Seeing into the past?

paranoid marvin

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I've been thinking about this. We see stars in the sky from how they were thousands/millions of years ago, because that's how long it takes for light to travel that far.

So if I was on a planet a sufficient distance away, I would be seeing Earth how it USED to look. And if I had a powerful enough telescope I would be able to see the surface of the Earth and what was going on?

So does that mean theoretically if I found a way to travel faster than light, or if I found a wormhole/blackhole that transported me to a different part of the galaxy/solar system. I could go to a planet and view Earth from the past (because light hadn't had the chance to travel that far yet)? And with a really REALLY powerful telescope I might not be able to hear what people were saying, but I could read their lips?
 

Elckerlyc

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The problem would the really, REALLY powerful telescope that you would need to bring along.
It would furthermore depend on the position of the sun; a position more or less - but not exactly! - between the Earth and your point of view. Unless your telescope has also tremendous infrared capabilities.
 

Brian G Turner

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So does that mean theoretically if I found a way to travel faster than light, or if I found a wormhole/blackhole that transported me to a different part of the galaxy/solar system. I could go to a planet and view Earth from the past (because light hadn't had the chance to travel that far yet)? And with a really REALLY powerful telescope I might not be able to hear what people were saying, but I could read their lips?
Kind of, yes, which is part of the paradox - because if you could do that, you'd be able to exchange information before you were supposed to know it. :)
 

paranoid marvin

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The problem would the really, REALLY powerful telescope that you would need to bring along.
It would furthermore depend on the position of the sun; a position more or less - but not exactly! - between the Earth and your point of view. Unless your telescope has also tremendous infrared capabilities.

But then it simply becomes a case of waiting for the right technological advances. So sooner or later it becomes a probability rather than a possibility. And considering it can take millions of years for light to travel to distant star systems, we have plenty of time to be able to look back into the Earth's past.
 

.matthew.

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Do you think that's what Musk is doing with all those satellites? Going to spell out a message future people can see from reeaaaallllly far away?
 

Ori Vandewalle

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For stars you can see with the naked eye, it's almost certainly the case they're all still alive. We can't see anything more than about 10,000 light years away, and stars live for millions to billions of years.
 

Venusian Broon

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Ignoring the likelihood that the light will very likely be absorbed and readily scattered by material between you and the Earth (Given the shear insignificant amount of light the Earth reflects or produces, I'm afraid most of the past light will have been absorbed or scattered into randomness by the surrounding universe - i.e. starlight, dust and gas clouds etc. - by now)

But ignoring that. By a very rough calculation to get the required resolution of say 1mm at only one light year distance, so one year back, which hopefully is enough to see lips move well enough so that you could read them, I think you'd need a 'telescope/interferometer' with a base line aperture of at least 4.7 billion km*. Trying to "go back further in time" requires your telescope to become even more stupendously huge as you go deeper into space.

That may be possible for a spacefaring race...but in order to see tiny details you'd probably need to collect virtually all the light produced. Which makes the construction of this machine even more daunting and even more impossible.

However even Very Long Baseline Interferometers are limited in the resolution that they can achieve. This is nothing that to do with technological advances but hard physics, I'm afraid. Purely by diffraction as the light travels, the miniscule amount of light that deliniates the tiny details in an image such as lips moving will easily be 'smeared out' into a blur quite quickly - at least on large to interstellar scales.

And yes as Ori states, faster than light travel is, as far as our understanding of the current physics of the universe. equivalent to going back in time. If you could do that...then our current view of the universe is wrong. You could probably also poop unicorns and have a disco with a gaggle of angels on the back of pin if that was the case, as anything could be possible ;)
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* back of fag packet calculation, bound to be wrong, yadda yadda yadda etc.
 
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