The Black Hole Information Paradox
Paradoxes – just thinking about one leaves you scratching
your head and sends you into endless spirals of thought. And what if it concerns one of the most mysterious objects of the
universe? Well, double the head-scratching! What do you say?
Today, we will discuss one such paradox that has been driving
physicists crazy since its introduction – The Black Hole Information Paradox.
Before we look at what the actual paradox is, it is important to wrap your head around a few concepts.
The first being, the Law of Conservation of Information.
This is a basic law of Quantum Mechanics. It talks about the
need for information to be conserved. It says information like energy can never
be destroyed or created. It has to be conserved. Information refers to the
specific state of every single particle. Its energy, mass, spin, temperature, and more. Atoms may react, be crushed or fuse, their quantum wave function that
describes them must always be conserved. The information must live on.
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| Quantum no-hide theorem confirmed experimentally for the first time |
The second concept is that of time dilation.
So, what is it?
In our previous article when we were talking about the
consequences of an object that falls in a black hole, I had once mentioned the
term time-dilation. It can be defined as the difference of elapsed time
between two events as measured by observers either moving relative to each
other or differently situated from a gravitational mass or masses (Think Interstellar!).
As we know, gravity is so strong near a black hole that even
time gets slow near it, and when one falls inside one, the mass is lost
forever. But for an observer who is looking at the falling object, the object
appears to be slowing down until it reaches the event horizon. It looks frozen
in space. As time passes, the object starts looking increasingly reddish
until it begins to fade and finally vanish. Its wavelength increases and thus
it is red-shifted. The wavelength keeps on increasing and would take an
infinite amount of time to completely vanish. Thus, we can be happy that
information is safe on the surface of a black hole or is conserved. The surface
of the event horizon holds information on all the matter that has fallen in.
Information of object which enters a black hole is preserved
by time dilation.
BUT, the real trouble started when Stephen Hawking in 1974
calculated that Black Hole has a temperature. It meant that it is radiating
energy. And anything that radiates energy loses mass. This meant the black hole
is losing mass and though slowly would evaporate with time. The radiation
unsurprisingly was called the Hawking Radiation.
Now, came the real question. What happens to the information
which was preserved on the surface? Until now, we were quite happy with the
explanation that time dilation is conserving information on the surface, and information
is not being lost. But the loss of energy from a black hole predicted
otherwise. The black hole will disappear one day and so will the information
which was supposed to be conserved.
This started a paradox which we now know as the Black Hole
Information Paradox. It puzzled physicists for decades. New possibilities flew
in. People began speculating and coming up with creative questions. Was Hawking wrong from the beginning to start with and there was
no such thing as Hawking Radiation? Or, does the black hole holds the information in it till
the very last and when the last of the two particles evaporate, all is suddenly
released in the Universe at once? Or, is the black hole compressing information in a
microscopic space that remains even after the black hole itself is evaporated. Who
knows?
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| The black hole information paradox |
At first, Hawking was not much concerned with this loss in
information. But over time he realized information had to be preserved in some
way. Conservation of information was too important a law to be abandoned. So,
he put forward some new possibilities. He put forward the idea that the new
Hawking Radiation preserves the information of all that is falling in. The
radiation can be imprinted by the information of the new matter that fell in,
and then releases the information when it escapes into the Universe. The information does not remain of much use after that. Much like a burnt encyclopedia!
Information that the encyclopedia holds is in some way conserved in the ashes
but does not remain of much use.
But a solid explanation has not been obtained to date. Even the
existence of Hawking Radiation has not been confirmed experimentally. This
shows how naïve we actually are when it comes to understanding the Universe. Much work has
been done but a whole lot needs to be done. We hope of finding an explanation soon...
Now, we have reached the end of the article. I hope you liked
it and found it useful and I was able to make you a bit curious at least because in the end that is what drives science. Thank you very much.
