If I understand it correctly, we measure time by how fast light passes, or something similar to that. Now if the universe expands faster than the speed of light, would that mean that the universe ages faster than earth, or maybe slower than earth? Maybe this doesn’t make sense but I have a gut feeling that there’s something to it…
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The “universe” itself doesn’t really age at all. Only “stuff in the universe” ages. We call this aging of the stuff “entropy”
The expansion of the universe “faster than the speed of light” at very large distance scales only results in the overall thinning and isolation of the stuff in the universe. A very long time (unimaginably long time) from now we’ll only be able to see our what was once our galaxy merged with it’s closest neighbor galaxies and then just empty blackness beyond.
So this stuff took me a while to even begin to understand, but there’s a couple problems with the premise here.
One is that there isn’t really a singlular thing you’d call “the universe” for the purposes of relativity. Every object in the universe is its own observer relative to the speeds everything else in the universe is moving relative to it.
Another thing is that the universe isn’t really expanding at a “speed” faster than light. It is expanding quite slowly, but it is doing it *everywhere.*
So lets say one inch becomes one point one inches over a period of time, right? Well because there are SO MANY goddang inches, and *every single one of them* is becoming 1.1 inches, the amount of distance increases drastically over a long enough distance. Two inches becomes 2.2 inches. 3 inches becomes 3.3 inches. And millions of millions of inches increase by an amount that light cannot cross in the same amount of time that the expansion happens. But again, the rate of that expansion can be quite slow and still have this effect over vast distances.
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I think you’re getting confused by the idea that the closer something gets to the speed of light, the slower time passes from its own perspective relative to other perspectives (typically called “frames of reference” in this context).
But the Universe as a whole doesn’t travel at *any* speed. It’s not a thing itself, it’s a collection of other things that all travel at their own individual speeds. None of those things travels faster than light. Rather the space between them increases, and that increase is fast enough that an object very far from you can appear to retreat faster than the speed of light even if it’s not actually moving at all.
All of that sounds bizarre, I realize. And it is. Space gets increasingly unintuitive the deeper you go into it.
> If I understand it correctly, we measure time by how fast light passes, or something similar to that
No, time is defined based on oscillations of an atom in some type of crystal. So a second is N amount of oscillations of that atom.
Yes, the universe does age faster than Earth. Imagine you and your friend both have a clock, but your friend lives in a different city. Even though both clocks are ticking at the same speed, your friend’s clock will seem to be ticking slower than yours because they are farther away. This is because time is affected by gravity and the speed at which things are moving. The universe is much bigger than Earth, so it’s affected by these things on a much larger scale. This means that time passes more quickly in the universe than it does on Earth. It’s like your friend’s clock ticking slower because they’re farther away, but on a much bigger scale.
As far as my limited understanding goes, there are two naturally occurring factors that can affect the speed of time.
1) The speed of movement of an object through space (and not the movement of space itself). Space expanding does not affect the flow of time by itself. You need to be moving THROUGH tha space itself, and relative to the region of space you’re occupying (not relative to a distant point in space that’s expanding at a different rate or direction
2) The distortion of space-time where the object is located. This occurs naturally due to gravity in case of large or celestial objects. Eg., the international space station needs to periodically adjust their clocks because they move at a very slightly different rate through time than we do on Earth (time moved a tiny bit faster for them than it does for us, but to a degree that can only be observed via an atomic clock over a period of time). Since the expansion of space itself doesn’t distort space-time in the same way gravity does (i.e., troughs due to large masses), the expansion has no affect on the passage of time.
Yes, time moves differently in parts of the Universe, but not because of expansion. If you orbit Jupiter, time will slow down compared to Earth. If you orbit Mars, it’ll speed up compared to Earth. If you travel to a distant point between Earth and Mars, it’ll be faster. And beyond Pluto but before the Oort cloud, it’s faster still.
For the record, relativity suggests nobody is moving per-se. It feels like you’re treating celestial bodies as if they’re ships moving through water, and the water (or space) is eroding. That’s not quite what’s happening.
Essentially, most celestial bodies are “standing still” and are not experiencing time at a significant difference (as far as I know). Yes, they’re still moving, but we’re not certain about the specifics, and anything I say will be hypothetical. It would be more accurate to say space is being added between.
By your logic, aliens on the opposite side of the galaxy perceiving time would affect our local time and everything would accelerate. That doesn’t make sense.
Although it would explain how aliens showed up to visit earth, if that really happened (which it didnt.)
The universe all ages at pretty much the same rate. When we look out into the sky, we see the universe in the past because that stuff is so far away that it takes a long amount of time for the light to reach us. Those things we are seeing may not even be there because they continued to change after emitting that light.
Now, the expansion of space happening faster than light, that’s not really happening inside of the universe. Once you get far enough away from Earth (where we are observing from) that the expansion of space is happening faster than light, that space it outside of the observable universe, and due to that fact, it essentially does not exist to us. It can’t interact with us, and we can never interact with it. We won’t even be able to see it.
Time does slow down when you’re accelerating, so near massive galaxies and black holes, things will age slower, but the universe still ages the same. Since space and time are really the same thing, any local time dilation really doesn’t change the universe as a whole.
Simply put, space time stretches with higher concentrations of *stuff*. The more *stuff* there is in one place the more time will dilate. So where there is no *stuff*, time goes faster. And a lot of *stuff* can make a black hole where time for all intensive purposes has to stop. Astronauts age slightly faster because they are farther from earth which is made of a lot of *stuff*.
The “observable universe” is our limit as to how far we can see into space. At some point the light being emitted from *stuff* cannot outpace how quickly that *stuff* is moving away from us. So the *stuff* appears younger to us than it actually is.
At the outer limits of our observable universe, relative to us, that *stuff* looks like it’s moving away at the speed of light. But that *stuff* is not moving THROUGH space at light speed. The actual place it exist in is getting farther so no laws of physics are broken.
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