# How can space be created faster than light during inflation?

## Main Question or Discussion Point

I have a question that bothers me. well, i have a lot of question that bother me. But for now, i will share only one.

When inflation began after the big bang, the amount of space that was created exceeded the speed of light. How was that possible?

mgb_phys
Homework Helper
Nothing stopping it !

The no faster than light rule in relativity only applies to information.
If two points in the universe move apart faster than light there is no way to transfer information between them and relativity isn't violated

marcus
Gold Member
Dearly Missed
Magnus,
It sounds like you are misapplying the vintage 1905 theory of special relativity. The "speed limit" only applies in certain situations. The 1905 theory was superseded in 1915 by General Relativity. In that framework it is perfectly OK for the distance between two objects to increase at several times the speed of light.

If you want to understand inflation, don't think of space as a substance. Don't think of it as some material that needs to be created. Inflation is studied within the framework of vintage 1915 General Relativity. In 1915 Einstein said that his theory deprives space of the last remnant of objective physical reality. Space as a something does not exist, instead what we have is a catalog of distances between things, events----a web of geometric relationships.

It's normal for some of these distances to be increasing at several times the speed of light.
Most of the galaxies we can see in the sky today were already receding faster than c when they emitted the light which we are now getting from them. And most of them still are receding faster than c. The distant ones, not the near neighbors.

The distance measure often used in this kind of discussion is the "proper" or "freeze-frame" distance. That's the distance you would measure if you could stop the expansion process at a certain moment and then use radar, or time a light signal. It is the distance right now at this moment.

It's not the same as the light travel time measured with the expansion process going on, which gets messed around in irregular ways because the expansion rate changes over time.

This online calculator, if you put in a redshift (say observed in the light of some galaxy) will tell you the freeze-frame distance THEN and NOW. The distance to the galaxy back then when it emitted the light, and the distance now on the day we received the light. You can also use it to figure out the natural travel time. But that won't correspond in any simple regular way to the then and now distances.
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html
It will also tell you the rate that the distances were/are extending, both then and now.

Chronos
Gold Member
Inflation also stretched the wavelengths of light traversing space as it was stretched. This permits us to receive photons from regions of space receeding FTL when those photons were emitted. This does not violate special or general relativity.

Special relatively breaks down at speeds of light. For example. If we were in a train going 100 MPH, and there was another train approaching us at 100 MPH, when we pass each other, it appears to us that the other train is moving 200 MPH. No problem. However, if the train i was in was traveling at the speed of light, and there was another train coming at us at the speed of light and when it passes us, it appears to be traveling at the speed of light and not twice the speed of light. What the hell?

nicksauce
Homework Helper
"Special relatively breaks down at speeds of light."

This sentence makes no sense. First of all, special relativity says, essentially, that nothing can travel at the speed of light. Second, the point of special relativity is to accomodate speeds close to the speed of light, so by definition it does not break down near the speed of light either.

i did not mean to distract you with my first sentence. i am still learning all this stuff. Still, you didnt answer my question. Forgot the first sentence. If you want to impress me, answer the riddle that i provided.

this 'riddle' is asked at least once a week.
In relativity, velocities are not added arithmetically.

So you will see that in GR c+c=c

It is incorrect to talk about 2 trains moving at c, say, they are moving at 0.99c
You will see the second train MUCH SHORTER
Both you perception of time, distance are affected in a way that nature is consistent

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Thank you Dmitry and Marcus. May you stop by a few of the topics I started in this forum? I hope i am not a gnat, but i really want to understand cosmology so please be patient if i say something naive.

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Try taking a different approach: Before the Big Bang, there was NOTHING; IT was everywhere. OK. Now, The Big Bang [BANG!]. OK. Now we have SOMETHING; i.e.the baby universe. IT is SOMETHING; i.e. it is finite. And EVERYWHERE else we STILL have NOTHING. That nothing is commonly called "Space". It is everywhere except where there is something; i.e. the Universe, which is free to expand, contract, blow up, reverse itself into another primordial atom, or whatever else it wishes to do. "Something" can always move into "Nothing" unimpeded. If it expands, it 'takes up "space"'; if it contracts, it 'leaves' "space" behind'. "Space" itself is unchanged because you cannot ever change "Nothing". I know this ain't what you're use to hearing.

Before the Big Bang, there was NOTHING; Now, The Big Bang [BANG!].
No
Time is not defined at t<=0 (at least we don;t know),
so we can't use the word BEFORE

Now, The Big Bang [BANG!] - you meant THEN it was a Big Bang, but it is not right again, as THEN is temporal thing again which is not defined at t=0

bapowell