Earth is a freeeeee faaaallin’ laboratory for testing general relativity

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And if I can be shameless: Forbes pays according to traffic, so the more of you who click on the link below and read my stuff, the better they pay me. Ahem.

Scientists Check Einstein’s Predictions Using Earth Itself As The Laboratory

For Forbes:

The modern description of gravity, Albert Einstein’s general relativity, is one of the most successful and best-tested theories we have. The core of that theory is a set of principles that say basically “physics is physics, wherever you are and no matter how fast you’re moving”. In particular, an experiment performed under the influence of gravity alone should work exactly the same as if you’re performing the same experiment deep in space without any gravity at all.

That’s a tricky concept to verify, but scientists at the National Institute of Standards and Technology (NIST) in Colorado have provided the best test for it yet, using Earth itself as the laboratory. They performed precision experiments in atomic physics (one of NIST’s specialties) and compared those results to those obtained at labs around the world, with data taken over a period of 14 years. The result: general relativity’s predictions were upheld once again.

[Read the rest at Forbes…]

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Testing Einstein’s theory with a new space probe to Mercury

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And if I can be shameless: Forbes pays according to traffic, so the more of you who share and visit and read my stuff, the better they pay me. Ahem.

New Mercury Space Probe Will Put Einstein’s Gravity To The Test

orbit of Mercury, including effects from general relativity and other planets in the Solar System

The orbit of Mercury, including effects from general relativity and other planets in the Solar System. I’ve exaggerated the effect for easy viewing; in real life, the orbit is very nearly an ellipse. [Credit: Matthew R Francis]

For Forbes:

Despite the discovery of other galaxies, black holes and other marvelous astronomical bodies, we keep returning to the orbits of planets to understand gravity at its most basic. Partly that’s simplicity: We’re inside the Solar System and can make measurements without spending billions of dollars or building virtual observatories the size of the whole planet. But that doesn’t mean we’ve exhausted all the ways to learn about gravity from the dance of the planets.

In a new paper in Physical Review Letters, University of Florida physicist Clifford Will showed that the upcoming BepiColombo space probe may be able to test an aspect of Albert Einstein’s theory of gravity, general relativity, that’s been out of reach so far. This effect comes from the gravity of other planets in the Solar System, leading to a tiny shift in Mercury’s orbit. But small doesn’t mean unimportant: If general relativity needs to be modified on this tiny level, the BepiColombo probe may be able to spot that discrepancy.

[Read the rest at Forbes…]

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!

How can we see black holes if they’re invisible?

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The Shadow of a Black Hole

From NOVA:

The invisible manifests itself through the visible: so say many of the great works of philosophy, poetry, and religion. It’s also true in physics: we can’t see atoms or electrons directly and dark matter seems to be entirely transparent, yet this invisible stuff makes and shapes the universe as we know it.

Then there are black holes: though they are the most extreme gravitational powerhouses in the cosmos, they are invisible to our telescopes. Black holes are the unseen hand steering the evolution of galaxies, sometimes encouraging new star formation, sometimes throttling it. The material they send jetting away changes the chemistry of entire galaxies. When they take the form of quasars and blazars, black holes are some of the brightest single objects in the universe, visible billions of light-years away. The biggest supermassive black holes are billions of times as massive as the Sun. They are engines of creation and destruction that put the known laws of physics to their most extreme test. Yet, we can’t actually see them. [read the rest at NOVA…]

This piece, which emphasizes the great science coming from the Event Horizon Telescope (EHT), is a  companion to my earlier NOVA essay, “Do we need to rewrite general relativity?”

Why do some want to modify general relativity?

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

And yes, I did refer to MOND as “a fungus in the basement of astronomy”.

Do We Need to Rewrite General Relativity?

For NOVA “The Nature of Reality”:

General relativity, the theory of gravity Albert Einstein published 100 years ago, is one of the most successful theories we have. It has passed every experimental test; every observation from astronomy is consistent with its predictions. Physicists and astronomers have used the theory to understand the behavior of binary pulsars, predict the black holes we now know pepper every galaxy, and obtain deep insights into the structure of the entire universe.

Yet most researchers think general relativity is wrong.

To be more precise: most believe it is incomplete. After all, the other forces of nature are governed by quantum physics; gravity alone has stubbornly resisted a quantum description. Meanwhile, a small but vocal group of researchers thinks that phenomena such as dark matter are actually failures of general relativity, requiring us to look at alternative ideas. [Read the rest at NOVA…]

Blogging about science for Forbes Magazine

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As of this week, I will be blogging regularly for Forbes on planetary science, climate change, physics, and math. My first two posts are up; go check them out and please follow my blog!

Why are Pluto’s moons so weird?

Pluto is a strange little world, but its moons are even weirder.

Whether or not you want to call it a “planet”, it’s a body strongly influenced by two other worlds: the giant planet Neptune and its moon Charon. Pluto crosses Neptune’s orbit twice during its long sojourn around the Sun. But Charon (which I pronounce KAR-on, but you’ll also hear SHAR-on and other variations) is the big deal: the moon is more than 10 percent of the mass of Pluto. It exerts such a strong gravitational pull that both objects orbit a spot in empty space between them, and forces Pluto to present one face to Charon, just like Earth forces the Moon to keep the same side faces us. If you lived on the “far side” of Pluto, you’d never see Charon in the sky.

Pluto and Charon together have four much smaller moons: Styx, Nix, Kerberos, and Hydra. We don’t know much about those moons yet: Nix and Hydra were only discovered in 2005, Kerberos was found in 2011, and Styx in 2012. Even in our most powerful telescopes, they appear as dots. (Pluto and Charon aren’t much better off — they look like blurry disks even to the Hubble Space Telescope.) But looking at their orbits around Pluto and Charon, astronomers found something weird.

Those tiny moons dance in tandem. [Read the rest at Forbes…]

New analysis shows Earth is warming faster than we thought

Politicians may dither and talking heads bloviate, but the scientific consensus is clear: climate change is real, humans are responsible, and its effects are already being felt around the world. At the same time, some details are in question, including how fast climate change is increasing and which specific effects we see are due to it as opposed to other sources.

That’s the context for a new paper in Science today from researchers at the National Oceanographic and Atmospheric Administration (NOAA, which is somewhat ironically pronounced “Noah”). Thomas Karl and colleagues took a second look at global surface temperatures — the ordinary temperatures we’re used to seeing on weather news or in our phone apps — and found the official numbers on rising temperatures are too low. To put it another way: the consensus opinion is that we are currently in a global warming “hiatus”, but Karl and coauthors report instead that temperatures are climbing as fast as ever.

As if we didn’t have enough to worry about. [Read the rest at Forbes…]

The region near a black hole is one of the most extreme environments in the Universe, but historically it’s been hard to study directly. Using the XMM-Newton and NuSTAR telescopes, astronomers have measured the rotation of gas near the supermassive black hole at the center of the Great Barred Spiral Galaxy. They found that this black hole is spinning nearly as fast as it can be, and that the matter orbiting the black hole is similarly moving near the speed of light—to the extent that the results of Einstein’s general relativity must be used to understand how it’s moving. The key measurement involved observing X-rays reflected off the matter whirling around the black hole, a significant observation of a relativistic phenomenon.

A new X-ray observation of the region surrounding the supermassive black hole in the Great Barred Spiral Galaxy may have answered one of the big questions. G. Risaliti and colleagues found the distinct signature of X-rays reflecting off gas orbiting the black hole at nearly the speed of light. The detailed information the astronomers gleaned allowed them to rule out some explanations for the bright X-ray emission, bringing us closer to an understanding of the extreme environment near these gravitational engines. [Read more…]

Measuring the spin of a black hole using X-rays