How Space Can Expand Faster Than the Speed of Light

StartsWithABang writes You know the fundamental principle of special relativity: nothing can move faster than the speed of light. But space itself? That's not a "thing" in the conventional sense. Two years after coming up with special relativity, Einstein devised the equivalence principle, and thus began the development of general relativity, where space itself would have properties that changed over time, responding to changes in matter and energy. This includes the ability for it to expand, even faster than the speed of light, if the conditions are right.

Comments

Space

[Anonymous Coward]

The Final Frontier. Or is it?

Re:Space

[UnknownSoldier]

No, mind.

60 years later

[Anonymous Coward]

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

Re:60 years later

[hcs_$reboot]

Indeed, we all keep him in our hearts.

Re:60 years later

[Anonymous Coward]

60 years later and we still don't give proper credit.

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

"Space itself" is just a mathematical trick

[michelcolman]

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

[Anonymous Coward]

Your post was lengthy, but not really correct. Lots of words and not really saying anything.

is not tied to our location but rather to local "space".

It's not tied to our location, just our locale? Great logical construction.

Re:"Space itself" is just a mathematical trick

[Anonymous Coward]

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

[Anonymous Coward]

Read it again.

Re:"Space itself" is just a mathematical trick

[WoOS]

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

[Anonymous Coward]

It was longer than TFA and said even less. No thanks, I have enough gray hairs.

Re: "Space itself" is just a mathematical trick

[Anonymous Coward]

Just curious, do you have a physics education? You seem very sure, but if just doesn't look right to me..

Re:"Space itself" is just a mathematical trick

[Anonymous Coward]

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

[Anonymous Coward]

Everything is possible in a Universe of ME.
Unless I declare it not.

Re:"Space itself" is just a mathematical trick

[deviated_prevert]

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.

Re:"Space itself" is just a mathematical trick

[burtosis]

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

[Bengie]

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

[michelcolman]

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

[duck_rifted]

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

[michelcolman]

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

[michelcolman]

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

[Bengie]

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

[Anonymous Coward]

Speed of light the fastest... How narrow minded that is. It locked everyone that relies on authoritarian learning into a box. Of course they are silly for trusting authoritarian learning in the first place instead of using observations and your own ideas and see where it takes you.
The problem with paper studies comes when you leave the physical universe and delve into theory alone, you'll be lost.
Einstein's theories are often quite workable, but who's to say they are based on actuality?
Better to say a number of theories points us down a direction, and if at some point there are things that cannot be explained properly? OK, so you have reached the edge of the workability of that theory, now you know you don't know everything about it. Time to not hold any theorem sacred if you want to break through.
Just look on all these formulas that has arbitrary values seemingly out of the blue because it makes something balance, but cannot be exactly explained. Or laws with exceptions. It's a law with limited workability if it has exceptions!
One has to look at any conclusions based on research as something that may or may not be an absolute truth. With that I mean it works exactly so under all applicable conditions. If it does not then it is something with limited workability.
Space being "a mathematical trick" is a kinda funny theory. It along the line of saying a falling tree would not actually make a sound if nobody was there to hear it. You'd better define nobody. Animals, insects affected by the shockwave etc. You have to be kinda lost if you are not certain which way it is. (If you are one of those then I hope you have some other way of being valuable to others. You the reader.)

Re:"Space itself" is just a mathematical trick

[michelcolman]

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

[BlueTrin]

... if the conditions are right

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

Re:Possible minor mistake

[Anonymous Coward]

I thinik they mean like you're going faster than 60 mph, but only if the conditions are right -- the condition that you're traveling faster than 60 mph.

Okay...

[rJah]

Not exactly news, but looks like a comprehensive article (just skimmed it, didn't read).

I remember reading about this years ago. The expansion of the early universe was due to strong gravity repelling instead of attracting, IIRC. Maybe someone can correct me if they know.

To use an analogy: space is the surface a balloon, and light is a snail on the surface of that balloon. Even if nothing can go faster than the snail on that balloon you can still blow up the balloon so it exapnds faster than the snail can go.

Re:Okay...

[blue trane]

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

Re: Okay...

[BlueTrin]

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

Re: Okay...

[ChrisMaple]

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.

Re: Okay...

[JimFive]

A. Nothing can go faster than the snail.

Not quite: Nothing on the balloon can go faster than the snail.

B. The balloon goes faster than the snail.

Not necessarily. Imagine that the balloon has equally spaced marks, for convenience we'll say there are 40(*) marks around the equator of the balloon and they are 10 mm apart. The snail takes 1 second to go 10 mm. However every second the balloon is expanded such that the distance between each mark increases by 1 mm. The snail is moving 10mm/second and the balloon is expanding 1mm/(10mm*sec).

Now, how long will it take the snail to get halfway around the balloon?
What, if anything, is moving faster than the snail?


(*)Note, I didn't do the math on this so it's possible the snail can make it halfway around, if so you can increase the initial circumference of the balloon until the snail can't get around it because inflation happens at a faster rate than the snail can move.

Correct me if I'm wrong

[skovnymfe]

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

[Anonymous Coward]

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

[Anonymous Coward]

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?

42

Re:Correct me if I'm wrong

[burtosis]

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

[skovnymfe]

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

[ZorglubZ]

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

[burtosis]

The result is correct in base 13

Re:Correct me if I'm wrong

[EricTheO]

We so often discuss what the "Big Bang" may be, but we rarely discuss what the... let's call it... Edge of the Universe is like. Would it be a discrete boundary or a diffusion of particles and energy perhaps even a new set of physical laws?

Re:Correct me if I'm wrong

[burtosis]

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

[wonkey_monkey]

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.

Re:You don't know what I know

[Anonymous Coward]

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

[pettik]

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

[Anonymous Coward]

The actual principle is that the speed of light is constant for any inertial reference system.

Re:I thought I did know the principles

[Anonymous Coward]

What acceleration would be required for a velocity to go from zero to the speed of light since the big bang?

Re: I thought I did know the principles

[BlackPignouf]

in vacuum.

Re: I thought I did know the principles

[Anonymous Coward]

for spherical chickens.

Re: I thought I did know the principles

[Anonymous Coward]

That are non-rotating.

Re: I thought I did know the principles

[Anonymous Coward]

that are electrically neutral.

Re:I thought I did know the principles

[Baloroth]

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).

Re: I thought I did know the principles

[Anonymous Coward]

African or European?

Re: I thought I did know the principles

[Anonymous Coward]

Actually, even in a non-vacuum. When light interacts with matter, it doesn't slow down; it just gets to the destination more slowly due to the detours.

Re:I thought I did know the principles

[Anonymous Coward]

if you want to be pedantic i believe it implies that all objects with mass can't go faster than the speed of light.

it says nothing about items without mass...such as space expanding

Re:I thought I did know the principles

[david_thornley]

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.

Re:I thought I did know the principles

[david_thornley]

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.

Stupid Question

[Puff_Of_Hot_Air]

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

[wierd_w]

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

[Puff_Of_Hot_Air]

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

[albacrankie]

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

[tomhath]

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

[burtosis]

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

[Anonymous Coward]

Unless you quite simply converted all of your information to light and then reconverted at ur dest.

Re:Stupid Question

[Shimbo]

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

[cjameshuff]

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

[Anonymous Coward]

That's why photons are still minty fresh when they reach you from the far side of the universe -- to them, it's still the first moment of existence.

Re:Stupid Question

[Anonymous Coward]

Acceleration is a matter problem... energy (light) has no problems moving at the speed of light.

I remember reading a scifi story where a beam of radiation was shaped/encoded such that to "construct" a physical thing at the destination... you hit interstellar gas just right, and it constructs to form more complicated things... (yes, scifi). Anyways, just saying, we can imagine far fetched ways that are in principle not absolutely impossible (e.g. using up all energy of the universe).

Re:Stupid Question

[Anonymous Coward]

If you're going to be slamming into all this hydrogen, why not fuse it for energy?

Re:Stupid Question

[david_thornley]

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.

Re:Stupid Question

[RespekMyAthorati]

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

[RespekMyAthorati]

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?

[Spy Handler]

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

Re:Isn't that how warp drives work?

[towermac]

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?

[Anonymous Coward]

question: How can space expand faster than the speed of light?

answer: why yes, some thing do seem to move faster than the speed of light, but that's because it's the space expanding between the objects at such rate, not the speed of the objects themselves....

But HOW AND WHY !?

Re:Isn't that how warp drives work?

[Anonymous Coward]

TFA doesn't explain 'how' the universe expands FTL; just that it does.

That's because it doesn't actually expand FTL.

You can find two points in space that are moving away each other, measure that they move at speed nearly c away from you, and conclude they move at speed nearly 2c relative to one another.

There is no violation of Relativity here, because these two points are in referential frames that cannot influence each other (they cannot send/receive any signal between them). You can see both, but they can't see each other, and nothing goes FTL.

What actually happens with space, is that to each distance X, a very small delta X is added every second. The next second, it's X2=X+dX grows with dX2=dX+k. And so on. Because of the cumulative addition of constant growth, you get exponential total growth, similarly how money on a bank account grows exponentially with a constant interest rate (if left untouched).

Re:Isn't that how warp drives work?

[Anonymous Coward]

Well, I did not expect the article explaining that, since no scientist has come up with such an explanation still...

If he did explain it he would have done it in a proper scientific paper...

Re:Isn't that how warp drives work?

[Bengie]

Relative to our frame of reference, there are objects moving away form us faster than 2c.

Re:Isn't that how warp drives work?

[ChrisMaple]

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.

Re:Isn't that how warp drives work?

[Anonymous Coward]

" but they can't see each other," That is the only part that you missed. They can see each other. Each interprets the other to be going nearly c away from themselves. They can signal each other. Each would each interpret us as moving away from them as well. If you are having trouble with this, imagine that object A and object B are both moving towards us at nearly c. They see each other, right? What do they interpret each other's speed to be? Assuming they are not on an exact collision course, they move past each other, just missing. Now they are moving away from each other. They both can see each other, because a photon leaving object A will reach object B. Instead of being blue shifted, now the objects are each red shifted, with respect to our inertial frame, and each other.

Re:Isn't that how warp drives work?

[Anonymous Coward]

No, it's you who fails to understand. What you describe is special relativity.
With metric expansion of space, general relativity applies instead.
If you can see a star right at the border of the observable universe, it will apear to move away at near speed of light. You will however never be able to get a signal to them, because the total distance inbetween will grow faster than light can travel.

Re:Isn't that how warp drives work?

[Anonymous Coward]

Anything we can observe will move away at at most 1c.
This includes any star/galaxy we can observe now at the edge of the observable universe.
But this is the relative speed of that star/galaxy when the light started its journey (14 billion years ago), and because space expanded meanwhile, that star/galaxy will be actually 47 billion light years away now.
So while these objects are currently moving away faster than c, we only see the light they emitted when they went almost 1c. Any light they send out now will never reach us and vice versa.

Re:Isn't that how warp drives work?

[Anonymous Coward]

Where did you get that? If such a discovery were made, it would disprove special relativity. Your statement is absurd on it's face. If an object were moving away from us at faster than 2c, the calculated red shift would put radiation emitted from the object at a frequency below 0 hz. Since we judge the speed of objects moving away from us by the red shift in the light, how does what you say make any sense? I think you need a citation for a claim like that.

Re:Isn't that how warp drives work?

[david_thornley]

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.

Seems obvious?

[Anonymous Coward]

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?

[Anonymous Coward]

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?

[burtosis]

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?

[burtosis]

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:Seems obvious?

[Anonymous Coward]

Wrong. When light reaches the edge of the universe, it simply falls off.

Re:Relativity

[Anonymous Coward]

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

[Anonymous Coward]

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

[Anonymous Coward]

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

[Anonymous Coward]

a=(v-v0)/t,
where v=c=299,792,458 m/s;
v0=0 m/s;
t=age of universe in seconds~(13.798e9)(365)(24)(60)(60)= 435,133,728,000,000,000 s

a=(3e8 m/s)/(4.35e17 s)~ .68e-9 m/s^2

Re:For a massive particle, no acceleration is enou

[burtosis]

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.

Or Space isn't expanding

[Anonymous Coward]

1. If a big bang can happen once, it can happen twice, it can happen three times or (v large number) times.
2. It can and must have happened elsewhere creating other universes.
3. These bangs are separated by what?, if its not space and time!
4. Hence space and time exist separate from the big bang. It did not create them, it is not creating space.
5. And there are an infinity of universes outside our visible distance. Because our universe is not special.
6. Hence the uniform radiation is just glow from these older universes
7. And hence the increasing rate of expansion, there is matter out there and its pulling the universe apart.

Re:Or Space isn't expanding

[burtosis]

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

Re:Or Space isn't expanding

[Anonymous Coward]

1) We don't know this, although it seems true.
2) We don't know this, although it may be true.
3) Not "space and time" but spacetime, and anyway, we don't know this.
4) This makes no sense. Just because space existed before doesn't mean more of it isn't coming into existence now.
5) If they exist, they're not just outside our "visible" distance. They're outside of our universe.
6) Obviously false. We see the cbr. Therefore it is not outside our visible universe. Unlike the infinity of universes you are supposing are outside our visible universe. If the uniform radiation was just glow from older universes then not only wouldn't they be outside our visible distance, but the theory of the big bang + inflation that we now believe would be false, which would bring into question the existence of those older universes in the first place.
7) If we're feeling a gravitational pull from something, then by definition it's inside our universe. It's not another universe. Secondly and most importantly, it's well known that the gravitational force from an infinite symmetrical sphere integrates to zero. So there is no net pull on our universe in this scenario. And even if there were a handwaved pull, due to your "space not being created" lemma, it wouldn't look the way inflation looks, it would be uniform, not increasing asymptotically.

Re: Or Space isn't expanding

[Anonymous Coward]

Huge leaps of logic and faith are required to get from item 1 to item 2 on your list. Stopped reading after that.

Re:Or Space isn't expanding

[Anonymous Coward]

5. Not so, there's no reason why one universe wouldn't intrude into the bounds of another, I use the word 'visible' since we only see the parts of OUR universe that the light can travel from since big bang. That limit doesn't apply to other universes. Other universes existed before us and hence their radiation could travel further, including into our universes space. Hence the background radiation that hits us from everywhere outside.
6. See 5.
7) See 5. Infinite is my shorthand for 'v large number', not the mathematical definition

You understand don't you, that space and time are things we defined? We described our world in those terms, we chose time, as a forward constant tick of 1,2,3,4 seconds independent of gravity because that's how our brains perceive it. We could have defined everything as polar coordinates and delta polar changes vs north star angle if our brains perceived it that way. If we could perceive time going backwards, then we would think we are going backwards in time.

So you need space to expand because the universe is accelerating and we defined our space in Newtonian ways so we need to twiddle with our xyz again. But is that space expanding or is that you twiddling with xyz to fix up a problem?

Re:Or Space isn't expanding

[Anonymous Coward]

Perhaps I can put 4) in a better way.

Space and time must separate Universes= 1 from Universes =2 creation. Like the third and fourth. Or the 100th and 101st. So why would 0 to 1 be special? If its not special, and there are no universes, how can there be space at n=0? Without a universe creation event to make it?

I'm saying that if Universe 2 is created SOMEWHERE and SOMEWHEN, then Universe 1 is also created SOMEWHERE and SOMEWHEN.

So once you drop the idea that space is created by the big bangs and somehow they're all compartmentalized by this (the assumption you make in 7), your now free-er to answer 6) in a less contrived way than inflation.

What if...
What was before the big bang? Nothing special its just a collision.
What happens after the universe hurtles off into the void? What void? If there's universes out there, they'll clump, they'll hit stuff, there will be bangs, big ones. What if the universe is just really really boring and not special.

Nobody will read you thesis paper because the magic god like creation of space and time is so much more compelling! But you physicists have just created another god, with great prophets and your bible and your unwillingness to question the prophets words. If you need to throw away 50% of physics, because its wrong, then throw it away. Don't end up with 'the book of Einstein' being read as gospel on a sunday.

The argument "that can't be true because then theory X must be false" is not valid because X can be false, and just because you were taught at uni that its true does not make it true.

Re:Or Space isn't expanding

[Anonymous Coward]

Your free thinking will not be tolerated by the gatekeepers and high priests of physics. They will ridicule you and mock you. But one day a hundred or so years from now a brave scientist will dare to see the contradictions and put forth a new construct. Then he will be lauded a genius, but you will forever be considered a troll. haha, that's life, enjoy the ride.

Re:Or Space isn't expanding

[Strangely Familiar]

He is a troll. He is equating physicists to preachers and magicians. He is saying that the Lorentz transformation is no better to help understand the world than, "And God created the earth in 7 days." Bull. Sh!t. That IS trolling. He is free to be ignorant. And you, my good friend, are free to confuse blissful ignorance with free thinking. I tell you, they are not the same. The predictions of the bible didn't land an ESA probe on a comet. The predictions of Einstein's special and general relativity did. I have not met a physicist who doesn't understand that the Standard Model doesn't have problems playing nice with General Relativity. If Mr. Troll has a fix that is more than just a bunch of handwaving, and it makes predictions, please let him enlighten all of us. Until then, you and he should quit comparing physicists to priests. Not. The. Same.

Re:Or Space isn't expanding

[david_thornley]

Why must spacetime separate two Big Bangs? If we can detect another Universe caused by another Big Bang, there's obviously something connecting us. If not (and I've heard of no such detection), they don't need to be in the same spacetime. You're speculating wildly, coming to conclusions that the evidence is positively against, and trying to build on that.

In fact, we can detect precisely one Big Bang. We can't detect anything before it, and we can't detect anything outside a certain boundary in spacetime. Parallel Universes are a fun speculation, and science fiction and fantasy can come up with unexplained ways to move between them, but AFAIK there's no evidence for them, and no way to find out.

BTW, your understanding of physics and physicists sucks. Physicists don't treat Einstein as gospel, but his Special Relativity and much of his General Relativity have stood up incredibly well to continual testing. We know that some known physics is wrong in some way, because we get inconsistencies, but physics theories are thrown away when we have theories that match the evidence better.

All you need to do to get taken seriously is to show that your theories account for observed reality about as well as existing ones do, and have at least a way of distinguishing them from current theories by observation or experiment. If you're unwilling to do that, you're a crackpot and not a physicist. If you don't have the understanding to do it, then go back to reading the popularizations and leave the real science to people who know what they're doing. If you have the will and understanding, and can't explain observed reality as well as the existing theories, then you're wrong.

Re:For a massive particle, no acceleration is enou

[Anonymous Coward]

Original AC here. I was thinking that the acceleration required to go from 0 to c in the age of the universe could be a constant (c would then be derived from these values and have been slowly increasing over time).

The estimated size of the universe (91 billion light years) divided by estimated age (13.79 billion years) is approximately 6.6 light years per year. This is the expansion being talked about?
https://en.wikipedia.org/wiki/Universe

The answer arrived at above (~6.8 e10 m/s^2) is 5-6x MOND's a0 constant ( ~1.2e-10 m/s^2).
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

Numerology?

Re:For a massive particle, no acceleration is enou

[Intrepid imaginaut]

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

Space first

[Livius]

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

The best source of physics info on the web

[burtosis]

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.

Obvious

[Anonymous Coward]

It expands in all directions at once, ergo at least twice the speed of light. :-)

Re:obvious

[ChrisMaple]

The properties of nothingness are changing to become space at a speed faster than the maximum speed at which matter can travel through it.

Congratulations, you win the Sarah Palin Word Salad Award.
To the extent and in the context in which the word "space" has a cosmological meaning, it is not finite, does not go into or come out of existence, and most certainly doesn't happen when the "properties of nothingness are changing".

"Space" is a mental and mathematical handle for grabbing hold of the universe. Many words in common English simply can't be applied to it and the attempt to do so results in nonsense. For instance, space has neither an "outside" nor an "edge".

Re:obvious

[Anonymous Coward]

I don't know why they're presenting this like it's some amazing new development.

That's because you don't understand it.

Re:For a massive particle, no acceleration is enou

[Anonymous Coward]

Nope, classical mechanics do not apply except in the realm of slow speeds.

My point still stands: no acceleration is fast enough to get to light speed for any finite time for any nonzero rest mass particle.

A space ship is not a photon...

[ninguna]

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.

Re:A space ship is not a photon...

[Anonymous Coward]

It is rockets?

Space expanding faster than light

[rossdee]

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

[arth1]

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.

Re:For a massive particle, no acceleration is enou

[Anonymous Coward]

I was thinking that the speed of light was increasing.

Backflip

[Anonymous Coward]

Another exercise in meaningless semantics. I got that without even bothering to read.

How do we know that

[Anonymous Coward]

I still don't get it, how do we know that space itself has no speed limit. Where is physical proof - lab measure of observation of it ? With no proof it is no different than religious belief.

Re:How do we know that

[burtosis]

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:How do we know that

[Anonymous Coward]

tenets ... just saying ...

Re: For a massive particle, no acceleration is eno

[Anonymous Coward]

How do we know this hasn't /isn't happening already?

Fuck that manchild

[Anonymous Coward]

and his exclamation points.

Quantum entanglement?

[Anonymous Coward]

A complete theory of cosmic time needs to account for quantum entanglement as well. We view distant entangled pairs as having a space-like separation but from their own vantage point there is no separation at all. They're still close enough to touch and effect each other. Perhaps every particle in the universe carries its own clock and measuring stick vis a vis every other particle. And what we experience as spacetime is just a sort of average of all of those measurements, weighted by gravity to give preference to our own local region.

What is the prevailing theory in this regard?

OK...

[Anonymous Coward]

So we're posting sophomore physics class notes on /. now? StartsWithABang is the Bennett Haselton of science - endless waffle about something that lots of people understand better. Philomena Cunk with a blog...

Does the speed of light change?

[GoodBuddy]

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?

[arth1]

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?

[Anonymous Coward]

Was it always that way? At some point someone must have tried to measure the speed of light...

Re:Does the speed of light change?

[arth1]

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?

[Anonymous Coward]

Then I don't understand your response to "Goodbuddy". His/her question is mathematically equivalent to asking why the "distance/time relation" is thought to be constant. Specifically, I don't believe this or have misunderstood it:

"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?

[arth1]

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?

[rawoke083]

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:For a massive particle, no acceleration is enou

[Anonymous Coward]

I see now that this has been noted by Mordehai Milgrom in the form of: a0 ~ c*H0*2*pi
http://arxiv.org/abs/1412.4344

I did not make the connection that 6.6~ 2*pi.

I believe the light speed limit is incorrect...

[Anonymous Coward]

You can argue and throw all the math at it that you want, but I've always believed the speed limit of light is flawed. I think the speed limit should be revised to "no faster than instantaneous travel from one point to the other, no matter how far away it is". Call me crazy, but there it is.

Faster and faster

[Anonymous Coward]

I keep reading that the Universe is expanding at an accelerated pace, because we see distant objects are more heavily red-shifted than nearer ones.

I can't quite get this into my head. By what I know about space, distant objects are also 'older' than nearer objects. When I see ancient objects moving faster than more recent ones, I draw the conclusion that the rate of expansion has decreased. So could anybody please enlighten me, where my line of reasoning is at fault?

Re:Faster and faster

[ChrisMaple]

By what I know about space, distant objects are also 'older' than nearer objects.

That's your flawed premise.
Distance doesn't imply the age of an object, but since we know the speed of light, we know that the light from something far away was emitted a long time ago. That "long time ago" establishes a floor for its age (after adjusting for relativity.)

To Make You Feel Better...

[Roger W Moore]

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:

1. The laws of physics are the same in all inertial frames.
2. 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...

[Bengie]

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...

[Roger W Moore]

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.

Re:For a massive particle, no acceleration is enou

[Anonymous Coward]

I will be.
But then again, i am immortal. Sucks to be you guys. :)

Space Nutter! Re:Space first

[Anonymous Coward]

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

Space Nutter!

Oh, wait.

Get your facts right

[Anonymous Coward]

"nothing can move faster than the speed of light" is one of the greatest mis-quotes of all time. What the theory states, and I'll just stress that it is still only a theory, is that nothing can *accelerate* past the speed of light. It does not prevent anything travelling faster than light if it was created at such speed. Perhaps not relevant in the current context but I do wish people who quote theories would learn them first.

Re:Get your facts right

[Bengie]

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.

Metric expansion of fonts

[Anonymous Coward]

Why are all the websites using huge fonts and going out of their way to make their sites look as childish as possible?

I'm so sick and tired of inane memes spreading FTL throughout the tech industry. If you want to cater to mobile devices then please do so without pissing on the rest of us who have better things to do than waste their time squinting at tiny displays.

Disappointed given title I was expecting something "new" about inflation instead this is just a retelling of same old relativity/dark energy 101 crap and they don't even do a good job of it. Clock differences are caused by acceleration not relative speed. Also megaparsecs to light years is off by four orders of magnitude.

Final "It simply does as it pleases" is a breathtaking copout.

obvious

[slashmydots]

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?

[Kevin Fishburne]

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?

Re:Light going faster than the speed of light?

[ChrisMaple]

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.

Re:Light going faster than the speed of light?

[Anonymous Coward]

It doesn't speed up, it blue-shifts. Light travels at the same speed in a vacuum, so if something moves into a potential well it gains energy, and so moves to higher frequency (E=hf for photons).

Re:Light going faster than the speed of light?

[cjameshuff]

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?

[Kevin Fishburne]

@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?"

Can Light Travel at the Speed of Space?

[Anonymous Coward]

Does that mean that photons could travel at the speed of space expansion, carrying history of events with it?

Isn't this already obvious to everyone ?

[Anonymous Coward]

Our universe, which is 13.8bn years old, is almost 100bn light years across.

More added value equals the speed of light +

[__aanbvm4272]

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?

[Tony Isaac]

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?

[david_thornley]

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".

Re:What about the objects in that space?

[Tony Isaac]

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:For a massive particle, no acceleration is enou

[ChrisMaple]

I think someone is failing to understand Zeno's paradox.

Re:More added value equals the speed of light +

[ChrisMaple]

If you are traveling at 0.9c relative to Earth, the speed of light is still 1.0c away from you in your frame of reference. No matter How fast you go relative to something else, the speed of light is always 1.0c away from you. That's just how the equations work out, speeds don't add arithmetically. That's why it's called relativity, speeds are relative to your frame of reference.

I think space is still expanding at FTL

[Methadras]

I'm beginning to think that the big bang really didn't happen considering you have an observable universe and an unobservable universe and that somewhere space is exuding/expanding at FTL from the 'center' of the universe outward. That location is extruding space outward (not-evenly) and pushing space across gravitation lines at FTL. So the next logical question is, where is this point of origin and what created it and how did it get there.

Re:I think space is still expanding at FTL

[david_thornley]

There's no point of origin. If you inflate a sphere, each Flatland observer on the sphere sees itself as the center of expansion. "What created it" is not currently answerable, since we can only perceive so far back and run the laws of physics backwards from there only so far. It seems likely that we'll never know.

Re:I think space is still expanding at FTL

[Methadras]

I believe there is a point of origin and that point has space moving through it into our universe. I do not subscribe to the notion of there being no center of the universe. There must be and that point or area is allowing more space to infiltrate and push current space outward. Even a sphere has to have an entry point for it to be allowed to expand. In this case our universe has a 'center' and from that more incoming space. However, I don't believe the shape of the universe is spherical in the sense that given that there may be, due to certain gravitational clusters within certain regions would make the universe look sphere-ish but with a lot of bumps and ridges.

ORIGINS: space Cosmology interlinks

[Anonymous Coward]

Sub: In search of Origins-Cosmology vedas
The video attachments by Ethan Siegel are very interesting -some are useful and many are mixing-up through- bigbang-Speed of Light-Redshift-electric Universe-Electric-Magnetic Phenomena. worth useful for think tanks.
Ultimately-one needs to realize the connections beyond Thunderbolts group -Plasma universe-cosmic plasmas as essential links to COSMIC FUNCTION OF THE UNIVERSE.
Plasma Regulated Electromagnetic Universe in Magnetic Field Environment -holds the at the Milky Way Galactic Plane-see my projections presented at COSPAR-2013 and my books-1993 to present that link up prime Concepts to base concepts-where Science needs to comprehend in dimensional frames.
More information is available through Space Cosmology studies-origins..19 Books-17 under US copyrights
http://vidyardhicosmology.blogspot.in
http://archive.org/details/CosmologyDefinitioncosmologyVedasInterlinksVidyardhiNanduriCosmology
Vidyardhi nanduri [independent Research]