This page is a beginner's explanation of the Big Bang. I intend it to be
accurate. It is my understanding of the matter, however, so I can't guarantee
That's how it started, or so they say. I have to admit, even with a science
background, I wasn't immediately convinced. Then I learned a discouraging
truth: it was easy to be swayed by superficial arguments if I remained ignorant
(happens in politics too, by the way). And it was difficult to accept, but I
How'd I find that out? I started reading. I had a physics degree already,
so I didn't think I was ignorant. Then again, my degree was nye onto 30 years
old, and I hadn't really been keeping up in some aspects of my own field. I'd
just been doing applied Newtonian physics for 30 years.
So when I started reading, I found out how ignorant I was, and how
compelling the arguments are for the Big Bang. That's right --
The Germ Of An Idea, Relatively Speaking
When did the idea of the big bang get started? That's a bit hard to say.
Even in Einstein's time, Einstein was intrigued by the story his relativity
equations were telling. The debate of that era was whether we lived in a static
universe or a changing one. At the time, around 1900, the discovery that our
Milky Way galaxy wasn't the entire universe was just being made.
Einstein's equations of general relativity told him that the universe could
not be static. His space-warping math said that the universe must be either
expanding or contracting, that the forces of gravity between all the stars and
their motions simply couldn't lead to a static arrangement. When he first
formulated his general relativity equations, the Milky Way galaxy was still
considered to be the entire universe, and it appeared to be quite static on
the large scale.
So Einstein tried to bring his equations into alignment with generally
accepted astronomical principles by adding his famous cosmological
constant into the mix as a repulsive force to balance gravity. He hoped in
this way to find a stable and static solution that would fit the current view
of the universe. But he could not find a static solution. Even with the new
cosmological constant, a static universe just didn't seem possible. We either
had to be coming or going -- universe-wise.
Which Is It? Are We Coming, Or Going?
A fellow named Edwin Hubble, whose discoveries are described in the book Edwin
Hubble: Genius Discoverer of Galaxies (Genius Scientists and Their Genius
Ideas), solved the coming or going part. In 1929 he
determined that galaxies external to our own, other than those bound together
in the local group, were all receding from us. The further away they
were, the faster they were receding. That showed, emphatically, that the
universe was expanding as Einstein's equations demanded.
Einstein promptly removed his ad hoc cosmological constant and declared
it to be the biggest mistake he'd ever made. Of course, now with the discovery that the universe's expansion rate is actually increasing, the term has been
It seemed logical enough even in that era to wonder what would happen if one
could turn the clock backward? If objects in normal time are getting further
apart -- wouldn't they be getting closer together if the clock ran backward?
That is, in the long past things must have been close together. And if that
was so, and it was also true that gravity pulls things together, something
spectacular must've happened to push things apart. In fact, push them apart
with such force that they are still moving apart today, some billions of years
So the Big Bang idea started to take place. But up to this point it
was largely a mental exercise. Galaxies that we observe receding must
have been closer at one time -- but in the same place? What was the
Shhhhh ... Did You Hear That?
Evidence began to mount when Penzias and Wilson of Bell labs were
having trouble getting the noise out of their radio telescope back in
1965. They tried everything from checking all of the electronics, to
double checking that they weren't picking up ground based interference, to
even making sure the pigeon droppings in the antenna housing weren't
bouncing transmissions around.
Their conclusion? They determined that the noise they couldn't get rid of
was from outer space. A microwave signal emanating from all directions, like
that which would come from a black body a couple degrees above absolute
As it happens, another group of scientists were already looking for such a
thing to explain their view of the beginning of the Universe. They were
ecstatic when they heard of the Penzias and Wilson discovery. It was just such
a result that should be seen if there had in fact been a massive explosion some
billions of years ago. We should see a low temperature radiation (due to the
expansion and cooling of the universe) from all directions. What else could
Now if you are into physics, you may know that it is a vast field of study
made up of a number of sub fields. Astronomy is one such sub field. Others are
thermodynamics, electricity and magnetism (called E and M), relativity, and
quantum physics, to name a few. I've already mentioned that relativity started
off the debate.
Is That All You Got?
It turns out that each of these other realms of physics have something
to say about the Big Bang. Only one field, you understand, would have to
be in disagreement with the evidence to cast doubt on the theory.
E and M is the study of electricity and magnetism, which gets into
microwaves, x-rays, light, and all forms of electromagnetic radiation. The
statement E and M makes about a Big Bang is that a vast amount of radiation
would be given off in a big bang. That's what Penzias and Wilson discovered
with their radio telescope.
Thermodynamics is the study of heat flow, the base of knowledge that
originally led to the invention of the steam engine. Thermodynamics predicts
the nature of the residual background radiation and it's apparent temperature
after the expansion. Again, an observation in agreement with relativity and
Quantum physics, not entirely understood by anyone, is the study of the
interior of the atom. I recall that when I was a young college student and a
beginning amateur astronomer, I considered astronomy and quantum physics to be
at opposite ends of the physics spectrum of study.
Quantum was the study of the very small, and Astronomy study of the the vary
large. Each had their own mathematics and methodologies for solving problems.
It was hard to see what relationship the two fields had with one another.
What's This Black Hole Nonsense?
Then the buzz about black holes started. Collapsing stars, infinite
density, the singularity, the break down of relativity, etc. That seemed pretty
far fetched. Certainly no one had ever seen a black hole. Besides, how do you
see one? A black hole against a black background?
It's true, black holes really can't be seen directly. But they exhibit a
gravitational attraction that can be revealed by the actions of objects and
atoms around them. Large objects, like stars, can be seen moving around
something that is obviously more massive than the star, yet invisible. It has
to be either a neutron star or a black hole -- what else?
Atoms in gas getting too close to a black hole get so accelerated that their
mutual collisions create high energy emissions, including x-rays. Not much
else is known that can cause that. Both of these phenomenon have been observed
repeatedly. Black holes are a fact of life. And the clash of the macro
work of Astronomy and the quantum world begins at the periphery of black
So black holes are the super massive objects of incredible gravity. That
seems very much an astronomy object, on the big scale. But they are collapsed,
and actually very small, singularities in fact. Within the vicinity of the
singularity, or during the collapse, all that mass gets crunched into a smaller
and smaller space. Eventually down to (and beyond) the size of nuclear
So Black Holes Are Really Small,
I Thought We Were Talking Universe Here
The nuclear force is incredibly strong. Under normal conditions gravity is
extremely weak in comparison. So weak, that trying to measure any relationship
that might exist between the nuclear force and gravity is impossible. But
something happened in the 19th century that started a revolution in
A fellow named James Clerk Maxwell figured out that the electrical force and
magnetic force, both discovered long before his time, were related. In fact,
one might say that electricity and magnetism are two aspects of the same force.
He created the equations that explain that relationship. Physicists say that
Maxwell unified electricity and magnetism. I think a better layman's
terminology is that Maxwell discovered the relationship between the forces.
That discovery led to a big question. There were four forces known by
the end of the 19th century: gravity, electromagnetic, weak nuclear,
and strong nuclear. If electricity and magnetism were considered to be
separate forces and then were found actually to be aspects of a single force,
were the other forces related in some way also?
Ah, you think I digress. I warn you, I've had too many courses in wholism
to think straight anymore. I assure you I will get back on track.
Not too long after the start of the 20th century, the question
began to get answered. In 1967, Abdus Salam and Steven Weinberg managed to
describe the mechanism that unified the weak nuclear force with the
electromagnetic force. Thus, the electromagnetic and weak nuclear were aspects
of a single force, observed within different realms of nature. At higher
temperature (and I mean really high), the forces became one. Sort of like ice
and water are really the same material, but under different physical
environments. Heat ice up and the relationship to water is revealed.
While still a work in progress, theories are now being explored that will
unify (explain the relationship between) the strong nuclear force and what is
now called the electroweak force (unified version of electromagnetism and weak
nuclear). So it appears that soon three of the four forces known in nature will
be unified. Gravity is the odd force out. Why? As I mentioned earlier, it may
be because compared to the other forces, gravity is so extremely weak. It is
not possible to measure any relationship with any device man has been able to
That is, until you start talking about black holes. When you squeeze the
mass of a star (or millions of stars) into a singularity, you have in effect
raised the value of gravity to the level of the other forces. Obviously,
to understand what goes on in a black hole, it is necessary to understand the
relationship between gravity and nuclear forces, now that they are on a more
The problem is, in the non-extreme areas of the universe (far away from
black holes), the nuclear force/gravity relationship is not measurable. But in
the extreme areas of the universe, inside the event horizons of black holes,
the events are not observable. How, then, does one figure out the relationship
between gravity and the other forces?
As a side note, it is also possible that we are completely wrong in our
interpretation of gravity. It may not be a fundamental force at all, which
could be the reason we can't unify it with the others. It may be what's called
a consequential force of something else going on at the atomic level. It's that
something else that may be the
fundamental phenomenon we need to
reconcile with the other forces. Something that we might identify at the
quantum level that causes minuscule distortion of space-time. Gravity, after
all, is in some way involved with the warping of space time.
Let's Get Back On Track, Shall We?
This relationship of particles at the extreme size and gravity aspects of
black holes (to bring things back together), is the clash point of the macro
world of stars, galaxies, and relativity -- and the micro world of electrons,
protons, quarks, and nuclear force. What was convenient to observe as two
completely different extremes, each with its own mathematics, comes crunching
together and must require a common mathematical description.
In the effort to study this micro/macro clash, a lot has been learned about
the nuclear world. The functioning mechanisms of stellar interiors, for
example. And some pretty good models of the Big Bang, as it relates to quantum
matters. Involved in that understanding is what atoms would be produced in a
It's called Big Bang neculeosynthesis. Based on knowledge of stellar
interiors (known pretty well now) and particle accelerator studies, the
neculeosynthesis model predicts the ratios of the production of atoms,
particularly hydrogen, helium, lithium, and beryllium. Heavier elements
up through iron are not produced in the Big Bang, they're produced when stars go nova. And it's long been a puzzle where the even heavier elements like the
heavy metals come from. Stellar collapse models can't account for them.
Since neculeosynthesis predicts element ratios, astronomers have been
able to locate primordial gas dispersions in space and with spectral
analysis, examine the mix of elements. The findings are consistent with
the predictions of neculeosynthesis.
Recently (2017), scientists with their latest equipment had the massively
(no pun intended) lucky opportunity to detect a neutron star collision in
progress. Studies of the aftermath of that collision revealed what had only
been postulated prior to the observation, and that is the idea that the
heaviest elements come into being at the collision of neutron stars.
Makes sense in a way. When stars run out of hydrogen, they collapse a bit,
increasing the internal temperature and pressure, allowing the fusion of
helium. The process repeats itself as the helium is consumed, on through
elements up to iron. At that point, as it happens, the ratio of neutrinos
to photons produced gets much greater. More neutrinos, less photons.
Why is that important? Because neutrinos don't react much (hardly at all)
with other particles. So they just leak out through stars as if nothing was
there. Leaking out so much energy without it providing any push back allows
stars at that stage to collapse. So beyond iron, fusion doesn't provide the
mechanism for making elements.
But neutron stars are themselves like uber nuclei. Huge masses of
neutrons held together by their own mutual gravity. They are like some super
duper elements whose nuclei masses exceed that of even stars. But neutron stars
are only stable because of gravity, not because of nuclear forces. Crash a
couple of neutron starts together so that chunks go flying off, and you end up
with clumps of nuclear material that don't have enough gravity between the
particles in them to remain stable, and the nuclear force isn't stable for that
much nuclear material either.
So the blasted off clumps of nuclear material degenerate to the largest
stable configurations as determined by nuclear forces -- leading to the
heaviest of elements. Of course you know that Earth has some of the heavy
elements, recall the 49 gold rush. So we can assume that not only did some
ancient star collapse distribute elements up through iron throughout our
region of space, but some neutron star interaction must have occurred near
enough to our region of space also, else we'd not have any heavy elements on
So What's It All Mean?
Ok, it was a long, drawn out argument. The point is, astronomy, relativity,
E and M, thermodynamics, and quantum physics all have something to say about the
evidences one can observe about the Big Bang. The conclusion is that the
findings in all of these areas of physics are consistent with the Big Bang
model. There is no other known model that brings all of these fields
So you see, by only speculating on perhaps one of these fields and being
ignorant of the others, could one say "it's only a theory." When you
dig around and see all that physics has to offer, the data leaves very little
So the Big Bang answers just about everything. Well, just about. There is
that little problem about galaxy formation. Classic models about star and
galaxy formation suggest that stars and galaxies formed much earlier in the
hot, expanding universe than possible. I suggest you read the
Dark Matter page when it comes available to put that problem to
I made the image with the The Gimp. The
Gimp is freely available for both Linux and Windows (I happen to use the
Linux version). The star burst pattern was already available, I only had to
mess with size, color, etc.
There are a number of good books out there that can fill in blanks in the
story of the Big Bang. One that I like is written by Nobel prize winner Steven
Weinberg, and titled The
First Three Minutes: A Modern View Of The Origin Of The Universe. Though written by a Nobel prize winner, this is a
book for the layman, and is a great introduction to the concept of the Big
Another book that is a sort of case study is that written by George Smoot
(another Nobel prize winner) and Keay Davidson. It's named Wrinkles
in Time: Witness to the Birth of the Universe, and describes the incredible and difficult quest to
discover and measure the quantum fluctuations in the microwave background
Quantum considerations of the Big Bang say the fluctuations had to be in the
microwave background, but up until George Smoot and his team got the COBE space
probe finally off the ground, there was no way to see them. Had the
fluctuations not been there, the entire Big Bang idea would have busted. In the
book, George gives a hair-raising account of a follow up mission to Antarctica,
necessary to validate the COBE measurements.