Wednesday, November 14, 2018

Close orbit to Milky Way black hole

The Bad Astronomer (aka Phil Plait) writes:
Because in the paper, a team of astronomers show that they have observed a blob of dust sitting just outside the point of no return of a supermassive black hole, where the gravity is so intense that this material is moving at thirty percent the speed of light. And this wasn’t inferred, deduced, or shown indirectly. No: They measured this motion by literally seeing the blobs move in their observations. ...

Sitting in the exact center of the Milky Way is a supermassive black hole… and astronomers don’t use that adjective lightly. It has a mass over 4 million times that of the Sun, and all of that is squeezed down into a spherical region of space only 20 million kilometers across. The Sun itself is over a million kilometers across, so this is a tiny volume for all that mass. The gravity of such a beast is so immense that if you get too close, you cannot escape. Not even light, which travels at the fastest possible speed in the Universe, can get out. It’s like a dark extremely massive infinitely deep hole. ...

Their motions can be directly seen, and one, called S2, circles the center on an orbit just 16 years long, taking it to within a breathtaking 18 billion kilometers of the exact center.

Using Kepler’s laws of motion, the shapes and periods of the stars’ orbits can be used to find the mass of the object they orbit, and that’s where the 4 million solar mass figure comes from. Yet we see nothing emitting light there, no huge object, no star cluster. It really must be a black hole. Anything else would be extremely bright.
This is interesting, but it really doesn't much to do with relativity.

The way relativity is usually described, a black hole is a singularity, and not "a spherical region of space only 20 million kilometers across". The distance across is infinite. Or as BA says, "a dark extremely massive infinitely deep hole." And nothing comes within any finite distance of "the exact center", because the exact center is the singularity, with infinite distance to everything.

So I am surprised that BA talks about black holes as if they can exist in Euclidean geometry, without a singularity.

We don't see inside the black hole, so we don't really know. On the outside, it looks spherical. The above paper just describes a plain old Keplerian orbit as it might have been understood four centuries ago. Just one involving bigger masses and faster speeds than has been seen before. We don't see any light from the central mass, but that is just what would have been expected two centuries ago.

It is to BA's credit that he does not lecture us on how this confirms Einstein's view of black holes.

Monday, November 12, 2018

Horgan interviews Maudlin

John Horgan interviews philosopher Tim Maudlin for SciAm. I sometimes trash philosophers, including Maudlin, so I will emphasize where I agree with him.
Filmmaker Errol Morris hates Thomas Kuhn. What’s your take on Kuhn?

The Structure of Scientific Revolutions contains some nice observations on the nature of what Kuhn calls “normal science”, which makes it out to have none of the heroic aspects that Popper insisted on. But when Kuhn goes beyond normal science to “revolutionary science” the book is a disaster. It promotes an irrationalist view of scientific revolutions that is both false and pernicious.
Exactly correct. Kuhn's popularity is a large part of why I trash philosophy of science.
Overwhelmingly most philosophers are atheists or agnostics, which I take to be convergence to the truth. Most are compatibilist about free will and believe in it, which I also take to be convergence to the truth. Almost all believe in consciousness and most don’t have a clue how to explain it, which is wisdom.
This is reassuring.
What’s your take on multiverses and strings and the problem of testability?

Some people have been mesmerized by fancy math. It is not interesting physics in my view, and has had a very, very bad effect on the seriousness of theoretical physics as practiced.
Yes.
Does Gödel’s incompleteness theorem have implications beyond mathematics? Is it a worm in the apple of rationality?

No. Absolutely no one should have ever been surprised that mathematical truth cannot be equated with theoremhood in some finite axiomatic system.
Again, I agree. Godel's theorem is fascinating and profound for logic and the foundations of mathematics, but nearly all applications outside math in the popular literature are nonsense.

He lost me with his favorite interpretation of quantum mechanics. I have discussed that elsewhere. He also lost me with this:
What’s your position on the status of ethics? Do any moral rules have the same status as mathematical truths? Do you believe in moral progress?

Yes (with qualification) and yes. Already in Republic (Plato again!) we have an argument — a clear and compelling rational argument — that even the highest political office should be open to women. The argument? List what it takes to be a good leader of the state, then note the conditions that distinguish the sexes. There just is zero overlap between the two lists. That is as compelling as a rational argument can be, and it follows that opening all political offices to women (much less acknowledging in law that women should have as much right to vote as men) is objective moral progress. Similarly for invidious legal restrictions by race. The civil rights movement was strict moral progress. That’s as true as 2 + 2 = 4.
Wow. Because of some logical, almost mathematical argument, known to Plato, someone like Hillary Clinton should be President of the USA?!

Donald Trump has that list of qualities. Fearless. Honest. Loyal. Blunt. Likable. Strength of character. True to his word. Alpha. Not intimidated by his enemies. Maintain hundreds of friendships and political alliances. Forceful. Smart. Competent. Just enough of a narcissist Machiavellian sociopath to be effective. Strong moral compass. Unflinching about sticking up for the people he represents. Vision for a better future. Communicates his ideas well. Owned by no one. Shitlord.

Neither Hillary Clinton nor any other woman has these qualities.

Maudlin is probably a typical academic leftist Trump-hater who voted for Hillary Clinton, so I am sure he disagrees. But I do wonder about his list of what it takes to be a good leader of the state. Is there really such a list where Donald Trump and Hillary Clinton do equally well?

Maybe Maudlin is making a joke here. He would probably be ostracized from his profession if he openly supported Trump.

When the thought-control police are forcing you to take a political stand, sometimes the best way is to give an argument that is so unreasonable that no one could take it seriously. Maybe Maudlin is doing that here, and trolling us. Can he really think that supporting Hillary Clinton is like 2 + 2 = 4?

He says he believes in free will. At least he says he believes Brett Cavanaugh has free will. We don't want any more pre-programmed automatons on the Supreme Court, do we? Did he say Cavanaugh has free will as a sneaky way of supporting him?

I should just agree with his arguments that made sense, and not try to decode his political sarcasm. I don't like to get political on this blog anyway.

Saturday, November 10, 2018

Physics rejects counterfactual definiteness

Lubos Motl rants, as part of a defense of string theory:
People enjoying terms such as the "counterfactual definiteness" have two main motivations. One of them is simply their desire to look smart even though almost all of them are intellectually mediocre folks, with the IQ close to 100. This category of people greatly overlaps with those who like to boast about their scores from IQ tests – or who struggle for 10 years to make a journal accept their crackpot paper, so that they can brag to be finally the best physicists in the world (I've never had a problem with my/our papers' getting published). The other is related but more specific: "counterfactual definiteness" was chosen to represent their prejudices that Nature obeys classical physics – which they believe and they're mentally unable to transcend this belief.

If something is called "counterfactual definiteness", it must be right, mustn't it? The person who invented such a complicated phrase must have been smart, listeners are led to believe, so the property must be obeyed in Nature. Wouldn't it otherwise be a giant waste of time that someone invented the long phrase and wrote papers and books about it? Sorry, it's not obeyed, the awkward terminology cannot change anything about it, the people who enjoy using similar phrases have the IQ about 100 and they are simply not too smart, and indeed, all the time was wasted.
He is correct that counterfactual definiteness is not obey in Nature, but I doubt that he is right about the term being invented to trick low-IQ ppl into falling for a false concept.

Believing in counterfactual definiteness is like believing in Many-Worlds. It literally means that your counterfactual fantasies have some definite reality. Things that never happened can be discussed as if they did.

Technically, nothing is really definite in Many-Worlds, so maybe it is not the best example. Newtonian mechanics is a better example of counterfactual definiteness.

It is opposite the more conventional quantum mechanical view that "unperformed experiments have no results". You cannot analyze the double-slit experiment by assuming that particles definitely went thru one slit or the other. If you do, then you don't see an interference pattern. We see the interference pattern, so counterfactual definiteness is wrong.

The essence of Bell's Theorem is that assuming counterfactual definiteness leads to conclusions that contradict quantum mechanics. The sensible conclusion is that counterfactual definiteness is wrong. There are some other possibilities, but they require rejecting more basic scientific principles.

Thinking sensibly about counterfactuals is the key to understanding quantum mechanics. Many of the paradoxes that make it hard to understand quantum mechanics are based on attributing some faulty meaning to a counterfactual.

Thursday, November 8, 2018

Astronomers excited about black holes

NY Times science writer Dennis Overbye writes about the black hole at the center of the Milky Way.

The article mentions Einstein ten times, even tho he had almost nothing to do with the concept.

Black holes were first proposed in 1784. The relativistic equations for a black hole were found by Schwarzschild and a student of Lorentz's, but many mistakenly thought that there was a singularity on the event horizon. Some modern theoretical physicists still think that there is such a singularity, in order to preserve their intuition about information emerging from evaporating black holes.

Much as I like to see relativity research research, the astronomy work on black holes does not have much to do with relativity.
Black holes — objects so dense that not even light can escape them — are a surprise consequence of Einstein’s general theory of relativity, which ascribes the phenomenon we call gravity to a warping of the geometry of space and time.
Not really. Since 1784 it has been understood that if gravitational force obeys an inverse square law, and the mass is sufficiently concentrated, then the escape velocity will exceed the speed of light and a black hole results.

Relativity does predict some strange things inside the event horizon of a black hole, but relativity also teaches that none of that is observable, so we will never know. There is no proof that there is any sort of singularity.

While general relativity is commonly described as explaining gravity as the warping of the geometry of space and time, that was not Einstein's view. He denounced this geometrical interpretation. And he did not believe in black holes.
“The road is wide open to black hole physics,” Dr. Eisenhauer proclaimed.
It is true that we are getting a lot more info about black holes. A few decades ago we were not even sure that they exist, and now they are crucial for theories of galaxy formation, for explaining the brightest objects in the universe, and for studying gravity waves.

But all that stuff about singularities, entropy, evaporation, firewalls, information conservation, and quantum gravity are completely out of reach.

Monday, November 5, 2018

Leaving true physics to wither

Bee quotes this NY Times article:
“Unable to mount experiments that would require energies comparable to that of the Big Bang genesis event, Dr. Chodos believes, growing numbers of physicists will be tempted to embrace grandiose but untestable theories, a practice that has more than once led science into blind alleys, dogma and mysticism.

In particular, Dr. Chodos worries that “faddish” particle physicists have begun to flock all too uncritically to a notion called “superstring theory.” […] Deprived of the lifeblood of tangible experiment, physicists will “wander off into uncharted regions of philosophy and pure mathematics,'' says Dr. Chodos, leaving true physics to wither.””
This was conventional wisdom among a lot of physicists in the 1970s. I remember hearing a lecture in the late 1970s explaining the exponentially increasing cost of particle accelerators, and how they will never get to the energies that they need to resolve the questions that they are really interested in. Finding some unified field theory would be a miracle of good luck.

It was known back then that even if susy had merit, there would be dozens of free parameters that would be hopeless to determine experimentally. The string theorists decided that they determine them by pure theory instead. By the year 2000 or so, it was established that the plan would never work.

Bee just wrote a book on how theoretical physics has lost its way, but it has been lost for 40 years

Thursday, November 1, 2018

Philosopher defends Many-Worlds

I mentioned the failure of many-worlds, but in fairness, here is a new philosophy paper with another view:
We defend the many-worlds interpretation of quantum mechanics (MWI) against the objection that it cannot explain why measurement outcomes are predicted by the Born probability rule. We understand quantum probabilities in terms of an observer's self-location probabilities. We formulate a probability postulate for the MWI: the probability of self-location in a world with a given set of outcomes is the absolute square of that world's amplitude.
There is no world's amplitude. This paper is just nonsense.

If MWI really predicted probabilities, or predicted any measurement outcomes, you would not need philosophy papers like this.

The whole point of every other scientific theory is to predict outcomes. If MWI does not, then what is it doing for you?

The paper claims that MWI can make predictions, but it is just a stupid hand wave. There are no physics papers that use MWI to predict and experimental outcome.