FTL and History

[Anachronous Rex]

This is made somewhat in conjunction with my other history thread as a possible answer to the subjectivity of history itself.

What I would really like is some input from the scientifically literate out there:
Would it be possible, provided one were able to travel faster then light (or otherwise negate the light-speed barrier), to place some manner of very large, very powerful telescope in the path of photons escaping earth from the distant past?

If so, could we not then observe even ancient historical events as they unfolded from afar? Perhaps augment our observation equipment with infrared and other capabilities that would increase our ability to see past obstruction? Perhaps even lip-reading provided the image could be made clear enough?

Could history someday become an objective science?




(as a side-note: if this is indeed possible, then one wonders why it hasn't come up more often in science fiction... one could essentially eliminate all uncertainty regarding past events provided one could get an observer in the right place and time.)

 

[Netheralian]

Assuming the day was perfectly clear and the people were outside in a clear area and they were identifiable by their hats then you would need some ridiculously big equipment.

(Someone please correct my maths if I fuck it up)

The average photon density at the earth's surface during the middle of summer on a clear day is about ~1000 W/m2 which is a photon density of 2.43E21 photons / second / m^2 (at 483nm - peak wavelength from the sun from Wiens displacement law). Assuming the people you are looking at are perfect diffuse reflectors and the atmosphere (or anything else in the universe) doesn't absorb anything, you will have a photon density of the following at the following distances:

LY ; Photons/m^2
1;2.72E-11
2 ; 6.79E-12
10; 2.72E-13
50 ; 1.09E-14
100; 2.72E-15

Not really sure how many photons you need to make a coherent image but you will need a collecting surface of at least 191km x 191km to collect a single reflected photon (based on the assumptions above) per second for a 1m^2 reflecting area on the earth's surface at 1 LY.

Does that satisfy your curiosity?

 

[Unwardil]

Theoretically possible, though to achieve that level of clarity at such a great distance, you'd be talking about a matrix of light receivers that would be spread out over light years, the way they use radio telescopes now. Shouldn't be impossible though, assuming that as you say the light speed barrier is overcome. I would question the utility of such a project, but theoretically, yeah, if we find a way to transport across great distances instantaneously, I don't see why it shouldn't be theoretically possible.

 

[Netheralian]

Theoretically possible, though to achieve that level of clarity at such a great distance, you'd be talking about a matrix of light receivers that would be spread out over light years, the way they use radio telescopes now.

If your receiver is spread out over light years, then you probably have general relativity distorting your image.

 

[Unwardil]

No, I'm assuming that if we have faster than light travel, then we also have faster than light communications. Also, each part of the receiver array would have to be properly aligned to the target and each piece would have to be able to travel at the speed of earth's solar orbit in order to maintain focus. Like I said, not physically impossible, just not really worth the effort.

 

[Nelson]

So I think the general response so far is pretty much correct.

If you could travel faster than light, or maybe just instantaneously arrive at some point thousands of light years from Earth, then yes you would see light that left the Earth thousands of years ago. There are all sorts of problems with the idea of FTL travel however, time travel paradoxes and what not, but we are just pretending and considering this very confined situation.

The other issue is whether or not it is feasible to build a device capable of observing individuals on the surface of a planet from a distance of thousands of light years and the answer is probably not.

Netheralian has already addressed the issue of intensity, so I did a quick calculation of resolution. In order to resolve a 2 meter tall individual at a distance of 2,000 light years at 600 nm wavelength (maybe we wish to observe Jesus performing some miracles), we would need an observational baseline of about 6e12 meters, or 40 AU (about the separation between the Sun and Pluto). And this would still just be 1 pixel per person.

So you would need some HUGE mirrors to collect enough light, and the baseline between them would have to be at least the size of our solar system. Cool fact, if we had such a device, we could map the surface of our nearest neighbor star (Proxima Centauri) on the scale of millimeters.

 

[Anachronous Rex]

Thank you all for the responses thus far.

It does seem, given the scales involved, that notion is probably infeasible. I wonder if the situation might be improved by taking multiple small observations rather then this enormous array. That is to say - since we are assuming that we can move faster than light anyway - why not simply have a relatively small observer travel repeatedly ahead of the light-wave so as to observe it once again from a slightly different angle; repeating this procedure many times. Or perhaps better still travel at the speed of light upon the surface of the wave - provided such a thing is possible - and simply siphon off it's photons in a grid, like a vacuum cleaner. Thoughts?

 

[Nemesiah]

I myself like the idea of a simulator computer better, a big (I talking The hitchhikers guide to the galaxy big) and complex computer could be fed big bang info, intermediary steps, some general rules and taking into acccount some determinism (disscussed somewere else) the computer could (sort of like what Paul and Leto Attreides with mentat's trainig did in Dune) give some insights into history, the present and even the future (I'm talking science fiction here I know but then aggain quantum computers are inching their way into reality as we speak)

About your Idea IF we could somehow travel faster than light maybe a colector sphere (like the expanding plastic ones) could be implemented and given that there is a lot of antimater and dark mater and anti whatever going through us; thinking that it could be some how be analised togeteher with all the light infrared visible and ultra violet then bingo bango you cound have a circular array that has the entire earth's history even on a cloudy day.

Of course... this asumes FTL while mine just asumes a really bigass computer