Where there's a will there's a way.
Is it possible to see the real live dinosaurs and mammoths? Of course no, everyone will say. But after some thinking, it appears that there are some options :). With the current state of technology, it is almost unreachable, but theoretically possible.
So, how is possible to see the past? To achieve it, light from the Earth, which was bent by Black Hole to 180 degrees should be caught. Distance to the black hole in light years should be equal to the half number of years, which have to be seen in the past. For example, if it is necessary to see dinosaurs, 100 million years ago, then the distance to the black hole should be 50 million light years. Then, the light will reach the black hole in 50 million years and 50 million years it will travel back to the Earth. The total light signal delay will be 100 million years.
Ideally, it would be good to get a picture like this photo with elephants on Google Maps, but instead of elephants — mammoths or dinosaurs.
One of the possible light trajectories near the black hole is shown in this picture from Wikipedia (green and red lines are possible trajectories of the light beam near the black hole, shown as gray).
So, how is possible to see the past? To achieve it, light from the Earth, which was bent by Black Hole to 180 degrees should be caught. Distance to the black hole in light years should be equal to the half number of years, which have to be seen in the past. For example, if it is necessary to see dinosaurs, 100 million years ago, then the distance to the black hole should be 50 million light years. Then, the light will reach the black hole in 50 million years and 50 million years it will travel back to the Earth. The total light signal delay will be 100 million years.
Ideally, it would be good to get a picture like this photo with elephants on Google Maps, but instead of elephants — mammoths or dinosaurs.
One of the possible light trajectories near the black hole is shown in this picture from Wikipedia (green and red lines are possible trajectories of the light beam near the black hole, shown as gray).
For example, photon can fly around the black hole like this, changing its trajectory for 180 degrees
Or even like this, bending for 220 degrees
The videos above was made with help of this demo of general relativity.
The videos above was made with help of this demo of general relativity.
It looks like an interesting theory, but how it will be in practice? Let's try to answer these practical questions:
- Are there suitable Black Holes?
- What kind of telescope is needed to see dinosaurs with resolution, for example, 10 cm?
Suitable Black Holes
If this Wikipedia article "List of black holes" would be open, then a pair of suitable black holes can be found. One in the center of our Milky Way (Distance 26000 light years) Sagittarius A* and another one in the galaxy М60, another name Messier 60 and NGC 4649 (60 million light years). Sagittarius A* let us see mammoths and Neanderthals — 52000 years ago, and М60 dinosaurs — 120 million years ago.
What kind of telescope is needed
Suitable black holes are found, it left only calculate and build an appropriate telescope. Every telescope has a limit for angular resolution, which is determined by a diameter of the objective (aperture). Precise calculation for the diameter of such objective, which allows seeing mammoth with 10 cm resolution from the distance 52000 light years, give the number 1.67*1012 km (1670000000000 km) or 1.67 trillion kilometers. For dinosaurs with distance 120 million light years number is 2000 time bigger — 3.85*1015 km (3850000000000000 km) or 3.85 thousand trillion kilometers. To imagine these numbers it is easier to compare them with Neptune orbit diameter. For mammoths, we need the telescope with aperture size 186 Neptune's orbits, for dinosaurs 428000 Neptune's orbits. It looks too much and absolutely unrealistic. But science is constantly developing. The latest research in quantum mechanics tells us, that it is possible to overcome diffraction limit for angular resolution for the telescope with the help of quantum entangled photons or quantum light amplifying like in the laser. There are some links about this topic:
http://physicsworld.com/cws/article/news/2014/apr/29/quantum-telescope-could-make-giant-mirrors-obsoletehttps://medium.com/the-physics-arxiv-blog/how-to-build-a-quantum-telescope-5f473cf5a4bc#.px6glqnha
https://arxiv.org/pdf/1604.06928.pdf
So it seems to be quite possible that after 50-100 years with technology like this the picture of dinosaurs and mammoths will be available. And listen to the 50 years old radio broadcasting might be possible even now with modern radio telescopes, but it is a different story.
Other technical issues
Probably, while bending light by the black hole, image will be distorted a lot, like for example on this picture
smile line is an image distorted by gravitation.
Might be it can be restored by postprocessing, and maybe not. To solve this issue normal stars, like our Sun, can be used. For example, The Sun deflect the light approximately on 1 arc second. In order to deflect the light for 180 degrees, 648 thousand suns will be needed. In our Galaxy (Milky Way) there are 200—400 billion stars, which is quite enough for this task :)
After additional calculations, it became clear that in our Galaxy (Milky Way) it is not possible to use normal stars (taking into consideration the average distance between stars, average star mass etc), because the round path of the light will be 2-5 times bigger, than our Galaxy (Milky Way). So, the black hole has to be used. Some other calculations showed, that with Hubble telescope we can see our Sun virtual image, created by the black hole. Sun image deflected by nearest black holes will be 21 apparent magnitude, when Hubble can see stars up to 31 magnitude. Details can be found in this article.
