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  • You're correct about saying you see everything in the past - it's just a matter of relative distance. You don't want to over complicate it and think about quantum mechanics or general relativity, you can get a good approximation just using Newtonian mechanics. The equation you want is speed = distance / time. We know that light travels at 3*10^8 metres per second, and we know that the distance between you and your phone is about a metre from your eyes. As a result we can calculate that the time elapsed between the light being emitted by your phone and it reaching your eyes is 1/3*10^8 seconds, or 0.00000000336 seconds. This is near instantaneous so you don't notice it.

    A scenario where you do notice it is if you're watching a someone hit something from a noticeable distance away (i.e. a cricket game) - where you see the ball get hit and then momentarily later hear the sound of it. It's because sound travels significantly slower than light and so you experience the moment of the ball being hit twice, because it's being reported to you via two different ways (sound and light). Each time, however, you were experiencing the instant at which the ball was hit at that moment in time.

    Going back to the example of the phone - the light we see from the sun was emitted around about 8 minutes ago (due to the distance between you and the sun) so if you were to stand the same distance from your phone to the sun and get someone to change what was displayed on the screen - you observing the phone from that distance would not see the phone screen change until 8 minutes later. Therefore, you are not seeing the phone in its current state, but you are always seeing the phone reported to you as it was 8 minutes ago.

    When you apply the principle to the galaxies, they are so mind-bogglingly far away that the light hitting your eyes is as it was emitted billions of years ago. So yes, you are looking back in time - in the same way that you are always looking back in time, because your eyes are simply receptors for light which has been emitted by a physical object at a point in time.

    You are correct that the concept of a universal "now" is somewhat flawed - but only when you think about time as something constrained by human reporting such as GMT or UTC. Particles experience less time the closer to the speed of light they are travelling, and nothing can travel faster than the speed of light, but in the context of the calculation of speed = distance / time, we know that the speed of light is constant, and as we are measuring the snapshot of when the light was emitted from the object we are observing there is a finite distance between the emitter and the observer - therefore the time being calculated is from the frame of reference of that light which has travelled that distance. That light has been travelling for x number of years therefore it is x number of years old and therefore we are looking x number of years back in time.

    I am a physicist, for what it's worth.

  • We look at the light emitted by the galaxy and we say, oh - cool, it's not the colour we were expecting it to be

    How do you decide what colour you expect a galaxy to be?

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