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Look into the past - physics say it's possible





bgillingham
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.
Cibes
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.
bgillingham
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.
xkobram
How about mirror spiral?
Sokken
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).
faker_phil
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.
chastise
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]
chastise
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.
FunDa
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 [Smile]

There is every possibility that satellites are recording everything they see even at this time. Twisted Evil
coolsmile
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
Indi
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?
Bikerman
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
Shin
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 Sad
Indi
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 Sad

The science of the 19th century said that. 20th and 21st century physics does not.
Bikerman
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
DVNT
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
bgillingham
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..."
alexp91k
I'm going to bump an old thread here but I only joined this forum just to respond to this thread.

First of all, there's no way you can see the past using a mirror (besides all of the logistical reasons). This is because if you send out a mirror in year 2000, it will have the image of the Earth on year 2000 on it and will continue to reflect the images of the Earth as the years pass from this date. For example, if the Earth sent out a mirror on the year 2000 and the mirror was literally 1 mile away from the Earth, the mirror would show a year 2000 earth (nearly an exact reflection because of such a short distance). Now it has traveled to 10 miles, and it may show a year 2000 day 1 Earth. Skip to 10 light years and it will show some year (like year 2100) passed year 2000 Earth, not before. This has already been answered in this thread but I just wanted to hammer this point home.

@Indi:
Quote:
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.

I know you get this, but just so it's clear to everyone who reads this thread, three nanoseconds in the past is so close to 0 that in actuality, everything you see within such a small distance basically occurs the exact moment you saw it. This is just a clarification for people who may have suddenly thought that their whole world is not quite how they see it (because they're looking into the past).. technically true, but realistically false because the time gap so incredibly negligible it's nearly nonexistent.

@Bikerman:
Quote:
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.

In adding to this, I'd like to point out the most common one I see, which relates to quantum physics: the Heisenberg Uncertainty Principle, which basically says you can't know both a particle's location and momentum at the same exact moment.
metalfreek
Practically this is not possible right now but this is a great thought. I enjoyed reading this thread.
snowboardalliance
metalfreek wrote:
Practically this is not possible right now but this is a great thought. I enjoyed reading this thread.


I enjoyed this too

Nice points on Relativity and Chaos. Reminds me of all the fun stuff I learned in physics last year like http://en.wikipedia.org/wiki/Twin_paradox
Bikerman
alexp91k wrote:

@Bikerman:
Quote:
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.

In adding to this, I'd like to point out the most common one I see, which relates to quantum physics: the Heisenberg Uncertainty Principle, which basically says you can't know both a particle's location and momentum at the same exact moment.
You need to be careful here. The uncertainty principle says you can NEVER know - it applies to various pairs of property, including momentum and position.
Chaotic systems are different in that there is a knowable precise solution, it is just that you would need to know every variable to an impossible degree of accuracy...
iman
Maybe if we have a series of "mirrors" placed far enough, we can look into the future.
And they don't have to be mirrors, it can be just data transmission.
Bikerman
You haven't really thought that through. Use as many mirrors as you like.. how will that help?
Information cannot be transmitted faster than c so that doesn't help either...
yagnyavalkya
When we see the stars it is light that was emitted in the past we see.
annpaulineparsons
Imagine there are mirrors, placed on all planets, designed to reflect back images from
earth back to earth. Some planets are 10,000 light years, some are only 10 light years away, and
some are millions of light years away. We would be interestd in seeing events
within the last 2 or 3 thousand years.

Theoretically, we could focus our mirror screen here on earth
on any distant planet, from 100 years to 1,000 , and look back in time to
earth events that were happening at that time.

If we can think beyond placing mirrors on these planets, but utilizing something
yet to be discovered (but is already in place and in existence) every event is recorded already.
We just have to find the technology or medium

For instance, We can now tell the compositions of planets by the colour of lights emitted, we don't have to visit the planet to do a chemical analysis.

Any comments?







bgillingham wrote:
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.
Bikerman
Ahh...OK I see where you are going with this.
So let's say we have a planet 20 light years away.
At time t=0 a photon leaves earth and heads for the planet.
Obviously to us it will take 20 years to get there. The photon, however, has no inertial frame and gets there in (localsubjective) time=0. It then bounces off a mirror and returns. Again, to us on earth that is a 20 year journey.So when the photon arrives we have moved 40 years and are looking back 40 years in time.

OK...but it seems like a hell of a lot of trouble to do something you can do with any decent camcorder....
yagnyavalkya
What about going to the past itself there must be someway there
People never thought man could fly it would have been wild imagination a couple of hundred years ago
I guess there must be a way to actually get into the past and some science to do it
Bikerman
No.
If there was a way then the paradox could destroy the universe.
The famous expression of it is the grandfather paradox. You go back and kill your grandfather. Thus you were never born. Thus you cannot have killed your grandfather, thus you were born.....etc
Causality is broken.
badai
why bother to look at the past? we do that all the time. no need big galactic mirror on the sky. a photo album will do it.
annpaulineparsons
Love this thread about mirrors on planets. We don't actually have to put mirrors on
plants (this is just an analogy for us to understand the concept)to have the past reflected back to earth. Sound travels and can be bounced back off an object, as light can be
reflected back (albeit much weaker than when it started)
ocalhoun
annpaulineparsons wrote:
as light can be
reflected back (albeit much weaker than when it started)

But if the surface it reflects from is not smooth and reflective, the reflected light will be scattered and distorted beyond recognition.
(It doesn't have to be flat; that can be compensated for... It does need to be smooth and reflective though.)
manisu
Bikerman wrote:
I'd add my support to Indi's comment above and perhaps take it further.


I too will add support for Indi's comment:
I am reminded of contemporary mystic OSHO's version of Heraclitus' famous quote "You cannot step twice into the same river". Osho declared "You cannot step into the same river even once". The river has already changed by the time you plan to step, then step and then gets the idea of stepping once!

Also, I like to add that a really ALIVE person cannot be predicted. Yes, for most values, he shows a chaotic behaviour!

-Manisu
Joenar
Forget the mirrors. Wouldn't it be completely possible using today's fiber optic technology? Using a long enough strand would be the same concept but with limited light absorption and no concern about earths positioning.
duytam28
2000 years ago, when people began watching the motions of the Sun, Moon and ... (as most people did) that the Earth was stationary at the centre of the universe.
IT's rificulous nowadays
Bikerman
duytam28 wrote:
2000 years ago, when people began watching the motions of the Sun, Moon and ... (as most people did) that the Earth was stationary at the centre of the universe.
IT's rificulous nowadays

Errr....2000 years? I think not. You need to multiply that up somewhat. We have direct evidence that the Babylonians made star catalogues around 1200BCE, but it is likely that the Sumerians also recorded astronomical details around 3000BCE or earlier. So your 2000 becomes 5000 - and that would be a highly conservative figure.
Nor is it true that the Earth has always been assumed to be stationary and at the centre of the universe. A Heliocentric model was proposed as early as 3rd century BCE by Aristarchus of Samos. Indeed Copernicus, who usually gets the credit, did little more than dust-down and tidy-up the work of Aristarchus - which gives an indication of just how 'dark' the intervening 2 millennia were, from the standpoint of learning and science.
anirudhsingh1998
Hey..i'm wondering that earth must have been reflecting it's image since very long(infact since it's existence) ! and that image must have got rflected by some object. And atleast one ray must have come back straight to our planet. So if we catch hold of this ray, then maybe we could see our past, maybe the ancient time too.
Looking forward to suggestions and corrections..
kelseymh
anirudhsingh1998 wrote:
Hey..i'm wondering that earth must have been reflecting it's image since very long(infact since it's existence) ! and that image must have got rflected by some object. And atleast one ray must have come back straight to our planet. So if we catch hold of this ray, then maybe we could see our past, maybe the ancient time too.
Looking forward to suggestions and corrections..


You need more than one "light ray" for image formation, so the answer is "no."

However, of course there is doubly-reflected light. You can see it for several nights every two weeks! Go out on a clear night when the moon is 1/4 full or less. You will see that the "dark" portion of the moon is not invisible, but is rather just very dim. What you are seeing is light reflected from the Earth (usually the Pacific Ocean, because it's so big) illuminating the moon. It's called "Earthshine."
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