Why the death of black holes is a big problem for physics

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Part 4 of my 4-part series on black holes for Medium members is up; part 1 is herepart 2 is here, and part 3 is here. If enough of you read, they may keep me around to write more, so please read and share! And yes, the title is a John Donne reference, because I was an English minor and am required to make literary references as often as I can get away with.

Gravity Be Not Proud

The discovery that black holes emit particles and might eventually evaporate threw theoretical physics into chaos. Here’s why.

For Medium:

Hawking ended up being one of the very rare ALS patients to survive the condition, at the eventual cost of being confined to a wheelchair and communicating primarily through a computer. And his work on black holes — along with the work of a small handful of other physicists — opened up a new field of research in quantum gravity.

The most shocking discovery to come out of Hawking’s work: Black holes can emit radiation and can eventually evaporate.

Unfortunately for physicists, the radiation from a real black hole is too faint to be seen, and even a smaller black hole, like the ones seen by LIGO, would take a mind-blowingly long time to evaporate. However, the prediction of this Hawking radiation and death of black holes exposed a major problem in theoretical physics, one that is still unsolved today.

Read the rest at Medium…

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The search for a “theory of everything”

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

All four one and one for all

A theory of everything would unite the four forces of nature, but is such a thing possible?

For Symmetry Magazine:

Over the centuries, physicists have made giant strides in understanding and predicting the physical world by connecting phenomena that look very different on the surface.

One of the great success stories in physics is the unification of electricity and magnetism into the electromagnetic force in the 19th century. Experiments showed that electrical currents could deflect magnetic compass needles and that moving magnets could produce currents.

Then physicists linked another force, the weak force, with that electromagnetic force, forming a theory of electroweak interactions. Some physicists think the logical next step is merging all four fundamental forces—gravity, electromagnetism, the weak force and the strong force—into a single mathematical framework: a theory of everything.

Those four fundamental forces of nature are radically different in strength and behavior. And while reality has cooperated with the human habit of finding patterns so far, creating a theory of everything is perhaps the most difficult endeavor in physics. [Read the rest at Symmetry]

Some heavy facts about gravity

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I’m not generally the type of writer who makes listicles, but I’m producing a few for Symmetry Magazine this year. The first covers the OG of fundamental forces: gravity!

Six weighty facts about gravity

Perplexed by gravity? Don’t let it get you down

For Symmetry Magazine:

Gravity: we barely ever think about it, at least until we slip on ice or stumble on the stairs. To many ancient thinkers, gravity wasn’t even a force—it was just the natural tendency of objects to sink toward the center of Earth, while planets were subject to other, unrelated laws.

Of course, we now know that gravity does far more than make things fall down. It governs the motion of planets around the Sun, holds galaxies together and determines the structure of the universe itself. We also recognize that gravity is one of the four fundamental forces of nature, along with electromagnetism, the weak force and the strong force.

The modern theory of gravity—Einstein’s general theory of relativity—is one of the most successful theories we have. At the same time, we still don’t know everything about gravity, including the exact way it fits in with the other fundamental forces. But here are six weighty facts we do know about gravity. [Read the rest at Symmetry Magazine]

Could gravity have mass?

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Might gravity have mass?

Click on the image to read the whole article for free, courtesy of Physics World.

Click on the image to read the whole article for free, courtesy of Physics World.

From Physics World:

When confronted with something unexplained in the data, scientists face several possibilities. Maybe there’s an error and the result is spurious. Maybe there’s a more mundane explanation they simply overlooked. Or perhaps the unexplained is a sign that a theory needs to be revised or supplanted. That last option is the rarest, at least when the theory in ques- tion is a successful one. After all, any new theory must explain all the same phenomena an old theory explained, and predict something new that can’t be handled with the old.

One unexplained result that’s been bugging physicists for more than 15 years is dark energy, which is the name we give to our ignorance. The universe is expanding at an accelerating rate, but we don’t know why. To make matters worse, dark energy comprises roughly three-quarters of the total energy content of the cosmos, so it’s not a minor thing we don’t get. For that reason, a small but dogged group of physicists thinks the existence of dark energy might be a clue that we need to revise one of the most successful theories we have: general relativity.

One way to revise general relativity is to modify the nature of the gravitational force so that it behaves as though it has mass.

The rest of this story is in the print edition of Physics World, which you can subscribe to through membership in the Institute of Physics, which costs £15, €20, or $25 per year. You can join by clicking here. You can also get a nice mobile- and tablet-formatted version of the story using the Physics World app, available in the Google Play and iTunes stores. However, if you just want to read the rest of this article, Physics World has kindly allowed me to offer it to you as a PDF download, which looks exactly like the printed version!

No quantum foam seen in the cosmic beer glass

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Light from distant black holes doesn’t surf on waves of quantum foam

Strongest check yet on quantum gravity effects in astronomy turns up nothing

For Ars Technica:

Quantum gravity is notoriously slippery. While the Standard Model successfully describes three forces of nature, it doesn’t include gravity, so gravity still has no consistent quantum theory. To make matters worse, gravity is so weak that it’s difficult to probe at the sorts of energies where any minuscule quantum effects would pop out. However, some researchers predict that those tiny effects could accumulate over cosmological distances: light traveling from far-off quasars would be changed by the “quantum foam” of spacetime, producing blurry images in our telescopes—or even making objects seem to disappear.

A new report by E. S. Perlman and colleagues examines the disappearance hypothesis using gamma-ray data from quasars. In particular, they investigated a possibility suggested by the holographic principle, the idea that all the information in the cosmos can be encoded on the two-dimensional boundary that encloses it. Disappointingly for fans of quantum foam, the gamma ray data did not show any measurable fading or blurring of the quasars.

As the authors point out, these results don’t rule out anything general regarding quantum gravity, quantum foam, or the holographic principle. But they do provide the tightest constraint yet on cumulative effects of quantum foam on light traveling across the Universe. [Read the rest at Ars Technica…]

Stephen Hawking, black holes, and scientific celebrity

The active galaxy Centaurus A, rendered in several different types of light. Note in radio waves (the central image at right), the galaxy itself seems to disappear, replaced by crossing jets of radio-emitting jets. Those are produced by the supermassive black hole at the galaxy’s core.

The active galaxy Centaurus A, rendered in several different types of light. Note in radio waves (the central image at right), the galaxy itself seems to disappear, replaced by crossing jets of radio-emitting jets. Those are produced by the supermassive black hole at the galaxy’s core.

For the upcoming ScienceOnline 2014 meeting, I’m leading a session titled “Reporting Incremental Science in a World that wants Big Results“. It’s an important topic. We who communicate science to the general public have to evaluate stories to see if they’re worth covering, then translate them in such a way that conveys their significance without hyping them (ideally at least). That’s challenging to do on deadline, and we’re not always or maybe even usually experts on the topics we report. I know a fair amount about cosmology and gravitational physics, but very little about galactic astronomy or planetary science — yet I must write about them, because it’s my job.

So Stephen Hawking’s recent talk on black holes is an interesting case study. I won’t rehash the whole story here, but I wrote not one but two articles on the subject yesterday. Article 1 was in Slate:

Hawking’s own thinking about black holes has changed over time. That’s no criticism: Evidence in science often requires us to reassess our thinking. In this case, Hawking originally argued that black holes violated quantum mechanics by destroying information, then backed off from that assertion based on ideas derived from string theory (namely, the holographic principle). Not everyone agrees with his change of heart, though: The more recent model he used doesn’t correspond directly to our reality, and it may not have an analog for the universe we inhabit. The new talk suggests he has now moved on from both earlier ideas. That’s partly what raises doubts in my mind about the “no event horizons” proposal in the online summary. Is this based on our cosmos or yet another imaginary one of the sort physicists are fond of inventing to guide their thinking? In my reading, it’s hard to tell, and in the absence of a full explanation we are free to project our own feelings about both Hawking and his science onto the few details available. [Read more…]

Article 2 was a follow-up on my own blog:

But at the same time, we have to admit that nobody—not Nature News, not Slate.com—would have covered a paper this preliminary had Hawking’s name not been attached. Other people are working on the same problem (and drawing different conclusions!), but they can’t command space on major science news sites. So, by covering Hawking’s talk, we are back on that treacherous path: we’re showing how science works in a way, but we risk saying that a finding is important because somebody famous is behind it. [Read more…]

We have no complete, consistent quantum theory of gravity. However, clues from other theories indicate that the physics we know breaks down at a certain fundamental length scale: the Planck length. In particular, the Heisenberg uncertainty principle in quantum mechanics must be modified if you can’t measure position to arbitrary precision. However, length and energy are two ends of a teeter totter: to probe to small lengths requires vast energies, and the Planck length would necessitate energy far beyond anything our particle accelerators can provide—maybe ever. As a result, researchers are using other ideas for getting at quantum gravity in the lab, including a certain kind of gravitational wave detector based on a huge metal bar.

When theory is silent, experiment must step in. A new paper analyzed results from the AURIGA gravitational wave experiment to check for deviations from standard quantum mechanics in the vibrations of a massive metal bar at cryogenic temperatures. The AURIGA results showed no deviation from standard quantum physics, yielding an upper bound on the energy of quantum gravity modifications. The experimenters concluded that the theorists needed to get back to work so that the experimenters have a better idea of what to expect. [Read more….]

(Alas, the excellent title for this article was not my idea.)

Speak softly and carry a 2.3-ton aluminum bar