Do you or have you ever use thought experiments to some practical end?
One of my favorites is the “ladder paradox” in special relativity, although I originally learned is as a pole vaulter rather than a ladder:
A pole vaulter is running carrying a pole that is 12m long at rest, holding it parallel to the ground. He is running at relativistic speed, such that lengths dilate by 50% (this would be (√3/2)c). And he runs through a barn that is 10m long that has open doors in the front and back.
Imagine standing inside barn. The pole vaulter is running so fast that the length of the pole, in your frame of reference, has contracted to 6m. So while the pole is entirely inside the barn you press a button the briefly closes the doors, so that for just a moment the pole is entirely closed inside the barn.
The question is, what does the pole vaulter see? For him, the pole has not contracted; instead the barn has. He’s running with a 12m pole through what, in his frame of reference, is a 5m barn. What happens when the doors shut? How can both the doors shut?
I will admit that I have never used this thought experiment for any practical end.
For those who haven’t studied relativity, this thought experiment is great at showing the “Relativity of Simultaneity”.
The only way the doors can shut from the pole vaulter’s reference frame is if they close at different times. The exit door opens and shuts first, before the tip of the pole has gone beyond it (otherwise it would hit the door, obviously), and then later, only once the back end of the pole has cleared the entrance door, does it close.
https://en.m.wikipedia.org/wiki/Olbers's_paradox
Olbers’s paradox, also known as the dark night paradox or Olbers and Cheseaux’s paradox, is an argument in astrophysics and physical cosmology that says the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe.
The night sky being dark has some profound cosmological implications.
With the Hubble Deep Field, they pointed the telescope at a seemingly empty patch of night sky - and it turned out to be filled with distant galaxies. Also, light traveling from far enough away gets redshifted into the infrared range, which means it can no longer be seen by the human eye.
The answer is very simple. Our universe is very likely not static. We already know that it is expanding (as of today). The further you look in space, the faster that space is moving from us. This causes more and more redshift of light the further you look away (the wavelength of light becomes longer and longer).
Beyond a certain point, space moves faster than the speed of light. Thus, we get no light.
Why? Doesnt that just mean absence of light or somethijt?
Yes. But why is there an absence of light?
If there are infinite stars, then every direction you look would encounter a star. (Things stay the same brightness per subtended angle as they get far away. Space dust doesn’t matter, as it would thermalize and radiate.)
So, the universe can’t have infinite luminous matter, be static and ageless, because if it were then the night sky would look like the surface of a sun.
This may all seem obvious, but it’s neat that you can figure that out with the naked eye.
Can’t we see stars that do not show up in the night sky? Like that spot looks dark to the naked eye, with a hobby telescope it looks dark, but with a space probe telescope you can see a distant star is there?
You discounted space dust. But there has to be a near infinite amount of asteroids out there. If I wanted to see 1m lightyears into a specific spot, like the odds of not hitting an astroid would be pretty hard.
Like if you had a Lite Brite globe with each Lite Brite peg representing a sun. In the middle of the globe it would be completely lit up. However, if you started throwing around astroids around inside the globe, you’d start blocking pegs. Suns, pegs, are still behind the astroid. It’s just blocking the light. A tiny astroid could cast a huge shadow. Even tiny space dust.
You discounted space dust.
No I didn’t — it would thermalize and radiate.
This is not my paradox, and it’s not really a paradox at all, as the big bang model explains it nicely. There are many nice articles on the topic of you’d like to read more about it.
I’m not trying to disprove you or anything, I know it’s not your paradox. Apologies that it came off that way.
But like a tiny flake of space dust is enough to eclipse a sun for us a near infinite distance away. Matter is not going to let light through it. Even if some space dust thermalizes and radiates. The chances something like an asteroid, planet, moon, etc. Is high. Space seems mostly void, but an infinite amount of mostly void is still a lot of stuff.
I’ll check then out!
I was influenced greatly by Robert Axelrod’s short essay about the Prisoner’s Dilemma titled “The Prisoner’s Dilemma Computer Tournaments and the Evolution of Cooperation” (link PDF warning)
tl;dr The essay explores an iterative game of Prisoner’s Dilemma, and demonstrates how cooperation can emerge from a group of self interested participants. It has implications for the statistical emergence of morality, and even remarks on politics.
My favorite is probably Russell’s teapot, but Daniel Dennett had some good ones in the intuition pump book too.
https://en.wikipedia.org/wiki/Russell’s_teapot
It demonstrates the burden of proof is on the person making claims, including if the claim is unfalsifiable.
