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04/01/2014
Einstein's Gravity Waves and Guth's Inflation Confirmed?
CHAPTER 44 Our Very Beginning and a Future Promise
It's time to celebrate, but not too much. In the past (archives, column posted 9/1/2012) I've talked about the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California and its effort to achieve "ignition" in a nuclear reaction that is self-sustaining and produces more energy than is put into the reaction. In essence, it's trying to harness the hydrogen fusion process utilized in the hydrogen bomb, as we have harnessed the nuclear chain reaction of the atom bomb in our nuclear reactors. The NIF workers have built a football-field size assembly of 192 lasers to shoot a highly focused pulse of energy in the form of X-rays at a small hollow plastic ball "less than the size of a peppercorn" containing a bit less than 0.2 milligrams of the frozen hydrogen isotopes deuterium and tritium.
A news article by Daniel Clery in the February 14 issue of Science describes recent results at the NIF in which a so-called "high foot" approach has yielded the most promising results to date. Specifically, in two runs the goal of compressing the hydrogen isotope mix to a density of a hundred times that of lead and at a temperature of some 50 million degrees Kelvin to achieve nuclear fusion has been achieved. In one of the runs, nearly twice the amount of energy was generated as the amount of energy delivered to the pellet. Previous unsuccessful runs had been done using a "low foot" approach in which the 20 nanosecond pulse consisted mainly of a low power burst with a high power burst at the end of the pulse. It turned out that the initial low power allowed the capsule to break up, not a good idea. In the successful "high foot" approach a high power, shorter pulse was used in an effort to better control the mixing of the super hot isotopes. Not only did this work but the researchers saw a self heating effect due to the alpha particles generated in the reaction. The alpha particles, which are simply helium atoms without the electrons, help to heat the cooler fuel up to reaction temperature.
This development is certainly a noteworthy achievement. However, remember I said not to celebrate too much. Why? The 192 lasers generate beams of ultraviolet light, not the X-rays that impinged on that tiny pellet. It took a lot of energy to convert that ultraviolet light into X-rays and to focus and deliver that X-ray pulse to the target. True, in that one run, almost twice as much energy was generated in the capsule as was delivered to it. However, when you consider the energy required to create the X-ray pulse and deliver it to the capsule, the energy output due to nuclear fusion was only about one percent of the total energy put into the experiment. There's still a long way to go!
Switching gears, I'm posting this column on April 1, April Fool's Day. Apropos of the date, in the April issue of Discover magazine there's a column by Jonathon Keats titled "20 Things You Didn't Know About Hoaxes". One of the "hoaxes" he mentions involved the Laser Interferometer Gravitational-Wave Observatory (LIGO). Back on May 9, 2000 (see archives), I posted a column in which I discussed LIGO and its objective, to detect gravitational waves, postulated by my scientific hero, Albert Einstein. I won't go into detail about how LIGO hoped to detect gravity waves but I was skeptical that the project would achieve its goal. However, in 2010, the LIGO researchers thought they had indeed detected gravity waves. Sadly for them, it was a hoax - actually an authorized hoax termed "blind injection", a deliberate simulation of what a gravity wave would do if real. This cruel trick was authorized to make sure that the LIGO team was operating at the high level needed to detect an actual gravity wave. The LIGO team was fully aware that what they were looking at might be a blind injection; and it was.
What did Einstein say about gravity? He proposed that anything with mass distorts space-time. A popular way of illustrating the effect is to imagine space-time as a rubber sheet. Put a bowling ball on the sheet and the sheet sinks around the ball. If there's another ball nearby, say a marble, it will want to roll down the sheet to the bowling ball; it is attracted to the bowling ball - gravity. If the marble spins around the bowling ball, as we do around the sun, we and the marble are balancing the pulls of these ripple in space-time. Einstein predicted that these ripples in space-time would propagate like waves throughout the universe. The problem is that gravity is a pretty weak force and detecting a gravitational wave, if it exists, requires hugely sensitive apparatus, such as LIGO.
Let's think of some things that should cause a hefty gravity wave. A couple of black holes bumping into each other would be pretty dramatic and I imagine would cause rather big ripples in space-time. On the other hand, it's hard to imagine anything more likely to generate monstrous gravity waves than the Big Bang, when our universe and our space-time itself came into being 13.8 billion years ago. One of the proposed features of the Big Bang put forth by Alan Guth in 1980 was inflation. He posited that, in the first trillionth of a trillionth of a trillionth of a second or so, our universe expanded faster than the speed of light from a tiny speck less than the size of an atom to about the size of a golf ball. After that, the universe continued to expand at a slower rate.
I've often discussed what has been termed the "afterglow" of the Big Bang, the cosmic microwave background (CMB) discovered by Penzias and Wilson of Bell Labs back in the 1960s. This light, now stretched out in the form of microwaves after emerging from darkness over 13 billion years ago, is remarkably uniform. The uniformity is thought to be due to that inflationary expansion in that teensiest of a second. Fortunately for us, there were quantum fluctuations that caused tiny clumps of stuff that eventually became stars and galaxies and planets. NASA's Wilkinson Microwave Anisotropy Probe mission detected small fluctuations in temperature in regions of the CMB that would bolster this view.
Although inflation should have created huge ripples in space-time, gravity is a relatively weak force and gravity waves from any source have not yet been detected. But now enter BICEP2 and what appears to be a truly monumental achievement that not only confirms the existence of gravity waves but also confirms Guth's inflation. Either of these would be a sure fire Nobel Prize winning achievement but proving both at once is mind boggling! I've just finished watching the press conference from March 17 at the Harvard-Smithsonian Center for Astrophysics at which John Kovac, leader of the BICEP2 effort, and his colleagues described their results. BICEP2 is a project involving a telescope at the South Pole which has been used to study the polarization of the light in the CMB over a patch of sky about the equivalent of 10 full moons. The researchers have spent three years checking and evaluating their data and now have confidence that it is real.
Polarized light is familiar to most of us. We use polarized sunglasses to filter out glare and liquid crystal displays on our TV sets involve polarized light. Polarization has to do with the orientation of electric and magnetic fields in light waves and there's a "handedness" factor, which pertains to either clockwise or counterclockwise rotation of the electric or electromagnetic fields in a beam of light. I'm not good at understanding waves - never have been and probably never will be. At any rate, what I gather from various accounts of the BICEP2 reports, is that gravity waves also would have handedness and because of this the inflation-induced gravity waves in the Big Bang would have imprinted on the light, i.e., on the CMB a very distinct pattern of polarization known as B-mode polarization. This B-mode polarization is a kindly of swirly or curvy pattern of polarization, as opposed to a more structured and what I gather is a more symmetrical polarization structure.
If you look at the chart they've derived from their data, it shows the orientations of the polarization of the CMB in the patch of the sky they looked at and you can see the swirly pattern. Therefore, the BICEP2 researchers believe they have proved is that there are gravity waves and that inflation did indeed exist. They've also shown that quantum mechanics and Einstein do come together, I gather, in those tiniest fractions of a second when our universe came into being. In their press conference, the BICEP2 team said they expect to have their findings challenged and eagerly await what they hope will be confirmation of their results. I'm not certain but I believe one of those present at the press conference was Alan Guth. If so, he and Peter Higgs (of the recently discovered Higgs boson) share the experience of seeing their hugely important ideas on the fundamental nature of our universe confirmed during their lifetime. Too bad Einstein didn't have that opportunity with his gravitational waves. I like to think they were all there in spirit in the first seconds of our beginning as a universe.
Longtime readers will know that I'm obsessed with origins. I don't often venture into the political arena in these columns but, since this column deals with the ultimate origin, I can't resist expressing my concern about a recent Pew Research Center poll. I first saw mention of this poll in an editorial titled "Declaring War on Darwin" in the January 3 edition of our Jersey newspaper, The Star-Ledger. In the survey, taken in 2013, essentially half of the Republicans surveyed (48%) said that they believed that humans and other living things have existed in their present form since the beginning of time. Obviously they don't believe in evolution. Of the Democrats polled, 27 % shared that non-belief in evolution. Extrapolating, I suspect that about the same percentages would question the existence of the Big Bang and our universe being nearly 14 billion years old. The lack of scientific knowledge in our country troubles me greatly and doesn't bode well for the future of the USA in a competitive world where China and other countries are training huge numbers of scientists and engineers.
Maybe this gloomy outlook reflects the horrible winter we've had and, hopefully, it will improve when golf season returns in two weeks. I thought March went out yesterday in a fashion meant to remind us of our winter. I was preparing to drive to the mall for my morning walk when I heard sleet hitting our windows, followed by a ten-minute snowfall and then a day in which the temperature rose to 55 degrees Fahrenheit. Oh, for a return to the good old days, whatever they were!
Next column, hopefully, will be posted on or about May 1, 2014.
Allen F. Bortrum
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