Question about Expansion Speed exceeding Ligth Speed

[Noaly]

I was recently watching "Into the Universe with Stephen Hawkings" (a general video about the universe on Science Channel) when I heard the statement "Just 10 minutes after the Big Bang, the Universe was 1,000s of light years across." How is this possible if nothing can travel faster than light. Even if two things traveled in the exact opposite directions from the initial start of the Big Bang at the speed of light, they would only be 20 lightminutes apart. Is this statement simply incorrect, or was it possibly to expand much faster than light in the Universe's infancy?

 

[marcus]

A pattern of uniform expansion is not like ordinary motion.
Nobody gets anywhere, nobody approaches a destination, everything just gets farther apart.

So it is not governed by the speed limit of Einstein's 1905 (special) relativity.

Think of expansion as a change in geometry, not as ordinary motion thru space.
the relative positions of things don't change, distances just uniformly scale up.

It may help you to watch the balloon model animation. That shows photons of light traveling at a constant speed across the expanding face of the balloon. The link is in my signature, or google "wright balloon model".
by contrast, the galaxies do not move. they stay at the same longitude-latitude position on the balloon.

The point of Einstein's 1915 (general) relativity is that we have no right to expect that distances between stationary observers remain constant. Geometry is dynamic. The theory explains WHY the angles of triangle add up to 180 in some places and add up to more or less in other situations. Why distances sometimes increase (or decrease) between stationary observers. You should be wondering what criterion for being stationary is used in cosmology. Ask about it if curious.

Don't think of the universe expanding from a point outwards into empty space. Think of of all space uniformly filled with matter, no space "outside" of space, because there is no outside. And expansion is an internal process, internal to the universe. It does not expand "into" anything. Distances simply increase by a certain percentage each year.

 

[Chalnoth]

Another way to state it is that General Relativity modifies the way the speed limit is stated: in General Relativity, nothing can outrun a light ray. That is to say, if a light ray follows some path through the universe, there is no way for any object to follow that same path any faster.

Things in the universe that are already far apart can get further apart much faster than c because the light rays are carried along with the expansion just like everything else: nothing is moving faster than a local light ray, so there isn't any violation of the speed of light limit.

 

[jmoorhea]

Put simply, nothing can travel faster than the speed of light, as predicted by theory.

But space (the medium through which everything is travelling) itself can expand faster than the speed of light.

 

[sardar]

I can provide an explanation for this statement. The expansion of the universe is not limited by the speed of light. This is because the expansion is not due to objects moving through space, but rather the stretching of space itself.

In the early stages of the universe, space was expanding at a much faster rate than it is currently. This is known as inflation, and it occurred within the first fractions of a second after the Big Bang. During this period, the expansion of space was so rapid that it exceeded the speed of light.

As for the statement about the universe being thousands of light years across just 10 minutes after the Big Bang, this is possible due to the concept of cosmic inflation. During this period, the universe expanded exponentially, causing it to increase in size by an enormous amount in a very short period of time.

It's important to note that this does not violate the laws of physics, as the expansion of space is not bound by the same rules as objects within space. The speed of light still remains the maximum speed at which objects can travel through space, but the expansion of space itself can occur at a faster rate.

Overall, the statement is not incorrect and is supported by scientific evidence. It is a result of our understanding of the early stages of the universe and the concept of cosmic inflation.