If you look through a telescope at a very distant object, you are seeing that object at some time in the past - due to the speed of light, as many light-years distant the object is, is how many years ago the light left those objects.
Now, suppose that we take a giant mirror and position that in space - 1 light year from earth. If we could then resolve the image that a telescope would get from that mirror, it would earth from 2 years ago. Perhaps, the resolution of any significant object would not be accurate enough unless there was a VLA (Very Large Array) of telescopes in space to focus in on the giant space mirror.
Imagine a series of these mirrors in space - at different distances. We could use them to get a second look at events that we missed the importance of when they initially happened. This could have all kinds of implications.
If implemented today, we could immediately look at images of the earth from the near-past. Hypothetically, it would be impossible to put a mirror out far enough to see something from even 2005 - unless we could go faster than the speed of light to a place far enough away, or if there were already some object(s) in space that act as true space mirrors or some other kind of reflector.
Interesting thought, somehow reminds me of the movie "Deja Vu", seeing 4.5 days back into the past.
But I think it would be much easier and cheaper to launch a bunch of satelites into orbit, record everything and save it until needed. Google Earth already showed what amazing things are possible like this.
Shazam! I never thought of satellites to record everything. That also covers both sides of the planet, eh? It looks like the space mirror will probably never be.
interesting thought.
The interesting about the mirrors is that we could then look as far back as we want if we just pretend there are no technical limitations.
The recordings would on the other hand only be from the day we begin to record (More plausible though).
What you propose is not possible. If we were to put up the mirrors right now, one lightyear away from earth, we would be able to see ourselves at this point, but only in two years.
See, it is true that you would be able to see two years back in time, but only as far back as we are right now. You cannot look further, because you didn't put up the mirrors earlier.
What "faker_phil" says is incorrect. If we did put mirrors -insert number of years- away, then we wouldn't actually see earth until -insert number of years-. It's a pretty simple concept. I like the idea about putting mirrors in outer space.[/code]
Wow, I just thought for a bit. And I just realized. If we did put the mirrors in different angles and made it so that each part of the earth could be seen. And say we made telescopes strong enough to see people, then we can analyze almost everything. Like wars, terrorist attacks. Of course, it would indeed be easier if we just used satellites. And it's not impossible that the government already has satellites secretly watching our every movement. If we did imploy mirrors into outer space, then chances are the mirrors will move around, orbiting.
Mirrors ? Seriously, I don't get it. Firstly, the light from Earth would just scatter out in different directions and would become too faint when it travels a long distance. Then gathering the scattered light back would be impossible.
Also, with mirrors, how do we choose what time we want to see ? Won't it just reflect the past from a certain time back (say, 1 year) always ?
Then we can have a viewing station for, The Earth - same time, last year [
]
There is every possibility that satellites are recording everything they see even at this time. 
Technically it is possible to look into the past. If you look at the sun, you are looking at the position of it 8 minutes ago because the light it relases reached us in about 8 minutes. I don't know enough about this though so I'm not going to argue about it unless somebody says something really stupid
| coolsmile wrote: |
| Technically it is possible to look into the past. If you look at the sun, you are looking at the position of it 8 minutes ago because the light it relases reached us in about 8 minutes. I don't know enough about this though so I'm not going to argue about it unless somebody says something really stupid |
You're correct, but it gets even wackier than that. ^_-
Think about it - the speed of photons (light) is finite. It is 299,792,458 m/s. Now, imagine you were standing just 1 metre away from someone, and you turned to look at them. What you see is photons that have been fired from a "light source", travelled between the light source and that person, hit that person, then bounced off that person and travelled between him and you.
Now, light travels at 299,792,458 m/s. The minimum distance from him to you is 1 m. To get the time it takes to travel x metres at v metres per second, you do t = x ÷ v. 1 ÷ 299,792,458 is 3.33564095 × 10^(-9), or roughly 3.34 ns.
So even when you're looking at an object that is only a metre away, you're still looking around three nanoseconds into the past. Cool, huh?
But wait! There's more!
Remember that momentum must always be conserved. Even when speed doesn't change (the speed of light is constant), a change of direction (as it bounces off the person and is redirected towards you) means a change in momentum. That change in momentum must have been provided by the mass the photons hit - the person they bounced off of. The person's mass hasn't changed, so in order for there to be a change in their momentum, their velocity must have changed.
What this boils down to is that everything you look at, by the time you finally "see" it, has moved, however slightly.
In effect, you are never actually seeing the present reality. Everything you see is as it was some time ago, and it has always changed since then.
Ain't science cool?If Indi has not weirded you out completely with that (well explained) picture, and you feel able to handle even more odd stuff, then you can think about a bit more weirdness in the picture of reality that we currently have.
Having seen that time and distance are related and that time is different as you look over greater distances, you also then find that the clocks you use to measure this time difference are running at different rates relative to each other
Time itself seems to be going at a different rate, depending on which frame of reference you are in. You notice no difference yourself, though, since the difference is only apparent with regard to another frame of reference (or, put another way, relative to another F.O.R. - hence Relativity theory). Your own frame of reference (the space you occupy) always seems normal to you.
A lot of this is can be put down to part of Relativity theory known as 'Special Relativity'. This basically says that physics works the same, whatever the frame of reference. In particular (and the bit that causes the 'problem') it says that the speed of light is constant in all frames of reference.
In other words, light is moving at a speed around 180,000 miles per second (mps) in outer space when observed from my frame of reference and at the same speed in your frame of reference, despite the fact that we may be moving in relation to each other.
To see why that is odd, imagine that you are moving away from me at a huge speed (say 10,000 mile per second) and I then shine a torch at you. Light that sped away from my torch at 180,000mps would pass you at 180,000 (NOT 170,000 mps).
This is not how we normally see things happening at all. Clearly this is weird and needs thinking about.
If you consider this carefully you might come to the conclusion that time itself must be different in the different frames of reference (yours and mine). It turns out that time runs differently according to the relative velocities of the different F.O.R.
In the example above, time in your F.O.R would be moving slow relative to my F.O.R. Notice that this is time itself, not just some imaginary clock - real time is slower for you than for me when observed from my F.O.R and you would age slower than I would.
I've attempted to show how this comes about and derive the formula for it (using only very simple algebra) in this document
To round-off I should also say quickly that General Relativity goes on to show how gravity fits into the picture but that is for another day.
Regards
Chris Science says everything happens for a reason, so yes we can predict the future given we have all the data needed for the equation. Just like we predict the weather, but unfortunately there is too many variables 
| Shin wrote: |
| Science says everything happens for a reason, so yes we can predict the future given we have all the data needed for the equation. Just like we predict the weather, but unfortunately there is too many variables |
The science of the 19th century said that. 20th and 21st century physics does not.I'd add my support to Indi's comment above and perhaps take it further.
Even in deterministic systems where we know exactly the formulas to describe events, there are a class of systems which cannot be predicted - regardless of how much data you have. These systems are non-linear (simply put they are expressed in formulae which used powers of x, such as y=x^2-1) and form a class called 'chaotic' systems, or more correctly, systems which display sensitive dependence on initial conditions.
The weather is one such system. There are many others. This whole field of work (which gave rise to fractals amongst other things) seems to indicate that certain systems in certain conditions can NEVER be predicted, even when you have the formulae.
One simple example that you can play with is the formula
where a is a constant. You can set up a simple spreadsheet to model this very easily.
Rather than settling down to a steady value, for certain values of a, the system enters a chaotic state. This is illustrated here :
Regards
Chris Hi All
Just one problem with this mirror in space concept. If you keep the mirrors aligned on the earth then they will not be in the correct allignment to reflect the light that is taking so long to get to it as the earth is moving....and if you keep the mirrors aligned to reflect the light (earth past) then you will not be able to focus your telescope on the mirrored image as the alignment from earth (present) will be wrong.
DVNT
I agree that the angle would be wrong for most of the time. The only time that the reflected image could be seen would be roughly at the time point in our orbit. Having said that, unless the mirrors are close enough to our sun that their relative motion to the sun would be negligible.
I don't think that the mirror in space idea is practical, but what if you could somehow control with great precision - a set of mirrors in a box... the idea here is the same, but the box controls the mirrors so that the light bounces back and forth for a period of time - this way further delaying the view into the past. I guess that a problem would be the absorption of light leading to a very dim images. If not a set of mirrors in a box, "millions of tiny little mirrors..."
