Can the Universe Expand Faster Than Light?

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Discussion Overview

The discussion revolves around the concept of the universe's expansion and its relationship to the speed of light. Participants explore whether the expansion of the universe can exceed the speed of light, the implications of such expansion, and the theoretical understanding of these phenomena.

Discussion Character

  • Debate/contested
  • Exploratory
  • Technical explanation

Main Points Raised

  • Some participants question the consistency of the speed of light being the fastest speed known, given that the universe may have expanded faster than light.
  • Others argue that the speed of light remains the ultimate speed limit, emphasizing that the expansion of space does not equate to motion in the traditional sense.
  • A participant suggests that the universe must be filled with something, like dark matter, during its expansion, proposing that this could imply motion faster than light.
  • There are claims about the recession speed of galaxies at the edge of the observable universe being around 3c, with some asserting that this is supported by empirical evidence.
  • Some participants express skepticism about the theoretical nature of current expansion knowledge, while others assert that significant empirical evidence exists.
  • Disagreements arise regarding the interpretation of expansion as motion, with some insisting it should be counted as such, while others maintain it is merely recession.
  • Concerns are raised about the validity of past experiments claiming to measure speeds exceeding light, with references to specific experiments and their outcomes.

Areas of Agreement / Disagreement

Participants generally do not agree on the implications of the universe's expansion in relation to the speed of light. Multiple competing views remain regarding whether expansion should be considered motion and the validity of various claims about empirical evidence and theoretical understanding.

Contextual Notes

Participants acknowledge limitations in understanding the past events of the universe's expansion and express uncertainty about the implications of current theories. There is a recognition that many ideas about the universe's behavior are still under exploration and debate.

Jakecp
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I have been thinking about light and i have read that the universe expanded faster than speed of light. So , then why people say that the speed of light is the fastest thing known if people know that the universe expanded faster than speed of light . Also , if the universe could have expanded faster than the speed of light , can we make something that can travel faster than speed of light using expansion ?
 
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Well, let me correct you on one thing- we know almost nothing about how the universe expanded, or even about how it expands now. It is all theoretical. If it is true, however, the speed of light still would be the fastest speed, because the speed of the universe really doesn't count. We will never achieve a speed greater than the speed of light. It is against the laws of physics. I am not sure, but I believe it is addressed in the FAQs why that is. I can kind of explain why, but I am going to let a more experienced person give you a more detailed explanation.
 
I just want to add, I checked, and there is nothing on the FAQs. (Mentors, I would suggest adding an FAQ about the speed of light, I have noticed a lot of similar questions on here).
 
Isaac0427 said:
I just want to add, I checked, and there is nothing on the FAQs. (Mentors, I would suggest adding an FAQ about the speed of light, I have noticed a lot of similar questions on here).

this thread isn't to do with the speed of light as such, rather the expansion speed of the universe
which is what the link I provided give lots of info on

there is a FAQ thread on the speed of light ...

https://www.physicsforums.com/threads/why-is-the-speed-of-light-the-same-in-all-frames-of-reference.534862/

Dave
 
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Isaac0427 said:
Well, let me correct you on one thing- we know almost nothing about how the universe expanded, or even about how it expands now. It is all theoretical.
Nonsense. We know quite a lot about the current expansion. For example, we know that the recession of galaxies at the edge of the observable universe is about 3c. There is nothing theoretical about our knowledge of the current expansion even to the point of knowing that the rate of acceleration is decreasing slightly over time. Things that are totally supported by experiments/empirical evidence are way beyond just theoretical.

If it is true, however, the speed of light still would be the fastest speed, because the speed of the universe really doesn't count.
True. It is not proper motion, just recession.

We will never achieve a speed greater than the speed of light. It is against the laws of physics.
also true although I hesitate to use the word "never" in such contexts even though I think it applies in this case.
 
I don't agree , it should count as motion because we are moving space while it expands because when the universe expand it can't be filled with nothing . It must be filled with dark matter or something so it should count as motion and then there is a speed faster than light even though it does not count as motion and we may be able to make some kind of expansion with 3c speed or more . Also , who wrote the rules of the universe? Why c is the fastest speed? Why it should be? It has no Mass right? it should also not count as motion because it is just a wave or nothing as the space expansion. Why space expansion does not count and light does? Light is not motion because nothing at all is moving because light has no mass.
 
Jakecp said:
I don't agree , it should count as motion because we are moving space while it expands because when the universe expand it can't be filled with nothing . It must be filled with dark matter or something so it should count as motion and then there is a speed faster than light even though it does not count as motion and we may be able to make some kind of expansion with 3c speed or more . Also , who wrote the rules of the universe? Why c is the fastest speed? Why it should be?

So you have a couple of PHD's hanging on your wall that you can make such unsubstantiated claims ?
it doesn't really matter if your agree or not, studies have been done on the subject by people well above your and my pay-rates and intelligence

Did you even bother to read through the link I gave ? did you try and understand any of it ?

I suggest strongly that you take a few steps back and do some learning before arguing against some well established theories

Dave
 
Jakecp said:
I don't agree ...
Irrelevant. It's not up for a vote. As Dave said, you should learn some basics before spouting nonsense. This stuff is not intuitively obvious but thinking that your opinion trumps facts is not science it's voodoo.
 
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  • #10
phinds said:
Nonsense. We know quite a lot about the current expansion. For example, we know that the recession of galaxies at the edge of the observable universe is about 3c. There is nothing theoretical about our knowledge of the current expansion even to the point of knowing that the rate of acceleration is decreasing slightly over time. Things that are totally supported by experiments/empirical evidence are way beyond just theoretical.
Yes, I shouldn't have added the part about the current expansion. I was just trying to make the point that what happened in the past is impossible to know. I have read many theories about what could have happened. We don't know anything about it for sure.
 
  • #11
Jakecp said:
I don't agree , it should count as motion because we are moving space while it expands because when the universe expand it can't be filled with nothing . It must be filled with dark matter or something so it should count as motion and then there is a speed faster than light even though it does not count as motion and we may be able to make some kind of expansion with 3c speed or more . Also , who wrote the rules of the universe? Why c is the fastest speed? Why it should be? It has no Mass right? it should also not count as motion because it is just a wave or nothing as the space expansion. Why space expansion does not count and light does? Light is not motion because nothing at all is moving because light has no mass.
Ok, then if you want to count it as faster than the speed of light, try recreating the Big Bang. As @phinds said, it is just recession, not proper motion, and light is motion. It just is. It is fact. Many, many expariments have tried to pass the speed of light. None have succeeded. One claimed to have succeeded but it was a bad expariment, and they retracted their results.
 
  • #12
Isaac0427 said:
One claimed to have succeeded but it was a bad expariment, and they retracted their results.

If you are thinking about the OPERA experiment it was not (and is not) their physics goal to pass the speed of light. Their neutrino speed measurement was a byproduct, something they could do in addition to their main physics goal (which is measuring neutrino oscillations into tau neutrinos). It is not a bad experiment in itself and it has been successful in its main physics goal. They simply suffered from being a bit too eager to announce their FTL measurement when they probably should have taken a step back and triple-checked everything.
 
  • #13
Isaac0427 said:
Yes, I shouldn't have added the part about the current expansion. I was just trying to make the point that what happened in the past is impossible to know. I have read many theories about what could have happened. We don't know anything about it for sure.
Yes, it is impossible to know what happened in the past with certainty, but that doesn't mean that all ideas are equally relevant. This is why humans have developed science: we can make observations, develop models, and make inferences about the universe -- both past and present -- that can then be tested.

Many historical observations can be well-understood in the context of modern science: if you came across a crater, how much would you bet it was due to a meteorite and not an abandoned excavation project by ancient earth-visiting aliens? Neither can be verified with certainty, but I suspect I know which explanation you're betting on.
 
  • #14
Jakecp said:
I have been thinking about light and i have read that the universe expanded faster than speed of light. So , then why people say that the speed of light is the fastest thing known if people know that the universe expanded faster than speed of light . Also , if the universe could have expanded faster than the speed of light , can we make something that can travel faster than speed of light using expansion ?
The universe does not expand at a given speed. That's misconception number 1. The speed at which objects recede from one another, v, is a function of the expansion rate, H, and their distance apart, r, via Hubble's Law, v = Hr. The more distant an object, the faster it appears to recede from us. This is true no matter what kind of expansion we're talking about. Notice that as long as H is positive, there is always a distance at which objects will recede with a speed greater than light, r = c/H. There is nothing wrong with this since the objects are at rest locally, their relative velocity due solely to the expansion of space. So misconception number 2, which is regrettably pervasive in the popular science arena, is that the universe underwent some kind of superluminal expansion early on. These are references to primordial inflation, which indeed was a unique phase of expansion in the early universe, notable because length scales increased exponentially.

So, no, space does not -- ever -- expand faster than the speed of light because expansion does not occur at a given speed. And, while objects do indeed recede from one another at certain speeds, and if they are far enough apart they will recede form one another at speeds surpassing that of light, this is true always and is not a unique property of inflation or any other type of expansion.
 
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  • #15
Orodruin said:
If you are thinking about the OPERA experiment it was not (and is not) their physics goal to pass the speed of light. Their neutrino speed measurement was a byproduct, something they could do in addition to their main physics goal (which is measuring neutrino oscillations into tau neutrinos). It is not a bad experiment in itself and it has been successful in its main physics goal. They simply suffered from being a bit too eager to announce their FTL measurement when they probably should have taken a step back and triple-checked everything.
That's interesting. I was not aware of that, all I knew was the false neutrino speed part.
 
  • #16
The OPERA result turned out to have a very mundane explanation eventually.
A fiber optic cable was wrongly connected.
 
  • #17
wait , i am not sure of what i am going to write but , galaxies are going apart from each other faster every time right? so you say that they receed at 3c which means that they are moving at 3c further away?
 
  • #18
Also , we know almost nothing of dark energy ( i think) what if dark matter and energy can travel faster than C? did Einstein knew of this in his relativity theory?
 
  • #19
Jakecp said:
wait , i am not sure of what i am going to write but , galaxies are going apart from each other faster every time right? so you say that they receed at 3c which means that they are moving at 3c further away?
That is a very garbled sentence so I'm not sure what you are asking. There are objects at the edge of the observable universe that are receding from us at 3c. There are objects that are closer to use that are receding at 2c. There are objects that are closer still that are receding at 1c. Pick a number. You can find an object at the appropriate distance that is receding at the number times c.

This is NOT the "rate of expansion of the universe", its just the recession of objects compared to Earth.
 
  • #20
Jakecp said:
Also , we know almost nothing of dark energy ( i think) what if dark matter and energy can travel faster than C? did Einstein knew of this in his relativity theory?
That makes no sense at all.

Dark energy is not a thing that can have a speed and dark energy and dark matter are totally unrelated to each other. Einstein did not know of either one, and that makes no difference to anything at all.
 
  • #21
I am sure it has been covered already, but the finite speed of light limits particles speed.

space is not a particle or matter. Matter can not move at the speed of light. Space is not matter.
 
  • #22
Well , if he didn't took that in consideration , why can't dark matter or energy travel faster than c? I know that is the rule einstein once said but why? i have not read the relativity theory yet and i know that c is that fast because it has 0 mass , but how did he knew that , that was the fastest speed ? I think light can be slowed down but don't know how. The fact , is there any chance of something beeing faster than light?
 
  • #23
If space is not matter , then what is it? How should i imagine the limits of space? What limits the space ? A wall? Nothing? If nothing limits the space , how can it have a limit if the limit is nothing ?
 
  • #24
So , another question , the universe is expanding from everywhere? or just from the edges?
 
  • #25
Jakecp said:
Well , if he didn't took that in consideration , why can't dark matter or energy travel faster than c? I know that is the rule einstein once said but why? i have not read the relativity theory yet and i know that c is that fast because it has 0 mass , but how did he knew that , that was the fastest speed ? I think light can be slowed down but don't know how. The fact , is there any chance of something beeing faster than light?

Not as far as we know. There are problems involving causality if something could travel faster than c. Note that c is the speed of light in a vacuum. In a medium, such as glass or water, light slows down and we can make things travel faster through these mediums than light does, leading to this effect: https://en.wikipedia.org/wiki/Cherenkov_radiation

Jakecp said:
If space is not matter , then what is it? How should i imagine the limits of space? What limits the space ? A wall? Nothing? If nothing limits the space , how can it have a limit if the limit is nothing ?

Saying that space has no limit does not mean that space has a limit and that that limit 'is nothing'. It means the limit does not exist.

As for what space is, space is, well, space. Literal space. The space between objects. The framework made up of three dimensions in which we can move freely in any of them.

Jakecp said:
So , another question , the universe is expanding from everywhere? or just from the edges?

There is no known edge to the universe. Universal expansion means that the distance between all unbound objects increases over time. It does not necessarily mean that there is an expanding edge to the universe, though that is a possibility.
 
  • #26
Jakecp said:
... just from the edges?
We know from observation that the observable universe is expanding and all of it expanding except gravitationaly bound matter, (galaxies etc).
So galaxies everywhere are getting more distant from other galaxies, but the galaxies themselves don't expand.
This is what leads to the conclusion of there being a 'big bang', a starting point in time for it.
We don't know if there is more universe beyond what is observable, (or what logically follows from what is observable.)
There could be infinite space beyond what we will ever be able to observe, or maybe the observable universe is all there is.
One possibility is that the universe as a whole is infinite, in which case it always was infinite, yet it is expanding too.

You might say 'wait a minute', how can something infinite get bigger?
Well 'infinite' can do things which finite can't.
https://en.wikipedia.org/wiki/Hilbert's_paradox_of_the_Grand_Hotel
 
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  • #27
rootone said:
There could be infinite space beyond what we will ever be able to observe, or maybe the observable universe is all there is.
The problem with this point of view is how could you possibly explain the boundary at the edge of the observable universe and how much hubris do you think it takes for us to assume that we are the center of everything? For those reasons, my opinion of the point of view that the OU is all there is is not printable within the forum guidelines :smile:
 
  • #28
I am not saying that this is my view, only that we don't know what there may be beyond the observable.
Hence we can't positively rule anything in as being most likely or anything out as being impossible.
I meant that space outside of the observable universe could be any possibility ranging from nothing to infinite.
 
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  • #29
Jakecp said:
Well , if he didn't took that in consideration , why can't dark matter or energy travel faster than c?
So you have 2 problems here:
1. Dark mater and dark energy are not the same thing, nor are they dependent on each other. They are completely different. I believe some scientists don't choose to call it dark energy, to avoid this confusion.
2. Scientists are in no position to make any claims about the speed of dark mater or dark energy. As a revision to number 1, they have a large similarity: we bearly know any of the properties of either.
 
  • #30
Jakecp said:
Also , we know almost nothing of dark energy ( i think) what if dark matter and energy can travel faster than C? did Einstein knew of this in his relativity theory?
The assumptions of dark energy and dark matter fit to the data we have. From this the dark energy is a vacuum energy which fills the universe homogeneous. So, its density is the same everywhere.

Think of a gas in the corner of a box. The gas (its molecules) will travel until its density is the same everywhere within the box. Once having reached this state of equilibrium the gas will not travel anymore, though the molecules it consists of are still able to move.

In contrast to the gas the dark energy is perfectly homogenous. It has this state from the very beginning, hence it can't travel at any time.
 

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