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An article in the New York Times by Dennis Overbye gives the latest chapter in Stephen Hawking’s saga concerning whether the properties of matter that has fallen into a black hole are lost forever, or whether there is a way out.

Forty years ago, Hawking showed theoretically that black holes were not ‘eternal prisons’ but could leak radiation. There ensued a long-running debate about whether this radiation retained any information or attributes of the original matter. If it does not, this violates a tenet of modern physics, that it is always possible, in theory, to reverse time. This became known as the ‘information paradox’ and was the subject of a famous bet between Hawking and Caltech professor John Preskill. (Hawking conceded defeat 10 years ago, admitting that advances in string theory, had left no room in the universe for information loss.)

In a paper published to be published this week in Physical Review Letters, Hawking and his colleagues Andrew Strominger (Harvard) and Malcolm Perry (Cambridge) announce they have found a clue pointing the way out of black holes. They new results undermine John Wheeler’s famous notion that black holes have “no hair” — that they are shorn of the essential properties of the things they have consumed.

Looked at from the right vantage point — from a far distance in time, technically known as “null infinity” — black holes might not be not be bald at all. A tell-tale pattern of light rays bordering the event horizon contains information about what has passed through. This has been dubbed in their paper a “soft hair” theory.

For a more complete description of this story, see the full NYT article.

In a subsequent article, Dennis Overbye answers questions on black holes submitted by his readers.

 

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From a news article in Nature, April 12, 2016:

After an unplanned 5-year detour, Japan’s Venus probe, Akatsuki, has come back to life and provided new images of Venus. These include a detailed shot of streaked, acidic clouds and a mysterious moving ‘bow’ shape in the planet’s atmosphere.

venus-combined-sideview

Credit: ISAS/JAXA

Akatsuki, which means ‘dawn’ in Japanese, launched in 2010 and was supposed to enter into orbit around Venus later that year to study the planet’s thick atmosphere. The mission would include looking for signs of active volcanos and other geology. However, upon entry, a fault in a valve caused the probe’s main engine to blow, and the craft entered an orbit around the Sun. As Akatsuki passed near Venus in December, Japan Aerospace Exploration Agency (JAXA) engineers managed to salvage the mission by instructing the craft’s much smaller, secondary thrusters to push it into a looping elliptical orbit around the planet. Its suite of five cameras capture light ranging from infrared to ultraviolet.

A highly detailed shot show dense layers within Venus’s sulfuric acid clouds. The highest-quality infrared image of this view of Venus, it suggests that the processes that underlie cloud formation might be more complicated than previously thought.

An update for Section 13.3f (pp. 352-355) in Pasachoff & Filippenko, The Cosmos, 4th ed:
In what many think is the most important step in astronomy since Galileo first turned a telescope on the heavens in 1609, ripples in space-time known as gravitational waves were detected on September 14, 2015, and reported to the world at large on February 11, 2016. Scientists gathered all over in auditoriums at the National Press Club in Washington, at Caltech, at MIT, in Moscow, and in many other places for the epochal event. “Ladies and gentlemen, we have detected gravitational waves,” said the executive director of the LIGO Laboratory. “We did it!”

The observational existence of gravitational radiation had been established by the changing period of the Hulse-Taylor “double pulsar” at a rate that matched the energy loss expected from the emission of gravitational waves (Section 13.3f, pp. 352-354), but the gravitational waves themselves – distortions of space-time – had not been detected directly until the Advanced LIGO (Laser Interferometer Gravitational Wave Detector) picked up a signal in its engineering run on September 14, 2015.  The signal, which could be heard as an upwards “chirp” in the audio range, resulted from two black holes 1.3 billion light years away, each containing about 30 solar masses, spiraling rapidly into each other and merging to become a single black hole with almost the same total mass but with 3 solar masses of material converted into energy in the form of gravitational waves.

Advanced LIGO has about 3 times the sensitivity of the earlier LIGO, and this event was within that advance of sensitivity. A further gain of 3x is expected with Advanced LIGO in the future.

Scientific papers were published February 11, 2016, in the Physical Review Letters and in the Astrophysical Journal Letters.

A few days later, I [JMP] attended a two-hour evening session at Caltech’s main auditorium to hear the principals of the LIGO project speaking, and I had the feeling that it was just like being at a meeting of the Lincei Academy in Florence in 1610 to hear Galileo speak about his new discoveries with the [optical] telescope.

There are many links to discussions and animations available. Here are some of them:

Popular and academic press:
New York Times coverage (includes movie); also NYT Opinion piece and an NYT Editorial a few days later, justifying scientific inquiry; a congressman’s letter, and sound bites from scientists.
Nature coverage (with explanatory graphics)
Science magazine in depth (requires subscription to access full text)
New Yorker article (with an account of LIGO’s inception and development)
Physics Today comparison of gravitational waves and sound waves
The Wall Street Journal and Michio Kaku’s desciption.

Societies and organizations:
American Physical Society Viewpoint
The Kavli Foundation Scientific spotlight
Caltech (press releasesillustrations, movies and animations)
NSF press release
AAPT resources on gravitational waves
STFC (UK) press release
Cornell Chronicle and media statement
University of Texas Rio Grande Valley press release
ESA congratulations
CSIRO (Australia) news release

LIGO websites:
LIGO labs (Observatories: Livingston | Hanford); Advanced LIGO; LIGO Scientific Collaboration; LIGO Partner Experiments and Collaborations

 

 

 

 

 

AAPT

The American Association of Physics Teachers have collated a set of educational resources on “Neutrinos: Teaching the science behind the 2015 Nobel Prize in Physics” (see The Cosmos, Section 12.7, pp. 322-325).

Find out more on their website.