Does the rapid inflation of the early universe violate the speed of light?

[zuz]

I just heard that the universe inflated from the size of an atom to the size of our solar system in 100 seconds. Wouldn't that exceed the speed of light?

 

[Bandersnatch]

I just heard that the universe inflated from the size of an atom to the size of our solar system in 100 seconds.
Wouldn't that exceed the speed of light?

Let's say you have a beam of light being emitted from one edge of the initial atom-size universe, while it expands to the size of the solar system over 100 seconds. Imagine what happens as the light beam travels while the distances grow.
Would the light beam be able to reach the other side of the (initial) atom by the time it will have expanded to the size of the solar system?
Does anything ever overtake the light beam as it travels? I.e., does anything start closer to the source, and end up farther from the source than the traveling light, after the same interval of time? (the 'overtake' bit is important, as that's what determines whether locally anything can go faster than light)

 

[Ibix]

I just heard that the universe inflated from the size of an atom to the size of our solar system in 100 seconds. Wouldn't that exceed the speed of light?

No, although I see where you are coming from. The point about nothing traveling faster than light is that nothing ever overtakes a pulse of light. And that is true during inflation too, because light isn't immune from the expansion of the universe. If a pulse of light is to the left of an atom and heading left, it will always be to the left of that atom.

Everyday notions don't always survive contact with extreme situations. Unfortunately, cosmology is an area where the apparently straightforward notion of "speed" is impossible to define unambiguously, except in the narrow sense that Bandersnatch and I are using it.

 

[phinds]

I just heard that the universe inflated from the size of an atom to the size of our solar system in 100 seconds. Wouldn't that exceed the speed of light?

Too add to what others have already said, I would point out to you that you are using the word "universe" when you are actually talking about the OBSERVABLE universe. They are not the same thing and if you are interested in cosmology you'll want to learn the difference.

 

[rootone]

The Universe still is expanding faster than the speed of light as far as any Earth based observer can see,
This does not violate relativity, but an object moving 'IN'; space faster than light, ... that's where yer problem is.

 

[timmdeeg]

I just heard that the universe inflated from the size of an atom to the size of our solar system in 100 seconds. Wouldn't that exceed the speed of light?

I think it is helpful first to have a good notion what 'expansion of space' in general and then specifically what 'superluminal expansion' means. The former means that comoving objects get farther apart from each other, in our actual universe the galaxies which participate in the cosmological expansion. The latter (and the former) is shown very nicely in the recommendable article Expanding Confusion of Davis & Lineweaver, Fig 1, top panel "Proper distance, D, (Glyr)". This spacetime diagram(*) shows that the angle of the lightcone in the very early universe is much below 45° (it is 45° in not expanding flat spacetime). You can still imagine two neighboring comoving particles in this era. If one emits a photon it will not reach the other, because this recedes superluminal.

(*) has anyone a link to this diagram?

 

[zuz]

Actually, in the beginning, there was no "light" the universe was opaque. I don't know if standard rules apply. Although, it takes light 8 minutes to reach the Earth from the sun. How can the universe inflate to the size of the solar system in under two minutes?

 

[Ibix]

Actually, in the beginning, there was no "light" the universe was opaque.

The speed limit isn't about light - light travels at the speed limit for various reasons, but the speed limit is there whether there is light or not.

How can the universe inflate to the size of the solar system in under two minutes?

Because when you feed various matter and radiation equations of state into the equations, that's what you get. You're bumping up against the limits of what anybody knows here.

As noted earlier, the speed limit only applies in the sense that nothing will ever overtake a light pulse. An expanding universe always respects this, whatever the expansion rate.

 

[zuz]

So how did it get so big so fast?

 

[Bandersnatch]

By expanding. There's no limit on the expansion rate.

 

[phinds]

So how did it get so big so fast?

Suppose you have a boat that has a maximum speed ot 30 mph. You put it on a river that's traveling at 70mp and then relative to the shore the boat ends up going 100mph. You are asking how the boat could possibly go 100mph when it is supposedly only capable of going 30mph.

 

[nikkkom]

I just heard that the universe inflated from the size of an atom to the size of our solar system in 100 seconds.

Actually, it's far more than that. In the first one second would-be Observable Universe reached the size of about 10 light years in radius. That would be expansion of about 300 million times faster than speed of light.

 

[zuz]

The universe didn't expand, in inflated. I don't know if this makes a difference or not, but I do know that light does not work that way in reference to the boat.

 

[Ibix]

The universe didn't expand, in inflated.

Inflation is a period of rapid expansion in the very early universe.

I don't know if this makes a difference or not, but I do know that light does not work that way in reference to the boat.

Thinking of the boat as light (or anything else) being carried along by expansion isn't a bad analogy. It isn't a completely satisfactory analogy, of course, but there isn't one. Really the only completely satisfactory answer is to learn the maths of cosmology. If you haven't done that, you'll just have to take our word for it at some point.