity gets there first.

Hint: Think about this effect as an alternative to dark matter/energy.

Re:There may be a way

[Anonymous Coward]

Hint: Head to a large bookshop and buy some textbooks on relativity adn cosmology because you're completely and totally wrong. The "speed of gravity" means very little, except that if you modify the curvature of a spacetime you can calculate the speed with which that change propagates through the spacetime - and that turns out to be exactly c. So in the only way that really means anything, gravity moves at the speed of light.

The Usenet Physics FAQ did it better

[AdamHaun]

For a more thorough and slightly more technical approach to the same subject, check out the Usenet Physics FAQ's article "Is Faster-Than-Light Travel or Communication Possible?". Here's the conclusion:

To begin with, it is rather difficult to define exactly what is really meant by FTL travel and FTL communication. Many things such as shadows can go FTL, but not in a useful way that can carry information.

There are several serious possibilities for real FTL which have been proposed in the scientific literature, but these always come with technical difficulties.

The Heisenberg Uncertainty Principle tends to stop the use of apparent FTL quantum effects for sending information or matter.

In general relativity there are potential means of FTL travel, but they may be impossible to make work. It is thought highly unlikely that engineers will be building space ships with FTL drives in the foreseeable future, if ever, but it is curious that theoretical physics as we presently understand it seems to leave the door open to the possibility.

FTL travel of the sort science fiction writers would like is almost certainly impossible. For physicists the interesting question is "why is it impossible and what can we learn from that?"

but...

[Anonymous Coward]

but to go faster then light one has to get to light speed thus it can never be achieved

Why can't catholics travel faster than light?

[Anonymous Coward]

It's because they have mass!

it's a freaking theory...

[SuperDre]

Even Einstein himself said it was a theory and he might be wrong...... Just like any 'laws' of nature aren't set in stone, they are 'laws' created by humans to help us puny humans understand what's going on, at least what we believe is going on...
Let's not forget, scientists a long time ago said the world was flat, and if you said otherwise you were a heritic... Now we know better...

Re:it's a freaking theory...

[Anonymous Coward]

"Let's not forget, scientists a long time ago said the world was flat, and if you said otherwise you were a heritic... Now we know better..."

Nonononononono!
Is that enough "Nos" for you?

If anybody thought about it much in the past at all, they knew that the Earth was Spherical, (Roughly). This has been known for at least 2500 years in Western Culture. What was in dispute at the time of Columbus was the _size_ of the Sphere.
Go ahead. Knock yourself out. Find just _one_ serious Scientist who _ever_ claimed that the Earth was flat! (Crackpots don't count, so you can exclude yourself.)
You win the Arrogantly Stupid Award For Today. And you can't even spell "Heretic".
Damn, you are denser than a box of rocks.
Here, read this, and then chew some Razor Blades:
http://rationalwiki.org/wiki/Flat_Earth

Captcha: flattery

Bad News

[Anonymous Coward]

Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws.
Douglas Adams, "The Hitchhiker's Guide to the Galaxy"

English humorist & science fiction novelist (1952 - 2001)

vacuum?

[Pro-feet]

TFS doesn't mention the word vacuum, anywhere.

Travelling faster than light in a medium is not that hard. The blue light in the water surrounding nuclear reactors is a result of neutrons doing exactly that: they travel faster than light in the water. Nothing fancy.

spin in circles

[Anonymous Coward]

At sunset, I spun in a circle. It took me a second to rotate 180 degrees, but what really happened was, the universe spun around me in that second. The sun traveled 288 million miles in a tight circle around me, moving at 288 miles per second, 1500+ times the speed of light.

The far stars? They moved much faster.

You mispelled "intensive purposes".

[Brannon]

otherwise everything checks out.

Re:You mispelled "intensive purposes".

[Anonymous Coward]

What the heck are "intensive purposes"? Is that like the English department ER?

Go read a book, would ya?

Re:You mispelled "intensive purposes".

[Anonymous Coward]

You fail: http://en.wiktionary.org/wiki/for_all_intents_and_purposes

Re:You mispelled "intensive purposes".

[Anonymous Coward]

Trolled son!

Looks like a great place to ask these questions!

[PyrousLavawalker]

If you look through a telescope at a mirror 1 light year away that is pointed back at the location you are standing. Would you see yourself, or would you see what was happening 2 years ago in that exact spot? If Bob was on a ship that is 1 light year long moving 3/4 the speed of light in reference to a stationary object and Sally launched her ship off of Bobs ship and has achieved 3/4 the speed of light in reference to Bob's ship. Then Billy launched from Sally's ship and was moving 1/4 the speed of light in reference to Sally's Ship. How fast is Billy moving in reference to the stationary object?

*light* always does. The photons, themselves.

[Anonymous Coward]

They get delayed by all those charges they meet on the way. Therefore the light train gets there later because the photons were delayed by being absorbed and re-emitted in the meantime. But between each event like that, it went at the speed of light. Tautologically and mathematically.

Re:Looks like a great place to ask these questions

[david_thornley]

If you look at yourself in the mirror, the length of the light path is twice the distance to the mirror, so you'd see what was happening two years ago. You want to see yourself, move the mirror closer.

There's a Wikipedia article on relativistic velocity addition that gives the details. Without actually going through the computation, the result is that everybody is going slower than the speed of light relative to each other (everybody including Frieda on the object we're taking as stationary for purposes of the discussion).

Who would've guessed?

[Tablizer]

So the secret really is going to plaid.

Re:Light itself will always move at this speed- fa

[Anonymous Coward]

Light, the information wave, can be slowed down. Light's information carrier, the photon, always moves at c.

Re: C is not what YOU think it means

[Pfhorrest]

Other people have already said this, but they're buried in replies to replies so I'll say this up here where it's more noticeable:

The practical upshot that a human can get to anywhere in the universe within their lifetime given enough fuel to keep up acceleration is correct, but from no frame of reference will you appear to have travelled faster than a beam of light.

In your traveling frame of reference, it will appear that the distance you travelled got smaller. That's why you can reach places that seemed too distant to reach in your lifetime before: because they don't seem so distant once you're on your way there.

In the rest of the universe's frame of reference, it will appear that you aged more slowly. That's why you can reach places that seemed too distant to reach in your lifetime before: because your lifetime got prolonged once you were on your way there.

In either frame of reference, when you get where you're going, you will still find that a beam of light sent at the same moment you departed will have arrived at your destination before you, and thus in neither frame of reference did you outrun the light. You just either aged more slowly or travelled less distance, depending on whose frame of reference we're talking about.

In a photon's frame of reference, there is no distance between anything and no at all time elapses to travel it. Given enough fuel you can get arbitrarily close to that and so travel to arbitrary locations with arbitrarily little aging along the way, and so get anywhere in your lifetime. But light can always do that better than you still.

Why why why

[Anonymous Coward]

What prevents light from moving faster than it already does? Does it suffer from something like air resistance? And why propels light forward? Does it not slow down to an eventual stop? Weirdo.

Re:Why why why

[lucien86]

The equations of motion mean that light travels with infinite velocity. The resonance or curvature of space time limits this infinity to the speed we know.

(Momentum p = mv, so v = p/m, so for light v = h/0 . (h = any value except zero) )

FTLt vs tftl

[Anonymous Coward]

There is a distinct different between "Faster Than Light travel" (FTL), which is getting from point A to point B in less time than it takes light to travel from A to B, and travelling faster than light, which means you travel the intervening space faster than light does. The first is easy (and as the article mentions happens often) while the latter is impossible. Einstein's famous equation states that the total energy of any system is based on the mass at the speed of light - once you reach the speed of light you have no mass and/or no energy so cannot accelerate.
FTL can be achieved by either bending space time so A & B are artificially close together (Warp drives) or finding a shorter 'tunnel' to pass through (hyperspace).

Re: C is not what YOU think it means

[Anonymous Coward]

As a theoretical physicist myself I think this is an excellent answer and should have been modded up.