If the big bang happened 13.8 billion years ago, and the universe is 93 billion light years in diameter, how did the universe expand faster than light?
In: Physics
I’m just postulating here, but if you start light out at a point, and you have 2 rays going in opposite directions, then the distance between the edges of them is getting larger by two times the speed of light. That is absolutely NOT how the universe expands, but it does show that shit is relative.
This is probably the most asked question on this sub.
Relativity only applies locally. There’s no rule about how fast incredibly distant objects can move relative to each other, and it’s not a true velocity. Which is why people say “the space between objects is getting bigger” and such.
The real answer: we don’t know.
The theoretical answer: It’s not the 2 balls on a fabric that’s accelerating.
It’s the fabric itself expanding.
WE can’t travel faster than light because of physics and matter, but space itself does not have those limitations.
13.8 being the radius of a circle. Times 2 for the diameter. Times 3.14 for the circumference. Equals 86.66. Pretty close for simple math. Seems legit.
The Universe is actually not 93 billion light years in diameter. That’s only the *Observable* Universe, which is the portion of the Universe that is potentially observable from Earth since light would have had time to travel from there to Earth since the Big Bang. The entire Universe is much larger (at least 23 *trillion* light years across according to Wikipedia) and possibly infinite.
The ELI5 answer is: We don’t know, but the Physics community has come up with a host of answers that are in some cases long winded and convoluted that (if stated concisely) means this is our best guess so far.
Those numbers are just guesses. The universe might be infinite for all we know. There is no proof for the big bang and no proof whatsoever when it happened. You can say the observable universe diameter but not the whole universe.
Follow up question though, the diameter of the known universe is based on how far we can observe. If the universe is expanding faster than C, then how come we can observe light from 93 billion light years away?
Wouldn’t it be more logical to assume that the universe expands slower than C so light can still reach us albeit at a much longer amount of time? Just like walking up an escalator that is going down. If you walk faster than the escalator going down, you will still reach the top but at a much longer amount of time.
Sorry if this is stupid
Space can expand faster than the speed of light. There’s no law that says it cannot. This happened during the inflationary period of the universe by a ridiculous amount.
There was a very very very short period of time at the beginning of the universe called “The Inflationary Epoch”. To get an idea of how short this period of time was, the difference between the entire length of the inflationary epoch and one second is the same ratio as the difference between one second and 31,000,000,000,000,000,000,000 years (roughly). And actually it may have been even shorter than that.
During this period, the universe stretched itself out a little. The space between everything grew.
A nanometer is a very very very small distance. The difference between a nanometer and a meter is the same as the difference between 1 meter and the distance to the moon, and back, and then almost to the moon again.
During the inflationary epoch, every nanometer of distance between things turned into about 10 light years, the distance to most of the nearby stars in the sky.
At least, that’s the hypothesis. There are other hypotheses, but none that match all the data we’ve collected quite so well as this one does.
Why did the universe stretch so much so quickly? Lots of scientists spend their careers trying to answer questions like that.
https://en.m.wikipedia.org/wiki/Inflationary_epoch
I’ll end this by alighting your imagination a little bit: if space can be stretched, and can be stretched faster than light, what might happen if *we* found a way to control that stretching? Well, maybe it would let us move through space faster than light too. (Probably not, but it’s a fun idea).
Real answer, we don’t really know. Theoretically the simulation you are in was launched yesterday, everybody and everything else is part of it and your memories are just starting defaults.
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