Physics Blogs 2

Have Cosmologists Lost Their Minds in the Multiverse? (Op-Ed)

By Luke Barnes, University of Sydney and Geraint Lewis, University of Sydney | May 14, 2014 09:23pm ET

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????????????The recent BICEP2 observations – of swirls in the polarisation of the cosmic microwave background – have been proclaimed as many things, from evidence of the Big Bang and gravitational waves to something strange called the multiverse.

The multiverse theory is that our universe is but one of a vast, variegated ensemble of other universes. We don’t know how many pieces there are to the multiverse but estimates suggest there many be squillions of them.

But (if they exist) there has not been enough time since our cosmic beginning for light from these other universes to reach us. They are beyond our cosmic horizon and thus in principle unobservable.

How, then, can cosmologists say they have seen evidence of them?

Seeing the unobservable

Unobservable entities aren’t necessarily out-of-bounds for science. For example, protons and neutrons are made of subatomic particles called quarks. While they cannot be observed directly, their existence and properties are inferred from the way particles behave when smashed together.

But there is no such luxury with the multiverse. No signals from from other universes have or will ever bother our telescopes.

While there is some debate about what actually makes a scientific theory, we should at least ask if the multiverse theory is testable? Does it make predictions that we can test in a laboratory or with our telescopes?

The answer is yes, but perhaps not as you’d expect. And the exploration of the multiverse theory involves some very complex, and very controversial, ideas.

The mark of the generator

If your multiverse theory generates its universes via some physical process, then that process may leave its fingerprints on this universe. This is what BICEP2 might have seen.

Cosmologists think that in its earliest stages, the universe underwent an extraordinarily rapid expansion, known as inflation. In many versions of inflation, gravitational waves leave an imprint in fossil radiation, recently observed as characteristic swirls in this ancient light; a successful prediction of inflation.

In some versions of inflation, the process that causes our universe to inflate is expected to produce huge numbers of other universes. Evidence for inflation isn’t exactly direct evidence for the multiverse, but it’s a start. Read More

Pinning Down the Universe’s Rate of Expansion

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db456444-fef0-4582-9ae6-d8555d72c411Paul Hooper at Spirit Design, with Mat Pieri and Gongbo Zhao, ICG
Visualization of the experiment carried out by the Baryon Oscillation Spectroscopic Survey (BOSS). Redshift data from 140,000 quasars collected by a 2.5-meter telescope at Apache Point, New Mexico, provide the most accurate measurement to date of the expansion rate of the Universe.

In 1998, observations of supernovae led to the remarkable conclusion that the Universe’s expansion is accelerating—a finding most often explained by a yet-to-be-deciphered form of dark energy. In a talk at a session on cosmology, Andreu Font-Ribera from Lawrence Berkeley National Lab reported on the most precise measurement of that expansion to date, carried out by the Baryon Oscillation Spectroscopic Survey (BOSS). And the new result pushes our knowledge further back in time: we now know that 10.8 billion years ago, the Universe was expanding by 1% every 44 million years.

The BOSS analysis relies on data from 140,000 quasars collected by a 2.5-meter telescope at Apache Point, New Mexico. BOSS researchers have measured the expansion of the Universe by mapping the redshifts of light passing through intergalactic hydrogen clouds. These clouds have been imprinted with so-called baryon acoustic oscillations—sound waves created in the exploding plasma of the early Universe.

Light from extremely distant but very bright quasars passes through the hydrogen clouds, which have high- and low-density regions caused by the baryon oscillations. The clouds are moving away from the quasars with the expansion of the Universe, so there are redshifts in the spectral absorption lines that yield information on the rate of expansion. And because the baryon oscillations are peaks and troughs of density, researchers can tie a given redshift to a particular position.

The team used two complementary techniques to get the uncertainty in the measured expansion rate down to 2%. One method, autocorrelation, compared the absorption in nearby quasar spectra. The other, cross-correlation, analyzes the amount of absorption as a function of separation from a quasar. As the analysis of the data set continues, researchers hope to be able to understand better the nature of the dark energy that is causing the accelerating expansion.

New Quantum Theory Could Explain the Flow of Time

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coffee_entanglement_webAs a hot cup of coffee equilibrates with the surrounding air, coffee particles (white) and air particles (brown) interact and become entangled mixtures of brown and white states. After some time, most of the particles in the coffee are correlated with air particles; the coffee has reached thermal equilibrium. Image: Lidia del Rio

Coffee cools, buildings crumble, eggs break and stars fizzle out in a universe that seems destined to degrade into a state of uniform drabness known as thermal equilibrium. The astronomer-philosopher Sir Arthur Eddington in 1927 cited the gradual dispersal of energy as evidence of an irreversible “arrow of time.”

But to the bafflement of generations of physicists, the arrow of time does not seem to follow from the underlying laws of physics, which work the same going forward in time as in reverse. By those laws, it seemed that if someone knew the paths of all the particles in the universe and flipped them around, energy would accumulate rather than disperse: Tepid coffee would spontaneously heat up, buildings would rise from their rubble and sunlight would slink back into the sun.

“In classical physics, we were struggling,” said Sandu Popescu, a professor of physics at the University of Bristol in the United Kingdom. “If I knew more, could I reverse the event, put together all the molecules of the egg that broke? Why am I relevant?”

Surely, he said, time’s arrow is not steered by human ignorance. And yet, since the birth of thermodynamics in the 1850s, the only known approach for calculating the spread of energy was to formulate statistical distributions of the unknown trajectories of particles, and show that, over time, the ignorance smeared things out.

Now, physicists are unmasking a more fundamental source for the arrow of time: Energy disperses and objects equilibrate, they say, because of the way elementary particles become intertwined when they interact — a strange effect called “quantum entanglement.”

“Finally, we can understand why a cup of coffee equilibrates in a room,” said Tony Short, a quantum physicist at Bristol. “Entanglement builds up between the state of the coffee cup and the state of the room.”Popescu, Short and their colleagues Noah Linden and Andreas Winter reported the discovery in the journal Physical Review E in 2009, arguing that objects reach equilibrium, or a state of uniform energy distribution, within an infinite amount of time by becoming quantum mechanically entangled with their surroundings. Similar results by Peter Reimann of the University of Bielefeld in Germany appeared several months earlier in Physical Review Letters. Short and a collaborator strengthened the argument in 2012 by showing that entanglement causes equilibration within a finite time. And, in work that was posted on the scientific preprint site in February, two separate groups have taken the next step, calculating that most physical systems equilibrate rapidly, on time scales proportional to their size. “To show that it’s relevant to our actual physical world, the processes have to be happening on reasonable time scales,” Short said. Read More


Big Bang backlash: BICEP2 discovery of gravity waves questioned by cosmologists

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Video: In March, scientists from the Harvard-Smithsonian Center for Astrophysics announced their discovery of gravitational waves created at the dawn of the universe. These waves were created in a period of rapid expansion called cosmic inflation. This new evidence could prove the definitive confirmation of the inflation theory. But other researchers are not convinced.

By Joel Achenbach, Published: May 16 E-mail the writer

It was the science story of the year: Astrophysicists held a news conference at Harvard on March 17 announcing that their South Pole telescope had found evidence of gravity waves from the dawn of time.

Cosmology doesn’t get any bigger than this. The discovery was hailed as confirmation of a mind-boggling addendum to the big-bang theory, something called “cosmic inflation” that describes the universe beginning not in a stately expansion but with a brief, exponentially rapid, inflationary spasm.

Science is a demanding and unforgiving business, and great discoveries are greeted not with parades and champagne but rather with questions, doubts and demands for more data. So it is that, in recent days, scientists in the astrophysics community have been vocalizing their concern that the South Pole experiment, known as BICEP2, may have detected only the signature of dust in our own galaxy.

These doubters say, in effect, that rather than seeing the aftershock of the birth of the universe the scientists may have seen only some schmutz in the foreground, as if they needed to clean their eyeglasses.

This is a delicate issue. Careers and prizes are potentially at stake. So too is the credibility of a field that dares to probe the deepest secrets of the universe no matter where that search may lead.

No one is alleging an outright scientific error. It’s more of a debate about how scientists should communicate their uncertainties when presenting blockbuster findings. This is a case of “extraordinary claims demand extraordinary evidence,” to use the formulation made famous by astronomer Carl Sagan.

The South Pole telescope saw something in the sky — of that there is little doubt, because the team took great care to eliminate systematic errors that could have come from the instruments. But what the telescope saw — polarization of ancient radiation from the early universe — could have been produced by either primordial gravity waves or by foreground dust, or by some combination of both.

“They have very nice measurements of something. We don’t know what that something is,” said Uros Seljak, a professor of physics and astronomy at the University of California at Berkeley. “We can’t tell if BICEP2 has measured dust or has measured gravity waves.”

John Kovac, a Harvard astrophysicist and the principal investigator for BICEP2 — part of a larger collaboration among institutions from coast to coast — stands firmly behind his team’s findings. But he acknowledges that there are lingering uncertainties that will remain until new data is presented, likely this fall, by the European Space Agency’s Planck Space Telescope.

“We are very confident that we have measured B-modes” — polarization of light that can be caused by gravity waves — “with high statistical significance in the sky, and we have looked at them in multiple ways. And the data suggest they are unlikely to be dominated by galactic foregrounds. That is not to say that there is not uncertainty about that,” Kovac said.

Now everyone is waiting for the Planck results. The Planck telescope is scrutinizing the cosmic microwave background (CMB) radiation, a remnant of the moment when the young cosmos became transparent to light. BICEP2 looked at the radiation in a small patch of sky, but Planck is doing an all-sky survey in multiple frequencies and should produce excellent estimates of foreground effects such as dust.

The big announcement March 17 thrilled the cosmology community. People stopped what they were doing to examine the results. Cosmic inflation had been discussed for more than three decades, but this would be the first strong evidence for it.

“What inflation does is pull apart the fabric of space-time much faster than the speed of light,” said Princeton professor of physics Suzanne Staggs, part of a team studying the cosmic background radiation with a telescope in Chile.

“It’s an amazing thing that quantum processes a moment after creation may have been stretched out by inflationary expansion and literally etched across space itself — stretched across the sky,” said Brian Greene, a Columbia University theorist who is not involved in the experiments. “If we are seeing that, it is an monumental moment.”

All the more reason, he said, to ask the hard questions about the discovery, and “hit it with a sledgehammer and see if it survives.”

The BICEP2 dust-up is being played out on, among other places, a Facebook page started by people who couldn’t access the live-streamed Internet feed of the March 17 announcement at the Harvard-Smithsonian Center for Astrophysics. The controversy has popped up in recent days on physics blogs and in several science-oriented publications, including the online news sites of the journals Nature and Science, as well as New Scientist and National Geographic.

Thursday morning, theoretical physicist Raphael Flauger, who has a dual appointment at New York University and the Institute for Advanced Study in Princeton, N.J., gave a presentation at Princeton University outlining his concerns about the BICEP2 conclusions.

“I think foregrounds are maybe larger than they thought, but I’m still hopeful that there’s a signal there,” Flauger said in an interview later. “It will be the biggest discovery maybe in my lifetime. It would be a measurement of the conditions, if you want, when the universe was 10 to the minus-30 seconds old” — a millionth of a trillionth of a trillionth of a second.

Flauger noted that the BICEP2 team estimated the amount of foreground dust by relying, in part, on a slide presented at a conference. The slide gave a visual representation of observations by the Planck spacecraft but did not contain the actual data. Critics say this is not a robust way to make an estimate.

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Electrons hurtle into the interior of a new class of quantum materials

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Scientists at Princeton University have shown that negatively charged particles known as electrons can flow extremely rapidly due to quantum behaviors in a type of material known as a topological Dirac semi-metal. Previous work by the same group indicated that these electrons can flow on the surface of certain materials, but the new research indicates that they can also flow through the bulk of the material, in this case cadmium arsenide. Using a technique called angle-resolved photoemission spectroscopy (left), the researchers measured the energy and momentum of electrons as they were ejected from the cadmium arsenide. The resulting data revealed each electron as two cones oriented opposite each other that converge at a point, a telltale sign of the quantum behavior that allows electrons to act like light, which has no mass. A 3-D reconstruction (right) shows that the cone-shaped electrons are able to move in all directions in the material. The top-right panel reveals that these electrons are linked, allowing them to move even when deformed by bending or stretching, an attribute that gives them their topological nature. Image courtesy M. Zahid Hasan and Suyang Xu.

As smartphones get smarter and computers compute faster, researchers actively search for ways to speed up the processing of information. Now, scientists at Princeton University have made a step forward in developing a new class of materials that could be used in future technologies.

They have discovered a new quantum effect that enables electrons - the negative-charge-carrying particles that make today's electronic devices possible - to dash through the interior of these materials with very little resistance.

The discovery is the latest chapter in the story of a curious material known as a "topological insulator," in which electrons whiz along the surface without penetrating the interior. The newest research indicates that these electrons also can flow through the interior of some of these materials.

"With this discovery, instead of facing the challenge of how to use only the electrons on the surface of a material, now you can just cut the material open and you have light-like electrons flowing in three dimensions inside the materials," said M. Zahid Hasan, a professor of physics at Princeton, who led the discovery.

The finding was conducted by a team of scientists from the United States, Taiwan, Singapore, Germany and Sweden and published in two papers in the journal Nature Communications. The first paper, published May 7, demonstrates that fast electrons can flow in the interior of crystals made from cadmium and arsenic, or cadmium arsenide. The second paper, published May 12, explores fast electrons in a material made from the elements bismuth and selenium. Read Full Article

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