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WHITE_HOLE
2009-Feb-04, 11:38 PM
I am assuming that for every particle, there is an anti-particle. So is there any such thing as negative mas? If we can make a mass object made of anti-atoms, then is the general charge of that mass negative.? So I am also assuming that Dark Matter is also made of positive mass. Or everything we see is positive. Or so?

Sandoval
2009-Feb-05, 12:18 AM
If Newton's equations hold true for negative masses, than pushing it would cause it to move towards you, whereas pulling it would cause it to move away from you. Gravitational attraction [between positive and negative masses] would still work the same, though (I'll concede to the next poster to explain that).

m74z00219
2009-Feb-05, 03:56 AM
Bear in mind that negative matter and antimatter are two completely different things. I'm not sure if every particle has an anti particle, but I believe every massive particle has an antiparticle.

positrion - electron
antiproton - proton
neutron - antineutron.

The only difference is the particle's charge. Though, I'm not sure how one differentiates between a neutron and an antineutron since it's electrically neutral.

Negative matter is a different beast altogether. It is hypothetical and there is no direct evidence for it.
Here's a good introductory read:
http://en.wikipedia.org/wiki/Exotic_matter
And this, though a little more heady:
http://209.85.173.132/search?q=cache:WYnoNgrMd8wJ:arxiv.org/pdf/0705.2908+negative+matter&hl=en&ct=clnk&cd=6&gl=us

gzhpcu
2009-Feb-05, 07:55 AM
I discussed this here: http://www.bautforum.com/space-astronomy-questions-answers/83505-quantum-foam-question.html#post1410883

Ivan Viehoff
2009-Feb-06, 05:04 PM
The only difference is the particle's charge.
Depends what sort of differences you are talking about. In the case of hadrons, which are made up of several quarks (usually 2 or 3), the antiparticle is often made up of quite different quarks from the particle, specifically, the respective antiquarks. So a proton is made up of two up quarks and a down quark, but an antiproton is made up of two up antiquarks and a down antiquark, three entirely different quarks. So the difference between proton and antiproton could be said to be more than just the charge. This is why an antineutron is different from a neutron and can annihilate it, it is made of three entirely different quarks.

Mesons are (to a first approximation) made up of a quark-antiquark pair. When they are the same flavour, then that meson is neutral and its own anti-particle. For example, the eta mesons.

Leptons are trickier, especially when they are neutral leptons. It seems to be the case that leptons, like quarks, come in particle/antiparticle pairs of opposite charge, at least for the charged leptons. The neutral leptons are more problematic. It remains unclear quite what is the difference between a neutrino and an antineutrino. They have opposite helicity (handedness), but maybe the helicity can change and really neutrino and antineutrinos are the same things, just in a different state.

antoniseb
2009-Feb-06, 05:27 PM
I am assuming that for every particle, there is an anti-particle. So is there any such thing as negative mas?...

Perhaps you are asking about the existence of anti-gravitons. So far they aren't theorized. If they find anti-photons, I suppose they'll look for anti-gravitons next. The hard facts are as gzhpcu points out, discussed in great detail in several other threads.

Jeff Root
2009-Feb-06, 06:34 PM
Perhaps you are asking about the existence of anti-gravitons.
So far they aren't theorized. If they find anti-photons, I suppose
they'll look for anti-gravitons next.
Has somebody hypothesized anti-photons??? I'm interested!

-- Jeff, in Minneapolis

Murphy
2009-Feb-06, 06:41 PM
Anti-Photons? Heh, what would they do? Project darkness and take heat away from objects? :lol:

And Anti-Gravitons? Wow, let's try to find out if the normal kind even exist yet, before we start talking about the anti-particle.

Though I suppose either of those would be good for Sci-Fi. "Fire the Anti-Laser!"

trinitree88
2009-Feb-06, 07:00 PM
The anti-photon is the photon. They are their own anti-particle, so they are not only hypothesized, they have been found and are indistinguishable from the regular photon..
Circa 1991...ish,.. they trapped an antiproton in a Penning trap and concluded it behaved like a particle with "regular" mass,too. pete

see:http://www.iop.org/EJ/abstract/1402-4896/46/3/010

Cougar
2009-Feb-06, 07:28 PM
I am assuming that for every particle, there is an anti-particle.

Well, careful how you put this. When physicists create particles in accelerators, they are always created in particle-antiparticle pairs. But if you look around the universe, "for every particle," the corresponding antiparticles are nowhere to be found. We can confidently say that if all those antiparticles exist at all, they are not within our visible universe.

Current thinking is that just after the so-called big bang, all the particles and antiparticles annihilated to produce photons. Well, almost all. For every billion annihilations, one particle couldn't find an antiparticle to annihilate with. These leftovers are what make up all the regular matter in our universe. We notice that there are about a billion photons for every proton or neutron, and most of those by far are CMB photons.


So is there any such thing as negative mass?

No. Gravity is always positive and attracting. Charge can be positive or negative.

Jeff Root
2009-Feb-06, 10:46 PM
The anti-photon is the photon. They are their own anti-particle,
Is there evidence to support that beyond the lack of evidence
for the existence of two separate particles? Can you describe
the theoretical reasons for believing that the photon is its own
antiparticle?

-- Jeff, in Minneapolis

grant hutchison
2009-Feb-06, 11:42 PM
Is there evidence to support that beyond the lack of evidence
for the existence of two separate particles? Can you describe
the theoretical reasons for believing that the photon is its own
antiparticle?I believe it's part of the definition for an uncharged boson.
Antiparticles are defined as having the same mass and spin as their counterparts, but opposite values for the other conserved quantities: charge, colour, flavour, lepton number, baryon number. Since photons lack all of these numbers, there is no way to distinguish an antiphoton from a photon.

Grant Hutchison

gzhpcu
2009-Feb-07, 04:22 AM
No. Gravity is always positive and attracting. Charge can be positive or negative.

Not so sure if you can definitely say no. Hermann Bondi came up with the concept of negative mass:


In 1957, Hermann Bondi suggested in a paper in Reviews of Modern Physics that mass might be negative as well as positive [1]. He pointed out that this does not entail a logical contradiction, as long as all three forms of mass are all negative, but that the assumption of negative mass involves some counter-intuitive form of motion.
source: http://en.wikipedia.org/wiki/Exotic_matter

and it has recently been proposed as a possible explanation of Hawking Radiation:


Several different explanations of Hawking radiation can be found in popular descriptions. A few of these explanations are summarized below.

(1) Quantum fluctuations lead to the production of pairs of particles and anti-particles just outside the horizon; one of these falls into the black hole and the other escapes as radiation with positive mass-energy. The in-falling particle has negative mass-energy, so its absorption results in a reduction in the mass-energy of the black hole.
source: http://www.mathpages.com/home/kmath591/kmath591.htm

grant hutchison
2009-Feb-07, 01:31 PM
and it has recently been proposed as a possible explanation of Hawking Radiation:

source: http://www.mathpages.com/home/kmath591/kmath591.htmThat's a different matter from a negative rest-mass, however. If you were to fall alongside the particle that crosses the event horizon (the infalling counterpart to the Hawking radiation), you'd find it to be a perfectly ordinary particle with positive mass.
The "negative energy" only appears in the accounting of a distant observer, and is due to the difference in reference frames between particle and observer.

Grant Hutchison

Cougar
2009-Feb-07, 03:02 PM
Not so sure if you can definitely say no. Hermann Bondi came up with the concept of negative mass....

Hermann Bondi? Ha ha ha ha ha! You mean Hermann Bondi, who is best known for developing the steady-state theory of the universe with Fred Hoyle? Ha ha ha ha!

OK, OK, Bondi was probably 100 times the cosmologist that I will ever be, and my unequivocal "no" to "negative mass" is probably going out on a limb... but it is a very massive limb, made entirely of positive matter, without so much as a quark's worth of antimatter or negative mass.

trinitree88
2009-Feb-07, 05:19 PM
Is there evidence to support that beyond the lack of evidence
for the existence of two separate particles? Can you describe
the theoretical reasons for believing that the photon is its own
antiparticle?

-- Jeff, in Minneapolis

Jeff. Hi. There's a few webbies, such as:http://www.mathpages.com/home/kmath246.htm I was in an audience of teachers in a particle physics course at MIT's Bates Accelerator, and one of them asked a presenter (Peter Demos, or Larry Sulak, I think)...the same question.
and at the Stanford Linear Accelerator...SLAC...the virtual tour guide says it too:http://www2.slac.stanford.edu/vvc/theory/antiquarks.html pete

gzhpcu
2009-Feb-07, 07:25 PM
That's a different matter from a negative rest-mass, however. If you were to fall alongside the particle that crosses the event horizon (the infalling counterpart to the Hawking radiation), you'd find it to be a perfectly ordinary particle with positive mass.
The "negative energy" only appears in the accounting of a distant observer, and is due to the difference in reference frames between particle and observer.


What I do not understand is the following: when a particle and an antiparticle annihilate each other energy is released in the form of a photons, whereas in quantum foam the virtual particles annihilate each other with no photons/energy released. Virtual particles do not behave like normal particle - antiparticles.

Nick Theodorakis
2009-Feb-07, 08:25 PM
What I do not understand is the following: when a particle and an antiparticle annihilate each other energy is released in the form of a photons, whereas in quantum foam the virtual particles annihilate each other with no photons/energy released. Virtual particles do not behave like normal particle - antiparticles.

Wouldn't that violate conservation of energy if they did?

Nick

grant hutchison
2009-Feb-07, 08:29 PM
Virtual particles do not behave like normal particle - antiparticles.That's what makes them virtual. Their energy exists only for the time stipulated by Heisenberg: so they cannot come from, or annihilate to, long-lived particles like photons.

Grant Hutchison

gzhpcu
2009-Feb-07, 08:30 PM
Wouldn't that violate conservation of energy if they did?

Nick

The thing is, that with Hawking radiation, the particle which escapes becomes real...

grant hutchison
2009-Feb-07, 08:32 PM
The thing is, that with Hawking radiation, the particle which escapes becomes real...So its energy has to come from somewhere: the gravitational field of the black hole.

Grant Hutchison

Jeff Root
2009-Feb-07, 08:51 PM
What I do not understand is the following: when a particle and an
antiparticle annihilate each other energy is released in the form of
photons, whereas in quantum foam the virtual particles annihilate
each other with no photons/energy released. Virtual particles do
not behave like normal particle - antiparticles.
My understanding is that the energy of a virtual particle pair is
"borrowed" from spacetime. It can be borrowed for only a limited
time before it has to be returned. The length of time depends on
the amount of energy borrowed. The more energy borrowed, the
sooner it has to be returned. If it were not returned before the
time limit, the particles would become "physical" and could be
detected directly. Virtual particles cannot be detected directly
because they return their energy to spacetime before the time
limit is reached.

-- Jeff, in Minneapolis

gzhpcu
2009-Feb-07, 09:01 PM
My understanding is that the energy of a virtual particle pair is
"borrowed" from spacetime. It can be borrowed for only a limited
time before it has to be returned. The length of time depends on
the amount of energy borrowed. The more energy borrowed, the
sooner it has to be returned. If it were not returned before the
time limit, the particles would become "physical" and could be
detected directly. Virtual particles cannot be detected directly
because they return their energy to spacetime before the time
limit is reached.

-- Jeff, in Minneapolis
Yes, it is allowed due to the Heisenberg Uncertainty Principle. When they annihilate each other before detection, no photons/energy is released.

So its energy has to come from somewhere: the gravitational field of the black hole.

Grant Hutchison

Yes, the black hole slowly evaporates as a virtual particle from the quantum foam is captured.

What I am saying, is that the escaping particle becomes "real", can be detected. So, isn't the virtual particle a real particle, which is so short-lived that it can not be detected? If so, why is there no energy release when the virtual particle pairs annihilate each other?

grant hutchison
2009-Feb-07, 09:10 PM
What I am saying, is that the escaping particle becomes "real", can be detected. So, isn't the virtual particle a real particle, which is so short-lived that it can not be detected? If so, why is there no energy release when the virtual particle pairs annihilate each other?Because it's not a real particle! The escaping particle becomes real because it receives energy to "promote" it from its virtual status: it can continue to exist beyond the limit set by Heisenberg. A virtual particle is a quantity of energy that exists for a very short time period, and then simply disappears. In order to conserve quantities like charge and lepton number during its brief existence, it has to be created with, and annihilate with, its own antiparticle.

Grant Hutchison

Jeff Root
2009-Feb-07, 09:34 PM
Is there evidence to support that beyond the lack of evidence
for the existence of two separate particles? Can you describe
the theoretical reasons for believing that the photon is its own
antiparticle?
Jeff. Hi. There's a few webbies, such as:
http://www.mathpages.com/home/kmath246.htm I was in an
audience of teachers in a particle physics course at MIT's Bates
Accelerator, and one of them asked a presenter (Peter Demos,
or Larry Sulak, I think)...the same question.
and at the Stanford Linear Accelerator...SLAC...the virtual tour
guide says it too:http://www2.slac.stanford.edu/vvc/theory/antiquarks.html
Thanks.

I gather that the first page is rather old. It says four types of
neutrinos exist: the electron and muon neutrino and their two
anti-particles.

I'm attracted by the notion, suggested near the end of that page,
that "helicity is not the only distinction between neutrinos and
anti-neutrinos." I would apply that to photons. For example, if
the energy of a photon were contained entirely within a single
wavelength, then there would be four possible configurations of
its electric and magnetic fields:

Jeff's hypothetical photon configurations (http://www.freemars.org/jeff/misc/cosmolog/4photons.png)

I'm afraid that, confusingly, the two on the left follow the
right-hand rule, while the the two on the right follow a left-hand
rule. The top two have positive first and negative after, while
the bottom two have negative first and positive after. Again,
this is just an example of a way photons might possibly differ
from one another.

-- Jeff, in Minneapolis

Cougar
2009-Feb-08, 02:42 AM
I gather that the first page is rather old. It says four types of
neutrinos exist: the electron and muon neutrino and their two
anti-particles.

I guess old. At any rate, wrong. Add in the Tau neutrino and its antineutrino. Three flavors, each with an anti-

gzhpcu
2009-Feb-08, 03:53 AM
Because it's not a real particle! The escaping particle becomes real because it receives energy to "promote" it from its virtual status: it can continue to exist beyond the limit set by Heisenberg. A virtual particle is a quantity of energy that exists for a very short time period, and then simply disappears. In order to conserve quantities like charge and lepton number during its brief existence, it has to be created with, and annihilate with, its own antiparticle.

Grant Hutchison

From a Scientific American article "Are virtual particles really constantly popping in and out of existence? Or are they merely a mathematical bookkeeping device for quantum mechanics?"


Thus virtual particles are indeed real and have observable effects that physicists have devised ways of measuring. Their properties and consequences are well established and well understood consequences of quantum mechanics.

source: http://www.sciam.com/article.cfm?id=are-virtual-particles-rea

Jeff Root
2009-Feb-08, 08:40 AM
Terminology: Virtual photons and physical photons. Both are real.

I first learned about virtual particles in an article by Yuval Ne'eman
in the World Book 1968 Science Year. It is clear and concise:


When electrons violently collide, as they do in the sun or in the hot
filament of a light bulb, small bundles of kinetic energy are knocked
free. The electrons slow down, due to dispersion of some of their
kinetic energy. These energy bundles, called photons, carry the
electromagnetic force that moves electrons in your eye-- and you
can see.

Photons, then, should also carry the force that exists between two
charged particles even when neither is moving. Although the static
charge on a too-easy-to-charge nylon shirt is often a nuisance, it is
scientifically illuminating. For the charge is not moving and can have
no kinetic energy, yet it does emit photons. I know of them because
they make the hair on my arm stand up. I cannot see these photons,
however, even when I am using the finest laboratory instruments.

A powerful principle of physics, the principle of uncertainty, explains
why we can observe some photons as lumps of energy but not detect
the energy of other photons at all. A photon is the smallest amount
of energy that we can measure. We must wait for all its energy to
pass by us or see none of it. A definite amount of time, then, depending
on the energy of the photon, is needed to detect it. The principle says,
for example, that a single photon of green light, 2 x 10^-6 mev of energy,
can be observed only if it exists longer than a million-billionth (10^-15) of
a second of time. When this photon exists for a shorter time, it cannot
be detected.

No photon having measurable energy can be emitted by a static charge
on my shirt, but unobservable photons can freely emerge from it at the
speed of light and act on a hair. Thus, a stream of "virtual" photons--
so called to distinguish them from the "physical" photons that we can
observe-- carries the charges' attraction or repulsion. The less energy
a virtual photon has, the longer the time it can act. Thus the farther
apart two charges are, the longer the virtual photons take to leap
between them, the smaller the energy the photons can possess, and
the weaker the force they transmit. The electromagnetic force has an
infinite range; infinitely weak virtual photons reach out from each charge
to the very horizon of the universe.

This also holds for the gravitational force. Its action is transmitted,
also at the speed of light, by particles of energy called gravitons.
Though virtual when simply binding the earth to its orbit around the sun,
they are, according to theory, emitted physically whenever matter is
accelerated. Gravitons must be exceedingly feeble. They have never
been observed.

I wrote to Ne'eman asking for more info about virtual particles, but he
suggested I get his book, 'The Particle Hunters'. It was a bit pricey,
so I haven't seen it.

-- Jeff, in Minneapolis

Fiery Phoenix
2009-Feb-08, 09:08 AM
Interesting comments everyone! I seem to recall reading somewhere that if negative mass did in fact exist, its bizarre properties would make the perfect space travel. And I don't think we have reason to deny its existence; nor do we have reason to actually believe in it. We just lack direct evidence is all.

I've always been fascinated with the idea of negative mass ever since the day I first heard of it.

Jeff Root
2009-Feb-08, 09:34 AM
The link gzhpcu has in post #27 to sciam.com made my browser
(IE 5.5) start opening new windows at a rate of about one or two per
second. They kept opening after I unplugged the cord to the modem.
I finally got it to stop with Alt-Ctrl-Del and going down to the bottom
of the long list of windows, finding the lowest one that said "Scientific
American", and clicking End task.

That has happened before on a SciAm page.

-- Jeff, in Minneapolis

gzhpcu
2009-Feb-08, 10:56 AM
Sorry about that Jeff. I am using Firefox 3 and had no problems...

grant hutchison
2009-Feb-08, 02:34 PM
From a Scientific American article "Are virtual particles really constantly popping in and out of existence? Or are they merely a mathematical bookkeeping device for quantum mechanics?"

Thus virtual particles are indeed real and have observable effects that physicists have devised ways of measuring. Their properties and consequences are well established and well understood consequences of quantum mechanics.
source: http://www.sciam.com/article.cfm?id=are-virtual-particles-reaAs Jeff says, we have a difference in terminology. The Scientific American article is saying that virtual particles do exist, and have demonstrable effects.
It's unfortunate that word "real" has also been used specifically to designate particles that live long enough to obey the conservation laws of momentum and energy, but that's life.

Grant Hutchison