If you are interested in the Universe, then you know a simple truth: the deeper we look, the farther we see. Then to see distant aliens on our planet?
The speed of light is 300 000 km / s. Therefore, we can say that we all see a little late. If something explodes on the moon, we will notice it only after 1.28 s. Is the sun gone? This news will reach us only after as much as 8 minutes and 20 seconds. The signal from the device near Pluto will move 4.6 hours.
Surprisingly, when reviewing the universe, we see not the objects themselves, but what they were when their light started for us. For example, you can admire the magnificent Pillar of Creation cluster, which is 7000 light years away. But they are not! Yes, scientists are convinced that a supernova exploded in this area, which swept away these wonderful accumulations of gas and dust. But millennia will pass before we really see emptiness there.
This scheme works for everything. Therefore, it is logical to assume that the aliens also see not the modern Earth, but the planet in the past. How far? Well, if they lived on Proxima Centauri (the star closest to the Sun), they could see the release of the first iPhone. However, we were unable to find extraterrestrial life in the immediate vicinity, so we have to go even further.
It turns out that hypothetical aliens, located at a distance of 65 million light years, can observe on our planet not people, but dinosaurs (or a meteorite flying in their direction). In theory, this idea works, but in practice everything is much more complicated. The fact is that 65 million light years is a huge distance. Our planet is small and at such a distance it will be extremely difficult to observe. In addition, the distance indicates that the alleged aliens are in a cluster of Virgo galaxies. That is, they have to look at a planet located in another galaxy.
It is incredibly difficult. Earth scientists are only learning to observe such objects. More specifically, only two such worlds were found. If the aliens want not only to find our planet, but also to see what is happening on the surface, then you need to know where to look and have a huge telescope.
For example, calculations show that for the resolution of the Earth the diameter of the lens should be as much as 5.8 x 10 10 m (half of Mercury's orbit). And if you want to consider a tyrannosaur, the diameter of the lens increases to 4.4 light years.
However, these findings are based on human technology. Perhaps aliens are much better developed and have long been watching dinosaurs. If their level of development resembles ours, then is it worth bothering to create such gigantic structures?