If an item moves at light speed away and at light speed back, it will be virtually the same age. Yet, from the item’s perspective, it is us who moved away and back again, so it should have been us who remained still in time. This suggests that there is a concept of ‘stationary’ in the universe and that movement isn’t just relative in space but also absolute.

In other words, if there are objects A and B, and one moves away and back, how can we tell which one actually moved and which one stayed still? According to Einstein's theory of relativity, one should be younger than the others, but which one since there is no difference between one and the other and we don't know which one of them actually did the traveling.

But when they come together again, one would be older than the other, but which one if there is no difference? Is object A younger or is object B younger? From their perspective, it was the other object that did the traveling. But when they meet, only one of them can be right. They can't be both younger than the other, only one of them can be.

The difference is that one experienced accelerations. (DEcelererations are accelerations too. They're just a special case of acceleration.)

If an item moves at light speed away and at light speed back

Objects made of matter generally cannot move at literal light speed. Are you talking about photons (particles of light / electromagnetic radiation) or are you just being approximate ('nearly as fast as light, but not quite))?

7874391 I'm being approximate.

The thing is, acceleration doesn't matter. The effects persist even at constant speeds after acceleration.

Let's say your twin accelerates to almost light speed within a day and travels for a decade. And after some quick accelerations, he comes back. He won't be 2 days younger. He will be 2 decades younger, even though he didn't accelerate for two decades.

Also, are you saying that acceleration is absolute and not relative? If I push you away, did you accelerate or did I?

7874348
Movement is absolute but speed is a function of time and time isn't absolute, seemingly "squeezed out of" space by gravity or, given that the particles interact with the Higgs Field more at high speeds, mass itself, so it would be hard to claim that speed would be.

That being said though it could be stated that movement is relative to time-space and fields like the Higgs Field but at that point you're bordering on arguing terminology more then topics.

7877073

particles interact with the Higgs Field more at high speeds

High speeds relative to what? To the stationary fields? Is there such a thing?

Or is it relative to to some object? But if that's the case, are you moving away from the object or is the object moving away from you?

So, can you answer my question then? If you trap your twin brother in object B and then watch object B move away really fast and then see it come back after some time, which among you is older? You don't know if the brother moved away or if you moved away, but since speeds are relative to object A and B, it doesn't really matter. Still, what is the result of such an experiment?