Look back in time – Look at stars
There would be none who don’t get fantasized by the appearance of a night sky adorned with billions and billions of stars and the moon. We know that they are incredibly distant. So when you gaze at the stars at night, you are actually seeing light that might have emitted long back. It implies that you are actually looking back in time. You are seeing a younger star than it actually is!!
It takes 8 minutes and 20 seconds for the sunlight to reach us. That means the light hitting your eye from sun has been traveling for more than 8 minutes. And this time lag implies that what we observe now is actually something in past. Likewise we see the Moon as it was 1.3 seconds ago.
So if it’s around 8 minutes from the nearest star to us, then how long does it take for light from more distant stars to reach our eyes? And since the light really takes so long to get to you, then what we see as what’s really there, is something what used to be there in the past!!
Yes, there is a window to the past, in the space time fabric of our beautiful universe.
Whenever we observe a distant star or any galaxy, we are seeing it as it was, not as it is. And probably, those twinkling stars we see at night need not be even a live one, they could have become supernova years ago and we wouldn’t know it yet. Likewise there could be stars being born in the mysteries of universe that we can’t see yet. So how does this all happen?
How can you see years into the past?
We think of light as instantaneous happening, but it only seems like it…
Speed of light, de facto the maximum speed, is definitely not infinite. In our universe it is 300,000 kilometers per second. And this finite speed of light actually makes us to look back in time.
Nothing can actually travel, breaking the rules of time (as far as we know). Every wave must elapse a definite time to get to where it is going. Just like the aeroplane which you try to locate in the sky hearing its sound seems to be no longer there where the sound seems to be coming from. Its because by the time the sound waves reach you, the plane has moved on. The sound you hear is the sound of the plane a few seconds ago, not the sound of the plane now. So, its like you are “hearing back in time”
Just like this, light also need some time to get anywhere. So looking back in time happens when you are gazing at distant stars. When you are watching the night sky, gazing at the stars, you are actually looking into the past.
Already people tell like your senses are struck in past, you are thinking more on past and grieving henceforth etc..and now ironically what we actually sense itself was something in the past as a billionth of fraction of a second delay can happen in anything you watch, not just with distant stars!! Now just keep on wondering if there is ever such a thing as the present!! Now is an illusion (read more Is ‘Now’ an illusion ?, an article written in 2016)
How far back are you looking in time?
Distance to be traveled is just proportional to time elapsed. The distance light travels in one earth year is called light year. One light year is 10 trillion (or rather visualize it as 1 followed by 13 zeros ) kilometers.
Andromeda, the nearest major galaxy to our milikyway is 2.5 million light years away. And it is bright enough to be seen with the unaided eye. The bright star Sirius is 8.6 light years away. That means the light hitting your eye tonight has been traveling for 8.6 years. So when you look at Sirius tonight, you see a 8.6 years back younger version of it actually.
We can see seconds, minutes, hours and years into the past with our own naked eyes. And what if there is a telescope, yes, obviously we can peer further millions and billions of years into the past.
The Hubble Space Telescope can see objects even more distant than your eyes can. When it takes a picture of a galaxy 100 million light years away, we are seeing the galaxy as it looked 100 million years ago. Because distant galaxies appear to us as they were millions or even billions of years ago, we can study how they change over time, how they change as they age (just as looking at babies, children, teenagers, and then adults can show how we humans change as we age) etc.
Wanna see the light from the star when you were born?
Now have a look here in this List of brightest stars and identify that star which is n light years away where n is your age. Now look at your birth star tonight, you see it as it was at the time of your birth. You are seeing light from when you were born. So when you look up and gaze at stars, remember you aren’t seeing things as they are now; you’re seeing things as they were.
Here’s where it gets even more interesting. Wish to see some light which had left before the Earth even formed?
We know that earth formed only 4.5 billion years ago. Now watch some quasars (extremely luminous active galactic nucleus feeding even supermassive black holes) which are further out, beyond 4.5 billion light years. Now, what you see would be the light which had left before the Earth even formed!!
The time elapsed between when we detect the light here on Earth and when it was originally emitted by the source, is known as the ‘lookback time’. For very distant objects, the lookback time is increased by the Hubble expansion of the Universe, which is causing the space between galaxies to increase with time.
Travel backward in time, not just look back ..??
What if you traveled back in time and killed your grand parent or prevented your father and mother from meeting? Then you are not gonna born at all. And then, if not born, means how can the unborn travel back in time to kill his so called grandparent. This paradox is known as time-travel paradox. Some scientists believe that some undiscovered laws of physics may be there to prevent such paradoxes
When you move through space-time with a speed closer to the speed of light, time dilation can happen. Time gets slow down for you while traveling at a speed near to the speed of light. Well, you would be younger than the people you had left behind while meeting them again.
Owing to the oddities of both special and general relativity of Einstein, there is still a possibility to travel back in time!!
This can happen by traveling at relativistic speeds or through the effects of gravity. And maybe in future such time machines would be invented which help us to travel back in time.
Now what if those stars looked back at us?
To those far-out celestial bodies how will our earth look like?
Suppose some aliens in Andromeda are watching us. They would be seeing our ancestors, probably First members of the genus Homo, Homo Habilis.
And who knows, if there are already some aliens with powerful enough telescopes watching even the dinosaurs roaming the Earth, right now!!