# Demo Relativity For A C-Note

If you are a science fiction fan, you probably hate the theory of relativity. After all, how can the Enterprise get to a new star system every week if you can’t go faster than the speed of light? [Nick Lucid] wants to set you straight: it is real, and you can prove it to yourself for under \$100.

The idea uses muons created in our atmosphere by cosmic rays colliding with gasses in the atmosphere. So how do you detect muons yourself? [Nick] shows you how to do it with a fish tank, dry ice, and rubbing alcohol. If that sounds like a cloud chamber, you aren’t wrong.

A cloud chamber is undeniably cool, but how does it prove relativity? You’ll see several kinds of particles interacting with your cloud chamber, but you can tell which ones are muons by the size and motion of the streaks. The muons don’t last very long. So you’d expect very few muons to make it to the surface of the Earth. But they not only reach the surface but go deep under it, as well.

So how do you explain it? Relatively. The muon experiences its average 2.2 microseconds lifetime in what appears to us to be over 150 microseconds, even if it is moving relatively slowly for a muon. Some muons are faster or live longer, so we see a lot of them hit the Earth every minute of every day. This is due to time dilation and also explains length contraction because the muon moves at a certain speed, yet it appears to go further to us than to the muon.

Coincidentally, we recently discussed this same effect relative to using muons for underground navigation. If you want an easier way to count muons with a computer, you can build a detector for about the same price as the cloud chamber.

## 16 thoughts on “Demo Relativity For A C-Note”

1. Mathias says:

This “prove” has like 20 assumptions you have to accept as true. If you can prove, that a muon only lives 2.2 us, how they are created, what the length of the streaks mean, …. then this maybe proves relativity to you.

It is still a cool project. But this barely proves anything to most people. (Or it proves 100% of whatever you tell them it should prove… “and that kids is why dinosaurs are extinct”)

1. mathman says:

This.

2. SB5K says:

Muons have been characterized years ago, and their lifetime measured in accelerator labs at fairly slow speeds. Thus, we know if they last longer when moving fast, it must be due to relativity.

1. Mathias says:

As a scientific experiment, this is true. But for a “prove relativity at home” experiment, IMO this is useless.

2. Alan says:

So, before I build this, I just need to prove muon lifespan – with a particle accelerator?

3. Echo_Hotel says:

Standard disingenuous garbage. Everything is based on thousands of assumptions. The unobserved universe existing is an assumption. A person standing next to you cannot prove they aren’t a vivid hallucination. It’s stupid to try and say “No this needs to go to some arbitrary level of principle to be proof” as a dismissal.

1. Echo_Hotel says:

Or perhaps slightly more kindly put, You are complaining that their pie isn’t made from scratch because they didn’t create the universe.

2. craig says:

Under \$100? More like under \$10.
If you don’t have a fish tank laying around no one is buying one just for this I hope. Plus pretty much any container should work- we did cloud chamber in a mason jar IIRC ages ago. And dry ice is free when they ship food sometimes. My parents sent me food for Christmas one year and it came packed in dry ice. or else, at least here in US, widely and cheaply available at welding supply or even grocery store. And IPA is like a buck.

1. paulvdh says:

With a bit of social engineering you can get all the parts for free.
Add some extortion, and you can have some left over money at the end.
But how is this all even relevant to the rest of the story?

1. craig says:

It’s the title of the article.

3. MarB says:

I find the video above completely unmotivated. And if you take a closer look at the general theory of relativity and especially at the work of Hawking and Penrose, there’s a lot of “science fiction”.

1. Comedicles says:

What does this have to do with GR?

1. MarB says:

General relativity generalizes special relativity. That’s way it’s called general relativity.

4. aki009 says:

To put a light spin (!) on this, I am married and I don’t need any additional proof for relativity. Every time I talk to my wife I am reminded yet again that everything is relative.

5. animal717 says:

Hey I like the science asylum. Nick was a teacher, wrote a book Advanced Theoretical Physics: A Historical Perspective. He also is I believe and correct me if I’m wrong autistic. Remember YouTube videos are a balance between captivating an audience , sparking further study on ones own, and the video becoming a full dissertation.

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