Among this year鈥檚 23 recipients of the 鈥榮 鈥済enius award鈥�, who have won $500,000 each, no strings attached, is , a quantum physicist at the Massachusetts Institute of Technology and a collaborator on the .
LIGO is on the hunt for gravitational waves, as-yet unseen ripples in space-time that are predicted by Einstein鈥檚 theory of relativity and should be particularly strong when neutron stars or black holes merge. So what does a gravity hunter spend half a million dollars on? And what do gravitational waves have to do with quantum mechanics? To find out, 快猫短视频 visited Mavalvala in her office at MIT.
Congratulations on the award. Was it at all expected?
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Oh my goodness, no. When I got the call I thought it was a prank. I really thought at some point somebody was going to say, 鈥淕otcha!鈥�
How do you plan on using the award money?
It鈥檚 hard to answer, with the few days I鈥檝e had to think about it. I鈥檒l almost certainly spend some of the money on trying out far-out ideas. 快猫短视频s always have some ideas that are very risky: you know that they may not pan out, but if they did 鈥� wouldn鈥檛 that be awesome? Those ideas are sometimes hard to get funded because they鈥檙e so speculative.
Are there any particular topics on your risky wish list?
There鈥檚 this idea that if you make a measurement on a quantum state you destroy it. But there are ways to get around that problem called techniques 鈥� these include ways to detect single photons repeatedly without destroying their delicate quantum states. The ideas are very sound but the implementations are quite difficult. My guess is the most likely place where an award like this would be used is in trying out these implementations and in seeing if our current technologies and knowledge can get us there.
A lot of your work has focused on using quantum mechanics to improve LIGO鈥檚 ability to detect gravitational waves. What鈥檚 the basic idea behind the experiment?
You take two laser beams at right angles to each other and you shoot them toward two mirrors, each one 4聽kilometres away. If there is a gravitational wave, the mirror positions will change and we鈥檒l see that the light will take either a longer or a shorter time to go out and come back. Each detector can detect mirror motion that is a thousand times smaller than the size of a proton.
Why is quantum mechanics important in taking these measurements?
This all comes down to the idea that you use a light beam to measure the position of the mirror. We have very powerful laser beams, so there are a lot of photons. These photons carry momentum and there鈥檚 some uncertainty in the momentum because they are quantum particles. This makes some uncertainty in your mirror position. One of the things that my group has done in the past few years is learn how to optically trap and cool a mirror, just the way people do optical trapping and cooling of atoms.
No gravitational wave has been directly detected yet. Why are they so hard to find?
Gravitational waves are weak, and they don鈥檛 interact very strongly with our detectors. So that鈥檚 the fundamental reason why it鈥檚 so hard to do. The other problem is that we live on a very vibrant planet filled with motion, so everything you can imagine wants to move our mirror more than the gravitational wave.
Do you ever think about what it will be like when you do find one?
Pure ecstasy, probably. I think it will be amazing. But I think the first detections will very much go in the direction of understanding whether we鈥檝e understood our instrument and making sure it really is a detection. It will probably be very much strengthened if the event we see is also seen by telescopes.
LIGO has been hunting for gravitational waves since 2002, and so far you haven鈥檛 detected any. Is that at all discouraging?
No. It shouldn鈥檛 be discouraging to anyone. We鈥檝e always known that this first generation of instruments we would build for LIGO would have the sensitivity to see a gravitational wave only if it came from one of the strongest sources, and it would have to be from a very nearby source. We鈥檝e always known that it was a bit of a long shot. What鈥檚 going on now at LIGO is a very major upgrade called Advanced LIGO [set to begin observations in 2015]. If we haven鈥檛 detected anything with this improved detector then I think disappointment and head-scratching will set in.
