# If you view the Earth from far enough away can you observe its past?

From my understanding of light, you are always looking into the past based on how much time it takes the light to reach you from what you are observing.

For example when you see a star burn out, if the star was 5 light years away then the star actually burnt out 5 years ago.

So I am 27 years old, if I was 27 light years away from Earth and had a telescope strong enough to view Earth, could I theoretically view myself being born?

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Could you see yourself born? Not if you were born indoors –  schem Jul 7 '11 at 6:37

Yes, you can. And you do not even need to leave the Earth to do it.

You are always viewing things in the past, just as you are always hearing things in the past. If you see someone do something, who is 30 meters away, you are seeing what happened $(30\;\mathrm{m})/(3\times10^8\;\mathrm{m}/\mathrm{s}) = 0.1\;\mu\mathrm{s}$ in the past.

If you had a mirror on the moon (about 238K miles away), you could see about 2.5 seconds into earth's past. If that mirror was on Pluto, you could see about 13.4 hours into Earth's past.

If you are relying on hearing, you hear an event at 30 m away about 0.1 s after it occurs. That is why runners often watch the starting pistol at an event, because they can see a more recent picture of the past than they can hear.

To more directly answer the intent of your question: Yes, if you could magically be transported 27 lightyears away, or had a mirror strategically placed 13.5 lightyears away, you could see yourself being born.

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I'd have to say yes - at least theoretically. If there was an observer (not you) 27 light years away, he could see your birth. Awesome as it sounds, it isn't practically feasible. For one thing, the observer would need a large enough telescope to observe you. If the telescope isn't large enough, the resolution would be low, and the observer wouldn't be able to make out things far away. To get an idea, the size (diameter of mirror for instance) of the telescope that'll enable you to see an object of about 10m at that distance is about $10^{8}$km while the diameter of earth is about 12800 km.

But again, you yourself wouldn't be able to make this observation, as the information regarding your birth would have gone at the speed of light, and you wouldn't be able to intercept it.

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No. Because you cannot reach the speed of light, even if you had started travelling away from Earth the day you were born, you could never catch the light carrying the image of your being born.

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Let me just (jokingly) add one word: mirrors. –  Willie Wong Jul 6 '11 at 16:25
Mirrors are a good idea, but unfortunately any actual mirror can't reflect 100% of the incoming radiation. But as far as a theoretical speculation goes, we can also consider gravitational lensing... –  Phoenix87 Jul 6 '11 at 16:40
+1 for being realistic, however I would add this: CURRENTLY[!], there is no known way for a human to reach the speed of light. –  ComputerSaysNo Jul 6 '11 at 21:31
or an alien race could record that light then transmit it back to earth for us to watch. –  ed209 Jul 8 '11 at 19:59
@ed209: Or your parents could just film your birth. –  C.R. Jul 9 '11 at 2:38
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I think the other posters are forgetting that nature allows for much more possibilities. True, you can't catch up to light, but that might not be necessary. As General Relativity tells us, space-time is a 4 dimensional manifold. Einstein's equations tie its local structure to the energy-momentum density. But that still leaves open a lot of possibilities for the global structure of the universe.

Imagine that the universe would be something like a torus or a sphere, that is finite but unbounded. This concretely means that if you go long in enough in one direction, you will ultimately end up where you started again. Now, that is also true for light. If then the expansion of the universe did not happen so fast that light going around got behind the cosmological horizon, it is theoretically possible that we could see our own galaxy in an earlier stage of its evolution.

The global shape of the universe is still an open problem. The most commonly accepted model though assumes an infinite flat space-time. Other models like Poincaré dodecahedral space and the Picard horn do seem to fit current cosmological data. Well, they did last time I looked, maybe they have been refuted by now.

But if the universe is well described by a Poincaré dodecahedral space FLRW model, then there is a chance that we can see our own past for a limited amount of time, i.e. until it disappears beyond the cosmological horizon. Don't hope to see yourself though.

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Technically, yes, though the idea of an absolute past kinda screws with the whole question. Better would be a light cone-based analysis. But yes, if you were in the past light cone of a past Earth, then you would see that past Earth.

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No, I don't think the concept of time works quite like that. Yes, if a star is 5 light years away and it burned out - yes it burned out 5 years ago for that point in time. Space time is relevant for that time period.

In your example: You are 27 Years old (Present Day Earth Time)

You are teleported 27 Light Years Away to Planet X (Your Present Age is 27 on Planet X).

You look back at Earth - You are non-existent on Earth.

Because Earth's time does not bend back. It took 27 years for Earth's image to reach you at the time you left. So unless you were at both planets at the same time you would be 27 on Planet X while on Earth you would be 54 Years old. Earth's time does not bend back, it only moves forward.

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Why would teleporting somewhere else negate your existence? This isn't time travel in the classical sense, more observing the historical artifacts that would otherwise be diffusing into space. –  tadman Jul 8 '11 at 15:26