How Space Can Expand Faster Than the Speed of Light

60 years later by Anonymous Coward · 2015-03-20 19:46 · Score: 1, Insightful

Dead for almost 60 years and still taking us to school...

Re:60 years later by hcs_$reboot · 2015-03-20 20:32 · Score: 1, Offtopic

Indeed, we all keep him in our hearts.

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"Space itself" is just a mathematical trick by michelcolman · 2015-03-20 19:47 · Score: 5, Interesting

Some time last year I wrote a lengthy explanation of what exactly "space itself" means. It's not really a physical thing, but rather a result of a particular choice of coordinates which turns out to be very practical.

http://science.slashdot.org/co...

"Speed" is just distance divided by time. Both distance and time are defined by agreeing on a particular set of coordinates. In our immediate neighborhood there isn't much discussion about what we mean, apart from which unit to use (miles, km,...) but on intergalactic distances in an expanding universe there are several different, perfectly valid choices of coordinates that yield wildly different results for distance, speed, simultaneity, etc... You can choose a coordinate system that obeys special relativity and find that nothing goes faster than the speed of light relative to us. But with different coordinates, the speed of light itself is not tied to our location but rather to local "space". That's just a mathematical convention because it turns out to be more convenient that way. Anyway, I explained it all in detail in the above link.

Re:"Space itself" is just a mathematical trick by Anonymous Coward · 2015-03-20 21:40 · Score: 1

If the OP means by space 'the location but in the context of the coordinate system being used' then there is a distinction between location and 'local space'. This is not a comment on the OP's longer discussion, though either for or against.
Re:"Space itself" is just a mathematical trick by WoOS · 2015-03-20 21:57 · Score: 2

So, assuming your post you are referencing is correct (IANAP), what you are saying is "Things (including 'space') can move faster than c as long as the people (aliens, computers, rocks, ...) relative to which it moves faster than c never know about it." (The laser light in your example never reaching us.)
Gives some great setting for SciFi: "People of Earth, we come in peace. When we left Alpha Centauri just 2 months ago ....." *instant disappearance* ;-)
Re:"Space itself" is just a mathematical trick by Anonymous Coward · 2015-03-20 22:53 · Score: 2, Interesting

It was all explained in "Bill The Galactic Hero" anyways. It's called the Bloater Drive
From Wikipedia: "The standard ways of circumventing relativity in 1950s and 1960s science fiction were hyperspace, subspace and spacewarp. Harrison's contribution was the "Bloater Drive". This enlarges the gaps between the atoms of the ship until it spans the distance to the destination, whereupon the atoms are moved back together again, reconstituting the ship at its previous size but in the new location. An occasional side-effect is that the occupants see a planet drifting, in miniature, through the hull."
Thus you can move an object to a new spatial co-ordinate without actually moving it.
Re:"Space itself" is just a mathematical trick by deviated_prevert · 2015-03-20 23:14 · Score: 1

It was all explained in "Bill The Galactic Hero" anyways. It's called the Bloater Drive
From Wikipedia: "The standard ways of circumventing relativity in 1950s and 1960s science fiction were hyperspace, subspace and spacewarp. Harrison's contribution was the "Bloater Drive". This enlarges the gaps between the atoms of the ship until it spans the distance to the destination, whereupon the atoms are moved back together again, reconstituting the ship at its previous size but in the new location. An occasional side-effect is that the occupants see a planet drifting, in miniature, through the hull."
Thus you can move an object to a new spatial co-ordinate without actually moving it.
"Bloater drive theory" is simply a drive space expanding relative to the time and square of the distance from installation and initialization of EULA acceptance in a local system. This is the Windows theory of drive space and time expansion. Anyone who reads /. should know this theory.

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Re:"Space itself" is just a mathematical trick by burtosis · 2015-03-21 00:19 · Score: 5, Informative

Not exactly. The op was relatively correct in explaining general relativity (pun intended). Nothing can move through space faster than light. However during inflation, just after the Big Bang (the first 10^-34 seconds or so) space was created much faster than light could traverse. Quantum uncertainty was able to affect locations right at the Big Bang. However general relativity shows us that if you have an unbelievably dense undilutable piece of space, it will double in size extremely quickly. This doubling separated portions of the universe that only now are reconnecting due to light speed. Dark energy will move the Big Bang from beyond our perception in only 4 billion years or so through a very similar process of space creation. Quantum uncertainty is what brought our portion of inflation in reality to an end, however it is hypothesized due to the percentage of space that rolls down the density curve is so small, inflation continues eternally somewhere. Both inflation and dark energy are mechanisms that create space directly and therefore do not violate relativity because nothing is moving through it technically. Therefore both mechanisms are a way to casually disconnect space that was once connected.
Re:"Space itself" is just a mathematical trick by Bengie · 2015-03-21 02:40 · Score: 1

Your link says " then find that the rest of the universe is moving away at very high speeds, approaching (but not exceeding) the speed of light", but we already see galaxies moving away over 2x the speed of light. Since these galaxies are technically not moving through space quickly, they experience little time dilation.
Re:"Space itself" is just a mathematical trick by michelcolman · 2015-03-21 06:12 · Score: 3, Interesting

Not our locale. The locale over there. In the post I linked to, I explained that you could use two different coordinate systems.
1. Obeying special relativity: speed of light is the same everywhere, c relative to us, and nothing can move faster. However, distant objects that are flying away at high speed (close to c) are lorentz-contracted and time is moving more slowly for them, so the universe "looks" kind of weird at a distance.
2. Modified coordinates so that the universe looks more or less the same everywhere. In this case, the speed of light in some different area is equal to c relative to the expansion speed of that area, which may be higher than c relative to us.
Really, try reading the post I linked to again.
Re:"Space itself" is just a mathematical trick by duck_rifted · 2015-03-21 07:02 · Score: 2

It's tricky to use layperson's language to describe frames, and even trickier to use layperson's language to describe concepts that developing experts can struggle with initially. The phrasing could be better, but this is how good phrasing is developed.

Consider a "frame" as a word describing a coordinate system with space and time, within which events and objects can occur. Your location can be described as a frame. In fact, your entire life can be described within the context of a frame moving in a larger frame that is, itself, moving in a larger frame, and so on. Einstein spent years trying to find a frame to which everything is relative, and he couldn't. The workaround is to treat spacetime as a physical entity.

Beyond that, this is more a topic for philosophy than physics. If we describe spacetime as Einstein instructed, then we can measure predictions that in turn show spacetime to *actually* be a physical thing that can be distorted. Whether that is a convention consequential to the way that we describe reality or a literal, physical truth will be a subject for metaphysics until the day when I can pick up a spacetime and hand it to you.

The topic in conjunction with the headline at the top of this page just says that Einstein needed something to measure against, and spacetime is that thing. Because spacetime is measured only against itself, parts of it can move faster than light, in theory. Spacetime sets the rules, so it's not subject to them. Yet in any frame, even in spacetime moving faster than light, the speed of light is still a constant and nothing in that frame can exceed it. So, if a bit of space is expanding toward you faster than the speed of light and somebody in that bit of space points a flashlight at you and turns it on, the light produced by the flashlight moves at the same speed as the light from a flashlight that you can turn on and shine back (neglecting refraction).

Without that conventional, all kinds of weird contradictions of causality arise. But the spacetime itself is still a construct that is immune to the rules that result from it. That's the great loophole in Einstein's work. If reality does not conform to that loophole then it means there is something more fundamental than spacetime that everything else can be measured relative to.
Re: "Space itself" is just a mathematical trick by michelcolman · 2015-03-21 07:55 · Score: 1

Master's degree in maths and just interested in physics. My explanation is probably not 100% accurate because it disregards things like gravity, but the general idea is correct as far as I know. It's certainly a lot more accurate than most popular explanations.
Re:"Space itself" is just a mathematical trick by michelcolman · 2015-03-21 08:10 · Score: 1

All depends on your choice of coordinates. I described two different systems:
1. A reference system that obeys special relativity. In this reference frame, nothing moves faster than the speed of light, not even those distant galaxies you are talking about. However, very distant objects are aging more slowly due to time dilation, and are compressed due to lorentz contraction. Even though the local aliens don't see anything wrong, in our reference frame they look like flat pancakes. This makes it a very subjective view of the universe, and not very practical, but perfectly in line with relativity.
2. A reference system that deliberately does not obey special relativity, but is instead chosen in such a way that the universe looks roughly the same everywhere (no lorentz contraction or time dilation from the speed of expansion). This is kind of cheating but very practical. In this reference system (which is the one most commonly used in cosmology), galaxies are indeed moving away at more than twice the speed of light, they are aging at the same rate as us, and their shape is "normal".
These two are not contradictory: we just stick different labels on the same stuff. Speed is just a change in space coordinates divided by a change in time coordinate, so by choosing different coordinates we can change the value of the speed. So yes, we do "see" galaxies moving away at 2x the speed of light if we choose to use cosmological coordinates. With special-relativistic coordinates, we "see" the galaxy moving away at a speed less than c with extra redshift because of time dilation due to its speed. The actual value for the total redshift is exactly the same. No one explanation is "better" than the other, they are perfectly equivalent descriptions using different labeling.
Re:"Space itself" is just a mathematical trick by Bengie · 2015-03-21 09:32 · Score: 1

Lorentz contraction and relativity only applies to objects moving through space. These distant objects are not moving through space. "extra redshift because of time dilation due to its speed" WTF does that even mean? When light gets emitted by an electron, it is the exact same, you know, quantum. The frequency of light is not affect by time dilation at all, it is only affected by red shifting.
Re:"Space itself" is just a mathematical trick by michelcolman · 2015-03-21 10:38 · Score: 1

They are not moving through space IF we define space in one particular way. If we define it in a different way (by using different coordinates), they do move through space. Space itself doesn't really mean anything, there's nothing physical to it, it's just a big vacuum.
Frequency is certainly affected by time dilation. If an object moves away from us at high speed (not due to the expansion of space, but simply passing by very quickly), the total redshift is a combination of classic redshift and time dilation. Time dilation slows down time for the object, so that it emits light of lower frequencies (photons with a lower energy). It's called the relativistic doppler effect. The same occurs for redshift due to the expansion of space if we use a reference frame that obeys special relativity. In cosmological coordinates, you get exactly the same value for redshift but caused solely by classic redshift (with those coordinates, there's no time dilation but the speed is higher, resulting in the same redshift).

Possible minor mistake by BlueTrin · 2015-03-20 19:47 · Score: 1

... if the conditions are right

I do not think the article mentions any special conditions ? Did I miss this part ?

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Re:Okay... by blue+trane · 2015-03-20 20:24 · Score: 1

In your analogy, the something blowing air into the balloon is moving faster than the snail.

Correct me if I'm wrong by skovnymfe · 2015-03-20 20:26 · Score: 2

Correct me if I'm wrong, but do we even know how big "space itself" is? I mean sure, we have an idea as to how much of it we can see thanks to radiation and whatnot, but who's to say it's not actually bigger than we ever thought? We live at the bum end of the galaxy, who's to say we don't also live at the bum end of a universe that expands twice or a hundred times farther in the other direction than we ever considered? And who's to say that all of what we can see actually belongs to our universe and isn't just spill-over from a bunch of intersecting universes? And who's to say our big-bang-bubble-universe isn't just one in countless universes expanding all throughout space itself? What is space itself anyway? Isn't it just an arbitrary construct created to give ourself some sense of importants, some sense of being in a specific place and time, because our simple brains can't cope with not knowing where we are and how the universe revolves around us? What is the question about life, the universe and everything, anyway?

Re:Correct me if I'm wrong by Anonymous Coward · 2015-03-20 21:43 · Score: 2, Informative

No, you're right.
We know it's bigger than a certain value, and that if the acceleration of space were constant, zero or some other value, that the currently visible universe is about 90 billion light years across "now", though when the distant regions shed their light that we're only now seeing ~14 billion years later, that space was ~40 billion light years across. But since there was an expansion faster than light at some time proposed to explain the look of the universe today, the universe THEN was bigger than ~30 billion light years. HOW MUCH BIGGER we don't know. But it wasn't *smaller*.
As to "what is space", space is the distance between things.
When traveling between two things separated by space, we call that speed, and it cannot be faster than light in a vacuum.
However, that distance between those two things doesn't have to be constant and doesn't have to move, therefore it doesn't have to increase below some maximum threshold.
Re:Correct me if I'm wrong by burtosis · 2015-03-20 23:27 · Score: 5, Interesting

Correct me if I'm wrong, but do we even know how big "space itself" is? I mean sure, we have an idea as to how much of it we can see thanks to radiation and whatnot, but who's to say it's not actually bigger than we ever thought? We live at the bum end of the galaxy, who's to say we don't also live at the bum end of a universe that expands twice or a hundred times farther in the other direction than we ever considered?

well because of the patterns we can measure in the cosmic microwave background we can measure the 'flatness' of space itself. Positive and negative curvature imply a finite size to the universe. As it is we have measured that space is at least 1000 times the volume we can 'see' in the visible universe. Possibly its infinitely large.

And who's to say that all of what we can see actually belongs to our universe and isn't just spill-over from a bunch of intersecting universes?

Because we can measure distance we know that we are sitting at the 'center' of the visible universe as it is isotopic (the same in every direction). Technically you yourself live across a nearly infinite number intersections of universes that were in contact during the early inflation times, but separated and only now are reconnecting. Your own two eyes each peer into a slightly different universe where the percieved 'center' of the visible universe is offset a few inches. Each eye can 'see' a few nano light seconds beyond the visible horizon of the other.
And who's to say our big-bang-bubble-universe isn't just one in countless universes expanding all throughout space itself?
actually about as many cosmologists agree this is the case as climatologists agree on anthropogenic climate change. It appears highly plausible if not actually true.

What is space itself anyway? Isn't it just an arbitrary construct created to give ourself some sense of importants, some sense of being in a specific place and time, because our simple brains can't cope with not knowing where we are and how the universe revolves around us?

Space itself is likely just a mathematical construct. It would explain why math works so frekishly well at explaining the physical world while no AI/purpose driven explanations make any sense at all. It's even possible that all possibilities of our physical laws (or even combinations of all possible laws) 'exist' statically and eternally with only the perception of time and choice when you find yourself inside a particular one, continually only ever sensing a tiny fraction of it. The the theory of everything may just be the ultimate ensemble theory.

What is the question about life, the universe and everything, anyway?
It's actually plausible the only 'purpose' of life is to increase entropy faster that without it. Like fire burning or water running down hill it simply is a pathway to diffuse energy. It's why all life has a version of eating and pooping. There is no 'purpose' but that actually is the best scenario for us all - we have the freedom to make our own purpose. The computational complexity of the universe itself is so vast free will really feels free, it is an amazing experience and one i have great trouble topping in my imagination.
Re:Correct me if I'm wrong by skovnymfe · 2015-03-21 01:13 · Score: 1

Hm. So I'm not completely off my rocker. That's actually quite comforting to know. I appreciate you taking the time to reply to all of my ranting.
Re:Correct me if I'm wrong by ZorglubZ · 2015-03-21 02:10 · Score: 1

That's the answer; apparently the question is whatdoyougetifyoumultiplysixbynine, or that's as close as we've got.
Re:Correct me if I'm wrong by burtosis · 2015-03-21 02:23 · Score: 1

The result is correct in base 13
Re:Correct me if I'm wrong by burtosis · 2015-03-23 06:26 · Score: 1

There really isn't an edge to the universe. We live inside a bubble due to the finite and fixed speed of light. So roughly 15 billion light years away, light took 15 billion years to reach us and therefore is comming from the early stages of the universe. The universe was too hot and dense for the first 350k years or so, the microwave background is left over from this time when the universe cooled enough to become transparent. Neutrinos can pass through matter easily, even an entire planet. It's possible in theory to build a telescope to see back 350k more light years to within 1 second of the Big Bang. But there is a hard limit, we cannot use particles to see any further because none existed before that time.
you can think of our universe being defined by paths of light, after all that's what you would 'see' and they trace space like a pen on paper. They ride the curvature of space caused by gravity. Let's day hypothetically there was no more matter after a point (and no particles either). In this case gravity would cause that space to bend back on itself. In such a case you essentially cannot escape as you would curve back into the existing universe. Similar principles hold if the matter is too dense or to sparse, the universe essentially becomes a closed off bubble. Within our physical laws only a very specific and exact value of density will allow for space to extend forever. There simply isn't an outer boundary that can ever be reached, in any case of our physics, just one that can be seen - the initial forming of our space time itself.
there are internal boundaries, such as black hole horizons. We are understanding more and more about them. While we don't have the means to actually test at those energies (maybe the large hadron collider will spit out some miniature ones we will see) there has been a great deal of debate about exactly what particles, entanglement, forces and energies infalling matter experiences.

You don't know what I know by wonkey_monkey · 2015-03-20 20:44 · Score: 2, Funny

You know the fundamental principle of special relativity

How do you know I know that? Nice way to make your less-informed readers feel stupid.

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Re:You don't know what I know by Anonymous Coward · 2015-03-20 23:54 · Score: 1

You know the fundamental principle of special relativity
How do you know I know that? Nice way to make your less-informed readers feel stupid.
If you had postponed your reaction until the end of the sentence, you *would* have known. This way, *you* made yourself look stupid. Congratulations!

I thought I did know the principles by pettik · 2015-03-20 20:47 · Score: 5, Insightful

And it does not say anything against going faster than light, just about accelerating from below the speed of light to the speed of light. Which would need unlimited energy. But actually just going faster than light is no problem at all.

Re: I thought I did know the principles by Anonymous Coward · 2015-03-20 21:04 · Score: 2, Informative

The actual principle is that the speed of light is constant for any inertial reference system.
Re: I thought I did know the principles by BlackPignouf · 2015-03-21 01:36 · Score: 1

in vacuum.
Re: I thought I did know the principles by Anonymous Coward · 2015-03-21 01:57 · Score: 1

for spherical chickens.
Re: I thought I did know the principles by Anonymous Coward · 2015-03-21 02:11 · Score: 1

That are non-rotating.
Re: I thought I did know the principles by Anonymous Coward · 2015-03-21 03:40 · Score: 1

that are electrically neutral.
Re:I thought I did know the principles by Baloroth · 2015-03-21 04:13 · Score: 1

And it does not say anything against going faster than light, just about accelerating from below the speed of light to the speed of light. Which would need unlimited energy. But actually just going faster than light is no problem at all.
No, it says nothing can go faster than the speed of light. At the speed of light, objects with mass would have infinite energy, and anything faster than light would require imaginary space-time to exist (since the factor for transformations involved a sqrt(1-v^2/c^2), if v is greater than c that means the object under the square root is negative, and you get an imaginary number, which is an unphysical result, i.e. it cannot happen).

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Re:I thought I did know the principles by david_thornley · 2015-03-23 08:37 · Score: 1

Light doesn't have mass (it does have momentum), and light doesn't go faster than the speed of light. Space isn't an object.

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Re:I thought I did know the principles by david_thornley · 2015-03-23 08:40 · Score: 1

Special Relativity doesn't mean nothing can go faster than light, and there's nothing obviously nonphysical about imaginary coordinates. Coordinate systems describe reality, they don't mandate it.
It is true that you can't accelerate to the speed of light. It's also true that, given Special Relativity, FTL travel is equivalent to time travel.

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Stupid Question by Puff_Of_Hot_Air · 2015-03-20 21:35 · Score: 2, Interesting

The fact that time slows for you as you go faster; doesn't this imply that if you could travel at the speed of light, then you could reach anywhere in the universe in 0 relative (to you) time? I mean the thing you were aiming for might be gone by the time you got there, but still. If that EmDrive thing is a real thing, doesn't long distance space travel become a real possability?

Re:Stupid Question by wierd_w · 2015-03-20 22:23 · Score: 2, Informative

No. The emdrive would have to accelerate endlessly, and would consume all available energy in the universe, and STILL not achieve lightspeed. It's the propulsion version of Xeno's paradox.
Re:Stupid Question by Puff_Of_Hot_Air · 2015-03-20 22:47 · Score: 1

I didn't ask can we get to the speed of light, I asked "does space travel become possible?" We would just need to go at some % speed of light. I thought this was impossible at the moment due to accelerating == throwing stuff over the side, and I had assumed even with EmDrive physics defying abilities it would still take "too bloody long". But perhaps not is the point.
Re:Stupid Question by albacrankie · 2015-03-20 23:42 · Score: 1

Doesn't seem a stupid question to me.

But at the speed of light not only does time slow, but space contracts. So I'm not sure we can say that light "travels" through space. It just attaches itself to whatever is touching it. So if we could convert all our body mass to photons, attach those photons to say a planet in another galaxy, and hope someone at the other end has a tool for reconverting those photons back to their original state, then perhaps it's possible. But if you did the return journey because you'd forgotten your swiss army knife, you'd find yourself a huge number of years in the future and that knife might be hard to find.
Re:Stupid Question by tomhath · 2015-03-21 00:09 · Score: 2

I didn't ask can we get to the speed of light, I asked "does space travel become possible?"
If you could accelerate yourself to a speed close to the speed of light then you could go to a distant star within your lifetime.

We would just need to go at some % speed of light.

Getting to a high enough % to make a difference is the part which is impossible.
Re:Stupid Question by burtosis · 2015-03-21 00:36 · Score: 1

Yes. From the perspective of a photon it travels infinately fast. From your perspective it looks like there is no light speed limit, time dilation is what causes outside observers to see you as never hitting the light speed limit, just as you say.
however you cannot travel through space faster than the speed of light. Any attempts to bend space or time to circumvent that require such unrealistic amounts of energy (such as entangling two black holes and pulling them apart, etc.) that it will likely never happen. Space travel is so slow the universe will age and die of old age before you go an appreciable distance.
Re:Stupid Question by Shimbo · 2015-03-21 02:09 · Score: 2, Informative

You need two things to make such a sort of a journey practical: as well as the reactionless drive, you need some sort of Star Trek like deflector shield: because to you every 'stationary' hydrogen atom is a cosmic ray travelling at near light speed. And God help you if you hit a grain of dust.
Re:Stupid Question by cjameshuff · 2015-03-21 02:19 · Score: 1

Stated another way, as your travel speed approaches the speed of light, your experienced travel time approaches zero. Note that time dilation actually happens both ways...the ship sees the surroundings as being time dilated just as much as they see it as being time dilated, and any physical measurements taken on the ship while it is coasting will be indistinguishable from those taken "at rest". It's only the fact that it's the ship that accelerates at the start and end of the trip that breaks the symmetry.
However, you reach a point where you have to convert most of the mass of your ship into energy well before you reach really high levels of time dilation. If the EmDrive worked as described, it would break a number of conservation laws and allow production of energy and momentum from nothing, which would be a way around this, but more realistically is an indication that the EmDrive doesn't work.
Re:Stupid Question by david_thornley · 2015-03-23 08:42 · Score: 1

Physics says you can't accelerate anything with mass to lightspeed. Engineering says you can't get close for any spaceship that can contain a human. These are two different kinds of impossibility.

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Re:Stupid Question by RespekMyAthorati · 2015-03-23 09:17 · Score: 1

What if the "starship" consisted of a 100 km diameter asteroid with a propulsion engine built on its surface?
A big rock can take a lot of abuse.

Also, the mass of the asteroid could be used as fuel for the engine (assuming that we can convert its mass directly into energy).
Re:Stupid Question by RespekMyAthorati · 2015-03-23 09:23 · Score: 1

Maybe you didn't notice that Puff_Of_Hot_Air said

If you could travel at the speed of light, then you could reach anywhere in the universe in 0 relative (to you) time?
The answer is yes.
For photons (the only thing that can travel at the speed of light) the passage of time is non-existent.

Isn't that how warp drives work? by Spy+Handler · 2015-03-20 22:19 · Score: 2

By expanding space behind the Enterprise and contracting the space in front of it?

Re:Isn't that how warp drives work? by towermac · 2015-03-20 22:42 · Score: 5, Insightful

Yes. And the summary is a lie: TFA doesn't explain 'how' the universe expands FTL; just that it does.
Re:Isn't that how warp drives work? by Bengie · 2015-03-21 12:23 · Score: 1

Relative to our frame of reference, there are objects moving away form us faster than 2c.
Re:Isn't that how warp drives work? by ChrisMaple · 2015-03-22 04:51 · Score: 1

Your understanding of relativity fails. I don't know the exact numbers, but roughly speaking, it goes like this. If planet A is moving left away you at 0.9c, and planet B is moving right away from you at 0.9c, then an observer on planet A will say that planet B is receding from him at 0.99c, and vice versa.

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Re:Isn't that how warp drives work? by david_thornley · 2015-03-23 08:49 · Score: 1

When you get into the weirder areas of physics, it becomes somewhere between very hard and impossible to describe the physics in nontechnical terms. We generally understand reality on a human scale, and all our intuition is based on massive experience with objects of a scale that you usually need neither quantum mechanics nor relativity to understand them. There's exceptions: the frequencies of black-body radiation and some other things depend on light coming in discrete pieces, which means you have to have some wave-particle duality, but we don't normally perceive the details.

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Re: Okay... by BlueTrin · 2015-03-20 22:31 · Score: 1

I don't understand your point: it does not invalidate his analogy

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Seems obvious? by Anonymous Coward · 2015-03-20 23:07 · Score: 1

This seems obvious to me because if you have light on either edge of the universe travelling outwards the distance between the frontiers will be growing at 2x speed of light.

But i am no physicist so i'm probably not understanding it.

Re:Seems obvious? by Anonymous Coward · 2015-03-21 00:52 · Score: 5, Informative

No, the result of that light would be, from our point of view, going at light speed too.
Any sublight speed plus any other sublight speed must itself be sublight speed. At the limit of the speed of light, adding the speed of light to itself results in the speed of light. What happens to light is that its energy doubles, not its speed, what happens to mass is its total energy increases, but still remains finite and therefore sub light speed velocity.
This is the basic result of special relativity.
Expanding space isn't traveling in space, therefore the gap between two things can expand faster than light because nothing is moving. Those two things can themselves travel in this changed space, but their velocity will be limited to light speed no matter what they are.
The space between us and something that was 15 billion light years from us is expanding faster than the light it is emitting toward us can travel, therefore we will never see the light and that thing is beyond our light horizon of the visible universe.
Re:Seems obvious? by burtosis · 2015-03-21 01:05 · Score: 1

Yes that is correct. The distance between those two points is increasing at 2x light speed. However that is not traveling through space faster than the speed of light. Space can be created, bypassing the light speed limit. Read more on inflationary theory, or watch susskind explain inflation on youtube.
Re:Seems obvious? by burtosis · 2015-03-21 02:01 · Score: 1

The space between us and something that was 15 billion light years from us is expanding faster than the light it is emitting toward us can travel, therefore we will never see the light and that thing is beyond our light horizon of the visible universe.
Technically dark energy is causing something 19billion light years away to expand faster than the speed of light (or so). This is outside the visible universe. If expansion was causing things to expand faster than the speed of light at 15 billion light years the cosmic microwave background would be more red shifted. In fact if it was 14 billion years away the microwave background would be completely wiped from our existence. Thus the background being visible is proof it isn't happening inside that radius.
every second as i type the light bubble of our universe expands by 386 thousand miles or so in radius, continually exposing new universe that was last connected only during inflation.

Re:Relativity by Anonymous Coward · 2015-03-20 23:53 · Score: 1

There have been numerous tests of both Special and General Relativity, so it has been "questioned" quite thoroughly. It's just that, so far, every single test has confirmed the predictions made by Relativity or derived from it.

For a massive particle, no acceleration is enough by Anonymous Coward · 2015-03-21 00:03 · Score: 1

You can accelerate at any rate you like, even infinity, and you will never reach the speed of light wrt your original reference frame within a finite time.

Re:For a massive particle, no acceleration is enou by Anonymous Coward · 2015-03-21 00:21 · Score: 1

Which is the (not news and not new) point of the article. By expanding the space between two objects they will appear to accelerate away from each other, even though they remain at rest in their local reference frames. Given enough time and distance - like billions of light years - the two objects will eventually be moving away from each other at speeds beyond the speed of light.

At that point they will for all intents and purposes be completely segregated, with no way for one to even detect the existence of the other. Nothing, not gravity, not light, nothing would be able to reach from one object to the other.

This is postulated for the "local universe" bubble that we live in. Beyond a certain radius, the rest of the universe might as well not exist. Because the expansion of the universe is accelerating, that bubble will shrink over time (as a fraction of the entire universe). Eventually only the locally gravitationally bound objects will be in our "experiential universe". All of the rest of it will be beyond our existence.

Of course, none of us will be around for that part of the evolution of the universe.....

Re:For a massive particle, no acceleration is enou by burtosis · 2015-03-21 00:30 · Score: 1

If you put a location to your original reference frame that's not entirely true. Space may be created along your path to effectively increase your apparent speed beyond light speed. For more reading study inflationary theory.

Re:For a massive particle, no acceleration is enou by Intrepid+imaginaut · 2015-03-21 01:04 · Score: 2

Unless we manage to harness the mechanism of spatial expansion (and presumably reduction), that is.

Re:Or Space isn't expanding by burtosis · 2015-03-21 01:08 · Score: 1

You should watch susskind on youtube discussing inflation. Not only can space be created, infinite space can be created within a finite volume due to infinite time. If you can wrap your brain around that, well it's not easy. Take a look here

Space first by Livius · 2015-03-21 01:17 · Score: 2

We'll understand the expansion of space better once we figure out what space is.

The best source of physics info on the web by burtosis · 2015-03-21 01:19 · Score: 5, Interesting

Search for susskind on youtube. He is a famous professor at Stanford who not only was one of the original creators of string theory but also beat up Stephen hawking on the nature of black holes and got him to admit he was wrong. I recommend special and general relativity series, also the one on inflation. He avoids the arcane and makes physics pedestrian yet provides the mathematical basis for each topic. He gets serious props in my opinion for freely sharing his knowledge online, giving anyone the ability to essentially audit his classes.

A space ship is not a photon... by ninguna · 2015-03-21 01:31 · Score: 1

Maybe I have this wrong, but wouldn't our imaginary space ship be able to turn on it's rockets and accelerate? So when it is a billion light years away, and in space that was receding from Earth, from Earth's point of reference, it could speed up to the local speed of light, in the rocket's now current frame of reference. And thus with repeated application of propulsion along its journey, make up for the recession of space.

Space expanding faster than light by rossdee · 2015-03-21 01:35 · Score: 1

I thought that for a short time after the big bang there was a period of 'inflation' when the universe expanded faster than light.
But its not expanding like that now.

Re:Space expanding faster than light by arth1 · 2015-03-21 08:11 · Score: 1

I thought that for a short time after the big bang there was a period of 'inflation' when the universe expanded faster than light.
But its not expanding like that now.
Sure it is. Not at the same rate, but given two spacetime points far enough away from each other, the distance between them can increase much more than the speed of light.
The thing about expansion is that it will appear "faster" the farther apart two points are. On the proverbial balloon you blow up, two marks that are close together will move much slower apart than two marks that are far from each other. And this is a very very big balloon. The ant called Andromeda crawls towards the ant called Milky Way faster than the expansion happens, because the expansion is very small at such a short distance. But an ant that's much farther away won't ever be able to reach us, because the distances involved means a larger distance increase too. And an ant that's far enough away won't even be able to send a light signal to us, because the distance expands more than the speed of light, relative to us and it. The edge of the observable universe simply means that anything beyond it recedes faster than c. But no movement is involved, just a distance increase.

Does the speed of light change? by GoodBuddy · 2015-03-21 02:44 · Score: 1

I've wondered for quite a while now how scientists know that light traveled at the same speed 14 billion years ago as it does now. Of course, if they decided this was a possibility it would throw a lot of calculations off.

Re:Does the speed of light change? by arth1 · 2015-03-21 04:04 · Score: 3, Insightful

The speed of light cannot change, because it's the definition of speed, not a measured speed. When we say that the speed of light in vacuum is 299 792 458 m/s, what we're defining is the meter and the second relation. If you "slowed" the speed of light, distances would shorten and time would expand and c would still be 299 792 458 m/s. I.e. you would not notice anything. Only an observer outside our universe could possibly detect it, because inside our universe, we exist relative to c.
Re:Does the speed of light change? by arth1 · 2015-03-21 06:13 · Score: 2

Was it always that way? At some point someone must have tried to measure the speed of light...
Oh, absolutely. Usually by bouncing light back and forth between mirrors far apart. And we still do - we've just have realized that's it's not really the speed of light we're really measuring, but the distance/time relation.
Because time itself is variable. A second here is not the same as a second at a GPS satellite. But the speed of light in vacuum is the same.
Anyhow, that's our current point of view, because it makes it easiest to do calculations and make observations. We could use a point of view where time was a constant, and have a very variable light speed instead. It's just as mathematically legal as a point of view, but it would complicate how we have to perceive things. Planck's constant would be variable, and atoms smaller or larger depending on location. We'd have to shift our view of distant galaxies to being very small, close, and low energy, but having a very slow speed of light compared to our speed of light. A headache, even if mathematically valid.
So Einstein took the simpler point of view, and let distance and time be variables with a fixed relation.
Re:Does the speed of light change? by arth1 · 2015-03-21 07:47 · Score: 1

If it weren't, it would be detectible. The cosmic background radiation, for example, would be doppler shifted and have larger temperature variations than what we observe. We'd see more older galaxies far away and more younger galaxies close to us, depending on how the speed of light had varied. That's not what we observe, though.
Also, gravity would behave differently, and stars would have different colors and spectral lines than what we observe, depending on what the speed of light were where/when the stars exist(ed). We'd have small stars turning into black holes, and giant stars much bigger than what is possible with c being what we think it is.
Again, we don't observe that.
Re:Does the speed of light change? by rawoke083 · 2015-03-24 01:11 · Score: 1

If ever you forgot the speed of light you can use this RILT: Basically you have to remember 3.10 but then I always forget to what power. The above rilt says you if you think about the speed of light being near infinite and turn the 8 on the side it looks infinite http://www.riltpedia.com/8/spe...

Re:How do we know that by burtosis · 2015-03-21 02:52 · Score: 3, Informative

We know that space can be created faster than the speed of light, this is the basis for inflationary theory and the big bang. Many measurements can be made that independently verify inflation, though it is true it does not have the level of proof a theory needs (almost though). For example, the size of temperature fluctuations in the cosmic microwave background support faster than light expansion of space.
it's a far cry from religion that has zero evidence in support and absolutely massive amounts of facts that disprove its tenants. There is no evidence to show inflation false.

Re:Space by UnknownSoldier · 2015-03-21 04:41 · Score: 1

No, mind.

To Make You Feel Better... by Roger+W+Moore · 2015-03-21 05:06 · Score: 2

How do you know I know that? Nice way to make your less-informed readers feel stupid.

Well actually, just to make you feel better, the OP clearly does not know the fundamental principles of special relativity because not going faster than light is not actually one of them. There are two "fundamental principles" of special relativity called "the postulates of Special Relativity" and these are:

The laws of physics are the same in all inertial frames.
The speed of light is the same in all inertial frames,

The limit on not going faster than light comes from adding a requirement for causality i.e. that if event A causes event B then everyone in all inertial frames had better agree that A occurs before B. Note that this is not 'see A before B' it actually affects the time-ordering of events so that you would be able to stop A from happening after seeing B occur.

If you can transmit information faster than light then this is exactly the same as being able to transmit information backwards in time under relativity. Apart from the issue with paradoxes, you can be very sure is not possible because you don't see us physicists winning lotteries or making a mint on the stock exchange.

Re:To Make You Feel Better... by Bengie · 2015-03-21 11:46 · Score: 1

The order of events do not always agree for all frames, but I assume that they'd have to agree for the ordering of certain related events for causality to work, but that may not be true either.

An example is assume there is a train, a tunnel, and another observer. Assume the train is longer than the tunnel. Now assume the other observer is watching the tunnel from a perpendicular view.

If the train is moving very fast, it will contract in the direction of its movement. From the perspective of the other observer, the train is shorter than the tunnel, but from the perspective of the train, the tunnel is shorter than the train. Now if this tunnel has the ability to close its entry and exist. from the other observer, both the entry and exit can close at the same time and the entire train fits within the tunnel, then the exit and re-open and allow the train to exit the tunnel.

From the perspective of the train, the exit closes first, then right before the train reaches the exit, the exit door opens, then the entry closes.

The events have a different ordering, they have to, because they cannot agree on the lengths.
Re:To Make You Feel Better... by Roger+W+Moore · 2015-03-22 17:28 · Score: 1

The order of events do not always agree for all frames
They do if one event causes the other: that is the very definition of causality. You are confusing causally connected events from ones which are not causally connected. In your example the two tunnel gates close simultaneously in one frame which means they cannot be causally linked i.e. the fact that one gate shuts does not cause the second gate to shut, some third event caused them to shut (e.g. someone pressing a button). This is easy to see because if I block one of the gates from shutting it will not affect the other gate.

However if we take the gate shutting and the train then hitting it ANY observer in ANY inertial frame will agree that the gate shut first and then the train hit it. If the train were travelling faster than c then I would be able to find a frame where the train hit the gate first and THEN the gate closed. If I then stopped the gate from closing (which I could do in that frame) you have a major paradox.

obvious by slashmydots · 2015-03-21 10:24 · Score: 1

Matter can't travel faster than light because of gravity. Space contains no matter. In fact, it's not "moving" either because it isn't a thing and existing space isn't being relocated. The properties of nothingness are changing to become space at a speed faster than the maximum speed at which matter can travel through it. That actually makes perfect sense because it prevents matter from ever flying out of the universe or hitting the edge of space. I don't know why they're presenting this like it's some amazing new development. It's extremely simple logic.

Light going faster than the speed of light? by Kevin+Fishburne · 2015-03-21 13:40 · Score: 1

This is probably a really stupid question, but if light has a maximum speed but is also affected by gravity, what would happen if you shined a flashlight/torch into a black hole? It's going the speed of light at the flashlight but should increase in speed as it approaches the black hole's gravity well. Does the light just keep the same speed until it joins the black hole?

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Re:Light going faster than the speed of light? by ChrisMaple · 2015-03-22 06:26 · Score: 1

You have posed a clever question to which I don't know the answer. Let me alter your question a bit to add some further possibilities. Suppose a photon is aimed off-center in the general direction of a black hole, so that gravitational forces alter the trajectory of the photon, but do not pull it into the center of the black hole or cause it to collide with something.
Depending on who you listen to, a photon either has some vestigial mass or it only has a resting mass equivalent to its energy. As it nears the black hole, its effective mass might increase, and/or its frequency/wavelength might change (implying a change of energy), and/or it might (magically) somehow split to shed the excess energy (I think I'm being silly here.) On to my more important point: if the photon passes the event horizon, still being aimed not to collide with anything, what stops it from coming back out again? Don't say it can't because nothing can come back out once having passed the event horizon, that's just begging the question. What mechanism actually prevents it from coming back out if nothing acts on it to reduce its energy? If something reduces its energy, what is it and how does it do so?
Keep in mind that close to a black hole calculations have to include relativistic effects, thus numeric results are going to be different for different frames of reference. Intuitive answers may be invalid.

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Re:Light going faster than the speed of light? by cjameshuff · 2015-03-23 07:08 · Score: 1

More than that...in the frame of the emitter at its higher location in the gravity well, the light actually appears to slow as it passes through the well (Shapiro delay). Measured locally, the light is traveling at the same speed no matter where you look, but it's taking a longer path through curved space-time and its speed in a distant reference frame can be something different.
Re:Light going faster than the speed of light? by Kevin+Fishburne · 2015-03-23 17:27 · Score: 1

@AC and cjameshuff: That is very interesting, and well-explained. Physics is beyond my areas of expertise, but I find it fascinating. As abstract as a lot of the science sounds to a layperson, I see it as a sort of attempt at answering a question we've always had, which is "What the hell is going on? What is all of this?" From the ocean disappearing into the horizon to the spinning pinpoints of light in the sky, physics and all its sub-disciplines someday will provide a solid foundation for us to usefully speculate on the ultimate question, which is "Why?"

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More added value equals the speed of light + by __aanbvm4272 · 2015-03-21 17:08 · Score: 1

It would seem obvious if we were able to attain the speed of light and we should, someday, that inching over that boundary with added thrust would simply happen. Much like the speed of sound, once thought to be a boundary proved a minor one. I don't suppose it will be like warp speed on Star trek, a flash. BUT it might appear to make one disappear if you were able to see it happen.

What about the objects in that space? by Tony+Isaac · 2015-03-21 17:33 · Score: 1

Just because space may expand faster than light, does that mean the objects within that space also move apart faster than the speed of light? I'm not sure that one implies the other.

Re:What about the objects in that space? by david_thornley · 2015-03-23 09:37 · Score: 1

Yes, at least in theory that happens. We can't actually observe it, since we can't observe anything going faster than light away from us. Over short distances, the expansion of space is negligible. There is speculation that the expansion will speed up so that it's significant even over shorter distances, tearing apart the local group of galaxies, then galaxies, then stars and planets, and finally ordinary things and molecules and atoms. That's called the "Big Rip".

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Re:What about the objects in that space? by Tony+Isaac · 2015-03-23 17:19 · Score: 1

Of course, since science is fundamentally based on observation, and you can't observe inflation, that would seem to make inflation lie outside the realm of science.

Re:Get your facts right by Bengie · 2015-03-22 02:29 · Score: 1

Information cannot move through any point in space faster than c. That simple. If you want to go faster than c, then you need to move the points instead of moving through them.

Re: Okay... by ChrisMaple · 2015-03-22 04:21 · Score: 1

A. Nothing can go faster than the snail.

B. The balloon goes faster than the snail.

A. contradicts B.. The argument shoots itself in the head before it gets moving.