News From Space: Hawkings’ U-Turn on Black Holes

blackholeA recent paper published by Hawking, in which he reversed himself on several of his previous theories about black holes, has created quite a stir. In fact, his new found opinions on the subject have been controversial to the point that Nature News declared that there is no such thing as black holes anymore. This, however, is not quite what Hawking has claimed.

But it is clear that Hawking, one of the founders of modern theories about black holes, now believes that he he may have been when he first proposed his ideas 40 years ago. Now, he believes that black holes may NOT be the the final graveyard for matter that gets sucked in by the gravitational pull caused by a collapsing star, or that they prevent light from escaping.

stephen_hawkingBasically, he was wrong in how he attempted to resolve the paradox of black holes, because apparently they don’t exist. It all comes down to what is known as the “firewall paradox” for black holes.  The central feature of a black hole is its event horizon, the point of no return when approaching a black hole.  In Einstein’s theory of general relativity, the event horizon is where space and time are so warped by gravity that you can never escape.

 

This one-way nature of an event horizon has long been a challenge to understanding gravitational physics.  For example, a black hole event horizon would seem to violate the laws of thermodynamics, which state that nothing should have a temperature of absolute zero.  Even very cold things radiate a little heat, but if a black hole traps light then it doesn’t give off any heat and would have a temperature of zero.

quantum_entanglementThen in 1974, Stephen Hawking demonstrated that black holes do radiate light due to quantum mechanics. In quantum theory, the exact energy of a system cannot be known exactly, which means it’s energy can fluctuate spontaneously so long as its average remains constant. What Hawking demonstrated is that near the event horizon, pairs of particles can appear where one becomes trapped while the others escape as radiation.

 

 

While Hawking radiation solved one problem with black holes, it created another problem – aka. the firewall paradox. When quantum particles appear in pairs, they are entangled; but if one particle is captured by the black hole, and the other escapes, then the entangled nature of the pair is broken. In quantum mechanics, the particle pair would be described as in a “pure state”, and the event horizon would seem to break that state.

blackhole_birthLast year it was shown that if Hawking radiation is in a pure state, then either it cannot radiate in the way required by thermodynamics, or it would create a firewall of high energy particles near the surface of the event horizon.  According to general relativity, if you happen to be near the event horizon of a black hole you shouldn’t notice anything unusual.

In his latest paper, Hawking proposed a solution to this paradox by proposing that black holes don’t have event horizons. Instead they have apparent horizons that don’t require a firewall to obey thermodynamics, hence the declaration of “no more black holes” in the popular press. However, all these declarations may be a bit premature, as the problem Hawking’s sought to address may not exist at all.

black-holeIn short, the firewall paradox only arises if Hawking radiation is in a pure state. And in a paper presented last month by Sabine Hossenfelder of Cornell University shows that instead of being due to a pair of entangled particles, Hawking radiation is due to two pairs of entangled particles. One entangled pair gets trapped by the black hole, while the other entangled pair escapes.

The process is similar to Hawking’s original proposal, but the Hawking particles are not in a pure state, which means there’s no paradox to be had.  Black holes can radiate in a way that agrees with thermodynamics, and the region near the event horizon doesn’t have a firewall, just as general relativity requires.  So basically, Hawking’s proposal is a solution to a problem that doesn’t exist.

FTL_MEWith black holes, its always two step forwards, one step back. And this is hardly the only news in recent months when it comes to these mysterious and confounding phenomena. I imagine that the new theory from MIT, which states that wormholes may exist between black holes and be responsible for quantum entanglements (and resolve the problem of how gravity works) may also need revision next!

Too bad too. I was so looking forward to a universe where FTL wasn’t junk science…

Sources: universetoday.com, cbc.ca

Apocalypse News: Sun’s Magnetive Field about to Flip

sun_magneticfieldThe sun is set to reverse its polarity in the next few months, something that occurs at the height of every Solar Cycle. The resulting ripple effect will be felt all across the Solar System and will even be detectable by the far-away Voyager probes. However, scientists are telling us not to fret, as this event will not lead to the end of the world.

In truth, the Sun’s reversal of polarity is something that occurs every 11 years. And the shift won’t spark an increase in powerful solar storms or other events that could have a damaging effect on Earth and its inhabitants, say the researchers. One such researcher is Phil Scherrer, a solar physicist at Stanford University, who insisted “The world will not end tomorrow.”

NASAsolar_radiationIn addition, from a human perspective, the effects of the field shift will likely be slight and even beneficial. For example, the polarity reversal will cause the “current sheet” – an enormous surface extending out from the solar equator on which the sun’s rotating magnetic field has induced an electric current – to become much wavier.

This crinkled current sheet, in turn, will provide a better barrier against galactic cosmic rays, high-energy particles that are accelerated to nearly the speed of light by faraway star explosions. Galactic cosmic rays can damage spacecraft and hurt orbiting astronauts who don’t get to enjoy the protection of Earth’s thick atmosphere. So for space exploration, at any rate, this is certainly good news.

Sun's Heliospheric-current-sheetAccording to Todd Hoeksema, director of Stanford’s Wilcox Observatory, a drop in galactic cosmic ray levels could also have a subtle impact on weather here on Earth.

One of the things that helps clouds form and lightning to flash is cosmic-ray ionization of things in the Earth’s atmosphere. So when the cosmic-ray intensity is lower, it means you have fewer places where lightning will occur, and so the storms will probably be a little less intense.

He added, however, that it’s pretty much a speculative endeavor at this point, as no conclusive link has ever been demonstrated between cosmic rays and the weather.

In any case, during a reversal, the sun’s polar magnetic fields weaken all the way down to zero, then bounce back with the opposite polarity. Researchers will keep a keen eye on just how strong this recovery is over the next two years or so. The sun has been quiet during its current 11-year activity cycle, which is known as Solar Cycle 24. So it would be particularly interesting to see a strong field emerge after the impending flip.

sun_magneticfield1Dean Pesnell, a project scientist for the space agency’s Solar Dynamics Observatory spacecraft at NASA’s Goddard Space Flight Center, the Sun’s latest field is likely to be a good indicator of what the next solar cycle is going to do. During its most recent cycle, known as Solar Cycle 24, the sun was rather quiet, so what happens next ought to be interesting:

If it quickly goes to a high value, then that tells us the next cycle will be high. We’ve had several of these solar minimums, and each time the polar field has been weaker. And each time, the next cycle has been a little bit weaker. So it would be nice to see one where the polar field strength was higher, and the next cycle was higher as well.

So rest easy, folks. No apocalyptic scenarios are likely to result from this latest, all-too-common solar phenomena. If anything, it will provide research benefits for scientists and aid in space exploration – especially for companies looking to mount missions to Mars in the next 11 years and trying to figure out a way around that tricky radiation problem.

As for the rest of us, we’re likely to maybe get a little break on the weather front. Maybe not. Kind of disappointing when you think about it…

But at least there’s a helpful video provided by Space.com. Enjoy!


Source:
space.com