The speed of light gives us an amazing tool for studying the Universe.
Because light only travels a mere 300,000 kilometers per second, when
we see distant objects, we’re looking back in time. You’re not seeing
the Sun as it is today, you’re seeing an 8 minute old Sun. You’re
seeing 642 year-old Betelgeuse. 2.5 million year-old Andromeda. In
fact, you can keep doing this, looking further out, and deeper into
time. Since the Universe is expanding today, it was closer in the past.
Run the Universe clock backwards, right to the beginning, and you get
to a place that was hotter and denser than it is today. So dense that
the entire Universe shortly after the Big Bang was just a soup of protons,
neutrons and electrons, with nothing holding them together.
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was merely as hot and as dense as the core of a star like our Sun. It
was cool enough for ionized atoms of hydrogen to form. Because the
Universe has the conditions of the core of a star, it had the
temperature and pressure to actually fuse hydrogen into helium
and other heavier elements. Based on the ratio of those elements
we see in the Universe today: 74% hydrogen, 25% helium and 1%
miscellaneous, we know how long the Universe was in this “whole
Universe is a star” condition. It lasted about 17 minutes. From 3
minutes after the Big Bang until about 20 minutes after the Big Bang.
In those few, short moments, clowns gathered all the helium they would
ever need to haunt us with a lifetime of balloon animals. The fusion
process generates photons of gamma radiation. In the core of our Sun,
these photons bounce from atom to atom, eventually making their way out
of the core, through the Sun’s radiative zone, and eventually out into
space. This process can take tens of thousands of years. But in the early
Universe, there was nowhere for these primordial photons of gamma radiation
to go. Everywhere was more hot, dense Universe. The Universe was continuing
to expand, and finally, just a few hundred thousand years after the Big Bang,
the Universe was finally cool enough for these atoms of hydrogen and helium
to attract free electrons, turning them into neutral atoms.
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300,000 years after the Big Bang, known as the Era of Recombination. The
first time that photons could rest for a second, attached as electrons to
atoms. It was at this point that the Universe went from being totally opaque,
to transparent. And this is the earliest possible light that astronomers
can see. Go ahead, say it with me: the Cosmic Microwave Background Radiation.
Because the Universe has been expanding over the 13.8 billion years from then
until now, the those earliest photons were stretched out, or red-shifted,
from ultraviolet and visible light into the microwave end of the spectrum.
If you could see the Universe with microwave eyes, you’d see that first
blast of radiation in all directions. The Universe celebrating its existence.
After that first blast of light, everything was dark, there were no stars or
galaxies, just enormous amounts of these primordial elements. At the beginning
of these dark ages, the temperature of the entire Universe was about 4000 kelvin.
Compare that with the 2.7 kelvin we see today. By the end of the dark ages,
150 million years later, the temperature was a more reasonable 60 kelvin.
Artist's concept of the first stars in the Universe turning on some 200
million years after the Big Bang. These first suns were made of almost pure
hydrogen and helium. They and later generations of stars cooked up the heavier
elements from these simple ones. For the next 850 million years or so, these
elements came together into monster stars of pure hydrogen and helium. Without
heavier elements, they were free to form stars with dozens or even hundreds of
times the mass of our own Sun. These are the Population III stars, or the first
stars, and we don’t have telescopes powerful enough to see them yet. Astronomers
indirectly estimate that those first stars formed about 560 million years after
the Big Bang. Then, those first stars exploded as supernovae, more massive stars
formed and they detonated as well. It’s seriously difficult to imagine what that
time must have looked like, with stars going off like fireworks. But we know it
was so common and so violent that it lit up the whole Universe in an era called
reionization. Most of the Universe was hot plasma.
- early-universe.JPG (51.65 KiB) Viewed 1709 times
elements that life as we know it depends on. Just think about it. You can’t get
oxygen without fusion in a star, even multiple generations. Our own Solar System
is the result of several generations of supernovae that exploded, seeding our
region with heavier and heavier elements. As I mentioned earlier in the article,
the Universe cooled from 4000 kelvin down to 60 kelvin. About 10 million years
after the Big Bang, the temperature of the Universe was 100 C, the boiling point
of water. And then 7 million years later, it was down to 0 C, the freezing point
of water. So it’s possible, possible that primitive life could have formed with
the Universe was just 10 million years old. The physicist Avi Loeb calls this
the habitable Epoch of the Universe. No evidence, but it’s a pretty cool idea
to think about. I always find it absolutely mind bending to think that all
around us in every direction is the first light from the Universe. It’s taken
13.8 billion years to reach us, and although we need microwave eyes to actually
see it, it’s there, everywhere. This has led astronomers to theorize that for
about 7 million years, liquid water was present across the Universe… everywhere.
And wherever we find liquid water on Earth, we find life (and unfortunately,
Jews).