Antigravity Could Replace Dark Energy as Cause of Universe’s Expansion

by Vanessa D'Amico on April 18, 2011

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Annihilation

Illustration of Antimatter/Matter Annihilation. (NASA/CXC/M. Weiss)

Since the late 20th century, astronomers have been aware of data that suggest the universe is not only expanding, but expanding at an accelerating rate. According to the currently accepted model, this accelerated expansion is due to dark energy, a mysterious repulsive force that makes up about 73% of the energy density of the universe. Now, a new study reveals an alternative theory: that the expansion of the universe is actually due to the relationship between matter and antimatter. According to this study, matter and antimatter gravitationally repel each other and create a kind of “antigravity” that could do away with the need for dark energy in the universe.

Massimo Villata, a scientist from the Observatory of Turin in Italy, began the study with two major assumptions. First, he posited that both matter and antimatter have positive mass and energy density. Traditionally, the gravitational influence of a particle is determined solely by its mass. A positive mass value indicates that the particle will attract other particles gravitationally. Under Villata’s assumption, this applies to antiparticles as well. So under the influence of gravity, particles attract other particles and antiparticles attract other antiparticles. But what kind of force occurs between particles and antiparticles?

To resolve this question, Villata needed to institute the second assumption – that general relativity is CPT invariant. This means that the laws governing an ordinary matter particle in an ordinary field in spacetime can be applied equally well to scenarios in which charge (electric charge and internal quantum numbers), parity (spatial coordinates) and time are reversed, as they are for antimatter. When you reverse the equations of general relativity in charge, parity and time for either the particle or the field the particle is traveling in, the result is a change of sign in the gravity term, making it negative instead of positive and implying so-called antigravity between the two.

Villata cited the quaint example of an apple falling on Isaac Newton’s head. If an anti-apple falls on an anti-Earth, the two will attract and the anti-apple will hit anti-Newton on the head; however, an anti-apple cannot “fall” on regular old Earth, which is made of regular old matter. Instead, the anti-apple will fly away from Earth because of gravity’s change in sign. In other words, if general relativity is, in fact, CPT invariant, antigravity would cause particles and antiparticles to mutually repel. On a much larger scale, Villata claims that the universe is expanding because of this powerful repulsion between matter and antimatter.

What about the fact that matter and antimatter are known to annihilate each other? Villata resolved this paradox by placing antimatter far away from matter, in the enormous voids between galaxy clusters. These voids are believed to have stemmed from tiny negative fluctuations in the primordial density field and do seem to possess a kind of antigravity, repelling all matter away from them. Of course, the reason astronomers don’t actually observe any antimatter in the voids is still up in the air. In Villata’s words, “There is more than one possible answer, which will be investigated elsewhere.” The research appears in this month’s edition of Europhysics Letters.

Torbjorn Larsson OM April 19, 2011 at 9:05 AM

Antigravity Could Replace Dark Energy as Cause of Universe’s Expansion

No. [Hey, shorter than HSBC!]

- There is no mechanism in GR for antigravity (but for negative pressure and/or diminishing what spacetime curvature there is). I don’t think Villata has managed to change GR. Conveniently for me I’m short on time and LC has studied GR anyway, so I can defer this for now. ;-)

- Gravitational mass = inertial mass in GR, and that has been tested many times over. And tests put antiproton inertial mass = proton inertial mass to 10 significant digits or so.

- Large scale structures. I agree on what has been said above, and I think it is the most damning prediction that this idea fails.

interI0per April 19, 2011 at 3:10 PM

seems to me that gravity is charge agnostic.
if it is then antimatter stellar systems could possibly form.
they would not radiate antiphotons but be indistinguishable from normal stars.

or not…

FleetFoot April 19, 2011 at 10:37 PM

Picking up on Todd’s point regarding the three types of mass, it seems qualitatively straightforward:

As far as any mass is concerned, it simply moves into its future following the GR equivalent of a straight line which is a geodesic as long as there is no force acting on it. This follows from symmetry since, without an external force, there is nothing to identify a preferred direction in which the particle would deviate from the geodesic. This means that anti-matter should follow the same path as matter under the influence only of the gravitational effect of other ordinary matter. “Passive gravitational mass” is really a pseudo-effect created by coordinate rotation and thus must be positive.

Inertial mass can be determined from the action of an electric or magnetic field on an anti-particle. We know it is accelerated in the oppposite direction from ordinary matter and tis could be attributed either to the particle having the opposite charge polarity or having negative inertial mass. If total charge is to be conserved, the polarities must be opposite hence the inertial mass must be positive.

That leaves the active gravitational mass. If that were negative, it would cause geodesics to curve away from anti-matter rather than towards, but as has been said above, both matter and anti-matter must follow those geodesics thus either anti-matter has positive active gravitational mass like ordinary matter or it must repel anti-matter as well as matter.

In conclusion, the idea that anti-matter could form galaxies which would repel normal matter galaxies doesn’t appear feasible either way, either anti-matter flies apart or it attracts matter.

On more general note, surely if say 1% of the universe were some form of exotic mass which generated “repulsive gravity”, surely that would only reduced the net expansion by 2% at all times. For the effect to grow with time, it needs to be stronger at long range and weaker at short, or evolving in time in some way.

Lawrence B. Crowell April 20, 2011 at 1:04 AM

Your conclusion is similar to mine. Antimatter does not have anti-mass. Besides all the anti-mass states in the Dirac theory compose the vacuum state as the so called Dirac sea.

LC

Hon. Salacious B. Crumb April 20, 2011 at 2:38 AM

I haven’t commented here, but I agree.
The only thing really special about antimatter, is that the nucleus has a negative charge (anti-protons) and positive electrons (positrons). They are essentially the same particles but or reverse in their polarity.
The other problem is if there were pockets or regions of antimatter still existing in the universe, the boundaries between matter and antimatter regions would be a blaze with energy and gamma rays; but there does not seem to be an astrophysical phenomena that would support that view.
Another issue would be with magnetic fields and jets whose positrons colliding with electrons along the field lines could easily travel significant distances and trigger astrophysical observable phenomena (which we do not see.) Also, if there was any repulsion, we would see either the matter jets antimatter jets travelling in a straight line, then at the boundary of the matter and antimatter a ultra bright gamma ray ‘star’ where the annihilations would occur. (Again not seen in nature.)
Finally, if the Big Bang is correct, I though that the energy seen in the universe was created by matter and antimatter, and hat the reason why the universe is one kind of matter, is that there was a slight excess of one for over another. This net energy drives and continues the expansion.
If the force was repulsive, wouldn’t the universe after all this time be like little clumps of matter and antimatter regions scattered everywhere? Instead we see galaxies distributed along surfaces akin to many many lathered soap bubbles. Also, would not the ‘centres’ of these bubbles (void) there should be anti-matter galaxies? f so, you would expect something to be observed there. (as far as I’ve read, there is no observational evidence to support this view!

Lawrence B. Crowell April 20, 2011 at 3:16 AM

As I showed yesterday, anti-mass (antimatter with negative mass) repels itself. I think in general we would be living in a different sort of world than the one we observe.

LC

Hon. Salacious B. Crumb April 20, 2011 at 4:16 AM

Lawrence
I am not as clued up with this subject as I should be. While I was surprised with this story popping up, I came across (admittedly from investigating our mutual ‘friend’s’; Hunter, J.H. Jr., “On the cosmology of Alfvén and Klein”, MNRAS, 137, 271 (1967).

This has some interesting ideas and discussion on matter / antimatter issues (pg.271) and the kinds of astrophysical objects that might be expected. Whilst the conclusions may have now been mostly rejected by astrophysics, this referenced article in this story has some quite interesting parallels.

After reading this article, it seems just another different way of trying to bring antimatter into the cosmos equation.

As for you saying; “I think in general we would be living in a different sort of world than the one we observe.” is truly the point. I.e.

“We are the way we are because the Universe is the way that it is… and no vice-versa.”

Lawrence B. Crowell April 24, 2011 at 2:13 AM

Antimatter clearly plays a role in the universe. The high energy universe is likely CP invariant. This means given a wave function Y_q(x) that CP Y_q(x) = Y_{-q}(-x) and CP invariance means this returns the same wave function. CP discrete symmetry is broken at lost energy and this gave rise to an excess of matter over anti-matter in the colder low energy universe. Antimatter states are due to the occurrence of sufficient positive mass-energy on the Dirac negative momentum-energy states which are filled up and define the Fermi-Dirac vacuum. This means that a negative mass virtual particle state with quantum number opposite those of the positive mass-energy particles now exist with positive energy.

The Dirac equation is the spinorial form of the square root of the Klein-Gordon equation. The KG equation is a quantized form of the special relativistic momentum interval

(mc^2)^2 = E^2 – (pc)^2.

Going into the spinor mathematics of the Dirac equation is a bit beyond the scope of UT, and further requires some graphic math-tools not available here. So looking this up, even on wikipedia, is advised. However, the square root of an equation has two roots, and just as y = x^2 has positive and negative x’s (and recall the binomial equation) the same happens with the Dirac equation.

The physics of CP violations is a big issue, and Fermilab has been looking hard at CP violations with the T-quark, which follows the Desy results on the B-quark factory results. The T and B quarks are in the highest mass doublet of QCD.

LC

Hon. Salacious B. Crumb April 24, 2011 at 2:49 AM

Funny you mention the CP violations. I read today on the New Scientist website “Lonely, spun-out proton reveals magnetic secret”, which talks about the g-factor.
According to this, there is a possible experiment to verify if the g-factor has the same value between protons and antiprotons.
In this story, if the fields of either are of different strengths, then it would pose an additional problem for astrophysical phenomena and even nucleosynthesis / stellar evolution. (This linked article has the arXiv paper attached with it.) Again, this is a possible broken symmetry.

Lawrence B. Crowell April 24, 2011 at 3:04 AM

I would be surprised if the Lande g-factors differed between matter and antimatter. The factor is g = 2.0023318416 for

mu = -geS/2m

for the magnetic moment. The straight forwards calcuation gives g = 2. It requires QED to get g – 2, where physics related to the Lamb shift give the departure. There are expected departures for the muon g factor, where there can be a virtual transition to the neutralino state.

LC

Vladimir Leonov April 20, 2011 at 8:08 AM

{Violation of comment policy: text deleted. There is a thread on this topic in BAUT’s Against the Mainstream section.}

FleetFoot April 20, 2011 at 3:29 PM

“For example, the electron and the positron have the plus mass, although the positron is an antiparticle in relation to the electron. However, this is a very large problem, which is outside the framework of this chapter.”

Why quote the chapter then? The suggestion that the positron (for example) would have negative active gravitational mass is the topic being discussed. You wouldn’t be trying to publicise your book, would you?

Olaf April 20, 2011 at 4:56 PM

I think we have a copyright issue here with such a big excerpt that clearly is a copy and paste of a book.

interI0per April 20, 2011 at 1:44 PM

here is a tidbit of some salience:

http://www.bbc.co.uk/news/science-environment-13097370

where are the antineutrons?

FleetFoot April 20, 2011 at 2:04 PM

Anti-neutrons are produced in anti-proton factories but last I heard they had no way to slow them down. You can’t use a moderator (e.g. graphite) of ordinary matter obviously and techniques like laser slowing only work well (if at all) on charged particles.

Lawrence B. Crowell April 20, 2011 at 5:26 PM

A high energy event with particles can generate a proton plus anti-neutron plus a positron and an antineutrino.

LC

Lawrence B. Crowell April 20, 2011 at 5:30 PM

Oops, sorry I wrote too fast. I meant an anti-neutron plus proton plus and electron and neutrino.

LC

Olaf April 20, 2011 at 5:03 PM

Recently I started to realize that a lot of people have a big wrong concept of what gravity is.
I think that a lot of conspiracy theorists think that gravity is a surface effect only. For example the moon pulls up the surface and thus cause tension inside the interior.

Reality is that gravity acts on every atom and in the complete Earth pulling all in the same direction. This includes the back side, the inner side, the left and right side and the front side. The resulting vectors is basically near zero in gravitational difference between the backside and the front-side. Earth does not get stretched like a big balloon but moves in the orbit as one whole thing.

wjwbudro April 20, 2011 at 9:37 PM

The “effect” of gravity is canceled (zero G) at the center of a mass which is located at the bottom of the space/time well it itself created. This center will be offset in the direction of the centers of other nearby masses (n-body physics).
This is what I came away with the many times this subject was tackled here on UT.

VIGNESHRAJU April 24, 2011 at 5:28 AM

I’m 10 std student,i cant able to understand all.But i know it is very difficult to explore the universe when expands

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