Re: How do we know antimatter has POSITIVE mass?
- From: solletica@xxxxxxxxx
- Date: Fri, 29 Feb 2008 19:07:57 -0800 (PST)
On Feb 29, 7:01 pm, "Androcles" <Headmas...@xxxxxxxxxxxxxxxx> wrote:
<sollet...@xxxxxxxxx> wrote in message
news:fefd0a85-d294-4d94-8ac7-8af6d5b81f3b@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| This is layman's question. I'm NOT a physicist so be patient with
| me :)
|
| Experimental evidence--the annihilation of matter w/antimatter, and
| QFT both suggest that like matter, antimatter has positive energy.
|
| So, based on that, one can conclude that antimatter must also have
| positive mass, since an antimatter particle's mass = E/c^2 and E is
| always positive.
|
| However, doesn't this conclusion rest on the assumption that mass is
| simply defined to be energy in a contained (i. e. non massless boson)
| form?
|
| What if we define an object's mass M in the gravitational sense, i. e.
| as F*r^2/(G*M2), where M2 is another mass near M. In this way, an
| object is said to have negative mass if it has a repulsive rather than
| attractive gravitational force on other (smaller) masses.
|
| Of course, if Newton's and GR's predicitions for matter also apply to
| antimatter, then antimatter falls toward a larger positive mass
| object. But how particles of antimatter fall to Earth and the
| particle's INNATE gravitational field are two different things.
|
| In the Newton equation, acceleration due to a gravity of a negative
| mass object would still be downward (because a = F/m, and so if F is
| negative for a negative mass, a will be positive, since m is also
| negative).
|
| But if the BIG object had a negative mass, then the smaller object--
| regardless of whether it had positive or negative mass, would fall up,
| according to NEWTON's laws. GR would likely predict the same thing if
| mass were in fact defined as a quantity proportional to an object's
| gravitational field.
|
| From what I've read, no one has ever done an experiment with
| antimatter to accurately measure its acceleration due to gravity,
| although it seems it can be theoretically proven that smaller
| particles would fall down. However, there has also never been an
| experiment done with a BIG antimatter mass to assess its gravitational
| effect on smaller objects.
|
| So my big question is how do we know antimatter DOES not carry a
| negative (repulsive) gravitational field?
The big answer is: you don't. But you knew that anyway, so all
you are really doing is inviting opinion.
As a matter of fact, I DID NOT know it for sure. That why I said I'm
a layman :) But I appreciate the responses of the posters here,
because now I know the answer--that it's unknown.
However, if antimatter has an attractive gravitational force, like
matter, then according to GR, if empty space is filled with infinite
matter and antimatter particles--as predicted by the Dirac equation--
then empty space would be well, INFINITELY HEAVY, at least, according
to my intuition.
I dunno if I'm seeing this right. But I'm thinking of empty space as
a giant net, and masses as balls placed on the net. When you place a
ball on the net, it distorts the space around it, which represents
gravitational distortion in space. But if you put infinite balls on
the net, all with attractive G fields, then the net would just drop.
Of course, the net would drop everywhere equally, making it flat. But
then how could you determine the presence of a particle in this net
dropped to the floor? If you tried to represent the presence of a
negative energy particle as a spot where the net was raised by an
amount A, then the net wouldn't be raised at that spot because
INFINITY-A = INFINITY.
(this is why I said I'm a layman! Trust me, I don't have any degree
in physics and much of what I read is solely based on my own
curiosity)
Correct me if I'm wrong, but QFT reformulates the Dirac equation in a
way that treats only localized bexcitations of the vacuum (whether the
excitations represent matter or antimatter or photons) as the presence
of particle(s), right? And from the point of view of QFT, excitations
represent positive energy densities, and where there are no
excitations, there is nothing but the vacuum, correct? So in QFT,
there is no need for particles with a negative G field, it seems to
me.
Still, the QFT formulation seems to hide the negative energy states
predicted by the Dirac equation. However, it seems to me (and I'm
only a layman), that if you give antimatter a negative G field, then
you can have this sea of negative energy as predicted by Dirac and
nothing strange would happen to empty space because the positive
gravity (matter) would push the net down and the negative gravity
(antimatter) particles would compensate by pushing it up, keeping the
net level and flat.
.
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