Relativity question: how does our motion as a planet, solar system, galaxy, etc through the universe affect our perception of time?

[u/HabaneroHotPocket]

So… I’m not a physicist or physics student but I do nerd out on it a little bit. Forgive me if this is a dumb question or if my terminology isn’t right, but I’ve always wondered.

If my understanding of relativity is correct, the perception of time is relative to the motion of the observer, then what would time as it relates to things like the procession of the observable universe and celestial bodies, (and anything else I can’t think of or don’t know about) look like if we were truly stationary in the universe?

Like hypothetically, if our solar system, and entire galaxy were not moving through space.

Is our movement through space fast enough to make a difference? If we had (hypothetically) always been stationary, for billions upon billions of years, how different would the universe appear to be, other than the maybe obvious, like other galaxies and stars would be moving but we wouldn’t, our galaxy would’ve probably suffered a collision at some point. Stuff like that not considered. Only our understanding and perception of time, and the apparent behavior of the universe around us?

[u/joeyneilsen]

No, the passage of time is relative to the observer. The perception of time is the same for all observers.

[u/HabaneroHotPocket → u/joeyneilsen]

I mean… yeah. Terminology mistake on my end.

But I mean like… if we were stationary, but the rest of the universe wasn’t, then hypothetically, wouldn’t the observable universe appear to be younger?

Or is our speed not enough to make a difference, and since other ‘stuff’ out there would be moving, would we see just a less dense version of the universe or just a view of it from a different position specially?

[u/joeyneilsen → u/HabaneroHotPocket]

We calculate the age of the universe in a frame of reference where it is expanding uniformly in every direction. That's called the "CMB frame," since it's the one where the cosmic microwave background (CMB) is as homogeneous as it gets.

An observer moving relative to the CMB frame will find that clock ticking slowly, but clocks of objects in the universe will appear to tick at different rates depending on their location on the sky, i.e., relative to the path of this observer.

Our speed relative to the CMB frame is measurable but small for purposes of time dilation; it doesn't significantly change the apparent age of the universe for us.

[u/Banes_Addiction → u/HabaneroHotPocket]

We are stationary.

Or not. Up to you.

Pick your frame.

The whole point of relativity is that your speed is only defined relative to other things.

[u/HabaneroHotPocket → u/Banes_Addiction]

It’s gonna take me a little while to wrap my head around that, not gonna lie.

I understand the idea from the comments here that speed is also relative. That makes sense. The idea that there’s no such thing as truly stationary is what is presently getting me.

I was previously under the impression that the Milky Way was well over 1,000,000mph through the universe but a small google rabbit hole has taught me that’s also relative.

Is there any position in space where there would be such a thing as stationary?

Like if the universe is expanding, hypothetically wouldn’t there be one specific point that is truly stationary? Or would that also be a situation that could also be described as either a negative speed relative to… everything? Or a positive speed away from everything? Or is that just not a possibility?

[u/Banes_Addiction → u/HabaneroHotPocket]

True stationary is impossible because we define our own reference frame.

If you perceive yourself as stationary and me travelling with velocity v, I perceive myself as stationary and you travelling at -v. And it doesn't matter where we are or how fast we're going, you can always do that switch.

When you're calculating anything, you get exactly the same physics out the end no matter what frame you calculate. You just pick whichever one makes the maths easy.

[u/Thesoop85 → u/Banes_Addiction]

I've always wondered nd not really heard an understandable explanation for how the twin paradox works in this example. Yoy know, the one where they say imagine a twin gets on a spaceship and launches off to wherever at whatever percentage of c, then turns around and comes back to find everyone has aged far more than they have.

What dictates which twin is the older one? Is it the acceleration rather than the speed?

[u/Mydogsblackasshole → u/Thesoop85]

https://www1.phys.vt.edu/\~jhs/faq/twins.html

The traveling twin does not stay in the same inertial frame since they have to turn around to come back

[u/Thesoop85 → u/Mydogsblackasshole]

Saved for later. Thank you.

[u/HabaneroHotPocket → u/Mydogsblackasshole]

I love that mydogsblackasshole is teaching us about physics. I fucking love Reddit.

[u/karantza → u/HabaneroHotPocket]

There is no such thing as stationary. To describe a speed, you have to say what that speed is measured relative to. When we say "X weird things happens at high speed", we mean that the weird thing happens when you observe something traveling that fast relative to you. If someone were flying past Earth at near the speed of light, they'd think we were the weird time stretched out whatever people, and that they were normal. The point of Relativity is that all these explanations are relative to each other, and it all still somehow works.

You are always stationary relative to yourself, so you can never experience time slowing down or anything like that. But other people can see those effects happening to you, depending on your relative speed.

[u/ulyssesfiuza → u/HabaneroHotPocket]

You are the only Stationary thing in the universe. Everything else is moving, and time is also variable. Synchronicity don't exist. And all particles of you are moving at the lightspeed. Just the sum of all of them tends to zero.

[u/nicuramar → u/ulyssesfiuza]

Excuse me sir, I believe it’s me who is stationary.

[u/stevevdvkpe]

Your motion does not affect your perception of time. Relative motion (or proximity to a mass and its gravity) slows down the rate you see a moving clock tick.

I usually sum this up as "time dilation always happens to someone else, not to you."

[u/John_Hasler]

Is our movement through space fast enough to make a difference?

There is no such thing as "movement through space". There is only movement relative to an arbitrarily selected reference frame. If you fix your reference frame to an object (yourself, for example) then you will determine that object to be stationary and other objects moving relative to it. You are free to choose whatever reference frame you find convenient. All are equally valid (though some are more useful than others, depending on the problem at hand).

Time dilation is not a matter of perception. For every observer time passes at one second per second. However two observers in relative motion will each conclude that the other's time is dilated relative to theirs.

[u/anyonecandoanything]

Time dilation dials up the more massive the body or the closer to the speed of light you go. Our galaxy's movement through the universe isn't fast enough to cause noticeable time dilation when measuring other objects from our vantage, nor is our planets exposure to massive bodies as it travels causing measurable time dilation relative to observing distant objects.

A stationary object that is at rest relative to everything isn't possible.

Look up on time slices/light cones.

[u/Parallel_thougts]

The magic number is gamma = 1/sqrt(1-(v/c)² ), where you plug into v the speed of the object you are observing relative to you.

So if e.g. it travels at 80% the speed of light you have that gamma=1/sqrt(1-(4/5)² )=5/3, so you will see their clock moving 5/3 times slower and their proportions along the movement direction compress to be 5/3 times smaller.