Although the term “antimatter” might sound like something from Star Trek, it is actually quite real. When I do nuclear chemistry experiments, for example, one of the ways I calibrate certain detectors is to use a radioactive sodium-22 source. One of the ways this isotope decays is by emitting the antimatter version of the electron (called a positron). That positron rather quickly finds an electron, and they annihilate each other, which results in two high-energy photons where there was once matter and antimatter. The energy of those two photons is well known, so they can be used to calibrate detectors.
Of course, this points to a big problem when it comes to studying antimatter – it doesn’t stick around very long. Since there is all sorts of matter around, any antimatter that gets produced rather quickly finds some matter, and annihilation is usually what results. Nevertheless, some scientists try to do all that they can with antimatter for whatever brief time is available to them.
One of the cool things you can do with antimatter is make anti-atoms. For example, consider boring old hydrogen. It consists of a single proton that is orbited by a single electron. How could you possibly spice that up? What about making anti-hydrogen? Take a positron (remember, that’s the antimatter version of an electron) and force it to orbit the antimatter version of the proton (which is called an antiproton). You now have the antimatter version of a hydrogen atom! Believe it or not, that has actually been done before. In the lab, scientists have made anti-hydrogen atoms. The problem is that none have been able to preserve the anti-hydrogen they have made for more than a fraction of a second.
Now a group of scientists at the European particle physics lab called CERN has managed to make anti-hydrogen and preserve it for the impossibly long time of fifteen minutes!1
Why am I excited about this? Well, first of all, it is just plain cool that we can make the antimatter version of an atom and then keep it around for such a long time. The second reason, which is far more important, is that it will allow us to test a key assumption of Einstein’s special theory of relativity.
Now remember, Einstein had two theories of relativity. The first one (special relativity) compared systems that are moving relative to each other at a constant velocity. This is the theory that tells us things like as your speed increases, time passes more slowly for you than it does for someone at rest relative to you. His general theory of relativity is based on special relativity, but is a theory of how gravity works. It led to the concept that time passes more slowly the stronger the gravitational field.
One of the very important assumptions behind special relativity is that there is symmetry to space and time. This symmetry ends up playing out in many ways, but one of them is that the antimatter version of an atom should have the same fundamental properties as the regular version of the atom.2 Unfortunately, because scientists haven’t been able to keep anti-atoms around very long, they haven’t been able to test it.
So now that scientists can keep anti-hydrogen atoms around for a long time, what will they do to test this assumption? Most likely, they will look at how it absorbs light. We have studied how the hydrogen atom absorbs light for a long time, so we know that really well. According to the symmetry demanded by special relativity, anti-hydrogen should absorb light in exactly the same way. Any deviation beyond experimental error will be a huge blow to relativity, as well as many other theories of matter.
I personally think that relativity has to be correct, since there is so much experimental evidence in its favor. However, it is important to test the key assumptions of any theory whenever possible. I look forward to seeing how this test turns out!
REFERENCES
1. “News of the Week,” Science 332:1248, 2011.
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2. Raymond A. Serway, Clement J. Moses, and Curt A. Moyer, Modern Physics, Brooks Cole 2004, p. 289
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Very anti-boring.
Lol Thanks, Josiah!
What does it say about me that I got so excited reading this??? So, do you think that antiprotons can ever exist naturally or are they a lab produced species only?
Vivielle, to me that means you have excellent taste! In answer to your question, they do exist naturally, but only where there is a lot of energy at play. So, for example, cosmic rays produced by the sun will sometimes collide with nuclei in space, and that sometimes produces an antiproton.
Dr. Wile,
Thanks for the article! Besides proving theories, is there any practical use for antimatter?
Good question, Enoch! There is already at least one practical use for antimatter. Have you ever hear of a “PET Scan?” It is a medical imaging test that allows doctors see how the organs in your body are working. Well, “PET” stands for “Positron Emission Tomography.” Essentially, a sample of a positron-emitting radioactive isotope is injected into the patient (usually in the bloodstream). There is a waiting period for the radioisotope to concentrate into the tissues, and then the patient is surrounded by gamma-ray detectors. When the radioisotope emits a positron, it quickly finds an electron, and the two annihilate one another. This results in two gamma rays (two photons of light) that move in opposite directions. The gamma-ray detectors detect those gamma rays, and then a computer uses the results to build an image of the organ being examined. This allows you to see an organ and how it is functioning without opening the patient up.
In Star Trek, of course, antimatter was used as a source of energy to fuel starships. That is also a theoretical possibility, if only we could figure out a way of storing antimatter until we need the energy. Then we could release the antimatter, which would quickly find matter with which to annihilate, and then high-energy photons would be produced, which could be harnessed for energy.
I expect the more we learn about antimatter, the more uses we will find for it.
Thanks for answering my question. Only your answer spawned another question… Are natural anitprotons as short lived as man made ones?
Thanks!
It depends completely on where they are formed. Antiprotons are stable, which means they could exist for a long, long time. However, they tend to find a proton rather quickly, and that leads to annihilation of both the antiproton and the proton. When an antiproton is formed in the lab, there are lots of protons around, so it is hard to keep the antiprotons away from them. As a result, the antiprotons don’t last very long. The amazing thing about CERN’s accomplishment is that they manage to keep antiprotons from finding a proton for 15 minutes.
If an antiproton forms naturally where there are also a lot of protons, then it won’t exist for very long. However, if it is formed in deep space, it will live a lot longer, because it will take a while before it comes across a proton to annihilate.
Here comes another question. (You can bet that my poor professors at college get asked an awful lot of questions…) Are there other antimatter versions of elements? For instance an antimatter version of oxygen or carbon? Somehow I would guess that those would be a lot harder to make in the lab.
You might find this interesting too – a man who tried to split atoms at home. http://www.thejournal.ie/swedish-man-arrested-over-attempts-to-split-atoms-at-home-193068-Aug2011/
Vivielle, if your professors are anything like I was when I was a professor, they must love you. I only wish more students would ask these kinds of questions!
The only anti-element I know is anti-hydrogen, and that has been built artificially. Theoretically, other anti-elements could be made, but anti-hydrogen is tricky enough. I am skeptical that anti-elements could form naturally, at least in the known universe. There is just so much matter around that I don’t see how naturally-formed positrons and naturally-formed antiprotons could last long enough to make anti-elements. When you throw in the fact that anything bigger than anti-hydrogen would also need anti-neutrons, things get even more unlikely. However, I have not actually done any calculations on this, so I can’t say with any certainty. That’s just my gut instinct.
Thanks for the link. I applaud the man for trying to do something like that at home. It’s unfortunate he didn’t go through the proper channels. If he had, he might still be working on his experiment. Of course, he might not have been approved, which means his experiment would never have started. I just think it’s best to work within government guidelines, not because the government is necessarily right, but because it is pretty powerful.
Dr. Jay, thanks so much for posting this! It was beyond fun for me to read about this. I’ll have to go research it some more! (On a side note, thanks for keeping up this blog and responding to your readers’ questions so well- I truly enjoy reading your posts. Also, thanks for writing your textbook series! I’m looking forward to taking the Chemistry and Advanced Chemistry courses in the next couple of years.)
Miranda, thank you so much for your kind words! I am glad that you find this stuff as interesting as I do, and I am thrilled to read that you are looking forward to taking chemistry and advanced chemistry! I think most students would replace “looking forward” with “really dreading being required”!
Well, I hope that my professors don’t mind, because I do ask an awful lot of questions. 🙂
Here’s another question. You said “We have studied how the hydrogen atom absorbs light for a long time, so we know that really well. According to the symmetry demanded by special relativity, anti-hydrogen should absorb light in exactly the same way. ” How then would a scientist know that they were looking at anti-hydrogen not just plain hydrogen?
Thanks! I really appreciate how you take the time to answer all the comments you get.
Vivielle, if the theory is correct, you wouldn’t know by looking at the light that is absorbed. However, because the sample must be so carefully handled to avoid annihilation, you would know that the sample itself is anti-hydrogen. You wold know it is not contaminated by hydrogen, because if it were, annihilation would take place, and you would see the gamma rays that result from that.
I love answering questions!