Well we can do, again going
back to this sort of prism, by measuring the spectrum of
colors coming from star, we see these
lines, which shows some colors are missing. This is called spectroscopy,
which is very important technique in studying
the astronomical objects. This particular star, which is actually
our sun, has a lot of these lines
which shows that is has many heavy elements. These stars
are called population one, a lot of metals, elements heavier than helium. This
is clearly contaminated by the past supernova explosions. If we look hard enough,
sometimes we find stars which seem much cleaner.Less contamination
of these heavy elements. So they are
called population two stars.
If you go way back into the beginning of the universe,
there must have been what is called population three
stars which are made of Hydrogen and Helium alone, without
any contamination from the previous generation of stars. We
haven't found those, but people still looking.
So, now we come to this question,
how do we know that big bang produced hydrogen, helium,
but not more? We need a different tool, as we
talked about. What we can look back to the point when universe was only 380,000 years
old, by using radio telescopes, because we can detect the cosmic
micro background. This is the start light
coming from the big bang itself we talked about it. But there's a wall,
right, we can't go beyond that using telescopes,
we need some different technique to understand
what's going on on the earlier moments of the universe. So we use a different tool, called particle accelerator. The idea is very simple, universe is so dense and hot, and we’d like to understand what happened back then, so there's something
we can try to do in our own laboratory.
We try to create an environment where similar
reactions can be created artificially.
Which must have happened early on, at the beginning of the universe? So this way, we can go back to the moment, when the universe was only three
minutes old. What we do is bring in
literally, neutrons and protons
together, smash them against each other, and see if they can form something heavier, like helium.So we can try to redo this kind of reaction
that happened right after big bang, in our own laboratory, and that’s the way we try to go beyond this wall of 300,000 years old universe. So, by studying these reactions in the laboratory, we can measure
the probability for a reaction like this to happen.
Once we've measured that we can make a prediction, on how much
of the helium must have been synthesized at the beginning
of the universe, and that process is called Big
Bang Nuclear Synthesis.That would give you
a prediction, that the ratio of hydrogen to helium in our universe must be
roughly 3:1. Indeed we
can measure the ratio of hydrogen, helium
by looking at the spectrum
of light coming from the far away objects,
and this 3:1 ratio agrees very well with
observation. So that's how we can compare, what you
would predict based on what you learn from particle
accelerators versus what we can actually go back, and see using telescopes. And if they match
up, that would give us enough, confidence
that we understand what happened in the Big Bang itself. So by putting this information
together, we can put them in computer,
and simulate how the first
stars had been
born.
contd....
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