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# Free energy or antigravity

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This thought came out of discussions with a mate of mine; he's working on testing the proposition that antiparticles display "negative" gravity - a proposition that CERN is also testing, I believe.

Now, let's suppose for a moment that particles and antiparticles both have "positive" gravity - this is the commonly accepted view. So, a kilogram of antimatter will exert a gravitational pull, exactly like a kilogram of matter.

Imagine we have a box of ideal mirrors, and assume that the box itself has zero mass (it's not essential, but it makes it easier to think about). Assume that, in this box of mirrors, we trap a lot of gamma photons, all bouncing back and forth.

Photons have zero gravity - meaning that they don't exert a pull on anything else. (They are acted upon _by_ gravity, but that's by the by.) So, our mirror box exerts no gravitational force on anything nearby.

We now take a mass, M, and we put it one metre away from the box. Because the box has no gravitational effect, the mass just sits there.

But now, all our gamma photons change into electron/positron pairs (which can happen). These pairs sit in the box and, assuming that both matter and antimatter have positive gravity, they create a gravitational field which attracts the mass M. We let mass M fall towards the box, and we harvest energy from that fall.

Once the mass M has fallen towards the box, we let our particle/antiparticle pairs annihilate eachother to re-create gamma photons trapped in the box. The gravity disappears, and we can now move our mass M away again, with no energy cost.

We can repeat this ad infinitum, harvesting energy from the fall of the mass M each time.

So, _if_ particles and antiparticles both have positive gravity, we have (in theory) a source of free energy. The only way to _not_ have a source of free energy is if antiparticles have negative gravity. In this case, the box never creates a gravitational field.

So, either we have a source of free energy (which will seriously annoy physicists), _or_ antimatter has negative gravity and we have a source of antigravity (which will somewhat annoy physicists).

 — MaxwellBuchanan, Sep 04 2017

Mass of a photon https://physics.sta...-they-have-momentum
[Wrongfellow, Sep 04 2017]

CERN ALPHA experiment http://alpha.web.cern.ch/
Scroll to bottom for the gravity bit. [MaxwellBuchanan, Sep 08 2017]

//ideal mirrors// - hmmmmmm - worried about all such 'ideal' things in the context of a thought experiment about free energy

//all our gamma photons change into electron/positron pairs// - how do you stop them immediately recombining (without expending energy to keep them apart)?

//and we can now move our mass M away again, with no energy cost// - no, you'll have to accelerate it away from the box to stop its fall towards the box, and this will consume energy. This can be avoided by having two boxes full of photons or electron/positron pairs and the mass falling alternately to one and then the other, but there's no way to make the contents of the boxes switch from photons to electron/positron pairs alternately.
 — hippo, Sep 04 2017

 //Photons have zero gravity - meaning that they don't exert a pull on anything else.//

Photons have zero rest mass - but they do have relativistic mass [link].
 — Wrongfellow, Sep 04 2017

 //how do you stop them immediately recombining (without expending energy to keep them apart)?//

 Yes, but the energy needed to stop them recombining can (in theory) be recovered when they recombine - it's a sort of elastic process in that sense.

//Photons have zero rest mass - but they do have relativistic mass [link].// Yes, but there seems to be some debate (on the linked page) over whether that mass is the same as other mass - i.e. whether a box is heavier if you fill it with photons.
 — MaxwellBuchanan, Sep 04 2017

//you'll have to accelerate it away from the box to stop its fall towards the box, and this will consume energy// but, again, that energy is recoverable (in theory). It can also be made arbitrarily small, if we don't care how long it takes to move the mass away from the box.
 — MaxwellBuchanan, Sep 04 2017

I often wonder (meaning almost never actually) why Casimir's force could not be used as a source of free energy? I'm sure a set of rotating plates linked to some magnets and a few wires to take away the free electricity could be hashed up with comparative ease. You could do it Max. You know all about ergs, fermions, and simple harmonic motion, etc. Make sure to post a video when you've got it all working properly, and don't make a mess! Use plenty of bakelite knobs on the control panels.
 — xenzag, Sep 04 2017

I think the problem with the Casimir force is that it's a bit like gravity - you can get energy out by allowing the plates to pull toward eachother, but then you have to put as much energy back in to pull them apart.
 — MaxwellBuchanan, Sep 04 2017

This resembles to me the thought experiment made by your (possibly) grandparent James Clerk: the Maxwell's demon. The energy spend to figure out that a pair of electron/positron has been created plus the energy for opening the ideal mirror for letting an electron pass thru will be greater than you can harvest.
 — piluso, Sep 04 2017

 Yes, that may very well be right. However, that only becomes a question if antimatter has normal (positive) gravity. If it has negative gravity, then there's no source of free energy even in the Maxwell's Demon sense.

And there's also the partly-open question of whether a photon creates a gravitational field. If it does (ie, if a box of light weighs more than a box of dark), then once again there is no free energy and also no need for antimatter to have negative gravity.
 — MaxwellBuchanan, Sep 04 2017

 OK, I think I've been blown out of the water.

 I found a web page with lots of words on it and no pictures or adverts, which suggests it's reliable. Some of the words on it were: "Thus, the mass of a box of light is more than the mass of the box and the sum of the masses of the photons (the latter being zero). "

So, the answer to the question "free energy or antigravity?" appears to be "neither". Or at least "not necessarily either".
 — MaxwellBuchanan, Sep 04 2017

In my mind it's not about free but rather useful conversion. That, and finding nature's unique cases. The cost usually comes in fiddly amassing of the small or not getting burnt controlling the large.
 — wjt, Sep 05 2017

Now is it antimatter that has negative gravity, or negative matter - matter with negative mass. Because positrons have mass and from what I understand these physics study places are swimming with them. If they were repelled by gravity I think someone would have taken notice by now.
 — bungston, Sep 05 2017

 //Because positrons have mass and from what I understand these physics study places are swimming with them. If they were repelled by gravity I think someone would have taken notice by now.//

 That's the problem - it's not easy to notice. Positrons are charged, and usually start out at high velocity. So you need to slow them down and then hold them in a magnetic field so they don't touch anything else. So then you're trying to determine the effect of gravity on something that "weighs" almost nothing, and which is being held by a field which is 10^40 times stronger than gravity.

 The Alpha experiment (and others) is trying to do exactly this, with (I think) antiprotons. But none of the tests so far have been able to tell either way.

 As for negative matter/negative mass - as far as I know that's still speculative.

And as for positrons having mass, yes, they do - the question is how that mass interacts with gravity.
 — MaxwellBuchanan, Sep 05 2017

 I read just a little about QCD (like updated QED) and it said that one of the things about particle collisions is that they only sometimes produced one product. So, just making up numbers, for say 100 events, perhaps 90 particle antiparticle collisions would predictably produce gamma photons. the other ten times they would produce other things which would then interact or decay variously. A quantum physicist might start there calculations trying to prove the energy of these was in some way equal to the "free" energy of the mass moving towards the mirror box.

Note that does not make the idea wrong, it could be there is something out there that has 100/100 combination fidelity and you could use the mirror box with those.
 — beanangel, Sep 05 2017

 // (They are acted upon _by_ gravity, but that's by the by.) //

No, they aren't. Gravity bends spacetime; the photons always move in a straight line, but appear to be affected because they follow the distortion. This is the origin of the "gravity lens" observation.
 — 8th of 7, Sep 06 2017

 Yes, that was my point. Spacetime tells light how to move, but light doesn't tell spacetime how to warp.

In which case, if particles and antiparticles both have positive gravity, there is a sort of "non-conservation of gravity" effect. I'm not sure if "conservation of gravity" makes any sense, but it feels like it might be a thing.
 — MaxwellBuchanan, Sep 06 2017

Sounds like standing in a room, waiting for the moment when all the cold molecules are on one side, and all the hot ones on the other, so's you can stick a Peltier in between.
 — FlyingToaster, Sep 06 2017

Yes, except that to know their positions you'd have to observe them, which would change their characteristics ...
 — 8th of 7, Sep 06 2017

 OK, I guess all of this boils down to a sort of "conservation of gravity" thing.

 Let's take a simpler case. We have a gamma photon in a box of mirrors. The gamma photon sometimes changes to become a positron/electron pair.

 Now we put a mass on a spring outside the box. If the positron and electron both have positive gravity, then the mass will bob up and down (down when there is a positron/electron pair, and back up when they change back into a gamma photon). And work could be extracted from that bobbing. Which violates energy conservation.

If the positron has negative gravity, though, then it's all OK: the total gravity of the box remains constant, whether it contains a photon or a particle-pair.
 — MaxwellBuchanan, Sep 06 2017

What if it just has positive gravity moving backwards through time?
 — RayfordSteele, Sep 06 2017

 First, the antigravity thing is not going to be true. Any physicist who pays attention to E=mc2 can see the fact that negative mass must be associated with negative energy, and therefore ordinary antiparticles, which are made from ordinary positive energy, must have ordinary positive mass.

Second, the likeliest flaw in the free-energy notion is the fact that "controlling events" takes energy. You (however subtly) have specified a need to control the conversion of gamma photons into positron-electron pairs, and later back to gamma photons. The original "Maxwell's demon" free-energy notion notion failed because of the need for energy to exert control over something.
 — Vernon, Sep 07 2017

 //negative mass must be associated with negative energy//

 We're not talking about negative mass. As far as I know, nobody doubts that antiparticles have positive mass.

 But, at least according to the people at CERN who are running the Alpha experiment, there is still a possibility that antiparticles respond to gravity in the opposite way to normal particles.

What I mean is, there is potentially a distinction between mass (presumably inertial mass) and response to gravity.
 — MaxwellBuchanan, Sep 07 2017

The thing that makes anti-particles behave like anti- particles is their electric charges, which are opposite from ordinary particles. We already know that ordinary electrically-charged particles behave ordinarily under the influence of gravitation. There is no reason to think that just because an anti-proton has a negative charge instead of a positive charge, while also possessing ordinary positive mass, the particle will be gravitationally repelled. (and ditto for the positively-charged anti-electron)
 — Vernon, Sep 08 2017

Well, apparently there's enough reason for CERN to be looking into it. See link. So far, they have only shown that antihydrogen has a gravitational mass between +110 and -65 compared to its inertial mass - meaning that a gravitational mass of -1 is still a possibility. (Scroll down to bottom of linked page.)
 — MaxwellBuchanan, Sep 08 2017

If -1 was on the cards, wouldn't the numbers be +65 and -110, taking a randomistic belly math approach? (gut math)
 — wjt, Sep 08 2017

 Well, if that were the case then they'd stop the experiment and just take the midpoint of the -6500% and +11000% to get the average of 2250%, which seems equally unlikely.

As they pointed out in a paper, we've only just discovered that we don't know what 90% of the universe is actually made of, so it's a bit presumptuous to rule out negative gravity on the basis of theory.
 — MaxwellBuchanan, Sep 08 2017

 It is most logical for negative gravity to be associated with negative mass in a particular way: Like masses attract; opposite masses repel. So here's a little something for you to think about:

 The biggest and most embarrassing discrepancy in modern physics, between General Relativity and Quantum Mechanics concerns the properties of the "vacuum", where virtual particles of all types are known to constantly pop into temporary existence and vanish again. According to QM, those particles should have a gravitational effect. According to GR, they don't, or it is negligible. The magnitude of the two theories' values, for that effect, is 120 orders of magnitude different from each other!

Well, if we imagined that half of all virtual particles have negative mass instead of ordinary mass, then their total gravitational effect simply cancels out. Meanwhile ordinary anti-particles still have ordinary positive mass. We will need to find the negative-mass equivalents of protons and electrons and antiprotons and positrons, to have particles that are gravitationally repelled.
 — Vernon, Sep 08 2017

 Uh, Vernon, as far as I know, the virtual particles are supposed to be particle/antiparticle pairs. So your argument would only work if antiparticles had antigravity.

We don't really understand what is "anti" about antiparticles anyway. It's not just charge - there's a neutron and an antineutron. It's unlikely but not impossible (either theoretically or on the basis of experiments to date) that they're anti with respect to gravity.
 — MaxwellBuchanan, Sep 08 2017

 Regarding the neutron and antineutron, remember they are comprised of electrically charged quarks, the total charge of which just happens to cancel out. The quarks associated with an ordinary neutron are oppositely- charged anti-quarks in the anti-neutron. We KNOW that the neutron MUST have internal electric charges because we observe that the neutron manages to have an overall magnetic field, despite lacking an overall electric charge. (I need to point out that I'm totally ignoring all electric charges inside neutrons in something I wrote a bit farther down.)

 Virtual particles consist of EVERY POSSIBLE type of particle. If it is possible for negative-mass particles to exist, then they will exist as virtual particles in the vacuum (and probably as particle-antiparticle pairs, both members of every pair having negative mass). It is exactly analogous to ordinary-mass virtual particles existing in the vacuum.

 In more detail, remember the Uncertainty Principle is the reason why it is possible for virtual particles to do their thing, popping into and out of existence. The ASSUMPTION is that even when a vacuum has no real energy in it, it Does Not Certainly have zero energy in it. The energy-content of the vacuum is allowed to fluctuate to some positive value above zero --and thus positive- mass virtual particles can manifest. HOWEVER, I see nothing preventing negative fluctuations below the zero- energy level, thus allowing negative-mass virtual particles to also exist.

 And, depending on just how "opposite" various particles can be, I wouldn't be surprised if a positive-mass particle sometimes pops into temporary existence accompanied by a negative-mass particle --but any such pair would be in addition to oodles of pairs of ordinary positive-mass particles, and oodles of pairs of negative-mass particles. Some examples:

 Ordinary neutron and ordinary anti-neutron, both with positive mass. Negative-mass neutron and negative-mass anti-neutron. Ordinary neutron and negative-mass anti-neutron. Ordinary anti-neutron and negative-mass neutron.

Things could be a lot more complicated when talking about obviously-charged particles, like electrons. Is the negative charge of an electron (a type of energy, right?) equivalent to a positive charge, if that same charge is part of a negative-mass particle? Inquiring minds want to know!
 — Vernon, Sep 09 2017

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