Posts Tagged ‘pair production’

Particle Pair Production in Deep Space

August 6, 2017

Many of you know that a matter-antimatter reaction results in a pair of gamma rays. Fewer of you will know that you can take a couple of gamma rays, run them into each other, and get a pair of matter-antimatter particles. This has been done experimentally, and there’s a bit of data about it under “Two Photon Physics” in Wikipedia. Generally, if a subatomic reaction can occur, then it’s reversible. Maybe not statistically probable, but still reversible. This is a concept I used in a story I recently sold to Analog SF. In an area of space with high-density, high energy gamma rays, you’ll get a lot of positrons and anti-protons produced (more positrons, since they are 1/2000th the mass, of course), but there will also be some small production of antihydrogen if the antimatter doesn’t recombine right away with normal matter. And the antihydrogen may be neutral enough to survive and drift in deep space for a while, maybe long enough to be used as a resource.

Some reactions result in the release of more than two photons. A particle and antiparticle meet, three photons are emitted. The photons are lower energy, but the reverse reaction, 3 photons meeting, is a much, much lower probability than 2 photons (gamma rays) meeting. Still, on rare occasions, it might happen.

In fact, it’s my belief that if you have enough photons, even low-energy photons, passing through the same bit of space at the same time, you can also have pair-production, spitting out particles and antiparticles. One calculation for photons from the cosmic microwave background radiation (CMB) estimates 400 photons per cubic centimeter, average, plus whatever higher-energy visible light and gamma rays pass through from billions of stars. And there are a lot of cubic centimeters in a light-year (about 4.9 x 1050). Even if the probability of pair production is very, very low, I still imagine that it would happen on occasion.

As a side-note, the probability of a positron and electron meeting in deep space is very high, since they attract one another, while the probability of two gamma rays meeting at just the right time in just the right way is fairly low. The reaction looks symmetric, but the probability of it happening in a certain direction is much higher one way than the other. Ditto for any two-particle reaction that creates three particles. This contributes to the increased entropy of the universe and the “arrow of time”; there’s a preferred direction for these subatomic reactions to occur.


Mass-creation From the Vacuum – Heisenberg Meets the 3-body Problem

March 27, 2010

I’ve been considering the conundrum of Mass-Energy conservation and the violation of this principle in light of the Big Bang. One of my friends described this as the “elephant in the room” with regard to the law of mass-energy conservation.

So we have to wonder if there are any existing mechanics that allow violation of this law. The first one that pops to mind is the Heisenberg time-energy relationship that allows virtual particles to pop into existence from the vacuum; the shorter the time, the greater the potential mass-energy. Sadly, the brief existence is confined to a duration so short that it’s impossible to detect, although certain effects, such as the Casimir effect, strongly suggest that virtual particle interactions are quite real (look it up on Wikipedia, if you’re curious).

Now put two of these virtual particle pair-productions adjacent to each other when they pop into existence (this has to happen some tiny fraction of the time) and the 4 particles produced are suddenly involved with the chaotic 4-body problem, interacting in such a way as to acquire stability before disappearing from our universe, potentially creating any variety of subatomic particles and pairs, half matter and half antimatter.

The net result is a continuous mass-creation with high-energy particles appearing from nowhere.

Your initial response will be, “Yes, but the antiparticles are going to combine with regular particles and annihilate a mass equal to that created.” Absolutely true. However, the energy produced will not be dragged back down into the closed-loop non-existence of a virtual particle. It will be released as two high-energy photons that go zipping around the universe and adding to the overall mass-energy of the universe, adding its little contribution to the light-pressure factor of its expansion.

Perhaps Fred Hoyle’s discounted steady-state universe still has a viable solution, and perhaps if we go back in time toward a Big Bang, we will find out that this mechanism decreases the mass of the universe so that there is no Big Bang at all, just a slow and continuous chaotic production of mass energy from the vacuum.

Perhaps it starting not with a bang, but a whisper (apologies to T.S. Eliot).