[gary_0]

Given that the speed of light is the speed of causality, technically it's not really 420 million years in the "past" in any meaningful sense. The present is relative, not universal. The collected light we see in our telescopes is a lie about a particular universe that will never be, at least in any tangible way. On a cosmic scale, every spot in the universe sees its own unique sequence of events going on around it, all of it rendered virtually immutable by the relative slowness of c.

It's a beautiful nightmare, isn't it?

https://en.wikipedia.org/wiki/Relativity_of_simultaneity

[codethief]

> Given that the speed of light is the speed of causality, technically it's not really 420 million years in the "past" in any meaningful sense.

Yes, it is. It is 420 million years in the past in our frame of reference. The link you posted is about how frames of reference of other observers might differ from ours. However, doesn't make the notion "420 million years in the past [in our frame of reference]" any less well-defined.

[conductr]

I’ll admit I’m severely undereducated in this stuff, probably less than an average high schooler these day but nevertheless I feel like I’ve considered this before and never knew it had a name. Which makes me feel not completely stupid.

> whether two spatially separated events occur at the same time – is not absolute, but depends on the observer's reference frame.

But What I don’t understand about this is why is “time” framed as observer based? In my mind, the events do happen at the same time and just are unable to be observed as such. I feel like time is a figment of our imagination, it’s just a measurement. In my pea brain time makes sense more as a constant and the other things are something else that impacts the latency of observance

[SJC_Hacker]

> But What I don’t understand about this is why is “time” framed as observer based? In my mind, the events do happen at the same time and just are unable to be observed as such. I feel like time is a figment of our imagination, it’s just a measurement. In my pea brain time makes sense more as a constant and the other things are something else that impacts the latency of observance

Its a logical consequence of the speed of light being constant in all inertial reference frames, regardless of the velocity.

This is an axiom of special relativity, but it has also been verified at (admittedly low) relative velocities.

That in itself is somewhat absurd, but it leads to further absurdities when you do the math. In order for the speed of light to remain invariant, you can no longer speak of an absolute (preferred) frame of reference.

You can of course, privilege certain reference frames e.g. Earth, but its rather arbitrary.

[alok-g]

>> In my mind, the events do happen at the same time and just are unable to be observed as such.

Not so, I would say.

Space and time are inherently linked under special (and General) relativity. For two observers who have relative motion between them, the space (distance between two 'events') and time (between the said events) are both different.

When some poem or a song talks about the universe being frozen at a given instant of time, that can be only in a given reference frame. There's no absolute time for the universe.

[satvikpendem]

If not for observation, what does "happen" mean? Keep in mind observation in the physics sense doesn't mean conscious observation but rather that anything experiences something at all.

[nullwriter]

Absolutely mind blowing - I've not thought of this and will be reading about it

[andrewflnr]

Don't think about it too much. It's wrong. Relativity of simultaneity only kicks in when you have reference frames moving at noticeably different velocities. Which is... not entirely wrong in this case due to the expansion of the universe, but would be equally true of a nearby reference frame moving away equally fast. It's nothing to do with light travel time.

Ed: I've slipped into the fallacy a bit. Reference frames don't have locations, so they can't be "nearby". Just pretend I said "reference frame of a nearby object".