if space is expanding and the known universe is wider in light years than years old it is, aren’t opposite ends of the universe traveling faster than light in relation to each other?
In: Planetary Science
The expansion of space is different from movement as we are familiar with it. Movement is something that happens through space.
You’d be right that the space between two very distant points is expanding faster than light. This just isn’t *movement*. At least, not the traditional version of movement. It’s not constrained by light speed.
Yup.
The speed of light is only a *local* speed limit. Things can’t move *through space* at a speed faster than light, but if the *space itself* is moving (or expanding) away faster than light, then things in the space can be carried by that space.
The light speed limitation only restricts anything that can transmit information from one place to another, such as you could do with light (e.g. radio waves).
If you aimed a laser pointer at a very distant screen, and then panned it across from point A to point B, the spot of light on the screen could conceivably appear to be going from point A to point B faster than the speed of light, but it can’t carry any information from point A to point B, so it’s not an issue for relativity.
Nothing is actually moving from one end of the universe to the other as a result of the expansion of space, so it’s not a situation that invokes relativity. Like the laser pointer, it’s just you looking at both moving points and ascribing some meaning to them
Yes.
Imagine two ants walking on balloon. Their top speed is 3mm/s. In theory they would only be able to part ways at a speed of 2x3mm/s. When we inflate the balloon however, we see them parting ways faster. Even parting ways when they stand still.
Yup! And not just the opposite ends. Most of the universe is moving away from us at greater than the speed of light. Only 6% is currently close enough that you could send a message to it at the speed if light. The other 94% is already going to fast and its getting faster every day, this is called the cosmic event horizon.
This is allowed because the things aren’t really accelerating… more like extra space is just appearing between two places.
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