Modern science is full of all sorts of mind-blowing theories that describe and explain the behavior
of the cosmos under conditions that nobody has directly observed.
Perhaps the biggest example is the study of the Big Bang, which is the beginning of the
universe itself.
I’ve talked about the Big Bang in other videos, and some of the comments are what
you might call skeptical, including people who dismiss the idea by saying that, since
nobody was there at the time, we can’t possibly know anything.
And, of course, we know a great deal.
But I find that a lot of people have some serious misconceptions about what the Big
Bang was.
So I thought I would dispel a few and then tell you what we do know.
Perhaps the most common misconception is what I call the universe began like a giant firecracker.
In this model, all of the matter of the universe was concentrated in a single spot and then
it blew up, spreading matter throughout space and across the cosmos.
The location could have been anywhere- perhaps over there somewhere.
This is absolutely not what happened.
The reality is much, much, stranger than that.
Another misconception is that the Big Bang explains the exact, precise, moment of creation.
It doesn’t.
It explains things after the moment of creation, not the start, and certainly not before.
We don’t understand either of those things in detail.
And that’s okay.
Scientists admit when they don’t know something.
A third misconception is that, prior to the beginning, the universe was located at a spot,
with zero size and infinite density- what physicists call a singularity.
Yeah- that’s not true either.
No scientist really believes in a literal singularity, in spite of what you might have
read in some books.
The singularity arises from pushing Einstein’s theory of relativity to the point where it
breaks.
It’s just a wrong idea.
So just what does the theory of the Big Bang say?
And, I want to be clear- this video doesn’t talk about the data that supports the idea.
Just the theory itself.
The Big Bang theory says that the universe was smaller and hotter and has been expanding
for billions of years.
To best understand the theory, maybe the best thing is just to start with what we see today,
and run the clock backward to the beginning.
Let’s start with what we see around us- a universe that is flat, or nearly so, which
means that we can use the simplest math.
The part of the universe we can see is 92 billion light years across and the universe
that is at least 500 times bigger than what we see.
In a previous video, I said the distance was at least 250 times bigger, but better measurements
have now extended that number.
The current universe may actually be infinite and let’s start with that as a good working
hypothesis.
If that’s true, our visible universe is just a bubble in a sea of eternity, extending
forever in all directions.
Now that’s a little hard to draw, so let’s just focus on one of the three dimensions,
say left-right.
If we do that, we can present that direction as just a number line like you learned in
grade school, with a zero point and then two arrows pointing off to the left and the right.
We can make a choice and define Earth as the center.
We can then separate the universe into parts that are close enough to see and parts that
are so far away that we can’t see them.
Picking the Earth as the center doesn’t mean the Earth is the center of the entire
universe, rather, it’s simply the center of the part of the universe we can see.
The universe is expanding now, but if we run the clock backward, we can see that in the
past the universe was smaller and smaller.
Run it all the way to time equals zero, and we see that all of the visible universe has
collapsed down to what looks like zero size.
But we also see that even though we shrunk the visible universe down to tiny size, the
number line is still infinite.
That means that, even when the universe began, it might have already started out to be infinite
in size.
So that’s kind of a mind-blower.
In addition, we see that all the points of the visible universe all collapsed to the
same point.
If all points in the universe were once the same, that’s another reason that we can
say that every point in the universe can be considered the center.
So, this dispels the idea of the firecracker Big Bang.
The Big Bang is just the expansion of space, not the movement of matter through space.
Now let’s address the idea that space is flat.
Certainly, the data is consistent with that conjecture, but it’s not proven.
Maybe space is curved, but just super big- just like parts of the Earth can look flat,
when it is (clears throat) very obviously a giant sphere.
How does that work in this expanding space picture?
Well, maybe it’s true.
Maybe space didn’t start out as flat, but rather is some contorted and complicated shape.
If that’s so, we need to reconcile the flat space we see with the possible curved truth.
And scientists do that by invoking an addition to the traditional Big Bang theory.
This addition is called inflation.
In inflation theory, just a tiny fraction of a second after the Big Bang, the universe
expanded crazily fast.
From about ten to the minus 36 seconds until maybe ten to the minus 32 or 33 seconds, the
universe expanded at speeds faster than light.
According to some calculations, during this time, the universe expanded by a whopping
ten to the 26 times, with our visible universe going from a size smaller than a proton to
about the size of a grapefruit.
Other calculations give different answers.
The precise numbers aren’t crucial.
But the big idea is that this superluminal expansion can take any weird shape for the
infant universe and make it look flat, which is what we see today.
And, after the inflation stopped, the universe continued to expand in the way we see today.
This expansion after inflation is what most scientists would call the big Bang.
Okay, so what about the singularity- the idea that all of the matter of the visible universe
was collapsed into a single point with infinite density?
Well it’s true that the visible universe was collapsed into a tiny volume, but the
volume probably wasn’t zero size.
Remember that the zero-size thing was something that came from Einstein’s theory of general
relativity and we know that his theory doesn’t work at tiny size scales.
For that, we need a new and improved theory, that we call quantum gravity.
Since we don’t have a theory of quantum gravity, we don’t know the details, but
what we believe is, because of quantum mechanics, the size of the visible universe was just
ridiculously small, just not mathematically zero.
Finally, what happened before the Big Bang, when the universe was perhaps still infinite
in size, but with the matter of the visible universe crushed into a tiny volume?
The simple fact is that we don’t know.
There are lots of ideas, including our universe budding off from another universe like a blob
in a lava lamp, or multiple universes floating around in a big space called a multiverse,
crashing into one another, or- and this is the least speculative- that there is just
one universe- the one we live in- and it existed essentially forever in the crushed state,
waiting to expand, like a bowstring just before it is released.
And, in this scenario, it’s familiar quantum mechanics that released the string.
So those are the key points of the Big Bang.
So, let’s pull it all together by starting at the beginning and running the clock forward.
We’ll start at time equals zero and ignore what came before it started.
Maybe I’ll make a video on the various ideas people have on that.
But not today.
To simplify the explanation, we’ll show just one dimension.
The matter and energy of the visible universe was crushed into an unimaginably tiny volume,
represented by this dot here on the number line.
The volume was crazy small, but it wasn’t zero size.
In fact, truth be known, we don’t know much about the conditions then.
While the conditions of the instance of creation are unknown, it could well have been some
sort of quantum foam, with particles winking in and out of existence.
Something caused the universe to begin expanding.
We don’t know what.
And the first thing that happened was inflation, which was an extremely rapid expansion of
space, where the visible universe grew from much smaller than a proton to maybe the size
of a grapefruit.
Remember that for our purposes, the exact numbers don’t matter.
Then, at a time of about ten to the minus 32 seconds or thereabouts, the energy that
drove inflation dissipated and turned off.
The expansion of the universe was then coasting, and this is the period that scientists call
the classic Big Bang and it’s still going on today.
From that point onward, we know a great deal about what happened.
The universe was hot.
Particle physics and then nuclear physics dominated the landscape.
The universe expanded and cooled leading to atoms, stars, galaxies, and, eventually, us.
The key message about the Big Bang is that it wasn’t an explosion.
It is simply the expansion and stretching of space.
And another important point is that no place in our universe is the location where the
universe began or, equivalently, every place in our universe could be considered the center.
No spot is special.
It’s also true that no reputable scientist will claim that we understand in detail what
happened at the exact moment when the universe began.
We just don’t.
But we’re looking at it and we know a great deal more than we did a century ago.
Imagine what we’ll know a century from now.
Hopefully my medical colleagues will come through with a breakthrough that will let
me still be around to see it.
Because- man- I sure want to know.
Don’t you?
In spite of the fact that we don’t know everything about how the universe began, I’m
constantly staggered by the fact that we know so much.
Hopefully this video gave you a better idea of what we know and some of the common misconceptions.
If you enjoyed the video, please be sure to like it and share it on social media.
And be sure to subscribe to the channel, including hitting the little bell icon so you get notified
the next time I make a video about the Big Bang, which I certainly will.
After all, the Big Bang is physics and, of course, physics is everything.