If you looked at the earth from 70 million light years away, would you be able to see the dinosaurs?

A light year is the distance that light would be able to travel in one year, which is a very long distance. A single light year alone is approximately 9.461e+12 km. (That's a large number!)Anyway, we see things because light bounces off objects, and goes into our eyes. Then, if we looked at earth from 70 million light years away, the light that we would be seeing is technically from 70 million years in the past, which is believed as the time that dinosaurs roamed the earth. So, we would be able to see the dinosaurs, right? Well, there is a technical problem. To see the dinosaurs from that far away, we would need a huge telescope, beyond human comprehension. Although the hubble telescope has seen stars from 10 billion light years away [1], current technology cannot see possible dinosaurs from any distance that is even close to 70 million light years, as most planets that far will appear very small on the telescope. Seeing does not mean being able to pick out very little details. For example, just because I can see a airplane in the sky, does not mean that I can tell which airlines it belongs to, what the pilot looks like, etc. And, adding another telescope onto the telescope will not exactly solve the problem either. So, to be able to see the dinosaurs, we would need a way larger telescope since there will be no more light particles reaching the telescope from distances as far as this. This is because the further the distance from the light source, the less chance of a light particle, reaching your eye. It's kind of like dropping a glass full of water onto the ground. If you're really close, you'll likely get hurt by the fragments, or get soaked. But, if your at the other side of a house, you'll likely not get hurt. (only that with light, it's not affected by gravity, and the fragments travels endlessly, until they impact something else)

Luckily for us, there is a galaxy that is just 75 million light years away from earth, which will be completely suitable for our imaginary scenario. The galaxy is called NGC 1407, and it is a elliptical galaxy in the Eridanus constellation, 75 million light years away from Earth. [2] Now, let's say that whoever or whatever was trying to look at earth was a incomprehensibly technologically-advanced civilization, and had a unlimited amount of supplies and energy. Would they be able to build the giant telescope? Well, according to Quarks and Coffee, who used this formula "Angular resolution = 1.22 * wavelength / Lens Diameter" to figure out how big out telescope would need to be, a telescope which could see the dinosaurs from 75 million light year away would need to be over 4.4 light years in diameter. [3]

To give you a sense of how gigantic the telescope would be, the distance from earth to Alpha Centauri, another solar system, is just over 4.3 light years. [4] That means, that the telescope would be filling up the space between our solar system, to Alpha Centauri. And, this is just the diameter of the telescope lens. Imagine a telescope (or google one), and just observe how many times bigger the body of the telescope is than the lens.

Even if some very advanced civilization managed to produce enough glass, and materials to make the telescope, Quarks and coffee states that with that much mass in one space, the telescope will collapse into a black hole. He also states that even a telescope with a diameter of 28 light minutes will very quickly collapse into a black hole, given the density of glass. [3] Our telescope has a diameter of 4.4 light years, so it is pretty obvious what would happen to our telescope, pretty quickly.

So, if any civilization tried this, unless they can stop a telescope that would span from Alpha Centauri to earth from collapsing into a black hole, (possibly using exotic matter)[5] the only thing that would be left would be no telescopes, and a possibly huge black hole, conveniently right next to them.

Sources I used------------------------------------------ 1. Cool Cosmos, Infrared Processing and Analysis Center, http://coolcosmos.ipac.caltech.edu/ask/284-How-far-can-the-Hubble-Space-Telescope-see- 2. Su, Yuanyuan; Gu, Liyi; White III, Raymond E.;Irwin, Jimmy (10 May 2014). "Joint XMM-Newton and Chandra observations of the NGC 1407/1400 complex: a tail of an early-type galaxy and a tale of a nearby merging group".

The Astrophysical Journal

3. Quarks and Coffee, Matt, July 8th 2015, "If we were far enough from the earth, could we see the dinosaurs alive?" http://quarksandcoffee.com/index.php/2015/07/08/aliens-and-dinosaurs/

4. EarthSky, Deborah Byrd, May 16, 2017, "How long to travel to Alpha Centauri?, https://earthsky.org/space/alpha-centauri-travel-time

5. YouTube, Kurzgesagt, 12 August 2018, Wormholes explained - Breaking Spacetime,https://www.youtube.com/watch?v=9P6rdqiybaw

(6:04 in the video)

Extra References;

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1. Quora, Corey S. Powell, Feb 1, "Scientists claim that if an alien 65 million light years away sees earth through a powerful telescope, they can see "dinosaurs". How can that be possible?", https://www.quora.com/Scientists-claim-that-if-an-alien-65-million-light-years-away-sees-earth-through-a-powerful-telescope-they-can-see-dinosaurs-How-can-that-be-possible

(This helped me further understand the topic)