by Dr. Robert E. Buxbaum,
The normal view of antimatter is that it’s just regular matter moving backwards in time. This view helps explain why antimatter has the same mass as regular matter, but has the opposite charge, spin, etc. An antiproton has the same mass as a proton because it is a proton. In our (forward) time-frame the anti-proton appears to be attracted by a positive plate and repelled by a negative one because, when you are going backward in time, attraction looks like repulsion.
In this view, the reason that antimatter particles annihilate when they come into contact with matter –sometimes– is that the annihilation is nothing more than the matter particle (or antimatter) switching direction in time. In our (forward) time-frame it looks like two particles met and both disappeared leaving nothing but photons (light). But in the time reversal view, shown in the figure below, there is only one normal matter particle. In the figure, this particle (solid line) comes from the left, and meets a photon, a wiggly line who’s arrow shows it traveling backwards in time. The normal proton then reverses in time, giving off a photon, another wiggly line. I’d alluded to this in my recent joke about an antimatter person at a bar, but there is also a famous poem.
This time reverse approach is best tested using entropy, the classical “arrow of time.” The best way to tell you can tell you are going forward in time is to drop an ice-cube into a hot cup of coffee and produce a warm cup of diluted coffee. This really only shows that you and the cup are moving in the same direction — both forward or both backward, something we’ll call forward. If you were moving in the opposite direction in time, e.g. you had a cup of anti-coffee that was moving backward in time relative to you, you could pull an anti -ice cube out of it, and produce a steaming cup of stronger anti-coffee.
We can not do the entropy test of time direction yet because it requires too much anti matter, but we can use another approach to test the time-reverse idea: gravity. You can make a very small drop of antimatter using only a few hundred atoms. If the antimatter drop is really going backwards in time, it should not fall on the floor and splatter, but should fly upward off the floor and coalesce. The Laboratory at CERN has just recently started producing enough atoms of anti-hydrogen to allow this test. So far the atoms are too hot but sometime in 2014 they expect to cool the atoms, some 300 atoms of anti hydrogen, into a drop or two. They will then see if the drop falls down or up in gravity. The temperature necessary for this study is about 1/100,000 of a degree K.
The anti-time view of antimatter is still somewhat controversial. For it to work, light must reside outside of time, or must move forward and backward in time with some ease. This makes some sense since light travels “at the speed of light,” and is thus outside of time. In the figure, the backwards moving photon would look like a forward on moving in the other direction (left). In a future post I hope to give instructions for building a simple, quantum time machine that uses the fact that light can move backwards in time to produce an event eraser — a device that erases light events in the present. It’s a somewhat useful device, if only for a science fair demonstration. Making one to work on matter would be much harder, and may be impossible if the CERN experiments don’t work out.
It becomes a little confusing how to deal with entropy in a completely anti-time world, and it’s somewhat hard to see why, in this view of time, there should be so little antimatter in the universe and so much matter: you’d expect equal amounts of both. As I have strong feelings for entropy, I’d posted a thought explanation for this some months ago imagining anti matter as normal forward-time matter, and posits the existence of an undiscovered particle that interacts with its magnetism to make matter more stable than antimatter. To see how it works, recall the brainteaser about a tribe that always speaks lies and another that always speaks truth. (I’m not the first to think of this explanation).
If the anti hydrogen drop at CERN is seen to fall upwards, but entropy still works in the positive direction as in my post (i.e. drops still splatter, and anti coffee cools like normal coffee), it will support a simple explanation for dark energy — the force that prevents the universe from collapsing. Dark energy could be seen to result from the antigravity of antimatter. There would have to be large collections of antimatter somewhere, perhaps anti-galaxies isolated from normal galaxies, that would push away the positive matter galaxies while moving forward in time and entropy. If the antigalaxies were close to normal galaxies they would annihilate at the edges, and we’d see lots of photons, like in the poem. Whatever they find at CERN, the future will be interesting. And if time travel turns out to be the norm, the past will be more interesting than it was.
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After giving it some thought, I wanted to make the prediction now before the experimental results come in that the antimatter drop will not fall upwards in gravity, but will instead be gravity neutral.
Think about it this way:
A normal particle will be attracted all other matter with a given gravitational force.
An anti-particle will be attracted to all other matter with a given gravitation force
however, since the antiparticle is time-reversed then in normal time it will appear to be repelling all other matter with a given gravitational force.
Since the apparent repelling force of the anti-matter in normal time is exactly opposite in magnitude from the attracting force of regular matter, the two should cancel eachother out.
Hence, a drop of antimatter should be gravitationally attracted to itself but not to regular matter.
So, if the gravitational pull of the drop of antimatter appears to be undetectable in the upcoming experiment we can call that continued evidence of antimatter simply being reverse time matter.
I like the way you’re thinking about it, Kristjan. Now all that remains is that we let the experiment be done. Last year, the expectation was that we’d have our experimental answer about now. The current expectation is next year.
Haha, the results will be ready tomorrow but tomorrow is always one day away…;)
Its funny though, after writing my previous comment about anitmatter and matter being neutrally attracted I had another thought that suggests the opposite is true.
I realized that if you watch a time reverse movie the people in it do not go flying out in to space, which would suggest that time reversed gravity works the same as regular gravity – the tendency during time reversal is still for objects to fall towards eachother.
So why do we have this notion that if time were reversed, objects would fall up? This is because if you time reverse an object in free fall it will reverse direction and fall up. But this is not because the force of gravity is being reversed. Rather, it is the kinetic energy of the object that is reversed. The object that is now falling upwards will slow by the same rate that an object in normal time being thrown upwards at the same speed would fall.
So then the new prediction will of course be that antimatter will be gravitationally attracted to itself and regular matter in the same way, with objects of either type of matter at rest tending to fall towards eachother.
So, back to the interesting part – why a reversed time object falls upwards…
In normal time if you were to observe a ball at rest on the ground it would invariably stay there in the same spot indefinitely unless it is disturbed by some force.
However, in reverse time that same ball can spontaneously jump into the air and bounce away. Why? Well, if one were to look closely one would see that the ball did not just jump up on its own through magic but in fact was propelled in to the air through the same method that the forward time ball would have needed to be – through being impacted by another object.
In the case of the backwards time ball, the material impacting the ball is actually a sound shockwave travelling through the ground that just by chance happens to focus on the exact location of the ball. Then, each time the ball falls back to the ground another shockwave travels up through the ground and strikes the ball again propelling it even higher.
You can see where I am going with this…
It would seem that you can indeed just reverse all the directions and energies of the particles in a given situation and time will run backwards. The reason why this normally does not seem to be the case, is because you have to reverse the direction of all the particles involved that contain energy emitted by the original event.
In practical terms this is impossible to do – how does one lasso and corral all of the low energy heat photons heading out into space that are the end result of a teacup breaking on the floor once all the pieces have come to rest and the sound waves have dissipated?
So, to finish what I guess turned into a rather long rant:) It would seem that what we call entropy is simply the fact that to have very specific events (such as the spontaneous re-assembling of a teacup) happen spontaneously you need to have a very specific set of initial conditions, and is therefore completely reversible although very very unlikely to spontanously reverse. The more different ways you can arrive at a given outcome, the more likely that outcome will spontaneously come to be. So if you look at the teacup breaking, you will see that regardless of the exact state of the air molecules and ground geometry, the teacup can still fall to the ground and break as there are countless ways that the event can occur. But in order to reverse and reassemble, the air and ground and even the radiation in the region need to be in a very specific state that is unlikely to occur.
So the direction of time ends up being away from some relative state of overall order in the universe. If some preternatural creature could corral enough of the particles of matter and energy though, and aim them all just right, then time would appear to run exactly backwards.
But I would guess that simply reversing the directions of matter and energy right now would not result in the past being replayed due to those pesky CP violations. But to tie it all together, if all the matter and energy’s direction and energy were reversed AND all the matter were switched with antimatter, you would then get an exact replay of history.
The end! Sorry for the longwinded and marginally relevant tangent;)
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Cooling anti-hydrogen to form drops probably won’t work because as you eliminate thermal motion repulsive gravity would become more dominate. Something like a centrifuge might work but testing for gravitational effects inside the centrifuge would seem pretty tricky.
If anti-hydrogen falls up I’d think antimatter really is matter moving backwards in time.
” Dark energy could be seen to result from the antigravity of antimatter.” – I’ve thought about that but it doesn’t seem like enough antimatter to account for the dark energy. Maybe we have a problem measuring the dark energy.
My guess is you have a good point – when you are going backward in time, attraction looks like repulsion. So the apple does fall up. Except there are no antimatter apples because antimatter particles don’t accrete. Attractive forces like gravity appear repulsive so antimatter is generally expelled from galaxies and lurks in the dangerous environs of interstellar space. We don’t see it because there are no bodies of antimatter. That is, there are not enough elements of antimatter available to form apples. So we live in a universe with time symmetry – that is half of matter is going forward in time and the other half backwards. Overall, the universe is going nowhere in space or time. And probably came from nowhere. So perhaps the big bang was really a phase change between matter and anti-matter. Just a thought.
Actually any object moving through space-time travels on its world line, meaning that the anti-apple falls down. If space-time curvature was reversed it would fall up, but you would have to have an anti-matter object to reverse space-time curvature enough to make it noticeable. An example is a photon which I understand acts as its own anti-particle. It is affected by gravity to form gravitational lensing. Actually the anti-curvature effects of antimatter may be noticeable only from a cosmic perspective. That is on a cosmic scale they cancel out the gravitational effects of matter so space-time appears to be flat as is actually observed.
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