Whoa. That was a long one.
That was a muon!
You've seen it? I seen it with my own eyeballs!
That streak of light you just saw is a muon, an elementary particle.
It came from space.
And the only reason we can see it is because of Einstein's relativity.
[Intro Music]
Hey, crazies.
We have over a century of evidence to back up Einstein's relativity.
But the traditional explanations aren't really relatable.
Nobody really experiences relativity in their daily life, so there's no basis for comparison.
To see effects like time dilation or length contraction, really fast speeds are required.
Like speeds close to that of light.
Fast fast!
Einstein often used trains in his explanation because they were the fastest form of travel at the time.
I use rockets in my explanations for the same reason.
Unfortunately, trains have gone out of fashion
and rockets are a pretty exclusive thing.
There just isn't anything to connect with, so these explanations come across like ...
“Trust me, bro.”
So how do we fix this problem? Muons.
These muons actually come from space.
(Giggle)
Muons from space!
Technically, they don't actually come from space space.
There are these things called cosmic rays,
which come in and collide with molecules in the atmosphere, and that collision creates muons.
Okay. So they're not from space. They're from the atmosphere.
Right. Okay.
Since most atoms in the universe are hydrogen, it's almost always just a proton.
Okay. So a cosmic ray is a proton moving at high speed that comes from the ... sun?
A cosmic ray is really high energy.
It came from some like distant supernova or something, and it finally got here. Okay. Okay.
It needs more energy than what the sun is putting out. Yes. Okay.
The sun does send out protons, but they're not really high energy enough for this. Okay.
There is kind of this collision cascade that generates particles
which then decay into other particles, which then decay into other particles.
Cascades are very common in nature.
Yes. We have plenty of cascades in biology and whatnot. Okay, so you're familiar with the idea.
Familiar with the cascade.
The big particle that gets generated in this decay is a muon. Okay.
Which at first might seem less relatable, but you can actually see them yourself.
Like with an experiment at home!
All you need is about $100 worth of items you can pick up at your local store.
A fish tank, a piece of felt,
some glue, a couple of cooking trays,
some isopropyl alcohol (the higher the concentration, the better, I use 99%),
a pair of thick protective gloves
(these are leather),
about 5 pounds or 2 kilograms of dry ice,
a decent flashlight, and a hammer.
Some of these items are pretty standard household items.
So if you've got them around, you can save some money.
Depending on where you live, the dry ice might be difficult to find.
But I live in rural America where I can just pick it up at my local supermarket.
Shout out to Meijer. Hashtag not a sponsor. Right.
Hashtag do you want to be sponsor? Hashtag please sponsor me.
Assembly is pretty straightforward.
First glue the felt to the bottom of the tank.
After the glue dries, pour some of the alcohol onto the felt.
Not too much. You don't want it to be dripping wet. Just wet.
But honestly it will work without the felt, if you want to skip it, it just won't work as well.
Next, while wearing the gloves, break the ice into pieces and evenly spread it across one of the trays.
Dry ice exposure to the skin can be dangerous. So always wear the gloves
After you get the ice situated, put the second tray on top.
[Dry ice against metal sounds like music]
Okay.
Cover the top tray in a thin layer of alcohol and place the fish tank upside down on top.
Now we wait like five or ten minutes.
Not only is the dry ice sublimating into CO2 gas,
but the cold is also turning the alcohol into a vapor.
You don't want to be inhaling either of them.
Make sure you do this in a well-ventilated area.
I cracked the garage door.
I honestly couldn't get this experiment to work very well the first time, for some reason.
But I tried it again the next day and got better results.
Once we've waited long enough, turn off the overhead lights and turn on a decent flashlight.
You should see the alcohol vapor wisping about.
When you finally get it working, you'll see streaks of light zipping through the vapor.
Those are particles.
[Montage Music]
And you can tell them apart by the kinds of streaks they make.
For example, helium nuclei, also known as alpha particles or alpha radiation, are really massive.
So we expect them to just plow through the vapor in a straight line.
They also take up a lot of space as far as particles go,
so their streaks are pretty beefy.
Electrons are a lot less massive, so their trajectory is affected more by the collisions.
They also take up a lot less space than the helium,
so they make shorter, skinnier, jagged streaks.
Muons are like a combination of the two.
They're more massive, like helium nuclei, so their streak should be longer and straighter,
but they take up less space like electrons, so their streaks should be skinny instead of beefy.
Whoa. That was a long one.
That was a muon!
You've seen it? I seen it with my own eyeballs!
I saw the particles. It was very exciting.
Before you go on any further ...
We just want to give a quick shout out to YouTube member ... No, no. YouTube Viewer Number 2014.
That's it. YouTube Viewer Number 2014.
They are a new channel member
and they are pledging at the Einsteinian level so they get a shout out.
Thanks so much for your support.
And if anyone else would like to help support us so that we can continue making these videos,
please consider signing up for Patreon or the YouTube membership.
Now, the thing about muons is they're unstable also. Okay.
So they're also not going to be around for very long. Right.
If you take all of this and average how long you expect a muon to last, it’s somewhere around 2.2 microseconds.
That is quite short.
We know exactly how many of these muons we would expect to finally make it down here. Okay.
Which is almost none. Right.
The muons got their energy from that original cosmic ray, and so they're going to be moving fast as well. Okay.
But if they're only around for a few microseconds,
there's only so far you can go. Right.
At 2.2 microseconds, we're looking at about 660 meters or 0.4 miles.
Look at them go! Right.
And how far up is the outer atmosphere? 60 miles.
It's a surprisingly long distance, but definitely not the thickness of the atmosphere.
It's fallen very short.
However, more of them reach the surface of the Earth than we expect.
Like a lot more. A lot more.
Like an order of magnitude? At least. Okay.
We need to be able to explain that. How can something that only lasts on average
2.2 microseconds make it to the Earth's surface? Right.
Right. Doesn’t make any sense.
And as it turns out, Einstein's relativity helps. Ooo!
One of the most well-known aspects of Einstein's relativity is something we call time dilation.
If some object like a space station or a train or a particle is moving relative to us,
then its time is passing slower than it is for us.
That difference becomes more dramatic the closer its speed is to the speed of light.
Let's say this bad boy is traveling at 99.99% the speed of light.
According to relativity, the muon’s clock is slower than ours by a factor of about 70.
If the muon lasts for the average 2.2 microseconds,
that would look like 0.15 milliseconds to us.
That's enough for the muon to travel over 28 miles instead of the 0.4 miles I mentioned earlier.
Which, granted, is still only half the atmosphere.
But that 2.2 microseconds is only an average. Some of them last longer.
Maybe twice as long.
Plus, some of them are going faster than 99.99% the speed of light.
That means some of these muons will reach the ground from our point of view.
In fact, it's exactly the amount we'd expect after factoring in Einstein’s time dilation.
But hold up. What does that look like from the muon’s perspective?
There's a pretty fundamental thing that we consider in relativity,
and that is that while different observers, different particles or whatever,
can make different observations of things like time,
everyone must agree on which events occur. Right, yes.
So if, from our perspective, the muons reach the ground,
then from the muons’ perspective, they must also reach the ground.
Which is interesting because ... so it must be a shorter distance for them. Yes. Yeah.
And so even though for them, they're only lasting on average 2.2 microseconds,
the distance must be shorter. Right.
And it is. We have this thing called length contraction as well. Right.
The entire Earth, along with its atmosphere, has length contracted, has compressed
to a distance that the muon can traverse in the time that it exists.
That's wild.
That's like, look at this little baby Earth here. Right.
To have a way to actually, like, see these muons in action. Right.
And you actually mean to see them, see them with your eyeballs. Right.
Not just like, you know, the figurative use of the word. Right.
We created a cloud chamber that was about the size of a small average fish tank.
And in that little fish tank, within an hour, we got muons.
Yeah, we got a couple of them. Yeah.
If you actually try this, it's a lot like watching a meteor shower.
You think there's going to be all these, like, you know, streaks across the sky,
but really, it's like one every once in a while.
But they're exciting when you get one.
Yes! You’re like “Ah! There's one!” Very exciting.
And this is a real life demonstration that we can actually see in our garage, you know? Right.
With just stuff that we picked up locally. Right.
Less than $100. Right.
And we got to see these muons that are living representations of Einstein's relativity.
Yeah. Which is wild. It's wild. It's so cool. It's very cool.
Of course, this isn't a scientifically rigorous experiment or anything.
In a real experiment, we would need to watch a lot longer
and record the proportions of each particle and so on.
There's a process.
This is more of a demonstration.
You can actually see the particles yourself, but you're not collecting any data.
The point is, a higher proportion of muons reach the Earth's surface than our instincts would expect.
Because of Einstein's relativity.
From our point of view, the muons last longer than they should because their clocks are slower.
From the muon’s perspective,
the distance it has to travel is shorter because the length contracts.
In either case, the result is the same.
The muon reaches the ground. Relativity is real.
And until next time, remember: It's okay to be a little crazy.
Quite a few of you commented that us humans are making artificial rings with our space junk.
There is a lot of junk up there, but not nearly enough to make a planetary ring ... yet.
Anyway, thanks for watching.!