The Big Bang is one of the most well known and most misunderstood of all modern science theories.
Indeed, when I talk to people or read viewer’s questions, it’s very clear that confusion abounds.
Since confusion impedes progress, we need to clear up that confusion to make further progress.
That sounds like an excellent topic for this week’s episode of Subatomic Stories.
The Big Bang is the current scientific understanding of the origins of the cosmos.
The visible universe, which is as far as we can currently see,
was once much smaller and hotter. About fourteen billion years ago,
something happened – we still don’t know what in detail – and the universe began expanding rapidly.
We know all of this to be true for several reasons. First, we see the expansion of the
universe because distant galaxies are moving away from us and more distant galaxies are
moving away faster. Second, we can look at the hydrogen and helium in the universe and the ratio
is exactly what the Big Bang predicts. And third, we see the remnants of the primordial fireball
in a bath of radio waves hitting the Earth called the Cosmic Microwave Background or CMB.
I don’t want to talk about any of that. Defending those statements is the subject of another video.
In this video, I want to talk about the ways in
which many people misunderstand the theory of the Big Bang. And,
in the interests of full disclosure, I had some of these same misconceptions when I was young.
So, the first misconception is the hardest to get your head around.
Most people think of the Big Bang as like a firecracker or a grenade that went off.
They think of empty space without any matter in it,
and with all of the matter and energy of the universe concentrated down into a single point.
Then the universe exploded and spread matter and energy through space. That didn’t happen.
A spinoff of that idea is that there is an edge of the universe. In this misconception,
if you look far enough away, there is a spot in the universe where there is nothing – simply
because the shock wave of the Big Bang hasn’t gotten there yet. That isn’t true either.
Another common incorrect idea is that the Earth is at the center of the universe. This thought
arises because, no matter what direction we look in space, we see objects moving away from us. That
could mean that the Earth is at the center of the universe, but the universe is huge and it’s just
incredibly unlikely that we happen to be at the center of it. There has to be another explanation.
By the way, these are all kind of sensible ideas, especially given some of the animations you see
on the internet. All of them look very much like the Big Bang was some sort of familiar explosion.
I’ve even used such videos, mostly because they are visually interesting.
But they are very misleading.
So, let’s start with what we know. We certainly are at the center of the visible universe. That’s
not surprising. The universe is big – at least 500 times wider and with a volume 125 million
times bigger than we can see – maybe even bigger – and we’re sitting in it in some random place.
There’s a sphere surrounding our location that marks the farthest distance we can see.
That’s the visible universe. But it’s not the entire universe. Not by a long shot.
For the purposes of discussion, we can assume that the universe is infinite in size.
If it’s not, that doesn’t affect what I’m talking about here. All that matters is
that the size of the entire universe is much larger than the size of the visible universe.
Okay… so, to get a better idea what the Big Bang really was all about, let’s start with
this picture here. The grid is a two-dimensional representation of the universe. The dark circle
represents a sphere centered on the Earth. This is the visible universe from our vantage point. The
grayed-out bit are sections of the universe so far away that light hasn’t had time to get here yet.
You’ll notice that the universe and the grid is much bigger than the visible universe.
OK, so let’s see what happens if time progresses in the way we experience it.
The visible universe, indeed, the entire universe, expands.
We can see that because both the circle expands, as does the grid. That’s what’s going on today.
Now let’s reverse time and see what happens. As we go back in time,
the visible universe gets smaller and the size of the grid gets smaller too.
This represents a time when the visible universe was half as far across as it is today.
Let’s run the clock back farther. When the universe was smaller, it was hotter.
This graphic represents that by turning the color orange, then yellow,
and finally white. You’ll notice that the grid and the visible universe is getting smaller.
If we run the time all the way back to time equals zero, you see that the visible universe
is very small. In the simple version of the Big Bang, the size is literally zero,
but we know that’s not completely accurate. The visible universe was merely super small.
But you’ll notice that the grid still covers the screen. That’s because even though distances in
the universe were closer together back then, it was still infinite in extent. Then the universe
began, and the expansion started. You see that no place in the universe was special in any way.
Space just began to expand, and it continues to expand today.
So that’s what the Big Bang theory really says. The universe was smaller – but that
just means that the distance between points was smaller.
The universe itself could well have been infinite in size, even when it began.
Then something triggered the expansion – and we don’t know what – and the universe was hot
and distances between points grew in size and the cosmos cooled into the universe we know and love.
Now my example had the universe infinite in size, but what I said is also true of a
finite universe that is bigger than the visible universe. If the 2D version of
the visible universe were painted on the surface of a globe and the globe shrank,
that’s basically the same thing that I’ve described.
That’s a lot to think about, so now I’ll give you some time to mull it over.
I’ll do a follow-on video that talks more about the stages of the universe as the expansion began.
But it will be a lot more accurate if you have this mental image in mind for that video.
Okay…let’s see what questions you have for me this week.
Question time. This week, the questions were quirkier than normal, which somehow seems
appropriate – quirks for quarks, so to speak. Ojama Black notes that a Nog is smaller than
a Quark. Hi Ojama. I am completely embarrassed that I never thought of that joke. And it’s about
my favorite TV franchise to boot. I henceforth pledge that if, in my career, I ever discover
and name a particle smaller than a quark, that I shall call it a Nog. Thanks for that great idea.
David Zaring asks me if the questions in these provides some insight or direction to investigate.
Hi David. No, not really. The thing is, pushing forward knowledge is hard work. You have to know
about all of the data that has gone before, and that takes years to master. It’s extremely
rare – and I mean >>EXTRMELY<< - that a casual question points in a direction that is both
original and productive. On the other hand, there have been plenty of witty and creative jokes.
Justpaulo asks about the hot and cold spots in the cosmic microwave background and what that really
means. Hi Paulo…that’s a great question that shows you’ve thought about this quite a bit.
So here’s the deal. There are a class of objects called black bodies, which absorb
all energy that hits them. Black bodies heat up and then emit electromagnetic
radiation over a range of frequencies. The range depends on the temperature.
For instance, for very hot things – hot enough to glow in visible light – the cooler things
glow red, then, as they get hotter, orange, yellow, blue, blue-white, and finally into the
ultra-violet. But, even though we see a specific color, they emit over an entire spectrum. For
instance this is the distribution of wavelengths emitted by black bodies of different temperatures.
Notice how the curves change for different temperatures. Hotter means shorter wavelengths.
For the CMB, it’s similar. But the CMB is much cooler, so what is emitted is a spectrum of
microwaves, which have much longer wavelengths than visible light. So, for the CMB, astronomers
look at the spectrum at different spots in the sky and figure out what temperature each spectrum
corresponds to. For the CMB, the differences in temperature are tiny, meaning that, to the eye,
the spectra would look the same. But they are slightly different. Good question.
Martin Heemance looks at the fact that the charge of the down quark is exactly one
third of that of the electron and states that he think that it’s telling us something important.
Hi Martin. Yep. Me too. I just wish I was smart enough to figure out what.
I always wanted to shake the hand of the King of Sweden.
Tobias Tomann basically asks if particles like protons could exist, but with other quarks.
Hi Tobias. They sure can. Protons are particles of a class called baryons, which include three
quarks, specifically two ups and one down. Charm and top quarks have the same charge as
up quarks and strange and bottom quarks have the same charge as down quarks.
So, can we make baryons with combinations other than two up quarks and one down?
So yeah, we can. There are baryons with one up, one down, and one strange quark, called Lambdas.
Then there’s the one with an up, a down, and a bottom, called the Lambda sub b. In fact you,
can take any combination of three quarks from the six known quarks and make a baryon. For
instance a bottom, bottom, bottom is possible. However, there is one thing I haven’t mentioned.
It takes about ten to the minus 23 seconds for a baryon to form.
The lifetime to top quarks is shorter – about 5 times ten to the minus 25 seconds. So top quarks
decay before baryons can form. So you can’t make baryons with top quarks. Thus really
only the other five can be found in baryons. That’s a total of 125 different types of baryons.
And, if you allow for different combinations of spin and motion inside the baryons, there
are many more combinations and many of them have been observed. But none of them have top quarks.
It’s all very amazing. Five quasi-stable quarks can explain hundreds of different particles.
And, finally, Dwight Schrute notes that the video length of 13:37 points to some very elite physics.
I admit that I had to Google that, but he’s absolutely right.
Everyone at Fermilab is 1337. And that sounds like a great place to wrap things up. If you enjoyed
the video, please like, subscribe, and share. And look forward to upcoming videos because,
even at home, 1337 physics is everything.