As reported on Wired.
- BY ADAM MANN
The detector inside the BICEP2 telescope that found primordial B-mode polarization in the cosmic microwave background. Image: Anthony Turner (JPL)
The physics world was on fire yesterday after an announcement that astronomers had detected a signal from the beginning of time. This is exactly as cool as it sounds. Maybe even cooler. And it might lead to us learning further crazy things about our universe.
Besides coming as a shock to most of the community, the discovery once again proved that we don’t quite know many things about our universe. Ordinarily sober-minded scientists went to hyperbolic lengths to describe just how significant the results were. Depending on who you ask, they were as important as finding the Higgs boson, directly detecting dark matter, or discovering life on other planets. Nobel Prizes are already being discussed.
“I find it hard to imagine a more powerful, more transformative experimental result anywhere in fundamental physics, short of a discovery of extra dimensions or of a violation of quantum mechanics,” wrote physicistLiam McAllister of Cornell University in a guest post on The Reference Frame, a blog dedicated to physics.
Now before they can be given the scientific seal of approval, the results need to be confirmed by an independent team. But if the same signal is seen in another telescope, they could potentially touch on many different areas of physics, including the origins of the universe, quantum gravity, particle physics, and the multiverse. As a way to get acquainted with this new world, let’s take a look at all the different ways that yesterday’s announcement could change our understanding of the cosmos.
To start off with, the BICEP2 experiment at the South Pole found what are known as primordial B-mode polarizations. These are characteristic swirls in light that comes from a mere 380,000 years after the Big Bang. While detecting the swirls is a monumental achievement, it’s what potentially caused them that is really impressing physicists: Gravitational waves created during the first trillionth of a trillionth of a trillionth of a second after the Big Bang during an event called cosmological inflation.
The story of inflation starts during the 1920s, when astronomer Edwin Hubble turned his telescope to the night sky. Hubble was plotting the distance to different galaxies and he noticed something odd. All galaxiesappeared to be moving away from Earth and, the further away a galaxy was, the faster it was moving. This doesn’t mean that Earth is giving off some sort of cosmic bad smell that drives the rest of the universe away. Because movement is relative, you can imagine what it would look like if you were located in any of these other places, thinking yourself to be sitting perfectly still while all other galaxies are moving away from you.
The expansion of space-time is like a raisin bread rising in the oven. Image: NASA
Hubble had discovered that the universe was expanding. The space between stars and galaxies is constantly growing larger. Such a finding was actually predicted a few years earlier, after Einstein published his equations of General Relativity, which govern the properties of space-time. The equations showed that it was impossible for the universe to remain static; it had to either expand or contract. Though Einstein himself didn’t initially believe the universe could expand, Hubble’s data soon convinced everyone that it was.
That everything is going to be farther out in the future sort of implies that everything was once much closer together in the past. Working backwards, scientists could deduce that the universe was once a much smaller place. In this early cramped universe, matter and energy would have been squeezed together, becoming denser and therefore hotter. Near the very beginning of time, the universe would have been denser and hotter than anything we can imagine.
But such an idea struck scientists in the 1940s as absurd. Everyone at the time was sure that the universe was eternal and hadn’t popped into existence on some specific Wednesday. During a 1949 radio broadcast, astronomer Fred Hoyle derisively called this model the “Big Bang,” a name that has unfortunately stuck ever since. Of course other than Hubble’s observation, there still wasn’t much proof that the universe started in a tiny, overcrowded ball.
It was in 1964 that two scientists, Arno Penzias and Robert Wilson, happened to be looking at the night sky in radio wavelengths. They kept seeing a signal they couldn’t account for coming from everywhere in the sky all at once. Penzias and Wilson had discovered the Cosmic Microwave Background (CMB), an afterglow from an earlier time in the universe. The CMB is made of light that was emitted just after the cosmos had become cool and diffuse enough that photons could sail forward unimpeded. This was a signal from 380,000 years after the Big Bang. The CMB, combined with other data that precisely cataloged the abundance of elements created during the Big Bang, boosted the idea that the universe once started as a hot, dense mess.
But just as scientists were feeling okay with the idea of the Big Bang, they realized there were a few niggling problems. No matter where we looked with our telescopes, the universe appeared to be pretty much exactly the same. Besides being boring, this was a major head scratcher. If you drop ink into a cup of water it will start to expand outward and eventually evenly permeate the liquid. That’s because the ink has enough time to reach all sides of the cup. But the universe is like a cup that is constantly growing, making it hard for the ink to evenly distribute. Moreover, the universe can expand faster than the speed of light, so that no matter how fast the “ink” traveled, it would never be able to perfectly spread out.
How had the universe’s ink –matter and energy — managed to do this impossible task of spreading evenly? Even in the very early universe, when the entire cosmos was just a speck smaller than an atom, there was no way for anything to move around fast enough to spread out evenly.
In the late ’70s and early ’80s, a few intrepid physicists thought up a solution. At its earliest times, they speculated, the universe was much smaller than we believe. Matter and energy could circulate and even out. But around 10-35 seconds after the Big Bang, it suddenly went through an insane expansion, equal to an object the size of your computer monitor growing to the size of the observable universe. The rapid expansion became known as inflation.
Along with fixing the problem of how the universe became so homogenous, this inflationary theory dealt with a few other difficulties of the Big Bang model. For example, physicists have long looked for exotic particles, like magnetic monopoles (think of a magnet with only a north, no south), that they calculated should have been created in the early universe. With inflationary expansion, these particles could have gotten so diluted out in the cosmos that we basically have no chance of spotting them.
This graphic of the history of the universe from the mid-2000s clearly has inflation marked on it, despite the speculative nature of this era.Image: NASA/WMAP Science Team
But inflation had a few problems of its own. Namely, why in the world did the universe suddenly blow up so huge? Scientists have suggested that maybe some sort of new field exists – sort of like the field created by the Higgs boson that gives particles their mass – whose entire purpose is to drive inflation. No one had ever seen such a field, but astronomers collectively thought “Sure, why not?” because inflation was an extremely useful idea.
In fact, inflation has been such a useful theory that for the last 20 or so years, it’s almost been considered a done deal. Look at any chart of the universe’s history from recent years and you’ll see a part early on marked “Inflation” (often with a question mark, if they’re being honest). But for all its success, inflation has remained in the “really good idea/wouldn’t it be great if it were true” category.
With yesterday’s announcement, inflation finds itself on much firmer ground. The swirly pattern discovered in the polarization of CMB light is a pretty good indication that these photons were warped by immense gravitational waves. These waves must have come from somewhere, and the most compelling source would be from the inflationary era, when space-time rippled as it expanded outward at a rapid pace. If the findings are confirmed, they provide evidence that inflation did indeed happen and could allow scientists to figure out precisely how big and fast the expansion was.
This brings us to another reason that the BICEP2 results are so intriguing. They give us some of the best evidence for the existence of gravitational waves in the universe. Gravitational waves are swells in the fabric of space-time that propagate outward, carrying energy with them. Though astronomers have seen how energetic pulsars could provide a signal for gravitational waves, there is no well-established direct way to see them.
Gravitational waves are to the force of gravity what light waves are to the electromagnetic force. And just as light waves can also be thought of as a particle, known as the photon, the existence of gravitational waves imply a gravitational particle, called the graviton. Physicists would like gravitons to exist. They would be immensely helpful for understanding everything from black holes to galactic orbits. But because they are so weak and hard to detect, gravitons have remained stubbornly theoretical for nearly 80 years. Every theory to describe how they would work ends up spouting mathematical gibberish. Data about the CMB primordial B-mode polarizations could help explain why our theories of quantum gravity keep coming to naught.
Along with gravitons, the new results could be a boon to particle physicists. The gravitational waves from inflation were created during an extremely energetic era in the early universe. At this time, the cosmos wasa soup of particles, each with 1016 gigaelectronvolts of energy. By contrast, the LHC’s peak energy production will be 14 gigaelectronvolts. Some theories predict that at this energy range, three of the four fundamental forces – electromagnetism, the weak force, and the strong force – were all mushed together into some sort of superforce. Data about the primordial B-modes would allow researchers to probe energies that they could never hope to achieve in particle accelerators on Earth.
Just as the LHC is searching for signs of new subatomic particles, the BICEP2 findings could confirm the existence of particles that have never before been seen. Namely, scientists think that there must be a particle whose job it is to drive inflation, called the inflaton. If the new results turn out to favor inflation, they would provide the first evidence for physics beyond the Standard Model, the currently accepted framework for how all known particles and forces interact. The LHC has been searching for this evidence but, so far,hasn’t seen anything.
Finally, the BICEP2 findings are being touted as a possible way to confirm or deny the existence of a multiverse, a theory that posits the existence of a whole slew of different universes existing outside our own. Some theories predict that our cosmos was born when it broke off from an earlier one and that new universes are constantly coming into existence. This theory, known as eternal inflation, has many adherents in the physics community. But it also has many detractors and it’s not quite clear how to best interpret the new results with regards to the multiverse. As with most things about this speculative theory, the BICEP2 findings seem too early to tell.