Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Harri on 23/09/2018 22:40:38

Title: Is the universe expanding faster than the speed of light?
Post by: Harri on 23/09/2018 22:40:38
Basically that is my question, is the universe expanding faster than the speed of light?

Title: Re: Is the universe expanding faster than the speed of light?
Post by: alancalverd on 23/09/2018 23:40:49
Is there any reason why it shouldn't?

Here's a thought experiment. Assume that the universe U is an infinite array of roughly isotropically distributed bits of stuff. Assume that for whatever reason (and Schwarzchild gives us a perfectly good one) we can only observe a finite sphere X within that array. And assume that "gravity sucks". Now since U >> X, there is more stuff outside X than inside it, so X will expand due to the "suction" of (U - X) - i.e.the stuff outside - so the density of X will decrease, and the rate of expansion will increase.

Suppose we have reached the stage  at which points on the boundary of X are receding from us at 0.55c. Nothing in that statement to contradict relativity. But diametrically opposite points, say to the north and south of us, are moving at 1.1c relative to each other. All this means, relativisitically, is that an observer at N will not have any information about S, which is fine, but the diameter of the observable universe is increasing faster than c.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: quantum321 on 24/09/2018 04:05:21
That is an excellent explanation from the Global Moderator. I believe the easy to understand answer is that space-time can expand faster than the speed of light and not violate Einsteins theories. It is believed that the force that is driving the expansion is called dark energy which permeates all of space.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: alancalverd on 24/09/2018 08:22:32
The beauty of U >>X is that you don't need to postulate stuff you can't see (dark energy) within the sphere that you can see (X), only that there is nothing special about X.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: quantum321 on 24/09/2018 08:56:03
I am sorry you lost me. Why can't U be much greater than dark energy which can be X?
Title: Re: Is the universe expanding faster than the speed of light?
Post by: chris on 24/09/2018 09:37:19
Very nice explanation Alan.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: alancalverd on 24/09/2018 09:44:20
I am sorry you lost me. Why can't U be much greater than dark energy which can be X?
Because U and X are volumes of space, not quantities of energy, and X is arbitrarily the bit of space we can see.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: Harri on 24/09/2018 19:32:41
Anyone reading my question title will know straight away that I will be questioning the possibility of anything travelling faster than the speed of light. After all we are told that NOTHING CAN travel faster than the speed of light.

So if the universe IS expanding faster than the speed of light how can we possibly endorse Einsteins 'theory' that nothing can travel faster than the speed of light? Shouldn't we be saying that well actually something can travel faster than the speed of light? And that something is the expanding universe.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: yor_on on 24/09/2018 20:11:19
Space isn't light
Title: Re: Is the universe expanding faster than the speed of light?
Post by: Bill S on 24/09/2018 21:37:15
Quote from: Harri
So if the universe IS expanding faster than the speed of light how can we possibly endorse Einsteins 'theory' that nothing can travel faster than the speed of light? Shouldn't we be saying that well actually something can travel faster than the speed of light? And that something is the expanding universe.

I may have it wrong, but I think Einstein didn't say that nothing could travel faster than light; only that we could not accelerate anything from subluminal to superluminal speed.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: Bill S on 24/09/2018 21:59:42
Great explanation, Alan.

Marcus Chown (New Scientist, 17.11.2008) considers a similar scenario.

.we might be sitting in the middle of a void  a vast spherical bubble in an otherwise homogeneous universe.  This bubble is not devoid of matter.  In fact, most of the stars and galaxies we can see from Earth would be contained within it.  Its just that everywhere beyond it, which is too far away to see, the density of stars and galaxies is much higher.

.In such a low density region, the breaking pull of gravity is weaker, and so the region would quite naturally be expanding faster than the more dense area enveloping it.Observing from within the bubble, but using distant supernovae as yardsticks, we would see a universe whose expansion seems to be occurring faster than it used to  without the need to invoke dark energy.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: alancalverd on 24/09/2018 22:35:58
Einstein was all about relativity, not absolutism. As others have pointed out here, the energy required to accelerate a mass increases towards infinity as its speed approaches c, but speed relative to what?

If objects A and C are converging towards their midpoint B, there is no reason why they cannot both be travelling at 0.6c relative to B , but neither can see the other approaching at greater than c (with a blue shift). From which we can derive time dilatation and all the rest of that wonderful stuff that happens in colliders.

Moving swiftly from subatomic particles to the observable universe (isn't physics wonderful?) we can observe the redshift of distant galaxies to be consistent with supraluminal Doppler shift. The standard explanation is that they aren't moving away from us, but the space between us is expanding. That's where I get off this particular bus!
Title: Re: Is the universe expanding faster than the speed of light?
Post by: jeffreyH on 25/09/2018 02:15:18
If objects with non zero rest mass cannot travel faster than light then this means that gravity itself cannot make them travel faster than light. We are embedded in a universe with an enormous amount of matter surrounding us. All this matter generates gravitational fields. Our view of time is therefore not absolute. Which means our view of speed is not absolute. That is the first point. The second point is what is space? How do we reconcile speed through the vacuum. We can't use a measuring device, since we cannot be considered stationary with respect to anything other than our own 'inertial' frame. Especially not with respect to a vacuum. Therefore we can only determine speed via the shift in frequency of incoming signals. If you have no absolutely stationary markers to go by then signals is all you have. You then determine what you think is the distance and also the speed of an object by interpreting those signals. Since the shifting is pretty consistent it can be taken to show an expanding universe.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: yor_on on 29/09/2018 17:26:10
Actually you can be very tricky here depending on views. presume SpaceTime to be a 'field'. Then define it as filled with 'virtual particles'. Then define those as the texture/substance of SpaceTime. Then you might be able to argue that 'space' is 'light', although as per HUP unable (mostly) to act in 'real/normal time', the time we define as cause and effect. And if you do :) Then time itself becomes a culprit.
=

If you do so, then equal time (a clock) to 'c', the way I look at it, then there should exist a threshold, quantifying time. shouldn't it? Furthermore it seems to imply that 'c' only exist over a certain 'scale'? Weird :)

and that 'scale' is then connected to time, which I then would define as your local time equivalent to 'c'
Title: Re: Is the universe expanding faster than the speed of light?
Post by: Bill S on 29/09/2018 18:33:39
Quote from: Yor_on
If you do so, then equal time (a clock) to 'c', the way I look at it, then there should exist a threshold, quantifying time. shouldn't it? Furthermore it seems to imply that 'c' only exist over a certain 'scale'? Weird :)

There's no way I'm going to try to argue with that, but what I will say is: Come back when you have a practical demonstration. :)
Title: Re: Is the universe expanding faster than the speed of light?
Post by: yor_on on 30/09/2018 10:19:55
Well, yea :)

A practical demonstration was it?

And scales are weird Bill. Quantum mechanics is about scales, Decoherence too.
At least the way I look at it. And then we have 'light', the idea of them being messenger particles.
A lot of physics is about dimensions, the ones we have and the ones that might be, but nobody asks why the scale matters, except decoherence. But decoherence is a try for a answer to the deterministic universe we observe macroscopically, isn't it?
Title: 5Re: Is the universe expanding faster than the speed of light?
Post by: yor_on on 30/09/2018 10:26:35
The dimensions you define macroscopically should disappear Quantum mechanically, and if you go to string theory, they are supposed to be 'one dimensional', aren't they? Actually Quantum mechanics goes one step further in that they discuss and define 'point particles' without any dimension at all. A similar effect can be seen if you think about the 'timelessness' of light. All of those are validated by our observations.
=

Also it should invalidate the question of 'flow' versus 'quanta', aka 'is time/the universe consisting of a flow or quanta'. Because it shouldn't be a flow microscopically, it would be more like a static field to me. Then again, who knows :)

Let's put it this way, macroscopically in your daily life there is space, you move in that space. The space you move in can have different densities with a 'perfect vacuum' being the 'emptiest', so to speak. But  if you think of it as a 'field' then nothing is empty anymore, it's just the scale of observation that defines it.

Not sure I get that clear enough so I will repeat it :) The scale you observe on, or at, defines what you see, meaning that for a thought up quantum object there shouldn't be 'dimensions' any more, probably not a 'clock' either, although the properties needed for a universe macroscopically must all exist. And connections has to be there.

Another point might be, how can 'dimensions' disappear just by using another scale? Because that is what we see.
Without 'dimensions' there is nothing defining a 'size', and a accelerating expansion or for that sake 'infinity' seems perfectly plausible, all depending on what scale you observe. What it seems to leave is the idea of magnitudes.

You could also put it this way. Scaling is what we use, but it should break down as we go down into something different. It's the same problem we have with 'dimensions' actually. A further argument is the idea I have of equalizing 'c' to your local clock. If you do then time 'ticks' :) for you over that threshold. But if you scale those 'ticks' down sufficiently they should disappear too, although impossible for us to measure as we use our local macroscopic clocks to define our experiments. At least as far as I can see.

A important point here is to divide between 'time' and a 'clock'. Thinking this way 'time' becomes a property, with your 'local clock' becoming a macroscopic expression of that property.
=

One more thing, the way I started to wonder about those things was thinking of the Lorentz/FitzGerald contractions. How to make them make sense to me :) And the only way I could do it was questioning dimensions. I really like relativity, it's the best mindgame there is. And the way I think now is that it is connections that create 'dimensions'. And those connections are fluid, dependent on a lot of things as mass, speed, time etc. And yes, the scale of observation you use.
==

Another clue to the way I think is the way light 'propagate'. You can, using a clock which means introducing time, break it down into a universe of layers in where each layer is a static representation of 'SpaceTime locations' with the layers following each other in a progression of 'one way arrow of time'. Not saying this is the way it is, but it's worth thinking of. To make it observer dependent though you still need those 'properties' of mass, speed etc. Which in a way makes every point the center of the universe.

to it you can add this " One of the problems to be solved in this respect is that if space-time is granular beyond a certain scale it means that there is a "basic scale", a fundamental unit that cannot be broken down into anything smaller, a hypothesis that clashes with Einstein's theory of special relativity.

Imagine holding a ruler in one hand: according to special relativity, to an observer moving in a straight line at a constant speed (close to the speed of light) relative to you, the ruler would appear shorter. But what happens if the ruler has the length of the fundamental scale? For special relativity, the ruler would still appear shorter than this unit of measurement. Special relativity is therefore clearly incompatible with the introduction of a basic graininess of spacetime. Suggesting the existence of this basic scale, say the physicists, means to violate Lorentz invariance, the fundamental tenet of special relativity. "

But what if it's not a 'basic scale' but a threshold?

What it introduce is a singularity, under some scale as f.ex Planck scale. Not saying that is 'the threshold' but it might be made to fit. And it's still fluid, it has to be because all definitions we use are local. That we then lift up 'repeatable experiments' to a global definition doesn't change the fact that all measurements are locally made. which should be read as a Lorentz contraction will hold to the limit of our most 'perfect instruments', and that the threshold I'm wondering about isn't about whether Lorentz/FitzGerald contractions will continue to be  'real' or not, to me its different regimes, we have the clock, 'they' don't.

As I said, weird stuff..
Title: Re: Is the universe expanding faster than the speed of light?
Post by: Bill S on 30/09/2018 16:07:28
Quote
A practical demonstration was it?

Ageing?  I've done plenty of that and it just seems to take me further from finding answers.  Perhaps there are none.  :)

Quote
Actually Quantum mechanics goes one step further in that they discuss and define 'point particles' without any dimension at all.........  All of those are validated by our observations.

Here we go again!  What observation validates the (physical) existence of anything without dimensions?

Title: Re: Is the universe expanding faster than the speed of light?
Post by: yor_on on 30/09/2018 16:15:27
That's not so strange Bill. Think about lights duality for example, a 'photon' or a 'wave'.

sorry, but I have to rush to work now, write Bill and I will read.
Although a little later :)
Title: Re: Is the universe expanding faster than the speed of light?
Post by: guest46746 on 01/10/2018 01:25:53
A wave implies a function. A function is limited to a set. That being said, with Universe as a set, a wave function is constrained within the set. Expandability is a growth model, as such it requires an catalyst that spurns growth yet does not intrinsically alter the nature of the medium. If the medium is light, the question becomes what was the catalyst?

The ubiquitous nature of photonic light make it a prime candidate for the medium.  The photonic nature of Light, incorporates a duality, wave and particle. Both wave and particle act in terms of a dimensional structure that supports temporal and inmaterial aspects. So, the question becomes what inmaterial catalyst produced a physical Universe that incorporates both aspects of duality?

Most aspects of physics such as frequency and amplitude functions, characteristics of a wave, can cancel out each other by injecting an opposite function of equal strength. This melting away of energy to a zero sum, implies a reabsorption of energy into another level or form, an obscure metadata field akin to dimension?  or is it the zero sum nature of Light re absorption? This zero sum ubiquitousness of Light, implies the level of Light in our Universe has not altered but it's distribution has. This explains our Universe's relative stable constant temperature.

The initial catalyst remains unaltered, however, Light is expanding and fragmenting in our Universe. This implies that the original catalyst that initiated the expansion/growth of our Universe has a metadata value undermining the physical Universe. It's attribute main would be the ability to physically separate and break apart light. If Light could be conceived of as originally as completely homogenous, and as a singular set, it would be a dimensional point. This would mean that the catalyst would also have to be an homogenous, singular set and dimensional point.

So, two points merging creates a new dimension. The catalytic reaction of two merging dimensional points creates a growth by the separating of the Light dimension. This growth/expansion produces a 3D aspect that incorporates a separate but present catalyst attribute (dark energy/matter) ?  and the a ubiquitous zero sum Light aspect.

As long as the catalyst aspect remains intertwined with a Light aspect, an artificial/hybrid Set will exist. Catalytic reactions produce violent bubbling reactions with the catalyst acting as a membrane.  This catalytic action ceases when the prime medium candidate or the catalyst deletes their potential.

So, to answer your question, our Universe is made up of Light bubbles each with their own catalytic membrane.  Our Universe is an ongoing reaction of separate encapsulation of primordial Light.

Title: Re: Is the universe expanding faster than the speed of light?
Post by: Bill S on 01/10/2018 12:11:15
Quote
So, to answer your question, our Universe is made up of Light bubbles each with their own catalytic membrane.  Our Universe is an ongoing reaction of separate encapsulation of primordial Light.

It's probably my limited knowledge of physics/maths, but I can't see the answer to the OP in that.
Title: Re: Is the universe expanding faster than the speed of light?
Post by: yor_on on 01/10/2018 13:06:43
No Bill, I missed it too, but it was beautifully written although in a language I find very hard to interpret.