Let me open up with a weird question.
“You are going out to watch a live match in the stadium how can you make sure that match is live. How and why do you believe that it‘s live?”
Now you might be thinking it’s not a weird question instead it is a stupid one. But keep in mind every brilliant idea seems to be stupid at the first point.
Now come back to the question why do you believe it is live.
The answer is very simple “You saw it with your naked eyes and you realized that it is happening as you see it, so it’s live”.
So what about when you look up and thank God for the final minute penalty save or a goal. When you do that you will see the stars in the sky.
Is that also live.
Another stupid question right, “Of course it is “.
Here is the twist. I would say “Of course not “
“Because of the finite speed of light, when you gaze up into the night sky, you are looking into the past.”
Let me make it clear.
When you look at the stars we are actually seeing the light which started from the star’s light years ago. The brightest star in the night sky Sirius is 8.6 light-years away. That means the light hitting your eye tonight has been traveling for 8.6 years
NGC4845 Galaxy is one of the distant objects we could track it is 65 million light-years away. This means the light we see right now is 65 million years old.
Imagine NGC4845 galaxy as a picture and if you could zoom in then what you will be seeing now will be the look of NGC4845 galaxy 65 million years back. We don’t even know what is the current status of that galaxy because we don’t have a mechanism to travel faster than light and see what is happening there.
Let’s reverse the situation, imagine there is life in NGC4845 galaxy which is like 65 million light-years away, and if they are looking at earth what will they be seeing. They will of course see the light from the earth which is 65 million years ago. If they have the technology to zoom in then they could see dinosaurs getting extinct and not us.
They could see this only if they have technology beyond human reach. Imagine we try to zoom into NGC4845 galaxy using the current technology we can’t even see the planets which are orbiting the biggest star in that galaxy. You cant zoom in that far because by the time you reach that far there won’t be any photons that get reflected from a planet or a Trex so we can’t see it.
The next question is, “Is this theoretically possible?”
“Yes it is”, that is why I said they can see us if they have technology beyond human reach.
In quantum physics, there is something called “Gravitational telescope”. It’s a proposed theory for studying exoplanets using an effect that occurs around massive celestial bodies where the gravity of the objects is strong enough to bend spacetime. An object viewed through this bent of spacetime will appear closer and larger than how you see in the ordinary telescope that is made by us.
We have the sun which is a large celestial body with substantial gravitational pull. If we point this camera towards the sun then we can zoom into exoplanets and see images in detail.
For us, there is a limitation because if we have to see the exoplanets that are clear then we will have to place the telescope at a point 14 times away from the distance between Sun and Pluto plus it has to be 20 times wider than earth.
That is why I said “theoretically possible” but might not be possible for us now, We are yet to reach outside the solar system.
I guess now we are clear “what we see in the sky is the past”
Now let’s add a fun fact to this, there is a list in the wiki which shows the brightest start in the night sky. If you sort the table on that page with distance and find the number closest to your age. That light has actually started traveling when you were born. ie “when you see it tonight you will see the light at the time of your birth”.