Planck Units

[Seasanctuary]

I was pondering last night how things like length and time could be expressed to an alien race if the Earth weren't handy and no good measuring devices were brought along as models.

Can't talk about the speed of light because both seconds and years are based on the Earth and Sun. Can't talk about Astronomical Units for the same reason. Parsecs are based on AUs.

Tonight I found an interesting article on Planck Units which are pretty much what I was looking for. Just thought I'd pass it along. Unfortunately it sounds like current measurement uncertainty for some of the values make it hard to be as exact as we'd like. Plus, a lot of the primary and derived units are really big or really small compared to nicely human-sized units.

We could solve that with a common 'dummy' base prefix that corresponds to a different order of magnitude for each primary unit. People wouldn't have to know these values for day to day use. I bet humans will adopt a system like this once we move away from the solar system.

Then again, we use time zones now. Why should we make any more sense later on?

[wildrow12]

You know there is something that always troubled me. Suppose for a moment that there is an alien race that is, for all intensive purposes, immortal. Their bodies do not age, wither, or die.

Would such a race measure time?

What do you think?

[Cyrus Johnson]

You know there is something that always troubled me. Suppose for a moment that there is an alien race that is, for all intensive purposes, immortal. Their bodies do not age, wither, or die.

Would such a race measure time?

What do you think?

For all intensive purposes? You're lucky the grammar police ain't here.

They'd still need to know when to go for supper at the mother-in-law's house, so they'd still need a concept of time. Even if they were unchanging, everything else in the universe isn't. I'd suppose they'd be like us and use a system based on some properties familiar to them, like their year or their day. Presumably their planet would still be orbitting some star, and presumably it would rotate on its axis. The speed of light would still be the speed of light, but instead of being 300,000 kilometers/second it'd be more like 2,356,908 glorgs/r't'plat!. Except they wouldn't use Roman characters probably.

[wildrow12]

For all intensive purposes? You're lucky the grammar police ain't here.

Oh boy....

[Sparko]

sea, if you could talk to an alien race at all, then you could describe units of measurement to them and discuss things like the speed of light and so on. Time is very easy. Tap something, wait, tap again. That is an interval of time.

Length? hold your hands apart, mark a line in the dirt, etc.

[NeilUnreal]

Somebody, it may have been Martin Gardner, wrote an essay which asked and answered a similar question:

How could we establish an understanding with an alien culture, via only radio contact, of the difference between "left" and "right."

-Neil

[sc_q_jayce]

Mathematics, transformations/translations, and vectors can help describe left and right without any need for semantics.

[sylas]

Mathematics, transformations/translations, and vectors can help describe left and right without any need for semantics.

That won't be enough. I don't think you will be able to do it without reference to some real physical phenomenon. I'm presuming, therefore, that we are communicating with aliens who experience the same physical laws as we do.

I'd distinguish right and left as follows.

First, establish the distinction between matter and anti-matter, and identify which is which. We can do this, because they are not not exactly opposites of each other; there is a very small (and physically intriguing) distinction (CP antisymmetry) which should be sufficient to identify what is matter and what is anti-matter.

Having done this, you can distinguish positive and negative charge, based on charges of an electron and proton.

Having done this, you can use establish the "right hand rule", for forces on moving charges in an electric field.

Finis.

Cheers -- Sylas

[Sparko]

and how do you do that sylas?

[sc_q_jayce]

Math is easier. Much, much easier than your method.

[Sparko]

Math is easier. Much, much easier than your method.

Unless the aliens have the same type of public education system that we have, then there is no hope.

[sc_q_jayce]

Well, then have the Chinese do it, then.

[sylas]

and how do you do that sylas?

I don't get what you are asking here. I'm presuming that we have a capacity to communicate with aliens who experience the same laws of physics as we do, and that communication allows us to identify object from their properties.

The issue is to find a way to distinguish right from left using some fundamental objects which are experienced by both us and the hypothetical aliens; and the heart of the question concerns physical symmetries.

NeilUnreal spoke of an essay which raised this thought experiment. I don't know what essay he means; but I'll take a wild stab in the dark and propose that presentation of the problem, as a problem, presumes CP symmetry of matter and anti-matter. But given an anti-symmetry (which seems to be the case physically) there is a basis for working up to a distinction of right and left.. My previous post gives the basics of the method, though I'll try to fill in gaps for you if you can be more clear as to where my previous post should be expanded. What's the problem?

Cheers -- Sylas

PS. Maths alone can't do it, sc_q_jayce. Really. Try and given a brief outline of the method just using maths, as I have done with reference to physical laws.

---

Postscript. After writing the above, I went looking for the essay, and found it almost immediately. It is "Left or Right" (1951) by Martin Gardner.

Just as I thought, the story presumed that the laws of physics have a symmetry of left and right, which would make the problem intractable; as our universe would be equivalent to its mirror image. However, five years after being published, CP violation was discovered, and this means that left and right are not actually perfectly symmetrical. The basis of the distinction between left and right is as I gave in my original post above, on CP violation.

See The Fall of Parity, at NIST.

[Sparko]

I don't get what you are asking here. I'm presuming that we have a capacity to communicate with aliens who experience the same laws of physics as we do, and that communication allows us to identify object from their properties.

I thought the question was how do we communicate with the aliens. If we can already communicate with them then resorting to your idea to convey left and right is not needed.

The issue is to find a way to distinguish right from left using some fundamental objects which are experienced by both us and the hypothetical aliens; and the heart of the question concerns physical symmetries.



NeilUnreal spoke of an essay which raised this thought experiment. I don't know what essay he means; but I'll take a wild stab in the dark and propose that presentation of the problem, as a problem, presumes CP symmetry of matter and anti-matter. But given an anti-symmetry (which seems to be the case physically) there is a basis for working up to a distinction of right and left.. My previous post gives the basics of the method, though I'll try to fill in gaps for you if you can be more clear as to where my previous post should be expanded. What's the problem?

If we are face to face, we could show left and right without resorting to all those complicated ideas. If we are not face to face and can't communicate (no common language or symbols), then how would we show them matter/antimatter, antisymmetry, etc?

[sylas]

I thought the question was how do we communicate with the aliens. If we can already communicate with them then resorting to your idea to convey left and right is not needed.




If we are face to face, we could show left and right without resorting to all those complicated ideas. If we are not face to face and can't communicate (no common language or symbols), then how would we show them matter/antimatter, antisymmetry, etc?

OK. We are talking of different problems. The essay Neil mentioned is about whether or not left and right have different properties; and the thought experiment for exploring this was whether you could describe the difference in terms that refer only to underlying physical fundamentals.

The original questions, like this thread, is really about fundamental physics.

I quite agree that establishing meaningful communication at all with aliens in some other galaxy would present intractable problems. There are some interesting fictional explorations of this, in which communication is gradually established, working from notions of number and laws of physics. Gardner's essay, and my answer, deals with a thought experiment in which these issues are resolved, but asks whether there's some difference in the properties of left and right that would give leverage for communicating a distinction just over the radio, with reference to shared physics rather than shared specific objects.

Cheers -- Sylas