The self-described physicist responds to a wise comment by Mark Srednicki who points out, using the example of Brian Greene, that real scientists are primarily asking and answering questions whether something is true or not, rather than asking whether it is compatible with their dogmas. The self-described scientist under consideration shows that despite Mark's patient explanation, he still has no idea about this basic goal of science:
- Dear Mark... Your selective quotation of me badly misstates my position. Not only do I acknowledge that the landscape is a possibility, I invented the idea, named it and was the first to explore its consequences, in papers from 1992 on.
The alternative physicist obviously can't distinguish a real discovery in science from a random sequence of buzzwords and guesses that can impress some of the laymen who read the newspapers but not the experts. These are extremely different things.
More seriously, the person above was certainly extremely far from being the first one who simply suggested that string theory could have a large number of classical solutions or backgrounds. For example, Wolfgang Lerche was talking about these things in the 1980s, using the number 10^{1500} as an estimate.
- My issue, since then has been how we can continue to make falsifiable predictions if the landscape is true. Back then I considered the use of the Anthropic Principle (AP), rejected it as unable to yield predictions, ...
Every high school student who is remotely interested in physics and who is explained what the anthropic reasoning assumes is able to figure out that if the anthropic principle is true, it is probably very difficult to make predictions. We don't need a supreme alternative physicist to tell us so and it is very silly if a person expects to be treated as a discoverer when he says these obvious words.
- and found that there are other non-AP scenarios for physics on the landscape that do imply falsifiable predictions.
They imply predictions that are not only falsifiable but they are falsifiable within a few minutes.
- My issue is then not with the landscape, it is with the use of the AP to do physics on the landscape. In fact, I had to wait many years for the string theory community to catch up and agree with me that the landscape issue was serious and needed to be addressed.
This is a nonsensical statement. The landscape "issue" can only become serious after the landscape is actually discovered. Once it's discovered, questions about it are obviously important. But the term "landscape issue" is ill-defined and can't be "serious". It's just a vague emotional combination of words that don't mean anything which is why it is impossible to imagine that physicists would have to "catch up" with these vacuous words. Physicists never try to catch up with nonsensical fog.
- To make this clear, let me give the full context of the quote of my book you use from p 165 of [his text]: …when it comes to the biofriendliness of our universe, we have at least three possibilities: ...
If the prefix "bio" is meant seriously, let me say that high-energy physics is not discussing the question of "biofriendliness of our universe" because it belongs largely to biology and most of it belongs to biology in the far future. The person continues with these options:
- Ours is one of a vast collection of universes with random laws.
- There was an intelligent designer.
- There is a so-far unknown mechanism that will both explain the biofriendliness of our universe and make testable predictions by which it can be confirmed or falsified.
Neither 1) multiverse nor 2) God or 3) the possibility of complete predictive laws was first suggested by this person. It is just crazy to see that the person constantly wants to be credited for these things, including the discovery of God.
- Given that the first two possibilities are untestable in principle, it is most rational to hold out for the third possibility.
Moreover, it is silly to decide whether the answer is 1), 2), or 3) in advance. If one discovers a particular physics mechanism, it may remain very uncertain whether the mechanism should be described as 1), 2), or 3). Of course, 2) God is way too disconnected from the usual language of science and almost no scientist would say that a realistic discovery in physics supports the existence of God, even though it is a terminological issue. But whether we have 1) or 3) is a matter of convention. Even if the 1) multiverse exists, no one can be sure that all predictions are impossible. People should try which will move them from 1) closer to 3). To summarize: the separation of possible solutions into those 3 philosophical categories is inconsequential for physics.
- Indeed, that is the only possibility we should consider as scientists, because accepting either of the first two would mean the end of our field.
This is a profoundly immoral statement. It is not scientist's job to be thinking whether something will bring bright future to his or her field. The scientist's task is to find the truth regardless of its impact on his profession. For example, if there is only the Higgs boson at the TeV scale, the task for the CERN experimenters is to demonstrate that there is only the Higgs boson at the TeV scale. And I am sure that they will do so even though it is clear that this won't be great news for the future of particle physics. But anything else would be a fraud.
The author of the lines above is proposing the same kind of fraud but in theoretical physics. An honest theoretical physicist must judge the available evidence in the most objective and wise way he or she can, and whether or not one answer will make the future of the field brighter or less bright should have no impact on his decisions whatsoever. You can see that what the author of the lines proposes is to introduce the same "moral" standards as a part of climatology has adopted: the goal is to generate "exciting" results that will guarantee that money will flow to their field. I am absolutely convinced that theoretical physicists won't tolerate such dishonest thinking.
- Then, two pages later, on p 167 I discuss my original approach to the third possibility, from 1992. I beg your indulgence to quote at length, given that there are people who don’t read [his text]: But what about the third possibility, which is an explanation for the bio-friendliness of our universe based on testable hypotheses? In 1992 I put a proposal of just this kind on the table.
One that was instantly falsified by many independent arguments.
- To get testable predictions from a multiverse theory, the population of universes must be far from random.
This whole strategy of reasoning is irrational. Nature doesn't care a single bit whether the theories describing Her will be easily testable or hardly testable or untestable. Searching restricted to easily testable theories is like searching for the lost keys under the lamppost only. Among many theories that describe certain parts of Nature that we already know, some were easily testable and others were not. Making assumptions that theories describing Nature should be easily testable is irrational bias, wishful thinking, and it is strictly speaking incompatible with the scientific integrity.
- It must be intricately structured so that there are properties that all or most universes have that have nothing to do with our existence. We can then predict that our universe has these properties.
Even if we adopted the wishful thinking, the statement above is scientifically vacuous until someone actually determines what these properties are supposed to be.
- One way to get such a theory is to mimic the way natural selection works in biology.
Well, it is nice to try to mimic something. As long as we only try to mimic, we shouldn't forget that the importance of natural selection was discovered by Charles Darwin and not by his late 20th century imitators. One may try to import Darwin's idea to other sciences but it can only be described as a valuable transfer once it leads to something that works. That has certainly not been the case in physics so far. It is baffling to see someone boasting about this worthless bogus "invention" that a real scientist would be ashamed of.
- I invented such a scenario in the late 1980s, when it became clear that string theory would come in a very large number of versions.
First of all, today we know - because of the discovery of dualities and various transitions in the 1990s - that it is not true that there are many versions of string theory. On the contrary, we know that there is only one string theory although it has many minima of the potential.
Another point. You can see that the author is using the word "invent" all the time. It is no typo. The person actually keeps on inventing various fantasies that can impress ignorant laymen. But this person has never discovered something and seems to have no feeling what it means to discover something and what's the difference between discovering something that objectively exists and inventing something new that has nothing to do with reality but makes you feel as an "inventor".
- From books by evolutionary biologists Richard Dawkins and Lynn Margulis, I learned that biologists had models of evolution that were based on a space of possible phenotypes they called fitness landscapes.
That doesn't seem terribly relevant for high-energy physics.
- I adopted the idea and the term and invented a scenario in which universes are born from the interiors of black holes.
One that could have been falsified in a few minutes, too. Some people are incredibly proud about all of their failures.
- In [a text] (1997), I reflected at length on the implications of this idea, so I will not go into it in detail here, except to say that that theory, which I called cosmological natural selection, made genuine predictions.
It made "predictions" only because the author of this "idea" didn't understand that his idea was ill-defined. At any rate, these predictions could have been easily falsified because they were naive and completely unmotivated kindergarten guesses that had no reason whatsoever to be correct. Physics is not about making random naive guesses all the time. Physics is about finding the most reliable framework to make correct predictions.
- In 1992 I published two of them and they have since held up, although they could have been proved false by many observations made since then.
Only the author of the sentence above, not a sane person, could say something along these lines. Most people find the theory so silly that they would never discuss it. Despite this fact, there have been quite many papers that have pointed out numerous holes in that theory that make it impossible to work on it.
- These are (1) that there should be no neutron stars more massive than 1.6 times the mass of the sun, and
Funny. A typical neutron star has mass between 1.35 and 2.1 solar masses. I wonder whether the alternative physicist agrees that 2.1 is greater than 1.6 and most of the observed interval actually disagrees with the silly "prediction".
- (2) that the spectrum of fluctuations generated by inflation — and, plausibly, observed in the cosmic microwave background — should be consistent with the simplest possible version of inflation, with one parameter and one inflaton field.
That's an ill-defined statement because there are many "simple" models of inflation even with one inflaton field. Moreover, as the CMB data get more accurate, we're revealing all kinds of new features such as the tilt (n=0.96) that is virtually a settled fact now and makes the multi-field models more likely. What is exactly the prediction above saying? It's a vague guess whose meaning is deliberately incomprehensible, much like the justification.
To summarize: the prediction 1) was falsifiable and easily falsifiable while the prediction 2) is confusing enough so that it is not falsifiable. This is not how good physics works: good physics always deals with theories on the fine edge that are good enough not to be shown wrong instantly, but that are still non-trivial enough so that they have some content.
- So I hope my point of view is clear: the landscape may or may not be a real feature of string theory - evidence is that I was right and it is.
For this person, claiming credit for the landscape is a symptom of an interruption of brain activity.
- But if it is we are not relieved of our obligation to test the theory by making falsifiable predictions for doable experiments.
The obligation of physicists is to find how the Universe works. They should do so without any bias that prefers developments that might be quickly rewarded. The more theoretical and mathematically inclined physicists we consider, the less true the statement about the "obligation" related to doable experiments is.
The harder it is to do relevant experiments, the more likely it is that most of the work will be done by theorists. Quantum gravity is, almost by definition, destined to be an arena where theory is more important than experiments. It has always been, it still is, it probably will be, and only stupid people misunderstand why this obvious basic fact is true. Unfortunately these stupid people were recently extremely loud in the media.
As Mark mentioned, we could also very well find a proof that string theory is the only theory of quantum gravity that is mathematically possible.
Quite a huge fraction of physics breakthroughs has been made more or less without any contact with doable experiments - including both theories of relativity - and calls to connect every piece of work in physics with "doable" experiments should be treated as what it is: a primitive Marxist screech of untalented people who feel uncomfortable when anyone else is doing something that transcends their own abilities.
Also, even if you like philosophers: Karl Popper never said that a theory is only scientific if it is easily testable or testable by cheap experiments in the near future, or anything like that. Of course he always meant that scientific theories must be falsifiable in principle. String theory clearly is; the general philosophical cliches of the alternative physicist are not.
- There is at least one scenario that stands both as an existence proof that this can be done and as a challenge to observers to falsify.
It has been falsified many times. It is just impossible, at least without an army, to force physicists to spend months or years with something that they can solve and clarify in a few minutes.
- Any newer proposal for doing physics on the landscape then has to do at least this well.
Well, that wouldn't be a real constraint. I hope that physics will do better not only than self-described new Einsteins and mediocre self-described seers but also better than the anthropic eternal inflation scenario. But my hopes are less important than the truth.
And that's the memo.
P.S.: In order to be superpolite, I have replaced the word "crackpot" by the term "alternative physicist" or its alternatives in the text above.
