Seeing the Sun and Earth's Past In The Sky

Most of us know that when we look at the stars in the sky we are seeing light which took thousands of years to reach us. So we are seeing what the stars appeared like many years ago, and not how they appear now. Essentially, we are looking into the past.

Most of us also know that gravity bends light. Stars, black holes, entire galaxies, and basically any object that has mass can bend light to a certain extent. It's called gravitational lensing.



So, with the billions of galaxies each with billions of stars in the sky, wouldn't it be possible for the light from the Sun and the Earth to be bent completely 180 degrees so that it shines right back towards Earth?

That would mean the light from the Sun and the Earth would travel many light years away, and then fall victim to gravitational lensing through multiple stars, and then travel many light years back to Earth. This would probably then appear just like another star in the sky with a neighboring planet, but it would be a mirror image of our own Sun and Earth, and it could be a million year old image!

It would then be possible to see into the past through a powerful telescope, and see how the Moon and Earth was formed. Maybe see the extinction of the dinosaurs, and or the so called great flood. Who knows, one or more of the stars in the night sky could be a mirror image of our Sun before Earth was even around, and not a real star! Of course these images would be of different points in time, depending how long the light had to travel.

Here is my crude drawing:



So what do you think? Possible?

a reply to: WeAre0ne

That would be a awesome view.

they could imvemt a telescopic camera to take photos of the light redlected from earth onto the moon. they already have a camera that can see round corners by adjusting light refraction. with a bit more hardware and tech they can video it then we van see the past.

So, with the billions of galaxies each with billions of stars in the sky, wouldn't it be possible for the light from the Sun and the Earth to be bent completely 180 degrees so that it shines right back towards Earth?

Not really. You are talking about a round trip of 160 million light years if you want to see dinosaurs.

There's this thing called the inverse square law which determines the transmission of electromagnetic radiation. Light loses intensity quite rapidly with distance. Bottom line, we can't see a star which is 160 million light years distant so we sure can't see dinosaurs on a planet orbiting that star. That's what you are suggesting is possible.

Large masses seem to bend light a bit. It would take a lot of caroms, perfectly aligned, and a lot of distance to do what you speculate. The light might reach us, one or two photons at a time, not a lot of information there.

Wow. If oly we could actually have fantastic cameras that could actually do that and we could find the right stars to do it too... We could view the sun and the earth in the past. We could view the earth thousands of years ago, etc...

a reply to: Phage

Actually, we have seen objects 13.4 billion light years away, because gravitational lensing created a magnifying glass, and focused light rays from multiple areas in the sky onto one point on Earth.

hyperphysics.phy-astr.gsu.edu...

amazing-space.stsci.edu...

Fortunately, nature provides its own intergalactic magnifying glass in large clusters of galaxies. The combined gravity of such galaxy clusters (below, Pandora's Cluster is shown) bends light in the same way that a glass lens does. Astronomers can use these galaxy clusters as "gravitational lenses" to see fainter, smaller, and more distant galaxies than otherwise possible.

So it is still possible to see dinosaurs... With the large quantity and randomness of the stars and galaxies in the universe, there must be a point, or multiple points, in the sky which not only bends the light around 180 degrees, but then focuses the light rays onto Earth like a magnifying glass.

a reply to: Phage

that's a shame.if we could actually get footage of dinosaurs from all that time ago it would put an end to the creationist argument.
still. in time we may invent FTL and send a telescope and recording stuff out there...

My idea of seeing dinosaurs was a little exaggerated. It would require some very powerful machinery / telescopes, and galaxy cluster acting like a magnifying glass... But, maybe seeing the formation of the moon, and Earth, that may be possible.

B.t.w. I didn't mean we could see actual dinosaurs, I meant we could see their extinction, like a meteorite hitting Earth and destroying everything on it.

a reply to: WeAre0ne

we don't need crtstal clear images. heat signatures of disparate dinosaur shapes would be enough.

a reply to: WeAre0ne

It would require some very powerful machinery / telescopes, and galaxy cluster acting like a magnifying glass

Gravitational lensing does not "magnify" a light source. It distorts it, bends it, causes multiple "mirages" of the same object. And it would not help viewing a planet at galactic distances.
www.roe.ac.uk...

imagine.gsfc.nasa.gov...

originally posted by: Phage
we can't see a star which is 160 million light years distant

Surely I am misunderstanding you. But, did you just say, "we can't see a star that is 160 million light years away"?

a reply to: Phage

That is not entirely true...

According to your source, a galaxy directly in line with a quasar and Earth would cause a ring of quasars to appear around the galaxy. If we had special software or hardware that would individually pick up each quasar image in the ring and superimpose / align them on top of each other, it would act as a magnifying glass, and create a more intense light / image.

The inverse square law of light just means the light is spread out over a distance, so you only see a small portion of the light the further away you are from it. This is why we create really huge telescopes, to collect as much of that spread out light as we can, and focus it onto a small point and magnify the image. Technically a group of stars or galaxies could do the same thing... and so could hardware / software.

Imagine 100 Hubble telescopes all collecting light from a different area of the sky, and collectively adding their images together. Or imagine we find multiple points in the sky that have bent the light from the Sun and Earth, and all exactly the same round trip distance, we could collect the light and add it together to amplify / magnify the light.

What if there was a magical arrangement of many stars that were close to Earth (between 5 and 20 light years away) that actually made the light from the Sun and Earth travel a very long distance round trip (about 130 million lightyears) because it had to curve around so many stars before reaching Earth. This would mean the light didn't travel a long distance away from Earth, but it did travel a long distance in general. Would it still be the same intensity light? I am not certain.

a reply to: smithjustinb

Surely I am misunderstanding you. But, did you just say, "we can't see a star that is 160 million light years away"?

Not much to misunderstand there.

a reply to: WeAre0ne
130 million light years is 130 million light years.

Shine a light at a mirror that is 100 feet away and the light travels 200 feet to get back to you.

a reply to: WeAre0ne

This is why we create really huge telescopes, to collect as much of that spread out light as we can, and focus it onto a small point and magnify the image.

Technically, not so much.
You are failing to consider such basic factors as focal length.

originally posted by: Phage
a reply to: smithjustinb

Surely I am misunderstanding you. But, did you just say, "we can't see a star that is 160 million light years away"?

Not much to misunderstand there.

But we can definitely see a star that is 160 million light years away. We can see 14 billion light years away.

a reply to: smithjustinb
Galaxies.
We can see the collective light of a group of hundreds of billion stars. Not individual stars.

We cannot resolve stars in Andromeda, our nearest neighbor.

Correction. Hubble has imaged individual stars in Andromeda. A distance of 2.5 million light years.

a reply to: Phage

Ah. Thanks. I didn't know that.

If this sort of thing were ever to be possible to any practical degree, it'd have to involve us seeing our reflection within the gravitational lens of a black hole. Black holes are capable of causing light to be trapped in orbit around itself (this occurs at the event horizon, the point at which the escape velocity of an object matches the speed of light) so they're easily capable of causing light to make a complete U-turn back to a point source. This comes with the added benefit that black holes produce no confounding light of their own; but the whole thing already has a number of catches that make it... rather unlikely.

The first thing is that neither a black hole, nor any other system capable of gravitational lensing, would really need to send the light on a 180-degree back towards its source. Our black hole would have to be sending our light on an intercept course towards our future location: and since the earth is in motion, that specific point and the angle to it will change depending on what specific point in Earth's past that you're talking about.

The second, related, thing is that a black hole capable of gravitationally lensing our image back towards us would have to be located at a very specific distance from us. For light from the Jurassic to reach our eyes today, the light must have spent about 150 million to 200 million years moving through space. Halve that number to account for the two-way journey, and what you get is that black holes 75 million to 100 million light-years away from us today are the only ones capable of having ever sent us an image of our own Jurassic.

The third thing is that in any situation where light from earth makes a turn towards us, light from the sun will be doing so as well. Earth's light would be drowned out by Sol's; so instead of trying to observe the earth directly, we would really have to be trying to observe the dip in Sol's light as the earth transits across its surface relative to the black hole. (This technique is the one we've used so far to find extrasolar earth-like planets.)

But read that last paragraph carefully; we'd have to have a transit occur in space-time between the earth, the sun, and the black hole. Those ain't betting odds, to put it mildly...

... at least not for any specific time point. I should admit here that at longer, more flexible scales, it might not be impossible per se to find such a black hole, one capable of receiving our light and then sending it back toward a place where we can observe it millions of years later.

The galaxy itself is only 100,000 light years wide, so there do exist plenty of black holes within the correct radius for such events as "the time of the dinosaurs". Also, the way the earth and the sun are oriented, there are times when the earth and the sun line up along a line pointing perpendicular to the plane of the galaxy. A signal returning to us from a black hole lying outside our galaxy would have less confounding light to deal with than one within our galaxy (assuming that there are such things as rogue black holes passing through empty inter-galactic space).

That all said, any would-be time-astronomer would face insurmountable problems.

First, cosmic dust gathers itself around black holes. It's simply unavoidable. This dust will scatter any light rays passing through it, clouding the face of any gravitational mirror; and in a situation like this demanding extreme sensitivity, it's unlikely we'd be able to see ourselves in any black hole's face.

Second, at the scales we'd be talking about here, the light would have to exit the galaxy and move many a distance times longer than the diameter of our galaxy itself (at least if we want to see events happening in the deep past, like the dino-age and the formation of the earth). What this means is that the sun's light will invariably be itself drowned out by the light of the rest of the galaxy; if the sun's not visible, then a transit between the earth and the sun won't be either.

But what if we had a good enough telescope? That's the third thing. Its short answer: we won't be able to do it without some serious breakthroughs in physics. Light itself doesn't have enough resolution for that.

The long answer is that light is quantized in a way that makes it extremely unlikely that we will ever be able to resolve objects in a meaningful way at that distance. (Readable explanation of photon quantization next: skip ahead if you want.) When light hits certain substances, they become electrically excited. This electrical excitation produces an electric field, and these electric fields can be measured as a way to measure the light hitting the object. If you take a laser, and shine it on such objects, you can then measure the field of electrical excitation across the area where the laser's light hits the object. This field looks like a smooth continuous space, just like how the laserbeam looks like a smooth, continuous circle; but as you turn down the laser's power lower and lower (past the point where a human can see) you eventually reach a point where the excitation field no longer looks smooth. It's grainy; the electrical field shows up in little blips here and there, like raindrops in a puddle: in discrete chunks. Stated in a general way, this observation means really that light is fundamentally similar to rain, in that both are made up of tiny, uniform parts, which are simply more or less frequent as the intensity of the rain or the light changes; and the name of a raindrop of light is a "photon."

So, in order for us to get any useful information about our planet's deep past, we would need a continuous stream of these photons. One photon wouldn't do it, because one photon alone could have come from anywhere. It could be random. And since the sun's light is not like a laser's, where all the photons are oriented in the same direction, a photon stream naturally coming from earth towards the right kind of black hole... such a stream of photons is inherently going to scatter with distance, to the point that at the scales we're talking about, it's extremely unlikely that any more than a single photon would be bent so perfectly as to reach us, even if there existed a black hole capable of doing so, and even if we assumed that any photons made it to us in the first place. The stream would simply be too dissipated at that point.

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That all said, this is the sort of thing that could make an interesting setting for a sci-fi book, or movie, or game; a planet whose sun orbits a distant black hole. If the black hole were sufficiently dust-free, the planet would likely be able to see its own twisted time-distant reflection in the black-hole's gravitational mirror. Information sent via laser beam toward the black hole at the proper direction could be bent around back towards receivers on the planet. And if the receivers and broadcast lasers were linked, they could potentially use the laser loop as an information-storage mechanism for some giant computer. (Except that the computer could be easily disrupted by an asteroid accidentally flying through the loop. Or an astrobird pooping on the receivers.)