# Big Bang

## Main Question or Discussion Point

I heard that at the time of the big bang the universe expanded faster than the speed of light, can anyone back me up on this? and if it is true then does that mean that the speed of light is not the universal speed limit?

hmm it cant remember back then what happened, my memory is a little blurry these days

you have a lot of matter really close, infinite density. The repulsion (of atomic charge) is approximately asymptotic as it gets closer. So the velocity as it breaks away would be huge no doubt. One must question whether it could supply enough to reach the speed.

Speed of light isnt a universal speed limit so much. things can theoretically break it and go beyond into infinite velocity if they lose energy (radiation).

I couldnt say for sure but it seems doubtful in my mind
i'd be interested to hear what others have to say

I'm not an expert, but I remember someone asking "basically" this same question. The answer given had something to do with the fact that space itself was expanding faster than the sol.

I'm sure someone with more more expertise will jump in here and fill in the details.

mathman
The speed of light is the speed limit for objects that are moving. The expansion of space itself has no speed limit.

All maths and physics tells us that the SOL is the barrier, how can something be an exception to what is an axiom????

Inflation is a neat response to so much but is it based on the assumption given by mathman above??

marcus
Gold Member
Dearly Missed
The speed of light is the speed limit for objects that are moving. The expansion of space itself has no speed limit.
That's certainly right. Relativity places no limit on the speed that distances can increase.

All maths and physics tells us that the SOL is the barrier, how can something be an exception to what is an axiom????
Einstein relativity is the basis for expansion cosmology which REQUIRES faster than light expansion speed. So you have gotten confused about something. Please read what mathman said carefully and find some authoritative text that gives an "axiom" contradicting it.

Inflation is a neat response to so much but is it based on the assumption given by mathman above??
what we are talking about is not specific to inflation. It is a general fact that large distances expand faster than c. It is happening now. It is not restricted to some hypothetical early-universe inflation era.

The speed of light is the speed limit for objects that are moving. The expansion of space itself has no speed limit.
could not an object without charge exceed this limit though?
say, a tachyon?

one other thing, what is space?
by that i mean what is it that limits an object from moving further out from it?
is there something there stopping something from pressing forward? (i dont read much about space normally but am very interested to learn about the subject)

What it is is that matter can not accelerate to a speed faster then the speed of light.

1) Space is not matter, therfore it can accelerate in expansion into speeds faster then light

2) If matter is already going faster then light (like a tachyon), then that is fine, but we can not have a car and push it past the speed of light.

Wallace
Remember that 'the expansion of space', including the notion that space can expand 'faster than light' is a co-ordinate dependent thing. Treat the same universe (ours) with the same theory (relativity) but in different co-ordinates and you don't any superluminal expansion. What this means in the end is that you shouldn't worry too deeply about what space expanding faster than the speed of light means, since this does or doesn't happen depending on the co-ordinates you choose to describe the problem in.

This may seem strange, but remember also that things you can actually observe will be the same regardless of the co-ordinate system (as long as you do the maths correctly!). This also means that clearly the properties of 'space' can't be observed as such.

Any question about 'space' in relativity has a different answer depending on the co-ordinates you use. So for instance, whether space expands, is curved or whatever else depends entirely on how you define co-ordinates.

Really what it boils down to is that space is not a physical entity in the way that it is often implied to be when people talk about relativity. As in so many cases, the experts know what they mean by the terminology they use but the meaning gets lost in translation when it gets to the pop-sci level.

but we can not have a car and push it past the speed of light.
Chuck Norris can push a car faster than the speed of light

out of interest, what is the border of space (if such a thing exists)?
you say it is expanding and i agree with that, but exactly what is expanding?
if its not matter, what is the border?
what if one was to reach the border and tried to pass through?

marcus
Gold Member
Dearly Missed
but exactly what is expanding?
extragalactic distances are expanding. Largescale ones (not like within our galaxy). The rate is about 1/140 of a percent every million years.

... what is the border?
No border.
what if one was to reach the border and tried to pass through?
No border.

Can it be specified where the expansion of space happens? It is not at the boarder, as there is none?

Can space we occupy be expanding faster than c? Is it that relativity exists as a framework inside a framework whose rules are different?

marcus
Gold Member
Dearly Missed
Can it be specified where the expansion of space happens?
No.

It is not at the border, as there is none?
That is correct. There is no border (in standard cosmology). It wouldn't make sense to think of the expansion of distances as localized anywhere. Largescale extragalactic distances simply increase by 1/140 percent every million years

Can space we occupy be expanding faster than c? Is it that relativity exists as a framework inside a framework whose rules are different?
Listen to what I'm saying. I didn't say SPACE expands. that is a loose sloppy pop-sci way of talking. what I'm saying is that DISTANCES increase a certain percent a year.

The increase of any given distance is not necessarily faster than c. It is a percentage rate. so if it is a comparatively long distance it can be increasing many times faster than c. And if it is a comparatively short distance it can be increasing slower than c.

Try not to imagine space as a substance. Focus on the distances between approximately stationary galaxies.

Chronos