Well, you're missing two things:

1. Earthlings did not originate in the andromeda galaxy

2. Faster than light travel is not possible.

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Okay but I could at least witness perhaps an extremely large explosion to propel them out of their galaxy.

The next observation would be when they arrive.. Which is sometime in the past?

If (hypothetical) Andromedan humans had left 2.5m years ago and managed to travel at very, very nearly the speed of light the entire way (tricky given acceleration, deceleration, turnover, and fuel), they would only just now be arriving on earth. Awkward. Alternately, they would have had to have left home 5m years ago to arrive on earth 2.5m years ago. Which is about the time the light from their departure would have arrived on earth too. You could go chasing that light, but you won't catch it, at least until you have FTL (and a telescope the size of a solar system to do anything useful with it like see the decaying remains of their hypothetical civilization).

Anyway, thanks to time dilation, whoever arrives from Andromeda under these circumstances could plausibly be the same people who left, which is fun.

Also, we evolved on this planet and are genetically all but identical to everything from chimpanzees to oak trees, on the scale of the universe.

The light from any such explosion would have arrived before they did and would be long gone by now.

You cannot travel faster than light. It is not possible for an object to travel from Andromeda to Earth faster than light does so.

But I just hypothetically saw it..

How did these ancient andromedans get here faster than the light emitted from them?

I don't know..supposedly when I look in the sky I'm seeing the light from 2.5mil years ago.

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No. If we were transported here instantaneously, then we wouldn't be able to see ourselves arrive because we've already arrived. Imagine running 100m, you can't turn around and watch yourself arrive. Even if you run the speed of light you can't turn around and watch yourself arrive.

You are. What does that have to do with my question?

You cannot arrive before the light of the explosion, you would have had to travel faster than the speed of light. If you travelled at the speed of light, you would have arrived at the same time the light from the explosion reached here.

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You're assuming they came here faster than light and then looked back at themselves. This is a paradox of FTL travel.

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This is all theoretical/hypothetical, but if they had used a wormhole (going around limitations of speed of light), yes they could arrive before the light showing them entering the wormhole

Or maybe one of these https://en.m.wikipedia.org/wiki/Alcubierre_drive

> Objects cannot accelerate to the speed of light within normal spacetime; instead, the Alcubierre drive shifts space around an object so that the object would arrive at its destination more quickly than light would in normal space without breaking any physical laws.[3]

This theoretical drive requires more energy than is in the universe though (among other problems)

Well first you have to believe that protons exist. The do not. How exactly do you think there are enough of them emitting from across the entire Universe for 13.8 billion years (The age of the Universe) to be visible to the human eye? The visible universe is 46.5 billion years across. (Even more impossible for protons to emit that far in every part of the universe.) There is not a "Grand theory" because there is no such thing, just look at how the speed of light is not consistent. Also the red shift for most galaxies except for our local cluster is moving away from us at the speed of light and the ones in the blue shift in our cluster are moving towards us at the speed of light. Life is but a dream. None of this is possible through math. You have only made up your own construct is all. Only you exist and it is a simulation. If you disagree, you can not prove me wrong with my above statements. Impossible.

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The speed of light in a vacuum is a fundamental physical constant, the currently accepted value of which is exactly 299,792,458 metr. es per second, or about 186,282 miles per second.

Incredibly untrue. Just look at the age of the universe and how many light years apart is is. Ridiculous. So many base so many things on incorrect measurements and false ideas. It is unreal. Pun intended.

Not really, people simply do not know what "dark matter" is. P.S. Math, physics, etc. has their measurements all wrong. It is NOT consistent in ANY environment. Everyone is looking to build on wrong older theories. String theory is a perfect example, yet they all are really.

Travelling at the speed of light, whenever they'd look back they would see their family waving them goodbye. Only on arrival their now ancestors would seem to pick up their lives again.

This is like asking what leprechaun farts taste like. What you're asking for is a solution to an impossible scenario. There is no correct answer.

It's more complicated than that. It isn't just that it takes light 2.5m years to span the distance from our perspective. Light also travels at the speed of causality, and nothing that occurred in Andromeda can reach Earth before the light.

Oh boy, where to start on this. I started writing a point-by-point response, but you'd do better to read some books on the topics. You've taken a few facts out of context, gotten others wrong, and misunderstood pretty much everything.

By the way, the observable universe is not 46.5bn light years across, it is actually about 90bn light years across. You were thinking of the radius, the distance from us to any point on the horizon.

This is possible for a few reasons. First, the Big Bang did not come from a singularity. It happened everywhere, all at once. The early universe was already a significant portion of its current volume.

Second, space itself expands. The rate of expansion of space is accelerating. This is where Dark Energy (not related to Dark Matter) ties in. The expansion of space accounts for why the radius of the universe is greater than 13.8bn light years, and why the horizon is effectively receding faster than the speed of light. The expansion of space is contributing to the red-shift that we measure to determine how fast objects are moving.

Dark Matter has little to do with hypotheses of FTL travel. Dark Matter is as-yet unobserved mass that appears to form primarily in halos around many, but not all, galaxies including our own. While we have not directly observed it, we still have significant observational evidence of its existence. We might never directly observe it as there may not be enough of it around the Earth for us to get usable data about it. It may even be repulsed by normal matter, in which case we really will never directly observe it.

There I go, writing a response when you'd really do better actually reading credible books on the topics. Maybe start with A Brief History of Everything by Bill Bryson. A lot of his book is not quite correct, but it is close enough and you can go from there to figure which parts are accurate and which are not. Just taking a few popular works from my own bookshelf I'd recommend In Search of Schrodinger's Cat by John Gribbon, The Particle at the End of the Universe by Sean Carroll, The Character of Physical Law by Richard Feynman, and The First Three Minutes by Steven Weinberg. These are all decent popular works as I recall. They won't replace a an actual undergraduate education, but they will at least give you a general introduction to cosmology, particle physics, and more importantly the processes and history of the science of physics. You could also benefit if you read some works on rational skepticism to help separate out the bullshit.

Also read some of the biographies and popular works written by the legends in physics, but keep in mind that even the greats had their flaws and logical failures. Stay away from anything that tries to tie quantum physics to the supernatural, or string theory in general because that is rich territory for nonsense. Even some of the mainstream theoreticians in string theory are nuts.

Hello u/gol4, your submission "light from galaxies" has been removed from r/space because:

• Such questions should be asked in the "All space questions" thread stickied at the top of the sub.

Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.

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