Viewing Earth from 4.5 billion light years away

Sightaridis

Hopefully this isn't too out of place, was just thinking about the Universe when I had a 'whoa' moment that I needed to share somewhere.

Let's say there is a planet, Planet X, 4.5 billion light years away from Earth with unbelievably advanced intelligent life. They have super telescope the likes we couldn't even imagine.

This telescope is capable of giving better coverage of Earth than our own satellites do. If we're talking present day, when they look through their scope, they will see a burning Earth as it was 4.5 billion years ago correct?

So in theory, 4.5 billion years from now, the people on Planet X could look through their scope and see me typing this message on my veranda sipping a cocktail, despite me being dead, despite the Earth being destroyed lets say!

Weird to think about.

wylo

its crazy alright, what i think is stranger is the fact that if a colony 4.5billion light years away was looking for life and stumbled across our planet they'd get nothing!!

BULLER

I had a dream very similar to that actually! Replacing 4.5 billion years with 12 months ago, I know what you did last summer style. Its a scary concept to grasp... (it was actually a nightmare now that I dwell on it)

acurno

Thats just too freaky. I had a very similar thought today and came onto this forum to post my own thought experiment!

Anyway, where I had my 'whoa' moment was thinking this:
Imagine that there was a stable wormhole/interstellar portal in the vicinity of the earth and through this we could traverse to the other side of the galaxy, where light takes 100,000 years to travel. The brave soul who makes this journey brings with him an ultra powerful telescope capable of viewing and recording earths history all that time ago in real time. He then makes the journey home through the portal with video evidence of earth 100,000 years ago in which we can all view through our 200" flatscreens. ( evolution of tv sizes havent come on that much).

So, is this theoretically possible??Taking away the realism, possibilities and practicalities, is this thought experiment a runner?Could we look into our own past? I'd love to know the answer and might post this in the physics forum for more debate and comments.

Alan

KoolKid

Yes I believe this is correct , in theory.
Say you are 30. If you can travel faster than light away from earth & have a powerful enough telescope you could see yourself in the past.

maninasia

If the universe is curved you could eventually see yourself in front of you (with a sufficiently powerful telescope and you lived forever). In fact you would see multiple yous as the light went round and round, as long as the speed of light is slower than the expansion of the universe.

Looking into space is indeed time travelling in a way. Einstein's theories of relativity came out of his thought experiments on conflicting perceptions of the nature of reality from the points of different observers moving in relation to each other. Each observer has their own reality, the only thing that could make sense of it was it the speed of light was fixed (still not fully convinced on that myself though ).

The wormhole idea is interesting, if you could manipulate space enough to create a wormhole it might not be such a stretch to jump into alternative universes, back in time etc. The multiverse theory seems to fit better and better. I see it as another step away from the 'we are special' arrogant thinking Humans>Planet>Solar System> Life> Universe..maybe each one of these things is really not special but a humdrum example of one of millions, even the universe!

It makes sense on an intellectual level to be many universes just as much as there are many galaxies and many planets. Why is the universe laws set in a balmy region for our type of life, simply because we are one of an infinite subset, not because of any creator.
There are other types of life existing happily in other types of universes with other laws of physics set 'just so' for their life that evolved there. In fact the idea of the 'big bang' and inflation promotes a multiverse more than a single universe. Since when did things just happen once in nature?

Who knows what's possible in the future and what's possible right now.

ddef

koolkid wrote: »

Yes I believe this is correct , in theory.
Say you are 30. If you can travel faster than light away from earth & have a powerful enough telescope you could see yourself in the past.

Only nit-picking here but...
If you did manage to travel faster than light wouldn't you, accourding to eistein, just become a big mass of pure energy?

maninasia

Einstein said speed of light was fixed (although it slows down going through materials). He said nothing can go faster than the speed of light. To go faster than the speed of light is not allowed by his theories (they anchor on the base of this fact, light is fixed, almost everything else is relative), that doesn't mean the speed of light doesn't change or that nothing can go faster than the speed of light in reality.
Maybe Einstein's theories are similar to Newtons, they work on one level but not at another.

Rulmeq

ddef wrote: »

Only nit-picking here but...
If you did manage to travel faster than light wouldn't you, accourding to eistein, just become a big mass of pure energy?

Not just big, infinite.

Gurgle

ddef wrote: »

Only nit-picking here but...
If you did manage to travel faster than light wouldn't you, accourding to eistein, just become a big mass of pure energy?

Nope.
Not unless you accelerated through / to lightspeed.

Actually getting somewhere faster than light is a different question, to which we have no answer yet.

rccaulfield

ddef wrote: »

Only nit-picking here but...
If you did manage to travel faster than light wouldn't you, accourding to eistein, just become a big mass of pure energy?

No einstein said we cannot go faster then light iirc!;)

maninasia wrote: »

Einstein said speed of light was fixed (although it slows down going through materials).

What materials are they? -interested! speed of light is fixed i thought?, even if your flying toward me at 1 million kms per hour, you wouldn't be catching your light at all it will still be leaving you at 300,000kph per second? Gravity does bend light(einstein proved this in 1919) but its speed remains constant!

Op the real whoa moment about it for me is that the light of you sitting on your balcony is heading out into space and after you die, you're there for everyone to see as that light hits them for all time for billions of years to come!(stength of telescope allowing!)

Cú Giobach

rccaulfield wrote: »

What materials are they? -interested! speed of light is fixed i thought?, even if your flying toward me at 1 million kms per hour, you wouldn't be catching your light at all it will still be leaving you at 300,000kph per second? Gravity does bend light(einstein proved this in 1919) but its speed remains constant!

The 300,000kph per sec is the speed of light in a vacuum, this speed changes depending on the medium.
Here are some links you might find interesting.
Link 1
Link 2

Here and Here is prof Lene Hau explaining light traveling through a Bose-Einstein Condenstate.

Trine

rccaulfield wrote: »

Op the real whoa moment about it for me is that the light of you sitting on your balcony is heading out into space and after you die, you're there for everyone to see as that light hits them for all time for billions of years to come!(stength of telescope allowing!)

Does light travel forever? Won't light diminish over distance?

I can't understand how light reflected off ourselves, which is surely very weak to begin with, could be emitted into space forever...surely it wouldn't matter how strong your telescope is, if the light isn't reaching the lens to begin with you can't see it.

Cú Giobach

Trine wrote: »

Does light travel forever? Won't light diminish over distance?

I can't understand how light reflected off ourselves, which is surely very weak to begin with, could be emitted into space forever...surely it wouldn't matter how strong your telescope is, if the light isn't reaching the lens to begin with you can't see it.

As light travels it spreads out so the number of photons reaching you telescope is diminished, but a photon itself will travel indefinitely and doesn't just disappear.
As far as I know (someone correct me if I'm wrong) a photon isn't affected by time or distance at all.

Edit; Just want to add, Except by the expansion of the universe, that will "stretch" the wavelength.

backboiler

If I remember right each photon spans the entire sphere of its influence. The whole wave-particle duality thing.
The example given is the one with light from a point source releasing a single photon that passes through a diffraction grating and gives a set of peaks and troughs, thus showing that the photon interferes with itself: it's a wave and yet a particle.
Give that concept a billion years and you have a photon whose "edges" make a sphere with a radius of a billion light years.
That would mess up your head.

maninasia

The photons would be diffracted by any material they encountered en-route, light will also be bent by gravity around galaxies and stars etc. The individual photon would carry on it's way but the energy and frequency may change and the photons may spread out aswell (not a physicist, maybe somebody else can chime in).

You would need an almost infinitely big telescope and a VERY powerful computer to put the image back together.

acurno

Okay lets put it in practical hypothetical terms again.
Telescope launched from Earth in the near future. Hubble 5. Infinitely powerful. Our nearest star system Alpha Centauri has a habitable planet.
If we looked through hubble 5, looking 4 years into the past, ( approx 4.3 light years away), would we be able to see the daily goings on in their life in real time(4 years in their history), just as we would looking through a normal lens in a telescope?

Follow on question, isn't it the case that when we look at anyone we're 'technically' looking into their past based on the time the light from their body takes to reach our eyes? Obviously an absolute miniscule time.
I remember reading some book about this theme saying that when you look in a mirror you're seeing yourself in the past, and that if somehow you reflected your image off trillions and trillions of mirrors and you could see the final image, it would take so long for the light to travel off each that you would be looking at yourself as a child in the final image. Thats a headspinner.

Cú Giobach

maninasia wrote: »

The photons would be diffracted by any material they encountered en-route, light will also be bent by gravity around galaxies and stars etc. The individual photon would carry on it's way but the energy and frequency may change and the photons may spread out aswell (not a physicist, maybe somebody else can chime in).

You would need an almost infinitely big telescope and a VERY powerful computer to put the image back together.

To say photons are affected by gravity is slightly misleading because a photon is just traveling along its straight line path, through space that has been curved by gravity. It's not like gravity reached out and grabbed the photon.
Time and distance don't exist for a photon and its journey from start to finish, from "it's perspective" happens simultaneously (or at the most within the Planck Time). Therefore anything that happens to it from our perspective is (how the fúck do I put this ..?) a part of its "whole" (like the grain is part of wood).
The change in wavelength due to the expansion of space is only a change from our percpective, due to our different frames of reference , not a change in the nature of the photon.
Regards reflection and refraction, The photons that leave a reflective or refractive surface are not the ones that entered. The initial photons are stopped by the medium and a different particle is emited.

acurno;
Okay lets put it in practical hypothetical terms again.

Everything you see is technically in the past and I mean everything.
The further you look, the further back in time you are seeing, this is very real.
You get this affect with sound all the time but are just so used to it it doesn't really mean much eg; Thunder and lightning occur at the same time but you hear the thunder after you see the flash due to the difference in the speed of sound and light.
When you look up at any star with or without a telescope you are looking at it in the past.
If you look at alpha centauri you are seeing it 4.3 years ago, there is no way to see it as it is today.
Since a telescope doesn't actually bring the viewed object closer, if you used a VERY strong telescope you will see the same thing, including planets and anything on these planets 4.3 years ago.
Below is a picture of the universe just after the big bang approx 13.7 billion years ago. Its the Cosmic microwave background and is the light from the big bang, stretched out over time into microwaves. We can actually see 13.7 billion years into the past.

6ix

I remember reading the exact point from the OP in Bill Bryson's 'A Short history of Nearly Everthing':

Still, statistically the probability that there are other thinking beings out there is good. Nobody knows how many stars there are in the Milky Way—estimates range from 100 billion or so to perhaps 400 billion—and the Milky Way is just one of 140 billion or so other galaxies, many of them even larger than ours. In the 1960s, a professor at Cornell named Frank Drake, excited by such whopping numbers, worked out a famous equation designed to calculate the chances of advanced life in the cosmos based on a series of diminishing probabilities.

Under Drake’s equation you divide the number of stars in a selected portion of the universe by the number of stars that are likely to have planetary systems; divide that by the number of planetary systems that could theoretically support life; divide that by the number on which life, having arisen, advances to a state of intelligence; and so on. At each such division, the number shrinks colossally—yet even with the most conservative inputs the number of advanced civilizations just in the Milky Way always works out to be somewhere in the millions.

Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least two hundred light-years, which is a great deal more than merely saying it makes it sound. It means for a start that even if these beings know we are here and are somehow able to see us in their telescopes, they’re watching light that left Earth two hundred years ago. So they’re not seeing you and me. They’re watching the French Revolution and Thomas Jefferson and people in silk stockings and powdered wigs—people who don’t know what an atom is, or a gene, and who make their electricity by rubbing a rod of amber with a piece of fur and think that’s quite a trick. Any message we receive from them is likely to begin “Dear Sire,” and congratulate us on the handsomeness of our horses and our mastery of whale oil. Two hundred light-years is a distance so far beyond us as to be, well, just beyond us.

Blew my mind

Cú Giobach

6ix wrote: »

I remember reading the exact point from the OP in Bill Bryson's 'A Short history of Nearly Everthing':

Great book!!

maninasia

And yet why would it be 200 light years between civilisations, there's no reason to think that at all taking the Milky Way Galaxy into account and its age. The likeliehood is in fact very high that there are already one or more fully galactic civilisations that have spread through the entire Milky Way. 14 billions years is a LONG TIME. Why would a civilisation stop spreading, once it's out it's out and can keep on going, splitting off and moving on. Just because we can't see anything obvious around us doesn't mean there isn't a civilisation, we can't even tell if there is life on other planets of the solar system.

Cú Giobach

maninasia wrote: »

And yet why would it be 200 light years between civilisations, there's no reason to think that at all taking the Milky Way Galaxy into account and its age. The likeliehood is in fact very high that there are already one or more fully galactic civilisations that have spread through the entire Milky Way. 14 billions years is a LONG TIME. Why would a civilisation stop spreading, once it's out it's out and can keep on going, splitting off and moving on. Just because we can't see anything obvious around us doesn't mean there isn't a civilisation, we can't even tell if there is life on other planets of the solar system.

In fairness he did say he was using the "Drake Equation". Thats where he got the figure.
And nobody (Even Drake himself) takes that as an accurate definitive statement of the reality of the universe . It's just a handy little tool to show one set of probabilities.

maninasia

I know the Drake equation, no use because too many variables, it's better to think in terms of Yes/No, if life (and proven by us) then very likely loads of it.
Then if loads of it it is a 99.99999...% certainty that life has already spread through the galaxy (from age of universe and speed of technological development of humans plus the fact that bacteria can survive in subsurface rocks and in vacuum and estimated number of planets).

Life is more likely to be either everywhere or nowhere in the Milky Way...since we know it is here already (us) than it is most likely everywhere, it's very unlikely to just be in some small part of the galaxy as life has a tendency to spread and colonise and move into new niches due to competition and evolution (as we can see very clearly on Earth). I think evolution and survival of the fittest is the thing people miss out on that would drive life to spread through space.

So basically Yes or No, not really an in between situation should be the analysis.

Very simple logic I know but is probably more useful. Saying 200 light years is just very misleading to the general public.

Cú Giobach

maninasia wrote: »

I know the Drake equation, no use because too many variables, ........

The poster quoted Bryson's book to show an alien intelligence looking at us 200 years ago in the context of the finite speed of light, and not an analysis on the nature of life in the universe. Thats the other thread .
Would you like to pop in next door for a discussion on the Drake Equation?

maninasia

OK, I got that, but he shouldn't have used 200 light years as gospel, as we all know the Drake equation is missing most of its variables.