Posted on 04/05/2013 5:46:23 PM PDT by LibWhacker
n March 2012, Joseph Polchinski began to contemplate suicide — at least in mathematical form. A string theorist at the Kavli Institute for Theoretical Physics in Santa Barbara, California, Polchinski was pondering what would happen to an astronaut who dived into a black hole. Obviously, he would die. But how?
According to the then-accepted account, he wouldn’t feel anything special at first, even when his fall took him through the black hole’s event horizon: the invisible boundary beyond which nothing can escape. But eventually — after hours, days or even weeks if the black hole was big enough — he would begin to notice that gravity was tugging at his feet more strongly than at his head. As his plunge carried him inexorably downwards, the difference in forces would quickly increase and rip him apart, before finally crushing his remnants into the black hole’s infinitely dense core.
But Polchinski’s calculations, carried out with two of his students — Ahmed Almheiri and James Sully — and fellow string theorist Donald Marolf at the University of California, Santa Barbara (UCSB), were telling a different story1. In their account, quantum effects would turn the event horizon into a seething maelstrom of particles. Anyone who fell into it would hit a wall of fire and be burned to a crisp in an instant.
The team’s verdict, published in July 2012, shocked the physics community. Such firewalls would violate a foundational tenet of physics that was first articulated almost a century ago by Albert Einstein, who used it as the basis of general relativity, his theory of gravity.
(Excerpt) Read more at nature.com ...
It’s a long story.
Well, I gave mine to my dad once, ‘cuz he was interested in it, and I bought another one. Then it came back to me.
I do like the idea of having two of them, though, weighty tome that it is.
For one thing, I was actually surprised that the classical expression for tidal forces in a 1/r2 field is exactly the same as the expression they derive from the Schwarzschild metric. They do an integration over a rectangular solid as a model of a human body, whereas I just took 1g/cm to be "huge". They do remark,
Consequently an astrophysicist on a freely collapsing star of one solar mass will be killed by tidal forces when the star's radius is R ~ 200km >> 2M ~ 3 km.
... which is the point I was making, except I used an earth mass, in which case the disparity is much more extreme.
You misapprehended the purpose of my comments. Prior comments neglested a number of factors that need to be addressed when talking about the “spaghettification” of the hapless astronaut. One of these factors is the effects of time dilation, special relativity, and general relativity in the presence of extraordinary gravitational fields. Another fact that did not receive enough consideration is the mass of the black hole. Everyone assumes, erroneously, that tidal forces must always disintegrate the hapless astronaut during the approach to the event horizon and before passing through the event horizon. This assumption holds true in the case of a static and non-charged singularity less than about 8 Solar masses. It is, however, quite untrue when considering a static and uncharged sigularity of 1,000 and greater Solar masses. In the case of such a larger singularity, the hapless astronaut can actually pass through the event horizon without noticing any differences in his body, until his body is suddeenly disintegrated about 7 secnds later and farther into the event horizon.
The assumptions may change in some cases and not in others with real singularities, because real singularities have phenomenonally high rotational speeds instead of being static. They also are highly charged, which makes them game changers under speecial circumstances. Although in the vast number of scenarios the hapless astronaut quickly suffers a fatal destiny no matter how fortunate in passing through the event horizon, blueshifted radiation for one example, some theorists still hold out some hope for defining a scenario for the astronaut’s survival in an Einstein-Rosen Bridge (wormhole) through the singularity. At that point I will stop, because all of this is of course highly speculative no matter whose physics is being used to support an argument. Sufficee it to note that these thought experiments are rife with unknowns which make any attempt to make pat conclusons perhaps untenable.
I guess I could say I had no apprehension of your purpose. I only noticed the error you made in stating that ...
"The reason the astronaut cannot tell thee difference is because he/she is stretched only from the perspective of an eexternal observer. "
This tidal stretching is not associated with crossing the event horizon, as I stated, and is in fact the same thing as the "stretching" of the earth's world ocean in the tidal fields of the moon and the sun, except at much greater magnitude, and hence smaller scale. It is, or would be, a decidedly real phenomenon.
I understood what you were trying to say from the beginning. The problem is not with what I wrote. it is with your not understanding what I was talking about when you quote it out of the context in which it was meant. For one of many possible examples of what I was implying:
A substantial proportion of black holes are goiong to be supermassive relative to only one to eight solar masses. Black holes with 1,000 to a million Solar masses are likely to be common on the scale of the visible Universe. With respect to these common black holes of great mass, an astronaut will pass into the event horizon a ceertain distance without being disintegrated. From the perspective of the external observer in orbit around the black hole, it is the common wisdom that what you would see at a supermassive black hole is the astronaut passing intact through the tidal field and simply fade from view over a nearly infinite passage of time as the light rays from the astronaut to the external observer are increasingly bent into the event horizon by the dense gravitational field of the black hole. The light is simply not fst enough in velocity to pass out of this gravitational field and dtravel to the eyes of the external observer.
One of the many things I was driving at with the thought experiment referring to the time dilation effect, relativity, and being smeared across the singularity was to challenge some of the assumptions about “spaghettification.” This is not to say “spaghettification” is wrong or categorically incorrect. It is to say the eader needs to thing about what the effects of relativity and quantum mechanics may or may not confirm about the assumed “spaghettification.”
One of the first things we need to know is the relative velocities between the external observer and the astronaut and the relative velociies between the astronaut and the singularity and its event horizon.
As the hapless astronaut approaches the event horizon, the black hole’s intense gravitationalattraction must impart some great acceleration of the astronaut into the black hole. How much is to be expected in each case?
If light cannot escape, what fraction of the sppeed of light is the velocity of the astronaut and/or equivalent gravitational effect upon the stronaut? The common wisdom holds the astronaut from the viewpoint of the external observer is slowing down to a nearly compltely frozen position as the effects of time dilation take effect in the strong gravitational field. Little is said about the other effects of relativity.
It stands to reason that relativistic effects are supposed to broaden the mass latitudinally towards infinity as the mass velocity increases towards the speed of light. likewise, the longitudinal dimension of the mass is said to increase towards infinity as the mass accelerates to nearly the speed of light. If so, then how do these apparent dimensions change from the point of view of the external observer as the astronaut is accelerated into the black hole? How much of the 360 degree sphere of the black hole would appear to be encompassed by the mass of the astronautif the astronaut would have an apparent velocity of 99.0 percent of the speed of light just before fading from the exernal observer’s view? In other words, how much of a smearing effect might the relativistic effects create at a black hole where the astronaut can pass into the event horizon without being disintegrated, spaghettified, or disintgrated by blueshifted radiation?
Assuming the astronaut is disntegrated after passing into the event horizon and out of the external observer’s view, what happens to the atoms and resultant quarksthat are spun into the rotation of the inner horizon? In other words, do the reo the relativistic effects and/or quantum mechanics effectively broaden and smear them around the inner event horizon even as it lngthens them down to an infinite point of the singulaity? It’s a weird concept of course, but it does make sense in a singularity to broaden to infinity even while reducing the sapce and time in which the broadening is occurring down into a point of infinity. See for example some of the videos which attempt to illustrate some of the paradoxes involved. Note how there are many strange paradowes implied and not stated in any of the videos.
The complexities invlolved with Einstein-Rosen Bridges are even that much more challenging.
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