I’ve taken a break from the lengthy, narrow-appeal old history book I’ve been reading (and blogging about) in favor of “From Eternity to Here” by Sean Carroll (not the evolutionary biologist of the same name). The book is about time and the mystery of why the past (and more specifically, the period near the Big Bang) has lower entropy. I was disappointed that there is so little attention paid in it to Julian Barbour’s “The End of Time”, since that really digs at the foundations Carroll seems to be concerned with and has an explanation of why the small, dense initial period is the logical beginning for all subsequent events. But this post isn’t to give an overall review, just to point out something I found out.
In discussing black holes and Hawking radiation, he writes “The total energy of a virtual particle/antiparticle pair is exactly zero, since they must be able to pop into and out of the vacuum. For real particles, the energy is equal to the mass times the speed of light squared when the particle is at rest, and grows larger if the particle is moving; consequently, it can never be negative. So if the real particle that escapes the black hole has positive energy, and the total energy of the original virtual pair was zero, that means the partner that fell into the black hole must have a negative energy. When it falls in, the total mass of the black hole goes down.”
I was confused by that, perhaps because I don’t know enough about antiparticles. One definition, that would fit well with Carroll’s themes, is that they are like regular particles with time reversed. Murray Gell-Man in “The Quark and the Jaguar” explains them as having the reverse charge and color of their opposite. The examples Carroll gives in his book like the positron and anti-strange quark (whose color might be “antigreen”) have positive mass, as I recall. And since the question of which member of the pair is absorbed is determined by which is closer to the black hole, how do we know it is the “real” one which will escape? Why can’t the mass of the rest of the universe be decreased while that of the black hole increases? Carroll notes elsewhere that gravity is an unusual force in that it is only attractive and never repulsive. By the usual equations of gravity, a negative mass would imply a reversed gravitational force, so I would expect a negatively-massed particle to be repelled by the mass of the black hole anyway. But if that’s impossible, I don’t know what it means for something to have negative mass/energy. If it was possible though, that could explain “white holes” which he notes sound similar to the Big Bang.
August 4, 2010 at 8:45 am
If there is actual ‘negative mass’, then there’s the potential for a workable stardrive!
It would also explain why all the stuff we see in the universe is composed of matter and not antimatter – antimatter would repel itself, and have a very peculiar interaction with matter. So the only things that would clump together and stay in one spot would be made of normal matter.
August 4, 2010 at 10:18 pm
A negative times a negative equals a positive, so maybe negative masses would be attracted to each other, but repelled by positive masses.
August 5, 2010 at 6:27 pm
No, negative masses repel each other.
(It’s the same reasoning that permits antiparticles to be treated as normal particles moving backwards in time.)
What they do with positive masses is… downright weird. Hence, stardrive.
August 5, 2010 at 7:40 pm
I have heard that while negative masses have negative gravity, they also have negative inertia, and hence act normally – unless they encounter positive mass.
Also, antimatter is not the same thing as a negative mass. Antimatter (which DOES exist) has a positive amount of energy, whereas negative matter (which may or may not exist) has negative energy.
If you really want to read something weird, read up on how as information becomes ever more tightly packed, it reaches a limit wherein the amount of information increases not proportionally to the volume of the space, but proportionally to the surface area of a sphere of equal volume to the space. It’s called the holographic bound.
August 5, 2010 at 8:50 pm
melendwyr, could you elaborate on the “weird” interaction? Also, I think you are right about backward time leading to mutual repelling. Example: three normal particles should all have gravitational attraction and converge, but three mutual repulsions is not compatible with a binary opposites-repel model.
daniel noe, right I discussed positrons & antistrange quarks as examples of antimatter with positive mass. And Scott Aaronson discusses the limits of computation due to the packing of information within an area in his diavlog with Anthony Aguirre.
August 6, 2010 at 12:12 pm
Relativity places restrictions on how quickly ‘stuff’ can move, but not on how rapidly space-time can be distorted.
If you have a concentration of mass, and a concentration of anti-mass, the former is repelled from the latter and the latter attracted to the former. Result: the combination moves towards the concentration of mass. And this can happen at any speed.
Any object in the neutral zone between the two concentrations would be carried along with it. Effectively, it would be uncoupled from the reference frame of the rest of the universe, and its motion would be definable only in terms of the bubble it was in.
So if you could generate and dissipate positive and negative spatial distortions, you could (so some think) operate an effective faster-than-light drive that gets around the rules of Relativity rather than breaking them. The implications are extremely disturbing.
The amount of energy necessary to create a usable distortion is greater than that which makes up whole planets, though, so it’s not something that pre-godlike entities could really pull off, even if the physics actually works.
See Alcubierre Warp Drive. Yes, it’s actually called a ‘warp drive’.
August 7, 2010 at 11:27 am
If you enjoy “weird” things about which you know little get this one…
As for the solution for being overweight use this.
(I did, lost 9kg in 3 months, still fit)
August 7, 2010 at 6:03 pm
Do warp drives permit information to move faster than light? I suppose wormholes could do the same thing.
I’m more underweight than anything, so Seth’s diet doesn’t matter to me.
August 8, 2010 at 6:28 am
Sorry guys, antimatter has positive mass, not negative mass. An antiparticle has the opposite *charge* to its partner. In real-world physics, negative mass and negative energy are something you don’t want in your theory, because they are permanently destabilizing: A system seeking its lowest energy state could keep going lower by producing ever more negative-energy particles.
This was actually an early problem faced by string theory: the naively quantized string has a “tachyonic” mode, where the salient property is not faster-than-light-ness, but imaginary mass, which means negative energy, which means that an infinite number of tachyonic strings should immediately materialize. The early string theorists solved the problem by fiat, by removing the tachyonic part of the string’s Hilbert space. Later on, tachyons made a limited comeback in conjunction with branes. When a brane and an antibrane are brought together, there will be a condensation of tachyonic strings stretched between them, whose negative energy exactly balances the positive energy of the brane tensions.
Regarding Sean Carroll’s comment about virtual antiparticles with negative energy… Well, this is one of those ‘interpretive’ issues where I know how the formalism, the machinery of calculation works, but what it means ontologically (i.e. in reality) is a little more problematic. Let’s first of all revisit the definition of virtual particle. It is a particle in a Feynman diagram, part of a sum over histories, which is not one of the initial or final sets of particles.
It is a fact about Feynman diagrams that they can contain all sorts of junk whose relationship to reality is questionable. For example, there can be ‘renormalons’ which are ‘particles’ which are there just to create the ‘counterterms’ needed for renormalization of divergent diagrams. There can be ‘ghost particles’ which have negative probability and which exist in order to deal with other technical problems associated with ‘gauge fields’.
The purely algebraic interpretation of Feynman diagrams (which goes back to Freeman Dyson) is that they are a bookkeeping device for a path integral involving quantum fields and field interaction operators, and if odd entities show up in the diagrams because of mathematical contrivances we carry out in order to solve the integrals (e.g. renormalization, or the introduction of redundant ghost variables), that means nothing physically. That’s not an entirely satisfactory response; every calculational method that works (“Wick rotation” into imaginary time is another good example) must ultimately work for a reason that has to do with physical reality. Even if there aren’t renormalons or ghosts in reality, they must have a physical meaning, e.g. the renormalon is a substitute for unknown real processes which cancel the divergences of an incomplete theory. (I’m not sure what the “practical” explanation of the ghost fields is.)
Virtual particles are perhaps the original example of an element in a Feynman diagram whose relationship to reality is questionable. This isn’t about positivistically asserting that entities postulated to exist between measurements are unreal, or that ideas about their reality are meaningless, it’s about concrete facts like virtual particles taking on negative energy values. The jargon refers to “on-shell” and “off-shell”, where the shell is the hyperboloid in Minkowski space of energy-momentum vectors with a length equal to the mass of a particular particle type. If the momentum-energy of a particle always stays on shell, on the surface of the hyperboloid, then it’s regarded as “physical”, as a real process. If it goes off-shell, it’s – something else. And a particle whose energy goes negative is going about as far off-shell as you can go.
In another context, the process which Sean Carroll is describing would be referred to as a form of quantum tunneling. Quantum tunneling occurs when, thanks to the uncertainty principle, a particle manages to temporarily acquire the energy to cross a potential energy barrier which classically it should not be able to cross. Virtual pair creation in the quantum vacuum refers to such fluctuations at the level of the zero-point energy of the field modes. Hawking evaporation occurs when something in the black hole quantum tunnels across the event horizon. There is apparently a space-time zigzag involved in such a motion, which gives the appearance of a virtual particle-antiparticle pair which, instead of recombining and annihilating, splits up, so that one half falls into the black hole and the other half radiates away. But it might be better to look at it in terms of something in the black hole which quantum tunnels across the horizon.
August 8, 2010 at 10:50 pm
Yes, we discussed above how antimatter has positive mass but opposite flavor and color.
Carroll does give space to tachyons in his book, but treats them as relevant to science fiction rather than reality.
Thank you for your explanation of Hawking evaporation.
“A system seeking its lowest energy state could keep going lower by producing ever more negative-energy particles.”
There’s a similar issue in computer science for finding the shortest path in a graph containing a negative-weight edge. You just go around in circles forever without arriving at a destination, but your time of arrival is infinitely lower than any other possibility!
August 9, 2010 at 1:01 pm
Ah, Zero-Point Energy. The modern equivalent of the Philosopher’s Stone.
August 10, 2010 at 12:44 am
Zero-point energy just means ground-state energy. I think it was Feynman who explained that the lowest energy level of an electron in an atom is a wavefunction of finite extent, rather than a point, because if the electron was at rest at a point we would know both its location and its momentum (zero) to an accuracy violating the uncertainty principle. The same thing goes for the Fourier modes of a quantum field: if they were completely still we would know both the strength of the field mode (zero) and its rate of change (zero). So instead the field always has some probability of activity in every mode.
For an ordinary harmonic oscillator, this lowest energy mode has a finite energy, but for the supersymmetric oscillator, the lowest energy is zero. I don’t understand in any insightful way why this is so, but it is one of the attractions of supersymmetry, because the vacuum energy should otherwise be observable as a gravitational source. The contemporary footnote to this is the idea that the acceleration in the expansion of the universe is due to supersymmetry being very weakly broken, so as to produce a very small vacuum energy after all.
I just want to make clear the difference between the role that ZPE actually plays in physics, and the idea of using the ZPE as a source of free energy, if that’s what you were thinking. The latter idea is like time travel – or like negative mass, or perpetual motion machines, or faster-than-light travel. It’s something we should expect to be impossible.
August 10, 2010 at 10:28 pm
Carroll similarly discusses “vacuums” reconceptualized as energy minima, making it possible to have multiple different vacuums, some of which are “false”.
August 10, 2010 at 11:20 pm
Vacuum?
But Does matter differ from vacuum?
August 11, 2010 at 8:15 am
Does antimatter have negative mass? This question is wide open. Theoretically there will be no answer until we are in the possession of a theory that could predict relationship between electromagnetic and gravitational interactions. Experimentally? Yes, it can be done, but it would be very challenging. If antimatter is ever found to have negative mass, it will deal a devastating blow to the Principle of Equivalence and General relativity. Does anyone know whether astronomers and cosmologists have detected ceestial bodies repelling somehere in the universe? [On a happy note, Mr Cavor would have his cavorite.]
August 11, 2010 at 11:39 pm
I think we’ve already produced antimatter and concluded it has positive mass. I appreciate the H. G. Wells reference though*.
*I believe in the story, mass was not actually negative, it was just much lower than the atmosphere. As a result, like a sphere of very low density at the bottom of the ocean, pressure caused it to rocket upwards.
August 24, 2015 at 1:43 pm
I beliebe that antimatter does not exist sabe in the early universe.then the antiparticles are holes of negative energy trave língua formar in universe.then the antiparticles are originated of transformation of mass into energy and viceversa, but the non uniformiza of transformation of energy into mass tô relativity velocities.there appear the time dilatation and contrato of spacetime are originated by the violations in of cp, and the antiparticles are mensurado by the pt symmetry breaking that does the speed of light as constant in the universe and vives the métrica of curvatures of spacetime
August 24, 2015 at 6:30 pm
I gather English is not your first language. Here is my attempt to translate:
I believe that antimatter does not exist, save in the early universe. Then the antiparticles are holes of negative energy [?]. Then the antiparticles originate in the transformation of mass into energy, and vice versa, by the non-uniform transformation of energy into mass via[?] relativitistic velocities. There appears the time dilation and contraction of spacetime from which originate the violations of cp [conservation principle?], and the antiparticles are [?] by the pt [I don’t know what that stands for] symmetry breaking that makes the speed of light a constant in the universe, and creates[?] the curvatures of spacetime.
August 26, 2015 at 9:05 am
Thank You Very much for try help me
August 26, 2015 at 9:17 am
All right.i have problems with typewriter from i pad
March 1, 2016 at 11:44 am
Antimatter makes not exist, white are the Antiparticles? Are subproducts of asymmetry of matter, energy, space and time.then transformation of mass into energy and viceversa is not conserved and non uniform occurbforbrelativistics speeds near the speed of light and time dilatation is non uniform and vinvulated by the violation of cp, the connection of spacetime generating the spacetime that has then symmetry as the antiparticles. PT symmetry breaking generate the constancy for the speed of light, it is the left handed tô right handed and viceversa transformations are non invariants ( rotational invariance is not totally conserved) that implies the existence of speed of light because the spacetime running b forward in time and backward in time generating the present are particles and antiparticles in 4dimensional spacetime continuum
March 3, 2016 at 7:38 am
If is vaccum nothing might for exist, must the topology and the geometry could generate internal distortions in itself, and therefore generate the spacetime in the fourth that is possible several fammilies of curvatures with differents smooth topologics. Then then vacuum is the quantum topological fields theory, where the intersection of two sphere S^3 in 4dimensionaltravel link tô appear nas knots that are subnuclear particles.then the quantic is not all continue, having discrete spacetime measuring then
differents degrees of energy coupled to the curves of spacetime.then the antiparticles has positive mass carrying negative energy because are particles running backward in time, for our inertial frame, turning the spacetime stretched and compressed, and these particles will go los ing energy, it is emmiting particles how much more goes going backward in time (that is not travelling for the past).Then the that all of vacuum are distorting of the proper fábrics of spacetimes, where the b shapes of topology for fourth dimensions with differents famílies of smooth and continue spacetime curves.then the vacuum has a pré metrics that generate the differents spacetime structures.for that reason does the appearing of vacuum spontaneous symmetry breaking, as the opperator PT, breaking that symmetry emerge the spacetime with differents metrics in the 4dimensional manifolds