Monday, March 31, 2014

High precision needed for quantum computing

Craig Feinstein asks:
Leonid Levin said, "Exponential summations used in QC require hundreds if not millions of decimal places accuracy. I wonder who would expect any physical theory to make sense in this realm."
Peter Shor replies:
If you believe the fault-tolerant threshold theorem for quantum computers, you do not require hundreds of digits of accuracy.

Levin does not believe this theorem. More precisely, he believes that the hypotheses required for the theorem to work do not apply to the actual universe.

I believe his mental model of quantum mechanics resembles the idea that the physics of the universe is being simulated on a classical machine which has floating point errors. I don't believe this is true. ...

The real question is whether the rules of the universe are exact unitary evolution or something else. If they're exact unitary evolution and you have locality of action (quantum field theories, including QED, satisfy these) then the fault-tolerant threshold theorem holds. If the universe has extra levels of weirdness under the quantum field theory, then it's not clear the hypotheses are satisfied.
I am not sure who is right here. Quantum mechanics is a linear theory and has been verified to high precision is some contexts. But a linear theory is nearly always an approximation to a nonlinear theory, and I don't think that the quantum computer folks have shown that they are operating within a valid approximation.

Shor assumes "unitary", but there are interpretations of quantum mechanics that are not unitary, and no one has proved them wrong. So how do we know nature is really unitary?

If being unitary is some physically observed law, like conservation of momentum, then we should have error bars that show us just how close to being unitary the world, and what confidence in different situations.

If being unitary is a metaphysical necessary truth, derived from the conservation of probability, then how have so many textbooks managed to get by with the Copenhagen interpretation?

I say that quantum computing is a vast extrapolation of known physics, and extrapolations are unreliable.

In other news:
An international team of researchers has created an entanglement of 103 dimensions with only two photons, beating the previous record of 11 dimensions.

The discovery could represent an advance toward toward better encryption of information and quantum computers with much higher processing speeds, according to a statement by the researchers.

Until now, to increase the “computing” capacity of these particle systems, scientists have mainly turned to increasing the number of qubits (entangled particles), up to 14 particles. ...

“The most immediate practical use is expected to be in secure communication,” Huber explained to KurzweilAI in an email interview.
I haven't read the paper but I am pretty sure than there is no practical application to secure communication. I expected them to claim that all those dimensions could be used for quantum computing.

Sunday, March 30, 2014

Lectures on the impossibility of quantum computers

Steve Flammia writes:
Gil Kalai has just posted on his blog a series of videos of his lectures entitled “why quantum computers cannot work.”  For those of us that have followed Gil’s position on this issue over the years, the content of the videos is not surprising. The surprising part is the superior production value relative to your typical videotaped lecture (at least for the first overview video).

I think the high gloss on these videos has the potential to sway low-information bystanders into thinking that there really is a debate about whether quantum computing is possible in principle. So let me be clear.
There is no debate! The expert consensus on the evidence is that large-scale quantum computation is possible in principle.
... For now, though, the reality is that quantum computation continues to make exciting progress every year, both on theoretical and experimental levels, and we have every reason to believe that this steady progress will continue. ...

And most importantly, we are open to being wrong.
No, there is no significant progress. No one has made scalable qubits, and no one has demonstrated a quantum speedup.

He sure doesn't sound like someone who is open to being wrong. Papers on this subject by physicists subscribing to this consensus never admit that the whole field is based on speculative premises. I am a skeptic.

Saturday, March 29, 2014

Evidence closes in on singularity

Modern physics teaches certain singularities in general relativity (black holes and big bang) and quantum field theory (renormalization). I have expressed skepticism about whether there is truly a singularity in the black hole and at the big bang. Max Tegmark has also expressed skepticism about actual infinities in nature.

Now that the BICEP2 has given us evidence close to the alleged big bang singularity, Matt Strassler and Lubos Motl have reopened the debate about whether there really is a singularity. Those are sensible mainstream views. Others will push back harder, and speculate about before the big bang and into the multiverse.

I have to agree with Strassler that the evidence points to energies high enough that our physical theories break down, so we cannot go further. I also agree with Tegmark that we never observe true singularities in nature. I am a positivist, and I believe in what has been demonstrated. Infinities and singularities are wonderful mathematical tools, but math is not the same as physics.

Depending on how the inflation evidence plays out, I am not sure the big bang has anything to do with general relativity or a spacetime singularity. The physics was not dominated by gravity or the standard model, as we know them. Something mysterious called an inflaton field was releasing huge amounts of energy. I am not even sure about the reports that BICEP2 saw gravity waves. Maybe they saw inflaton waves. Some physicists have said that this proves gravity is quantized. I don't know how they can say that, when no one knows what the inflaton is or how it relates to gravity.

I expect the meaning of BICEP2 to be settled in the next year or so, but unwarranted speculation about time and multiverses to go on for the foreseeable future.

Update: Strassler argues:
Who is still telling the media and the public that the universe really started with a singularity, or that the modern Big Bang Theory says that it does? I’ve never heard an expert physicist say that. And with good reason: when singularities and other infinities have turned up in our equations in the past, those singularities disappeared when our equations, or our understanding of how to use our equations, improved.

Moreover, there’s a point of logic here. How could we possibly know what happened at the very beginning of the universe? No experiment can yet probe such an early time, and none of the available equations are powerful enough or usable enough to allow us to come to clear and unique conclusions.
Lumo responds:
But by endorsing the idea that the Big Bang singularity exists, we don't claim that the classical general relativity is exactly accurate and all of its conclusions about quantities' being infinite at the singularity are strictly right. We never mean such things.

Thursday, March 27, 2014

Mermin resolves metaphysical issues in Nature

I posted before on Mermin taking Bohr seriously, SciAm pushes Quantum Bayesianism, and Counterfactuals: Time on the metaphysics of time. Now Cornell Physicist N. David Mermin has an essay in the current Nature journal:
Schrödinger wrote in a little-known 1931 letter2 to German physicist Arnold Sommerfeld that quantum mechanics “deals only with the object–subject relation”. Another founder of quantum mechanics, Danish physicist Niels Bohr, insisted in a 1929 essay3 that the purpose of science was not to reveal “the real essence of the phenomena” but only to find “relations between the manifold aspects of our experience”. ...

People who believe wavefunctions to be as real as stones have invested much effort in searching for objective physical mechanisms responsible for such changes in the wavefunction: ...

Another celebrated part of the muddle produced by the exclusion of the perceiving subject is 'quantum non-locality', the belief of some quantum physicists and many mystics, parapsychologists and journalists that an action in one region of space can instantly alter the real state of affairs in a faraway region. Thousands of papers have been written about this mysterious action at a distance over the past 50 years. A clue that the only change is in the expectations of the perceiving subject7 is that to learn anything about such alterations one must consult somebody in the region where the action took place. ...

The issue for Einstein was not the famous revelation of relativity that whether or not two events in two different places happen at the same time can depend on your frame of reference. It was simply that physics seems to offer no way to identify the Now even at a single event in a single place, although a local present moment — Now — is evident to each and every one of us as undeniably real. How can there be no place in physics for something as obvious as that? ...

When I recently mentioned to an eminent theoretical physicist that I was writing an essay explaining how the QBist view of science solves the strictly classical problem of the Now, he said: “Ah, you're going to explain why we all have that illusion.” And a distinguished philosopher of science recently derided the attitude that there ought to be a Now on my world-line as “chauvinism of the present moment”9.
My only quarrel with Mermin is that he acts as if he is saying something new. He is just reciting the view of Bohr and everyone else not infected with Einstein's disease.

There are physicists and philosophers today who (1) believe wavefunctions to be as real as stones; (2) assert quantum non-locality; and (3) deny Now as just chauvinism of the present moment. They have bizarre and foolish philosophies that lead to unresolvable paradoxes. Mermin's common sense explanations from a century ago are perfectly adequate.

Wednesday, March 26, 2014

Counterfactuals: Hard Science

Counterfactual reasoning is used all the time in the hard sciences. When you learn the formulas for gravity, the first thing you do is to answer questions like, “If you drop a rock off a 100-foot cliff, how long will it take to hit the ground?”

Dropping a rock from a cliff could also be called hypothetical reasoning, because one can easily imagine conducting the experiment. However physics also has all sorts of thought experiments that have no hope of ever being carried out. For example, explanations of relativity frequently involve spaceships taking people near the speed of light or being swallowed up in a black hole.

Counterfactuals are essential to the scientific method. Science is all about doing experiments that favor some hypothesis over some counterfactual.

The ability to make a precise prediction from a counterfactual is what distinguishes the hard sciences from the soft.

A famous example is Hendrik Lorentz's discovery of space and time transformations (now called Lorentz transformations) to explain the Michelson-Morley experiment. The counterfactual was aether motion, as Lorentz interpreted experiments to show that no such motion was detectable. He then used his formulas to predict relativistic mass, which was then confirmed by experiment. (Einstein later published similar theories, but the consensus of historians is that he paid no attention to the experiments.)

An example that failed to disprove the counterfactual was the 1543 Copernicus heliocentric model of the solar system. The established theory was Ptolemy's, but both theories predicted the sky with about the same accuracy. Experiments and models with much greater accuracy were achieved by Tycho Brahe and Johannes Kepler around 1600. The 20th century theory of relativity taught that motion is relative, and heliocentricity could never be proven.

Kepler's theory was superior not only for its accurate predictions, but for its counterfactual predictions. He had a complete theory of what kinds of orbits were possible in the solar system, so he could have made predictions about any new planet or asteroid that might be discovered. But he did not have a causal mechanism.

Causality is closely connected with counterfactual analysis. If an event A is followed by an event B, we only say that A caused B if counterfactuals for A would have been followed by something other than B. If rain follows my rain dance, I only argue that the dance caused the rain if I have a convincing argument that it would not have rained if I had not danced. A truly causal argument would provide a connected chain of events from the dance to the rain, with every link in the chain causing the next link.

Isaac Newton found a more powerful theory of mechanics by positing a gravitational force between any two massive objects, and saying that the force causes the orbital motion. Laplace argued in 1814 that all of nature is predictable with causal mechanics, given sufficient data.

This Newtonian causality was not true causality, because it required action-at-a-distance. One planet could exert a force on another planet over millions of miles, without any intermediate effects. A truly causal theory required the invention of the concept of field, such as electric or gravitational field, that can propagate thru empty space from one object to another. James Clerk Maxwell worked out such a theory for electric and magnetic fields in 1865, and that was the first relativistic theory.

A field is a physical way of describing certain counterfactuals. Saying that there is an electric field, at a particular point in space and time, is another way of saying what would happen if an electric charge were put at that point. The field is one of the most important concepts in all of physics, because it allows reducing the universe to the mechanics of locally defined objects. Thus physics is rooted in counterfactuals at every level. You could say that reductionism works in physics because of clever schemes for distributing counerfactual info over space and time.

A trendy topic in theoretical astrophysics is the multiverse. This involves a loose collection of unrelated ideas, but they all involve hypothetical universes outside of our observational abilities. It is a giant counterfactual exercise, with no experiment to decide who is right.

A particular fascination is the possibility of intelligent life in other universes. It appears that our universe is finely tuned for life. That is, it is hard to imagine the development of life in most of the counterfactual universes.

The most bizarre approach to counterfactuals is the many-worlds interpretation (MWI) of quantum mechanics. It simply posits that every possible counterfactual has an objective reality in an alternate universe. The extra universes do not really explain anything because they do not communicate with each other. There can be no experimental evidence for the other universes. There is no theoretical reason either, except that some physicists are unhappy with counterfactuals being just countefactuals.

The many-worlds seems like an endorsement of counterfactual thinking, but it corrupts such thinking by declaring the the counterfactuals real. A counterfactualist might argue, "if a new ice age were beginning, then we would probably notice cooler termperatures, but we don't, so we are not in a new ice age." But in many-worlds, all exceptionally improbable events take place in different universes, and we could be in one of them. Thus many-worlds leaves no good rationale for rejecting counterfactuals.

Tuesday, March 25, 2014

Stapp on quantum consciousness

Henry Stapp has a new edition of his book:
Mindful Universe: Quantum Mechanics and the Participating Observer (The Frontiers Collection)
March 24, 2014

Author: Henry P. Stapp
Publisher: Springer (4/26/2011)

The classical mechanistic idea of nature that prevailed in science during the eighteenth and nineteenth centuries was an essentially mindless conception: the physically described aspects of nature were asserted to be completely determined by prior physically described aspects alone, with our conscious experiences entering only passively. During the twentieth century the classical concepts were found to be inadequate. In the new theory, quantum mechanics, our conscious experiences enter into the dynamics in specified ways not fixed by the physically described aspects alone. Consequences of this radical change in our understanding of the connection between mind and brain are described. This second edition contains two new chapters investigating the role of quantum phenomena in the problem of free will and in the placebo effect.
He is right that quantum mechanics was created as a subjective theory, and that made it different from previous physics theories.

Monday, March 24, 2014

Aaronson says Tegmark devoid of content

Scott Aaronson reviews Max Tegmark's book on the Mathematical Universe Hypothesis (MUH):
Briefly, I think it’s a superb piece of popular science writing — stuffed to the gills with thought-provoking arguments, entertaining anecdotes, and fascinating facts. I think everyone interested in math, science, or philosophy should buy the book and read it. And I still think the MUH is basically devoid of content, as it stands. ...

Putting the two points [about the laws of physics] together, it seems fair to say that the physical world is “isomorphic to” a mathematical structure — and moreover, a structure whose time evolution obeys simple, elegant laws.   All of this I find unobjectionable: if you believe it, it doesn’t make you a Tegmarkian; it makes you ready for freshman science class.

But Tegmark goes further.  He doesn’t say that the universe is “isomorphic” to a mathematical structure; he says that it is that structure, that its physical and mathematical existence are the same thing.
I am glad to see that Aaronson does not believe in any of Tegmark's multiverses, but this review is nonsense.

When Tegmark says that the universe is a mathematical structure, that is just a shorthand for saying that the universe is isomorphic to a mathematical structure. So Aaronson takes two versions of the same statement, accepts one as trivially obvious and rejects the other one.

And why is Aaronson promoting a book whose main point is such a dopey idea?

I think that the MUH does have content, because I believe that it is false.

The public face of physics is largely shaped by popular books written by big-shot MIT professors like Tegmark and Aaronson. I expect more from these guys. Tegmark apparently bet $100 on the success of BICEP2. Maybe he could be explaining that to the public.

Aaronson responds:
As far as falsifiability goes, please help me understand how the string landscape is any more falsifiable than MUH?

Well, the string landscape has well-known falsifiability issues too! But if (hypothetically) you could build a particle accelerator the size of the universe, capable of reaching the Planck scale, then you could at least imagine doing experiments that would definitively confirm or rule out string theory. Whereas even with such resources, it seems to me that the MUH would remain just as empirically inaccessible as before.
This is like talking about the equipment to count how many angels can dance on the head of a pin.

Update: Here is another answer:
Nex Says: English language describes the World so well that it cannot be a coincidence. And it’s not. But the right conclusion is not that the World and the English language are one and the same thing, rather the language was tailored to serve that purpose.

Same thing with mathematics.

Scott Says: Nope, try again! The view that analogizes math to the English language seems totally unable to account for things like complex numbers, linear algebra, Riemannian geometry, or group representations, which were all developed decades or even centuries before anyone thought of any applications to physics, but then turned out to be exactly what physicists needed.

Which English words were coined decades or centuries before anyone needed them?
That is an argument, but thousands of English words were coined before being applied to physics. Those math concepts were all needed when they were developed, just not needed by physicists. So both English words and math concepts were developed long before being applied to physics.

Thursday, March 20, 2014

Denying present time

I have mentioned how Einstein, Greene, and others deny the flow of time. Now also Present time, by Gustavo E. Romero, an Argentina astrophysics professor:
The idea of a moving present or `now' seems to form part of our most basic beliefs about reality. Such a present, however, is not reflected in any of our theories of the physical world. I show in this article that presentism, the doctrine that only what is present exists, is in conflict with modern relativistic cosmology and recent advances in neurosciences. I argue for a tenseless view of time, where what we call `the present' is just an emergent secondary quality arising from the interaction of perceiving self-conscious individuals with their environment. I maintain that there is no flow of time, but just an ordered system of events.
I don't know what to say to this nonsense. First, the present now, and the flow of time, are intuitively obvious and self-evident. Second, our physical theories involved differential equations in time, where the present is used as an initial condition and the flow of time is given by solving the equation.

Thus our beliefs about present time are directly reflected in our physical theories.

Romero writes:
There is no passage of time. There is no moving present. The mere idea of a flowing time simply does not make any sense. An additional problem is that if time flows, it should move with respect to something. If we say that there is a super-time with respect to which time flows, then we shall need a super-super-time for this super-time, and we shall have an infinite regress. In addition, there is no flow without a rate of flow. At what rate does time go by? The answer 1 sec per sec is meaningless. It is like saying that a road extends along a distance of one km per each km that it extends!
You could make this silly argument against anything.
On the physical side, the theory of special relativity seems not to be friendly to the idea of an absolute present, at least in its usual Minkowskian 4-dimensional interpretation. Special relativity is the theory of moving bodies formulated by Albert Einstein in 1905 (Einstein 1905). It postulates the Lorentz-invariance of all physical law statements that hold in a special type of reference systems, called inertial frames. Hence the ‘restricted’ or ‘special’ character of the theory. The equations of Maxwell electrodynamics are Lorentz-invariant, but those of classical mechanics are not. When classical mechanics is revised to accommodate invariance under Lorentz transformations between inertial reference frames, several modifications appear. The most notorious is the impossibility of defining an absolute simultaneity relation between events. Simultaneity results to be frame-dependent. Then, some events can be future events in some reference system, and present or past in another system. Since what exists cannot depend on the reference frame adopted for the description of nature, it is concluded that past, present, and future events exist. Consequently, presentism, the doctrine that only what is present exists, is false.
Others have made this argument,b ut it is wrong. First, the Minkowskian 4-dimensional interpretation of special relativity is due to Poincare and Minkowski, and Einstein had nothing to do with it. Second, it is possible to define an absolute simultaneity relation between events. One can say that events are simultaneous if they have the same proper time since the big bang, just as we do when we speak of the age of the universe. Third, relativity paradoxes have little to do with our sense of now. We have have a sense of now even if someone else has a clock that is not synchronized. Fourth, Maxwell's euqations are differential equations in time, and hence describe a flow in time.

Possibility a black hole was involved

Mediaite reports:
CNN’s Don Lemon has been entertaining all sorts of theories about the missing Malaysian Airlines Flight 370, including the chance something “supernatural” happened, but on Wednesday night, he actually asked panelists about the possibility a black hole was involved.

Lemon brought this up along with other “conspiracy theories” people have been floating on Twitter, including people noting the eerie parallels to Lost and The Twilight Zone, and wondered, “is it preposterous” to consider a black hole as a possibility?

Mary Schiavo, a former Inspector General for the U.S. Department of Transportation, said, “A small black hole would suck in our entire universe, so we know it’s not that.”

Here’s another theory I’ll just throw out there: what about the plane entered a wormhole into another dimension? I don’t know if that’s how the science works, though.
Schiavo's comment is crazier than Lemon's. All of the proposed Flight 370 theories appear to contradict some of the supposed facts, so it is almost reasonable to list some outlandish theories. They both seem to have some misconceptions about black holes. They have probably been watching PBS TV or the Discovery channel.

Wednesday, March 19, 2014

Cosmic inflation smoking gun announced

Has cosmic inflation been proved? SciAm reports:
Physicists have found a long-predicted twist in light from the big bang that represents the first image of ripples in the universe called gravitational waves, researchers announced today. The finding is direct proof of the theory of inflation, the idea that the universe expanded extremely quickly in the first fraction of a nanosecond after it was born. What’s more, the signal is coming through much more strongly than expected, ruling out a large class of inflation models and potentially pointing the way toward new theories of physics, experts say. ...

The Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) experiment at the South Pole found a pattern called primordial B-mode polarization in the light left over from just after the big bang, known as the cosmic microwave background (CMB). This pattern, basically a curling in the polarization, or orientation, of the light, can be created only by gravitational waves produced by inflation. “It looks like a swirly pattern on the sky,” says Chao-Lin Kuo, a physicist at Stanford University, who designed the BICEP2 detector. “We’ve found the smoking gun evidence for inflation and we’ve also produced the first image of gravitational waves across the sky.”
We will have to wait and see whether their is any other good explanation of the data. I have expressed skepticism about a lot of modern theoretical physics, but not that inflation might be at least partly correct. It seems plausible that the early universe was in a false vacuum, and then made a quantum leap to a lower state.

I have been skeptical about a whole set of ideas associated with inflation, such as string theory, multiverse, eternal inflation, etc.

John Horgan is still skeptical about inflation:
Indeed, inflation, like string theory, has always suffered from what is sometimes called the “Alice’s Restaurant Problem.” Like the diner eulogized in the iconic Arlo Guthrie song, inflation comes in so many different versions that it can give you “anything you want.” In other words, it cannot be falsified, and so–like psychoanalysis, Marxism and other overly flexible hypotheses–it is not really a scientific theory.

Inflation enthusiasts have claimed vindication before—for example, in 1992, when the COBE satellite produced a detailed map of the cosmic microwave background, the afterglow of the Big Bang; and in the late 1990s, when astrophysicists discovered that the expansion of the universe is accelerating. But neither of these supposed confirmations of inflation held up.

Just two months ago, inflation pioneer Paul Steinhardt wrote on the website “I think a priority for theorists today is to determine if inflation and string theory can be saved from devolving into a Theory of Anything and, if not, seek new ideas to replace them. ...”
Considering that inflation seems to mean so many different things to different people, I am waiting to see exactly what was confirmed by the new experiment. We have what appears to be the remnant of a violent event in the early big bang, but I am not sure what all the consequences are yet.

Monday, March 17, 2014

Counterfactuals: Math

Counterfactual reasoning is essential to mathematics. A mathematician might assume some dubious hypothesis, derive an absurd result, and conclude that the hypothesis must be wrong. The method is called reductio ad absurdum. For example, the Greeks proved that there are infinitely many prime numbers as follows. If there were some largest prime N, then all larger numbers could be divisible by primes equal to N or smaller. But you could multiply all those primes together and add one, and get a contradiction. Therefore there must be prime numbers larger than N.

A more trivial example of this reasoning is to prove that there is no largest integer. For any integer N, the integer N+1 is larger. So assuming that there is a largest integer quickly leads to a contradiction. They also used an argument by contradiction to show that the square root of 2 is irrational -- that it cannot be written as a fraction a/b. If it could be, then a2 = 2b2. But 2 is a factor an even number of times on the left, and an odd number of times on the right, a contradiction. That is why the decimal expansion of the square root of 2 is an endless and non-repeating sequence of digits.

Counterfactual reasoning is also used to create new numbers. Even tho there is no rational square root of 2, we can just hypothesize one anyway. We have to expand our notion of number, and no longer require that a number is a ratio of integers. We still have many other properties, such as every number being less than, equal, or greater than other numbers. We can also lose that property by allowing a counterfactual square root to -1. Other counterfactuals give us infinitesimal numbers and non-Euclidean geometry.

Mathematical logic carefully distinguishes the counterfactual from the false conditional. A statement of the form "if A then B" is always true if A is a false conditional. That is, a false hypothesis allows you to prove anything. For example, if 0 = 1, then I am the Pope. There is no use to a truly false conditional. The value is in a hypothesis that might be true on some alternative universe of mathematical facts.

The statement about the Pope may be proved as follows. If 0 = 1, then add 1 to both sides, getting 1 = 2. The Pope and I are 2 different people. But 2 = 1, so we are 1 person, and I am the Pope. Or you can prove it without this sort of cleverness by just appealing to the meaning of a conditional.

A mathematician might also say, "if pigs have wings, then I am the Pope." That is because pigs do not have wings. If you want to posit some counterfactual world in which pigs have wings, then you need a grammatical modifier or mood to show that.

Sometimes even mathematicians are unhappy with counterfactual reasoning. A century ago L. E. J. Brouwer proved that any continuous function from the disk to itself must have a fixed point, but his proof relied on counterfactual reasoning and gave no way to find such a point. He adopted the view that such a theorem is dubious unless it gives a way to construct the solution.

Mathematician Terry Tao explains his version of counterfactual reasoning in three posts on The “no self-defeating object” argument. As he explains, many elementary theorems are very confusing to students because they are based on constructing some impossible object. There can be no impossible object, so the proof seems like a paradox. The contradiction is avoided by precise mathematical definitions and analysis.

As a simple example, Tao proves that there is no largest integer. The proof is trivial, as any largest integer N would be less than N+1. But the counterfactual subtlety of this argument is sufficient that a child is more likely to learn it from another child on the playground, than from a teacher or textbook.

A very widely promoted AT&T TV commercial focuses on this proof as a way of arguing that bigger is better in phone networks. Sure enough, the kids grasp the concept as the teacher has a difficult time explaining it.

Thus the counterfactual is one of the core concepts in mathematics. You will never learn proofs without it.

Friday, March 14, 2014

Pi Day and Einstein

Einstein biographer Walter Isaacson celebrates Pi Day with a podcast about the genius of Einstein.

His main point is that Einstein's 1905 papers on light and relativity were each a revolutionary quantum leap that was independent of previous work and not properly understood or appreciated by experts at the time. The truth is more nearly the opposite.

The podcast credits Einstein with the original notion that light is both a wave and a particle. [at 6:07] No, it was Planck in 1900 who proposed that light was a wave, but emitted and absorbed discretely, and that is much closer to the modern view in quantum mechanics. Einstein opposed that modern view at every opportunity.

Then it says Planck, Lorentz, and Poincare were all working on physics related to relativity, and Einstein makes the big disconnected leap. Furthermore he says the other guys read the paper, and still don't quite get it.

Nonsense. Planck understood Einstein's paper, and immediately wrote a paper on it. Lorentz lectured on relativity in 1906, and correctly explained how Einstein's paper was just a minor embellishment on his own ideas.

What we know as special relativity today comes mainly from Lorentz's 1895-1904 work and Poincare's 1905 paper. Poincare had the spacetime geometry and Einstein did not. Einstein did not understand Poincare's paper until at least 1908.

These points are all detailed in How Einstein Ruined Physics, and on this blog.

Thursday, March 13, 2014

The present is real, the past is gone

Brian Greene has released his World Science U special relativity course, with and without the math. It is slick, free, and appears to be well explained.

He falsely credits and idolizes Einstein, but probably has not read my book, How Einstein Ruined Physics.

In the module on "The Reality of Past, Present, and Future", he makes some faulty philosophical comments about time, that I recently attacked. After explaining some of the difficulty with relativistic simultaneity, he concludes:
So what this collectively tells us is that the traditional way we think about reality -- the present is real, the past is gone, the future is yet to be -- that is without any real basis in physics. What we are really learning from these ideas is that the past, the present, the future, are all equally real.
So does relativity really require us to give up this basic intuition about time? I say no.

The essence of Greene's problem can be understood with pre-relativistic causality. Suppose I am on Earth, an alien is on another planet, and we somehow come to agreement about time. For me, "now" means that I can affect events in the immediate future, and likewise for the alien. But I cannot affect things in the immediate future on the other planet, because anything I cause on Earth will take some time to get to the other planet. So while the alien and I may agree about the meaning of "now" as it relates to our local clocks and our notion of local causality, it will still be the case that I can affect my environment before the alien can, and the alien can affect his before I can.

Relativity makes this more precise by saying that causality is limited by the speed of light, and by giving formulas for how motion can de-synchronize clocks.

The essential point is that the present now makes sense for me, and I can cause changes in the future, but only nearby, because there is no action-at-a-distance. Technically, I can affect my future light cone.

The alien might agree on what now means, and he can affect his future light cone, but my future light cone is different from his.

Thus Greene's conclusion above is entirely wrong. Our traditional notion of time, with its distinction between past, present, and future, does have a real basis in science. I explain this below in terms of time counterfactuals.

While Greene's explanation of relativity is mathematically correct, and his paradoxes might be confusing, the world would be more confusing without relativity. Suppose that my present now was dependent on the whole universe in the immediate past, and my actions affect the entire universe in the immediate future, without any time lag. That alien on another planet could do something to affect me a second later, and I could respond, to affect him in another second. That alien would never make sense of his world because some capricious intelligence in another galaxy could be interfering with his experiments. Relativity puts a lid on that, and ensures that local causes have only local effects.

Relativity gives us more reason to believe that we live in the present, not less. Time is more intuitive when causality has relativistic limits.

Wednesday, March 12, 2014

Others disappointed with the Bruno multiverse

I am still annoyed at the Cosmos TV show. Neil deGrasse Tyson had previously refused to join the atheist anti-religion cause, so I am surprised that he got conned into the Bruno multiverse nonsense.

One review says:
I re-watched the original Cosmos a few years ago, some of the episodes with my kids. They are still fun to watch, but I realized something in seeing them again. Sagan made mistakes. Big mistakes, as with Hypatia and the burning of Library of Alexandria ...

I was looking forward to the new Cosmos.  But I saw the trailer and Bruno getting burned, so I knew it was just going to be more of the same. but I didn’t know how much more of the same it would be. ...

I think they chose Bruno because somebody said Galileo was getting a bit old, let’s find another scientist that religious people persecuted. Then they hit a problem. There really are not that many besides Galileo. In fact, there aren’t really any more good examples, at least not in Catholic Europe, where the Church over the ages was stuffed full of scientists and scientists-wannabes, ...

Problem was, Bruno was not much of a scientist, he was a weird mystic hermeticist who liked to insult people.
That's right. If the Catholic Church were really so anti-science and anti-knowledge, couldn't they find a another example?

Salon explains:
And, of course, it is no accident that Giordano Bruno appeared in the first episode of “Cosmos.” Because whether or not Bruno himself was a scientist, there’s not a whole lot, besides their relative lack of access to killer barbeque tools, that differentiates the current crop of intelligent design advocates and Texas textbook revisionists and inheritors of the Moral Majority mantle from the shame and terror of the Holy Inquisition.
A "longtime Giordano Bruno fangirl" writes:
His belief in an infinite universe, reflecting the infinite glory of God, got Bruno shunned and exiled from country after country. He grew impoverished and largely friendless, but refused to recant. Eventually Bruno was imprisoned by the Church, and burned at the stake in 1600–10 years before Galileo announced his first observations that confirmed Copernicus was right.

It’s a powerful, tragic, and cautionary tale, right?

Meet the Real Giordano Bruno

That depiction in the new Cosmos matches the standard textbook story of Bruno, but it is misleading and in some ways downright wrong.
Hank Campbell points out that Sean M. Carroll is a fan of the Bruno multiverse, and writes:
Then suddenly we get a claim that Giordano Bruno is responsible for the concept of the universe - because he read 'banned' books. Lucretious wasn't science - there was no scientific evidence for his claim that wind caused earthquakes or worms spontaneously generated - it was philosophy, and his book was not rare in 1600 AD, people were also not martyred for reading it, and yet we get told a philosophical belief in infinity was what got Bruno into trouble.

It's an immediate disconnect for people who know science history because it smacks of an agenda. I instead object because it is flat-out incorrect. To claim that Bruno promoted the concept of the universe, a "soaring vision", despite persecution, while simultaneously being hired over and over by the institutions we are told were oppressing him, makes no sense. That segment of the show makes it sound like he was a devout Christian tormented by reason rather than what he was - a cultist who engaged in confirmation bias to pick and choose anything that matched his beliefs.(1)

Bruno's "science" was never mentioned during his trial, he was on trial for being a cult worshiper. He only took up the cause of Copernicus because he believed in the Egyptian god Thoth and Hermetism and their belief that the Earth revolved around the Sun, not because he had perceived anything radical. Galileo rightly dismissed most of Bruno's teachings as philosophical mumbo-jumbo. Bruno was only revived as a 'scientist' and a martyr for science by anti-religious humanists in the 19th century.The church didn't even bother to ban his writing until well after he was dead.

Bruno was not a martyr for science, the way the cartoon in Cosmos: A Spacetime Odyssey alleges, he was a martyr for magic. He actually was a heretic.
Salmons writes:
Two reactions: 1) That’s not the real story. 2) With no evidence either way, how does holding to one superstition over another make Bruno an example for science?

On the first reaction, the Church didn’t overly care that Bruno believed in a heliocentric model of the solar system (link). They didn’t overly care in his belief of Copernicus’ views (many people did…even the Gregorian Calendar, adopted years earlier in 1582, was based on Copernicus’ observations).
A Catholic site writes:
The ignorance is appalling. “The Catholic Church as an institution had almost nothing to do with [the Inquisition],” writes Dayton historian Thomas Madden. “One of the most enduring myths of the Inquisition,” he says, “is that it was a tool of oppression imposed on unwilling Europeans by a power-hungry Church. Nothing could be more wrong.” Because the Inquisition brought order and justice where there was none, it actually “saved uncounted thousands of innocent (and even not-so-innocent) people who would otherwise have been roasted by secular lords or mob rule.” (His emphasis.)

As for Bruno, he was a renegade monk who dabbled in astronomy; he was not a scientist. There is much dispute about what really happened to him. As sociologist Rodney Strong puts it, he got into trouble not for his “scientific” views, but because of his “heretical theology involving the existence of an infinite number of worlds—a work based entirely on imagination and speculation.”
Thomas L. McDonald writes:
Before we begin, just who was Bruno?

He was a Dominican friar who lived from 1548 to 1600. He was not a scientist, conducted no experiments, looked through no telescopes, and wrote no scientific works. He was a mystic, a radical heretic, and an occultist. He abandoned Christianity in favor of Hermeticism (believed to be derived from ancient Egyptian wisdom) and magic.

Giordano Bruno, who enjoyed the patronage of King Henry III after abandoning his monastery, is shown as a poor and wretched drifter.

His place in a documentary ostensibly about science is inexplicable. Actual scientists worked on similar ideas, but only Bruno is called out in a ten-minute long segment.

The question is: why?

The narration begins by telling us that in “1599 everyone knew the sun, planets and stars were just lights in sky revolving around the earth.” It was “a universe made for us.” And “there was only one man who envisioned an infinitely grand cosmos.”

We’re barely seconds into this farrago and we have our first lie.

“Everyone” knew the earth was the center of the universe?

Wow, who’s going to tell Copernicus? Kepler? Stigliola? Diggs? Maestlin? Rothmann? Brahe? All of them believed in models of the cosmos that were not considered orthodox, and lived at the time of Bruno. All of them escaped the fire, and indeed weren’t even pursued by the Inquisition. Right here we have the major lie at the heart of modern anti-religious scientific propaganda: the war between faith and science.

We’re supposed to just assume this ignorant backwards world of the past hates smart people. Tyson himself says it matter-of-factly: “How was [Bruno] spending New Year’s Eve [in 1599]? In prison, of course.”

Of course! Because that’s what the Church does to smart people! Bad church! Bad!

Next: “This was a time when there was no freedom of thought in Italy.”

God, I really hate it when historical illiterates try to read church history through a modernist lens.
Casey Luskin attacks the Cosmos materialist agenda, and gives examples of modern scientists who are supposedly persecuted.

I don't really mind the atheist materialist agenda, if the scientists would stick to legitimate facts and science. But this is an attempt to promote completely unscientific reasoning in favor of a foolish multiverse belief system, both by Bruno in 1600 and by silly publicity seekers like Sean M. Carroll today.

Even the New York magazine review sees the show as left-wing anti-religion propaganda:
This new Cosmos is not so easygoing. The post-1980s rise of the Evangelical right wing created a hostile environment for ­science and science teachers. Recently, Louisi­ana governor Bobby Jindal became the latest conservative politician to ominously warn of a war on religion, even as certain public-school districts allow the discussion of creationism to undermine evolution in classrooms — a development that would have been unthinkable 30 years ago. Bill Nye, the former host of Bill Nye, the Science Guy, recently took part in an evolution debate with Ken Ham, ...

The new Cosmos feels like a pushback against faith’s encroachments on the intellectual terrain of science.
No, the Louisiana schools are not teaching creationism, and debates over evolution have gone on for over a century. Faith or religion is not interfering with science in any significant way. Not in the Western world, anyway. Has religion ever censored a scientific publication? Gotten an atheist fired? The mainstream Christian and Jewish religions have no quarrel with science at all. I realize that some religious folks have some beliefs contrary to modern science, but they have no power over the scientific community whatsoever.

I don't see why it is any better to teach unscientific multiverse ideas than to teach unscientific theological ideas.

I wrote a book on how physics has lost its way, and idolizing the Bruno multiverse is an excellent example.

Update: A reader complains that I have quoted an intelligent design advocate, and that a Discovery Institute official has admitted that there is anti-religious opposition to intelligent design.

I quoted a Catholic and an atheist also. I credit them all for pointing out historical and scientific errors in a popular TV show. I understand that some people are motivated to defend religion, while others are motivated to attack it. One thing I have liked about Tyson is that he is a science enthusiast, without getting bogged down into political or religious battles. I am happy to credit someone with a different view if he is correct about something.

Update: Leftist-atheist-evolutionist Jerry Coyne organized a campaign to censor a class that mentioned intelligent design and praised the Ball State U. president for saying "Intelligent design is overwhelmingly deemed by the scientific community as a religious belief and not a scientific theory." Then he attacks Casey Luskin for saying that religion had something to do with the issue. I don't mind criticism of religion, but the new Cosmos and Coyne's blog are just weirdo religious hatred. And my quoting Luskin is not an endorsement of his religious views, as I don't even know what they are.

Update: Also unhappy with the Cosmos treatment of Bruno is the pro-evolution anti-intelligent-design site NCSE, saying:
As our own Peter Hess observed, the first episode took a long detour from its history of the cosmos to tell a cartoonish history of Giordano Bruno. The intent seems to have been to revive the long-debunked and historically-discredited metaphor of warfare between science and religion.
The site is very happy with the "somewhat spiritual defense of evolution" in the second episode.

Tuesday, March 11, 2014

Strings compared to quantum computation

Now that Scott Aaronson has banned the leading defender of string theory from his blog, he gets the embarrassing question:
A layman question: Regarding string theory, is it really true that there’s a total dearth of any testable empirical predictions? At least for the foreseeable future of our experimental reach?
Aaronson answers:
What I think is uncontroversial is this: there are various phenomena that, if they were observed (either at the LHC or in cosmology), would provide an enormous boost to string theory. The most important and plausible of those is supersymmetric particles; but there are also more exotic possibilities, like large extra dimensions and cosmic strings. The central problem is that, if those phenomena are not observed (as indeed they haven’t been, despite searches for them), that doesn’t falsify string theory at all. For it’s perfectly compatible with string theory that these phenomena would only show up at much higher energies than are currently accessible to us.
This is like saying that there are experimental findings that would support telekinesis, and they are never seen, but that's no reason to doubt telekinesis.

Mathematician Greg Kuperberg tries to answer:
There is a “dearth” of *directly* testable empirical predictions in string theory, but it’s misleading to use the word “dearth”. It’s been acknowledged from the beginning that it’s difficult to make any new predictions from any reasonable model of quantum gravity. What theorists can do, however, is offer a better explanation of the evidence that already exists. That is the main driving force of string theory: How to keep quantum mechanics and general relativity from contradicting each other; and how to keep the Standard Model of particle theory from contradicting itself. String theory is an incomplete effort to do that, but it is also “the only game in town”. It is the only known attempt at quantum gravity that isn’t in the hospital and close to flatlined. And, resolving the Standard Model of particle physics would be extra icing on the cake.

Of course, any kibbutzer can talk about the problems of “theory without experiment”. But the truth is that the best theorists can get pretty far with just parsimony and logical consistency. Both general relativity and cosmological inflation — both of which are cousins of quantum gravity and string theory — were correctly developed before any help came from experiment. In the case of inflation, 20 years before good experimental confirmation.

Indeed, quantum computation has the same intellectual feature. Theoretical quantum computation gets a little help from experiment, but really hardly any. It is for the most part a compelling extrapolation of existing physics.
That is, string theory needs no experimental evidence because there is no known observational conflict between quantum mechanics and general relativity. And while string theory is not consistent with any known physics, the competitors are not either, and are not as fashionable. Just like theoretical quantum computation, which also has very little known relevance to experiment.

As a historical argument, it is not true that general relativity was "correctly developed before any help came from experiment." First, special relativity arose directly from experiment, as expressed at the time:
The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality. – Hermann Minkowski, 1908
Second, general relativity also follows from those same experiments, in spite of the mathematical difficulty. Lubos Motl explains:
While it's true that special relativity is a limit of general relativity obtained for gravitational fields going to zero, the actual "hierarchy of power" is the opposite: general relativity is just one application of special relativity – the incorporation of the gravitational field in a special-relativity-invariant way. While general relativity is arguably the prettiest (and geometrically most non-trivial) classical application of the rules of special relativity, in principle it is on par with Yang-Mills theory or any other (special) relativistic field theory.
Third, Einstein was driven to explain Mercury's orbit anomaly, following Poincare's relativistic partial explanation. So the development of general relativity was driven by experimental evidence, just like all the other great scientific theories.

Cosmological inflation has not really been confirmed, and remains just a loose collection of ideas for how the early universe might have expanded. There has been no Nobel prize for it.

I am a stickler for the history of relativity because it is always being misrepresented to justify bad science.

Monday, March 10, 2014

The clutches of the thought police

The first episode of the much-hyped TV series Cosmos: A Spacetime Odyssey was broadcast last night, and it made a big deal out of Giordano Bruno being a "martyr" in 1600 for expressing his expansive view of the cosmos. It did admit that he was not a scientist, and just made a "lucky guess" because he had no evidence.

His lucky guess was that the universe had an infinity of worlds like Earth. The show gives the impression that his guess was true, even if he lacked the evidence. But it is not. The overwhelming view of cosmologists today is that there are only a finite number of worlds in the universe.
He [Bruno] could not keep his soaring vision of the cosmos to himself, despite the fact that the penalty for doing so in his world was the most vicious form of cruel and unusual punishment. ... It wasn't long before Bruno fell into the clutches of the thought police.
No. Bruno's heresy was that he was a Catholic monk who denied the divinity of Jesus Christ.
Our entire universe emerged from a point smaller than a single atom. Space itself exploded fire launching the expansion of the universe, and giving birth to all the matter and all the energy we know today.
This is not helpful. I accept the Big Bang theory, but there is no real scientific evidence that the start was a point smaller than an atom. A naive extrapolation leads to that model, but the universe could have started with something the size of the Earth, for all anyone knows.

Anyway, we did not get an infinite number of worlds from a point smaller than an atom.

There is a lively debate between Scott Aaronson and Lubos Motl over whether P=NP. Aaronson eventually goes into a name-calling rant, and bans Motl from commenting on the blog for 3 years.

Aaronson has also banned me from his blog, because he was irritated about my skepticism of the possibility of quantum computers. Motl is his usually obnoxious and over-opinionated self, and he has called me names as well. Aaronson is like the Roman Inquisition, while Motl is like Bruno.

At the core of the dispute is the difference between math and science. P=NP is an open mathematical question, and until it is proved true or false, both outcomes must be considered possible. Aaronson's point is that the question should be considered settled under the lower standards of science, by analogy to the evidence for how green and yellow frogs might be separate species. Both Aaronson and Motl have weak arguments.

Aaronson is a typical academic knee-jerk liberal, and people like that usually despise political conservatives like Motl who can back up their opinions.

I once credited Aaronson with a plausible argument against P=NP, but I am doubtful about his frog argument:
He also argues that P != NP because verifying a proof ought to be much easier than finding an original proof. That is a reasonable argument. If it turns out that P = NP, then we would have to revise a lot of what we think about complexity, so we should be very skeptical of any such claim. Likewise we should be skeptical about quantum computing.
While my intuition says that there can be no efficient algorithm to solve NP complete problems, there could be a very inefficient polynomial-time algorithm, thereby allowing P=NP.

Maybe I should have expressed my objections to quantum computing as a parable about frogs. Instead of the evidence and arguments, I could have told about a naked emperor who gave grants to find a purple frog, and everyone always reported great progress even tho no one ever found a purple frog.

Update: Jennifer Ouellette, wife of cosmologist Sean M. Carroll, reviews Cosmos in the LA Times:
And Tyson adds a 21st century twist by invoking the multiverse: the notion that our universe might be just a bubble among bubbles in a vast infinite sea of universes. That’s the kind of notion that used to fall firmly into crackpot territory – or make for bestselling science fiction novels -- but is now taken quite seriously by many cosmologists, even if it’s not (yet, if ever) a testable hypothesis. And it’s the perfect set-up to a charming animated sequence relating one of my favorite stories from the history of astronomy.
Maybe taken serious by popularizers who promote fringe ideas like her husband. If an idea is never testable, then real scientists do not take is seriously as scientific.
Giordano Bruno was an Italian mystic who was among the first to adopt the Copernican cosmology at a time when doing so could prove hazardous to your health. In fact, he went one step further and suggested – based on a vision when he was 30, perhaps because he read the forbidden text of Lucretius, "On The Nature of Things" – that the sun and its planets were just one of millions of other solar systems in an infinite universe. It made sense to Bruno. God was infinite, he reasoned, so why shouldn’t the universe he created be infinite too?

The Catholic Church begged to differ and excommunicated him. So did the Protestant church. ...

But as Tyson points out, the dude was right. Sure, it was a lucky guess, and he wasn’t really a scientist, but “It gave others a target to aim at, if only to disprove it.”
No, the dude was wrong. Where is the Inquisition when we need it?

This show could have told the story of any of 1000s of great scientists who made observations, formulated a hypothesis, did an experiment, and then correctly analyzed the data to come to a valid conclusion. Bruno did none of that. It is crazy for this first Cosmos episode to focus on idolizing someone who was so contrary to the scientific method.

Thursday, March 6, 2014

Supersymmetry is dead

Ethan Siegel writes:
Have you ever wondered why the masses of the fundamental particles have the small values that they do, compared to, say, the Planck scale? Whether the fundamental forces all unify at some high energy? And whether there's a natural, compelling particle candidate for dark matter? Well, in theory supersymmetry (or SUSY, for short) could have solve all three of these problems. In fact, if it solves the first one alone, there will be definitive experimental signatures for it at the Large Hadron Collider. Well, the LHC has completed its first run, and found nothing. What does this mean for theoretical physics, for SUSY in particular, and what are the implications for string theory?
Supersymmetry started around 1970, along with various grand unified field theories. Theoretical physics started to diverge from what was observed, to how theorists thought that the universe ought to be. String theory followed, and it was almost entirely dependent on SUSY.

Physicists praised SUSY as correct in the same way that they say the Copernican model should have been accepted in the 16th century. It solved several independent theoretical conundrums, and just seemed more natural.

The trouble with SUSY is that it predicts new particles pairs with the known quarks, leptons, and bosons. None of these has been found. It is possible that they are all of such high energy that we will never find them, but then they are not so natural. To really solve the problems, we should have seen them. A lot of physicists have invested their whole careers on a wrong idea.

The above story is from May 2013, but is is only more true today:
For some insight into the current concerns of particle theorists, you can watch some of the videos at last week’s KITP conference. In particular, there’s Matt Strassler’s talk, where he got all Peter Woit and argued that “one could make the argument” that not seeing SUSY (or anything else stringy) at the LHC “would be significant circumstantial evidence against string theory as a description of nature” and that just seeing the SM at the LHC would be “circumstantial evidence against effective quantum field theory as a complete description of known particle physics”. This got him an argument from Gross about his insufficient enthusiasm for a 100 TeV collider. Gross then also got all Peter Woit, arguing that the failure of the “naturalness” argument for new physics was no big deal since it wasn’t a very good argument to begin with (I get all sorts of grief when I do this..).
You can be sure that physicists will find arguments for building a 100 TeV collider, at a cost of $20B or more.

Monday, March 3, 2014

Counterfactuals: Time

Time is what distinguishes the past from the future. The chief intuitive difference is that we remember the past, and we cause the future. Time marches forward, and as we cause events, they become the history that we remember.

While this view of time seems obvious to a small child, there is an opposite view that the present flow of time is just an illusion. That view is sometimes called block time, and its roots go call the way back to the ancient Greek philosopher Parmenides. Albert Einstein and other smart people have subscribed to such a view, and even claimed that relativity theory requires it. A 2010 SciAm article says that many physicists argue that there is no such thing as time, and explains:
As you read this sentence, you probably think that this moment — right now — is what is happening. The present moment feels special. It is real. However much you may remember the past or anticipate the future, you live in the present. Of course, the moment during which you read that sentence is no longer happening. This one is. In other words, it feels as though time flows, in the sense that the present is constantly updating itself. We have a deep intuition that the future is open until it becomes present and that the past is fixed. As time flows, this structure of fixed past, immediate present and open future gets carried forward in time. This structure is built into our language, thought and behavior. How we live our lives hangs on it.

Yet as natural as this way of thinking is, you will not find it reflected in science. The equations of physics do not tell us which events are occurring right now — they are like a map without the “you are here” symbol. The present moment does not exist in them, and therefore neither does the flow of time.
That view of time certainly is reflected in science, and in my opinion, adopted by all sensible people. There is not a shred of scientific evidence against it. Most of the fundamental equations of dynamics are expressed directly in terms of the flow of time. I quote the article to point out that more than one view of time is possible.

The scientists who deny the flow of time will typically argue that the fundamental laws of nature are deterministic and reversible, and so the progress of time is an illusion and we have no free will to affect the future. Many argue for retrocausality, as they say the future determines the past as much as the past determines the future. Some people also deny that we can speak definitely about the past, as they say that quantum mechanics allows for multiple histories.

Some argue that relativity is contrary to the flow of time, because time is just another dimension like the three spatial dimensions. That is even the consensus among philosophers. But the flow of time is essential to relativity, as every object travels along its world line into its future light cone. The dynamics of relativity, as well as other physics theories, use the flow of time.

Einstein was unhappy about the flow of time:
Once Einstein said that the problem of the Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation.
And also:
Three weeks before his death, in 1955, Einstein wrote, “People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.”
Hermann Weyl wrote in 1949:
The objective world simply is, it does not happen. Only to the gaze of my consciousness, crawling upward along the life line of my body, does a section of this world come to life as a fleeting image in space which continuously changes in time.
A recent paper on The flow of time in the theory of relativity demonstrates the confusion over alternate ideas of time:
When we consider any experiment related to the theory of [special] relativity, like the Michelson-Morley experiment (see, e.g., Møller 1955, 26-8), we can always describe it in terms of an intuitive notion of passage or flow of time: light is send through the two arms of the interferometer at a particular moment – the now of the experimenter –, and the process of light propagation takes time to occur, as can be measured by a clock calibrated to the adopted time scale.

However when we consider the theory, in particular focusing on its development in terms of the Minkowski space-time and its application using the Minkowski diagrams, we immediately became puzzled by the implications of the theory regarding our intuitive notion of time, and the passage or flow of time seems difficult or even impossible to ‘find’ in the conceptual-mathematical structure of the theory (see, e.g., Dorato 2010, 1-2).
Of course it is not really difficult to find the flow of time. If you understand how those experiments follow from the theory, then you have the flow of time.

The supposed problem is with "probabilism", which has been defined as the doctrine that "the universe is such that, at any instant, there is only one past but many alternative possible futures". There is also a technical problem that what one person perceives to be the present might differ from what another perceives. But that does not really affect the philosophical issue of time.

Without getting into the subtleties of relativity and quantum mechanics, I am adopting the commonplace view that time flows from the past (that we remember and is certain) to the future (that we cause and is uncertain). In philosophy jargon, I am following the A-theory of time and maybe presentism, instead of the B-theory and eternalism. As the ancient Greek Heraclitus said, it is impossible to step into the same river twice. As the above SciAm article says, how we live our lives hangs on this structure. I want to explain how this view relates to counterfactuals.

Past events are definite, and cannot be changed. Hypothetical events are in the future, and may depend on our free will to choose courses of action. Counterfactual events are in the past, and did not happen. We cannot make them happen. What we can do is to discuss the causal effect of the counterfactual events.

Counterfactual events are always earlier in time than the hypothetical consequences. For example, the counterfactual might be that you jump off a cliff. The consequence is that you fall to your death. Because you understand this causal reasoning, you don't jump off the cliff.

Free will is the idea that you can voluntarily eliminate counterfactuals from your life. At any given time, there could be several counterfactuals in addition to whatever you actually do at that time. If you have the free will to choose what you do, then you are making the decisions that prevent those counterfactuals from happening.

Thus counterfactual thinking is how people imagine alternatives to reality, and make decisions. As such, psychologists and others have attributed poor decision-making to a faulty assessment of counterfactuals. For example, someone might refuse to fly in an airplane because of an exaggerated opinion of the risk of a plane crash.

Again, the Einsteinian physicists and B-theory philosophers reject all of this. Their reasons are more religious than scientific. There are no experiments contrary to the intuitive flow of time, and no generally accepted theory that is inconsistent with it. Their view is deficient, because they cannot grasp counterfactuals.

Update: N. David Mermin recently wrote a paper on trying to escape the B-theory of time:
Rudolf Carnap succinctly stated the problem of the Now in his report of a conversation with Albert Einstein:7 “Einstein said that the problem of the Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation.”
Mermin says that this is "a longstanding puzzle in classical physics." The problem disappears with a suitable positivistic philosophy, altho Mermin does not exactly express it that way. You just have to rid yourself of warped Einsteinian thinking.