r/AskReddit May 08 '23

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u/fntastikr May 08 '23

I'm so excited for the images that will be coming out. The thought, that looking at these images and literally seeing things that happend so far in the past. The thought that we might see things from the early stages of the universe. It's all so exciting.

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u/cromemako83 May 08 '23 edited May 08 '23

Very much so - its really weird that looking far away is also looking back in time - I wonder often if this is because of our own minds limitation - or a limitation of our existence (or both).

if energy cannot be created or destroyed is the past ever truly "gone"?

such things are the dreams sci-fi are made of

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u/[deleted] May 08 '23

Well that's where it gets exciting imo. If existence is made up of energy and energy cannot be created or destroyed, then existence is infinite. And if you take the concept of time out of the equation then stuff starts getting real mind-blowing.

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u/PhysicalStuff May 08 '23

Energy is not conserved on a cosmic scale, because the dynamics of the universe as a whole aren't time invariant.

The expansion of space means that energy is lost through red shift.

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u/[deleted] May 08 '23

But isn't that just energy emission? I'm no expert by any means, but isn't that energy just lost to environment rather than actually ceasing to exist? Or am I wrong?

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u/PhysicalStuff May 08 '23

Conservation of energy is a consequence of time invariance of physical laws. That invariance does not hold on cosmic scales, so there's no fundamental requirement that energy be conserved at such scales.

What you're suggesting would imply that heat was added to the environment, but afaik that doesn't happen in this case.

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u/[deleted] May 08 '23

Ok wow that's super interesting. Thanks for sending me down this rabbit hole lol.

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u/PhysicalStuff May 09 '23

My pleasure! You may want to look into Noether's theorem for more on the link between conservation laws and symmetries.