wackhead_uk
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I thought of that, but...how do you tst which is a magnet if they are both now magnets, as they would still be attracted to each other...

eytanz
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A simpler solution - Touch A to the center of B. If A is attracted to B, A is the magnet. If not, B is the magnet.

Note - this solution assumes that the poles of the magnet coincide with its ends. If it is magnetized differently, then it won't work. Neither will Hix's solution.

[Edited by eytanz at Local Time:03-29-2005 at 02:09 PM]

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Garlonuss
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Yes, the solution assumes that the rod is polarized along the length of the rod and I should probably have mentioned that, but that is the way most bar magnets are anyway.

At the polar center of the magnet, there is practically no magnetic force so if you touch the rods in the way that eytanz says, you can tell which one is the magnet.

Your turn eytanz.

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Blondbeard
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I kind of like this thread. Since it has certanly gone moore than one day since eytanz answerd the last question I´ll try to blow life to the thread with a question of my own.

I am sure that almost everyone has heard the word antimatter, but I suppose that everybody doesn´t know a lot about it. Like for example how exotic it really is.

So... my question is: How long would the avarage guy need to travel to encounter some antimatter?

zex20913
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My guess is "Just as long as an atypical guy". But that's because I'm pedantic.

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mrimer
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Just as long as an atypical guy would need to travel to find some matter.

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Blondbeard
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How curious! You are both right. You might call me pedantic, but I would prefer a length as an answer. (But I do like your answers )

And by the way: A little early for a clue, but I´ll give one nevertheless. This is not difficult!

Mattcrampy
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Well, antimatter explodes when it comes into contact with matter, so he'd just need to go until he exploded.

Or go into space. One of the two.

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wackhead_uk
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I'd say either to one of those places where they make antimatter, or back in time a few billion years, and due to time being all strange like it is, possibly a few billion/trillion years into the future, depending on how you think the universe will end.



[Edited by wackhead_uk at Local Time:05-27-2005 at 12:40 PM]

Blondbeard
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Well... Two hints.

What I am asking for is an exact length. And I don't expect you to know this. Given these two things there is only one logical answer.

And that answer might very well seem surprising to you.

[Edited by Blondbeard at Local Time:05-27-2005 at 02:01 PM]

Tablesaw
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Blondbeard wrote:
I kind of like this thread. Since it has certanly gone moore than one day since eytanz answerd the last question I´ll try to blow life to the thread with a question of my own.

I am sure that almost everyone has heard the word antimatter, but I suppose that everybody doesn´t know a lot about it. Like for example how exotic it really is.

So... my question is: How long would the avarage guy need to travel to encounter some antimatter?

I know a lot about the word antimatter. For example, it uses every letter of the word "raiment" at least once. It was coined in 1950. And an average guy like me wouldn't have to go any distance to encounter the word antimatter, since it's right here in front of me.

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zex20913
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The average guy would have to go to his aunt's home. There, he sees the matter forming his auntie, thus auntiematter.

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Blondbeard
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In fact mrimers statement is very correct. And there are places where they "make" antimatter. But you don´t have to go that far. In fact I feel kind of bad. I might have chosen a more conventional puzzle. But the guess that is the answer to this queistion is the most trivial of all guesses. And I think the answer is a little cool. So... anyone care for a guess? If I post here some time else I promise to go for a moore puzzlelike puzzle

silver
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This isn't a guess.

The answer is: approximately 0.000000m

matter and antimatter appear and virtually immediately annihilate around us all the time - inside us, in the air around us, even in vaccuum.

Mattcrampy was only partially correct about explosions. what happens is that they release all their energy - for very small particles, this isn't much energy. like, perhaps a photon's worth. the "explosion" isn't very impressive (or even noticeable).

this fact is related to black hole evaporation, in fact. When such a pair is created just above the event horizon, the antimatter goes in, the matter goes out(*), resulting in a net loss of mass for the black hole.

this fact is also the basis of all the little arrow pairings in Feynmann diagrams. (Photons don't actually travel the speed of light or in straight lines. they travel a bunch of paths, some faster, some slower. and along the way sometimes spontaneously split into pairs of particles/antiparticles which annihilate shortly thereafter. but you always end up observing them where they'd be if they travelled a straight line at c. weird, eh?)

That's all I know off the top of my head, I'd need to dig out and reread some books and SciAm articles to give more precise details.

When I first read QED by Feynmann and partially (who ever fully?) understood it, I became convinced that physicists are wrong about something. They talk about the law of conservation of matter/energy as if there were some number which the universe maintains. I think that there is, sort of. It's just not a positive number like they seem to believe. That number is 0: we are currently in the midst of a runaway episode of matter/antimatter pairings that split and then split and then split and then split... well, it's not likely, but it'd only have to happen once for us to be talking about it. But my theory only makes sense if space existed as infinite vaccuum before the Big Bang. which isn't a very good understanding of spatial expansion. so I'm probably wrong wrong wrong.

Anyway, I don't have a puzzle to follow up with. I just wanted to clear the air and dump what I know about exotic physics before people flailed around with too many more wrong guesses

Now I'm just waiting for newly-minted-Doctor OneI to show up and beat my head against a wall for all my mistatements and bad information I'm spreading . Obviously, I have a poor "real" understanding of physics, just a casual layman's high-level and no doubt terribly wrong understanding.

--

(*) no, I don't know why. I didn't understand everything Hawking wrote.


[Edited by silver at Local Time:05-27-2005 at 06:56 PM]

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Blondbeard
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Very good! Actually several positrons are produced in our own bodies every second in a radioactive decay from Kalium 40. A positron is an antielectron. Thus you do not have to travel very far to encounter antimatter (all of the physical effects you mentioned doesn´t seem to be entierly correct though ) Anyway I figured that if I asked for something that most people couldn´t really know zero or infinity would be the only logical guesses. And since antimatter do exist it could only be zero. I suppose the question was kind of ugly, and I´m sorry if that disturbed anybody. But I do think it´s pretty cool that antimatter actually is created within your own body. A fun fact to know.

Oh, and do anybody have a problem? As I said before I do think this forumgame is rather fun. And since silver doesn´t have one, please feel free to post your own problem.

trick
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I really don't know anything about any of this, but ...

Blondbeard wrote:
A positron is an antielectron.

... this seems wrong.

An electron is negatively charged matter. I thought a positron is positively charged matter (a "positive electron") ?

That leaves positively and negatively charged anti-matter, which is something else entirely.

Of course, as I said, I don't really know anything about this, and have probably made a fool of myself . Have I misunderstood things completely ?

- Gerry

[Edited by trick at Local Time:05-27-2005 at 09:50 PM]

silver
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if only we knew someone with a PhD in physics


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Blondbeard
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All antimatter has reversed charge compared to the matter it represents. There are also uncharged particles and corresponding antiparticles. The neutrinos. If you think about it this is just logical. After all matter and antimatter should be able to cancle each other out. That goes for the charge too. So, yes. You have misunderstood things. Well, no harm there...

trick
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Okay . So, (just to make sure), electrons have negative charge and positive mass, while positrons have positive charge and negative mass ?

- Gerry

Blondbeard
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Nah! Mass is usually produced in matter antimatter pairs (not entierly true, but it mostly holds for the elementary particles.)

That means that both matter and antimatter have positive masses. Actually it is perfectly possible to make a kind of "atom" consisting of a positron and an electron cirkling around their mutual center of mass. This is called positronium, but it colapses after a very minor fracture of a second and two highenergetic photons (the "particles" we percive as light) are released carrying the energy represented by the mass of the positronium. Positronium kind of resembles hydrogen.

So... an antiparticle has opposite charge and the same (positive) mass as the particle. After all they represents the same amount of energy. (E=mc^2)

I hope this makes things more clear

[Edited by Blondbeard at Local Time:05-27-2005 at 10:48 PM]

wackhead_uk
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Don't need a PhD, I ahve an A in physics for at least part of an A level and I'm supposed to understand it all. Supposed to.

trick
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Oh! I thought anti-matter was the name of matter with negative mass.

So, what do you call matter with negative mass/energy (ie: (-e)=(-m)c^2) ? Negative matter ?

- Gerry

wackhead_uk
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Energy and masss are scalar, and therefore can't have negative values. Unelss me is misunderstanding as well (Damn you Dr Bremner!).

Also, You could have been sitting still in the time machine whle you travelled back in time...

[Edited by wackhead_uk at Local Time:05-27-2005 at 11:01 PM]

Blondbeard
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Trick wrote:

Oh! I thought anti-matter was the name of matter with negative mass.

So, what do you call matter with negative mass/energy (ie: (-e)=(-m)c^2) ? Negative matter ?

- Gerry

Well, actually that would kind of represent negative energy (if there where such a thing) I am sure that you could have a metaphysical discussion on the topic, but in the known universe such a thing as negative masses do not exist.

Also wackhead_uk wrote:

Energy and masss are scalar, and therefore can't have negative values. Unelss me is misunderstanding as well (Damn you Dr Bremner!).

Hehe Why shouldn´t a scalar be able to have a negative value? Scalars is quantitys without direction (nonvectors). A physical scalar is temperature. When you messure temperature in Celsius, does that make it less of a scalar than if you messure the absolute temperature?

Well... it wasn´t my intention to start a physics discussion. I hope someone comes up with a good puzzle soon.

silver
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ooo, time for my degree in math here

Because "negative" is a direction on a one-dimensional surface (known more commonly as a "line"). Celsius temperatures are a vector quantity - the "amount" (scalar) and the "direction" (positive or negative) together make it a vector.


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Blondbeard
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silver wrote:

ooo, time for my degree in math here

Because "negative" is a direction on a one-dimensional surface (known more commonly as a "line"). Celsius temperatures are a vector quantity - the "amount" (scalar) and the "direction" (positive or negative) together make it a vector.

That makes sense . I guess one might be a little sloppy with that kind of language in physics. Usually when you talk about multiplying a vector with a scalar that means that the "scalar" could be a negative or positive number. Or perhaps my bad english leads me into some kind of misunderstanding here

silver
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scalar has two definitions:

scalar

adj : of or relating to a directionless magnitude; "scalar energy"
n : a variable quantity that cannot be resolved into components

the second one is used more in math and programming, and can include negative numbers no problem. the first is how wackhead meant it.

The reason Celsius is a vector while temperature is scalar(1) is that Celsius is temperature relative to a point which is not absolute zero (this is actually why we say "54 degrees Celsius" but just "54 Kelvins" the degree of difference in inherint in the Celsius scale). Similarly, you can have negative energy and mass all day, as long as you mean relative to a non-zero point, but no one uses it that way because we can conceive of 0 energy easier than we can conceive of absolute 0 temperature.


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Oneiromancer
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silver wrote:
if only we knew someone with a PhD in physics

And if he only still read the Forum Games board...

Edit: okay, I'll make a more substantial comment (or two). silver, you're one up on me for even having studied Quantum Electrodynamics...I never took a course in it, and never really needed it for my (very experimental) research. Anyway, as for matter and antimatter being conserved, that's actually something that, from what I understand, hasn't been proven yet. That is, high energy physicists and astrophysicists think that it probably should be, but matter is practically infinitely more present than antimatter. I think I remember being told that there were equal amounts of matter and antimatter near the beginning of the universe, but then at some point matter got an advantage, and just ran away with it. But it's not really my field of study, and I don't remember so well.

Now, as for other things...Kalium40 I assume is the Calcium-40 isotope. Mass can't be negative, just like absolute (Kelvin) temperature can't be negative. Well, I suppose there is a caveat: if anyone ever found a mass that repelled instead of attracted, I suppose the best explanation would be a negative mass. But that hasn't been found yet. It's probably hiding somewhere with the magnetic monopole.

And finally, I definitely always used the definition of scalar as something that doesn't have a spatial direction, like vectors. Something like temperature (in Kelvin) or mass that can't go negative I would probably describe as "absolute" instead. But as silver said, this may be a difference between mathematicians and physicists.

Game on,

[Edited by Oneiromancer at Local Time:05-28-2005 at 02:57 AM]

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zex20913
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I'm a fan of the theory that matter and antimatter actually repel each other, or are strongly attracted to their own type. Even though it goes against all other physics stuff.

That way, there's an anti-Earth somewhere in the universe. And an anti-everything else.

That would also shoo away the "matter won!" and give rise to "matter won here!".

This is purely out of my own head, in that I didn't read it anywhere, because there's probably absolutely zero empirical evidence, but I still think it's neat.

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Blondbeard
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Oneiromancer wrote:

Anyway, as for matter and antimatter being conserved, that's actually something that, from what I understand, hasn't been proven yet. That is, high energy physicists and astrophysicists think that it probably should be, but matter is practically infinitely more present than antimatter

Actually that´s not entierly true. Scientists do belive that there might have arisen a small abundanca (1:10^9) of matter over antimatter. (don´t ask me how )