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I was wondering, if inflation caused space to expand so rapidly, what happened to slow it down to the current rate?
I was wondering, if inflation caused space to expand so rapidly, what happened to slow it down to the current rate?
This is almost correct, Landrew. The key to getting inflationary expansion is maintaining a nearly constant energy density of a negative pressure fluid. In the simplest examples, this energy density is constant: as the universe expands, more fluid is 'created'. Inflation is not related to the creation of space or time, although it does tell space and time how to behave. The space is already there -- inflation just causes it to expand, or stretch.My crude understanding is that inflation is the creation of time and space itself, therefore space itself is constantly being created (expanded) with the expansion of the universe.
This is all true, but it's true of any expanding spacetime, not just inflating spacetimes. Hubble's law, which relates the recession velocity of an object a distance r away from an observer, [tex]v = Hr[/tex], holds (approximately) in any expanding spacetime. You can see that there's a special distance (r = c/H) at which distant objects have superluminal recession velocities.This would seem to explain the apparent violation of Einstein's relativity laws, whereby some objects appear to be traveling faster than light. It also seems to explain why the more distant the object, the faster it appears to be traveling away from us.
Good question! If the energy density driving inflation remains constant, then indeed nothing slows the expansion -- the universe goes on inflating eternally. However, in realistic models of inflation, this energy density is not, afterall, constant. The energy density decays, and in doing so, the rate of expansion decreases. In fact, the transition from inflationary to non-inflationary expansion is very important, since it coincides with the reheating of the universe -- much of the energy associated with inflation gets converted into matter and radiation, replacing all the radiation and matter that the inflationary expansion dilutes.I was wondering, if inflation caused space to expand so rapidly, what happened to slow it down to the current rate?
This is all true, but it's true of any expanding spacetime, not just inflating spacetimes. Hubble's law, which relates the recession velocity of an object a distance r away from an observer, [tex]v = Hr[/tex], holds (approximately) in any expanding spacetime. You can see that there's a special distance (r = c/H) at which distant objects have superluminal recession velocities.
Einstein postulated that the speed of light was the same for every observer, regardless of their state of (non-accelerated) motion. That is, two observers moving relative to each other at a constant velocity both agree that the speed of light is c= 3x10^8 m/s. Your raise an important point -- shouldn't light also be subject to the additive nature of velocities? The answer is no! Light doesn't seem to care much whether its source is moving or not -- it always travels at the same speed.Due to my own misunderstanding of physics no doubt, but I've always thought there was a problem with Einstein's speed limit on the speed of light. If someone drives away from you at 3/4 the speed of light, his headlights on, the light should be going 1.75 times the speed of light, except to you, who can't see it, but in real terms, isn't that a superluminal light speed?
Due to my own misunderstanding of physics no doubt, but I've always thought there was a problem with Einstein's speed limit on the speed of light. If someone drives away from you at 3/4 the speed of light, his headlights on, the light should be going 1.75 times the speed of light, except to you, who can't see it, but in real terms, isn't that a superluminal light speed?
I was wondering, if inflation caused space to expand so rapidly, what happened to slow it down to the current rate?