# Someone explain antimatter to me, please

Ok, I just saw the movie “The Time Machine” and a certain unexplained event at the end of the movie (don’t worry, no spoilers) got me trying to give it a logical explanation, and then I realized my knowledge of antimatter is virtually non-existant (the movie really has nothing to do with antimatter, and I think I’m giving the movie more credit than is due by trying to explain it). So, could someone please explain to me the concept of antimatter (what it is, how to make it, what it does, etc.) in not-too-hard-to-understand terms? It doesn’t need to be dumbed down a great deal, but probably a bit. Thanks.

(It’s what fuels the Enterprise dope! :rolleyes: )

Dictionary.Com states that:

Great…but that begs the question, ‘What are antielectrons, antiprotons, and antineutrons?’

Sorry Kwyjibo but there is nothing hypothetical at all about antimatter. IIRC there is some sitting in a magnetic bottle at Fermi Lab outside of Chicago. Even if that is not the case antimatter has certainly been observed.

Antimatter is simply an exact match for a given particle but with an opposite charge. For an antielectron its counterpart in a positron. Antimater/matter collisions are also a near perfect source of energy. 1Kg of matter with 1Kg of antimatter would run your car for about 100,000 years.

The whole thing was speculated and thought up by physicist Paul Dirac in the 1920’s when he was attempting to solve a problem for particles moving at relativistic speeds. However, his solution showed two answers. The example I saw was x[sup]2[/sup]=4 has an answer of 2 and -2. In the same fashion Dirac’s equations suggested an antiworld out there.

As for the movie The Time Machine I’m not sure what they were getting at but in general many postulated ways for managing time travel involve the use of negative matter which is NOT the same as antimatter. Antimatter still has weight and responds to gravity like you’d expect regular matter to. Negative matter would be exactly opposite of ‘normal’ matter (gravity would repel it for instance). Unfortunately for would be time travelers negative matter is still just science fiction. (Also, if you broght normal matter and negative matter together you would not get an energy release as you do with antimatter…instead both would just wink out of existence).

Antimatter is composed of antiparticles, which are identical to the respective matter components with one exception - an oposite electrical charge. And antimatter is no longer just theoretical. It does exist, although not for very long periods of time, as our universe is mainly composed of matter, and when matter & antimatter come in contact they annihilate each other. Antimatter can be created in a particle accelerator. Check out [http://www.sciam.com/askexpert/physics/physics56/](this article) in Scientific American.

Hey, I didn’t say it! It was in the **dictionary **!!!

Several of you have defined antimatter as having the opposite electrical charge of “normal” matter. What about neutral particles such as the neutrino? What makes an anit-neutrino “anti”? Not opposite charge. Is it opposite spin?

You brought it in, you clean up after it!

Ah, yes but -2 is not a real number? Could you use that to prove that anti-mater then cant be real either? <Just a thought>

Aside from antimater, i would like to know how they somehow tied that into a time travel theory. I mean, they’re both matter and isnt is said, “Space can only modify space”.

Of course, to disprove that, gravity is always brought up

so we dont really know all that much about this subject, but what do you think is hint of a good time travel theory?

• Cap’n, The matter- anitmatter converters have been destroyed!

-We need that energy now, Scotty!

-But sir, she cant take much more!

-Well change the laws of Physics!

-Reverse polarity, Mr. Spock!

-All fixed! now time for a lame joke!

``=PK``

Aside from antimater, i would like to know how they somehow tied that into a time travel theory. I mean, they’re both matter and isnt is said, “Space can only modify space”.

Of course, to disprove that, gravity is always brought up

so we dont really know all that much about this subject, but what do you think is hint of a good time travel theory?
(Just dont bring in Hugh Everet)

• Cap’n, The matter- anitmatter converters have been destroyed!

-We need that energy now, Scotty!

-But sir, she cant take much more!

-Well change the laws of Physics!

-Reverse polarity, Mr. Spock!

-All fixed! now time for a lame joke!

``=PK``

What’s so unreal about negative numbers? Even dealing with normal (non-anti) matter, you can have positive and negative charges.

It’s a bit incomplete to say that antimatter is identical except for the opposite charge. In fact, everything except for mass is opposite (mass is the same). For most particles, mass and charge are the most interesting quantities, but an antineutrino, for instance, will have the opposite lepton number and chirality from a neutrino. There are also some particles which don’t have any such properties, such as the photon: Since the photon has a charge, lepton number, baryon number, etc., of zero, and no prefered chirality, an antiphoton is the same thing as a photon.

A minor nitpick, by the way:
Quoth Whack-a-Mole:

Perhaps surprisingly, negative matter would react to gravity in the same way as normal matter. Gravity would repel it, but the inertial mass is also reversed, so when you put a force on negative matter, its acceleration is in the opposite direction. Hence, negative matter would be pushed up, but still fall down. For other qualities of negative matter, we’re entirely ignorant. All we know is that it has negative mass, by definition. We don’t even know whether it can exists, much less in what form.

sorry to be off topic but to ‘I’m a loser’, your teacher sounds like the one who needs help!!

If you can participate in this thread you are definitely not a loser!!

tt (who was once a teacher years ago and knows it is not an easy job but scarcasm and humiliation to students is NOT what the schools need)

ps sorry again for the rant…

Ah, well–I had a nice lecture on lepton numbers and such typed up, and Chronos (unsurprisingly) beat me to it. I’ll just content myself with pointing out something he glossed over a bit:

Bear in mind that there are three different kinds of neutrinos in the standard model; an anti-tau-neutrino is not the antiparticle of either an electron neutrino or a muon neutrino. Each pair has its own lepton number.

I have a question on neutrinos and conservation of lepton number.

If a neutrino is massless then it’s helicity is immutable and lepton number can be conserved. However if neutrinos are not massless (can’t travel at c) then there is a frame where its momentum is reversed but not its spin. It would seem that, in this case, a neutrino would be converted to an anti-neutrino and lepton number could not be conserved.

What am I missing here?

Ok, if a photon is its own anti-particle; and

matter + antimatter = annhiliation; then

what happens when photon hits photon?

Do they cancel eachother out? (Not necessarily, it seems to me)

Is there a big burst of energy?

Here’s my stab at it:

Matter and energy are the same (thought E=mc^2). - they are in just a different ‘state’. Antimatter is just another form of matter (think antiparticles for antimatter if that makes it easier).

It would seem that when energy is converted to matter there is a greater probability that it will become ‘regular’ matter then ‘anti’ matter (from space.com somewhere). But that doesn’t make the ‘anti’ matter non-real. It is theorized that because of the tendency to ‘regular’ matter we have the universe that we have today, if it was 50% 50% then shortly after the big bang the matter and antimatter would have annihilated each other.

How do you make it - The only way I know is to take ‘normal’ matter particles and collide them into each other in a particles accelerator - sometimes the byproduct is antimatter partials.

got to love them smilies

Quoth Ring:

The answer is that I was sloppy, and really unjustifiably sloppy, considering that my current research touches on this. It’s true that a massive neutrino can’t have a definite helicity, and current indications seem to show that neutrinos are, indeed, massive. There are two resolutions to this: The first says that if you transform to a faster-than-neutrino frame, a left-handed neutrino becomes, not a right-handed antineutrino, but a right-handed neutrino, still with lepton number +1. Admittedly, a righty neutrino would be a mighty rare beast, but allowable. The second possible resolution is that the neutrino is not a Dirac particle as is commonly thought, but a Majorana particle. In short, this would mean that there’s no such thing as lepton number, and what we call neutrinos and antineutrinos are distinguished only by their helicity. A massive neutrino, then, would, in fact, be its own antiparticle.

One should note, by the way, that even though neutrinos don’t have a preferred helicity, the weak interactions which are (almost) the only way to produce them do have a preferred helicity. If, for instance, you have a neutron which decays into a proton, an electron, and an antineutrino, the antineutrino produced will always be right-handed, in the center of mass frame.

On photons and antiphotons: When you put an electron and a positron together, you have two photons. When you put a photon and an antiphoton together, you have two photons. Of course, they’re indistinguishable from the two you put in, so it doesn’t make much difference.

I am not an expert such as Chronos, but from what I know, all subatomic reactions can go either way. That is, if an electron and positron react to give two photons, two photons can react to give an electron and positron.

But it’s not just any two photons that will do this. They have to have energies that add up to exactly the mass of the electron+positron which I believe is 1022 KeV. But this rarely happens in real life, of course.

Am I right?

Ok, let me clarify something that I thought I had made clear. Anti-matter has nothing to do with The Time Machine. The actual machine in the movie does it’s stuff without any scientific explanation whatsoever, so my friend and I were trying to give a logical explanation to something that the time machine does near the end of the movie. Oh, what the hell…(SPOILER WARNING)…if you want to see The Time Machine, go away now…but don’t worry if you can’t decide, it’s not that great…
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Ok, near the end of the movie, Guy Pierce puts a pocketwatch in one of the gears of the time machine, and starts her up. The time machine’s “time-o-meter” (my own term, thank you) starts going forward in time, but you can still see the machine in the present time, thanks to that magical jammed gear. The glowing blue bubble then slowly closes around the machine itself, and the “time-o-meter” (can’t get enough of that) suddenly stops with a click, and a huge blue explosion results, vaporizing everything in its path. So…my friend and I were trying to give explanations for why the hell an explosion would occur, and what the hell that one special gear did. In the resulting conversation, I believe antimatter came up in an argument that went something like, “Let’s say the time machine goes so far into the future that the universe is dominantly antimatter, and then it stops within its bubble in the future and brings back a crap-load of antimatter, annhilating all of the surrounding matter.” The most illogical of the ensuing arguments, believe me. So that’s where this originated, and it just made me realize I don’t know jack about antimatter. So this antimatter stuff really has nothing to do with time travel, but I would be curious to hear some explanations for this silly blue explosion (most of which probably won’t involve antimatter ). Sorry for the initial confusion.

No, they just have to have at least 1022 keV (in the zero-momentum frame). Any extra energy will just go into kinetic energy of the resulting electrons. It’s just that photons that energetic are a bit rare in our common experience. But then, so are positrons.