String theory and the Popperazzi

Karl PopperIn a couple of weeks I will be participating to a workshop in Munich, Germany, on the current status of string theory, the multiverse, and other cutting edge ideas in fundamental physics.

The event is organized by physicist and philosopher of science Richard Dawid, and its goal is to get some cross-disciplinary talk going among people who vehemently disagree on the future of physics.

I asked Dawid why he invited me, since I’m a biologist and philosopher of biology, not physics, and he said he is interested in outside perspectives and parallels with other fields. Fair enough, it should be fun!

In preparation for the workshop, I wrote an essay over at The Philosophers Magazine Online on the whole debate, which has recently taken a nasty and very public turn.

Lee Smolin a few years ago wrote an influential book, The Trouble with Physics, which called into question the whole string theory operation on grounds that it is leading the fundamental physics community to detach itself from empirical reality. To which Leonard Susskind responded accusing Smolin of being a “Popperazzi,” an obviously derogatory term referring to the philosopher Karl Popper and his idea of falsificationism as a criterion of demarcation between science and pseudoscience.

More recently, George Ellis and Joe Silk wrote an op-ed in the prestigious Nature magazine, dramatically entitled “Defend the integrity of physics,” again criticizing their string and multiverse colleagues. To which cosmologist Sean Carroll responded via Twitter (not exactly a prestigious scientific journal, but much more effective in public discourse) with, and I quote: “My real problem with the falsifiability police is: we don’t get to demand ahead of time what kind of theory correctly describes the world.” The “falsifiability police”? Wow.

As I explain in the essay, I find all of this both amusing and disturbing. Amusing because it turns out that a number of physicists who cavalierly dismiss philosophy (though Sean is not one of them) resort to invoking their (incomplete, misguided) understanding of philosophy of science to score rhetorical points against their colleagues. Disturbing because the very public nature of the debate, and — let’s be frank — the rather crass tone that it sometimes takes, are doing nothing to improve the already troubled public image of science.

Stay tuned for more after Munich…

55 thoughts on “String theory and the Popperazzi

  1. Philip Thrift

    In looking at the Program for “Why Trust a Theory? … I suppose a pragmatist’s point of view would be that the goal should be to find the “use”ful theory, not the “truth”ful theory. Whether that helps, … .

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  2. brodix

    Massimo,

    As you profess to be a skeptic of the mathematical universe theory, I can only wonder how far down the rabbit hole you are willing to tread.

    Even the premise of something so taken for granted as “spacetime” treats the measures of duration and distance, of which it is composed, as more fundamental than what is actually being measured, action and space. Thus such arguments as that time is symmetric, because a unit of time is a scalar and is the same whichever way it is measured, rather than taking into account the inertia of the action actually being measured.

    From which we then get such interesting ideas as time traveling through wormholes, etc.

    Then going on to such nonsense as saying space expands, based on the premise of spacetime, which completely overlooks the fact that in order for the math of General Relativity to apply, the speed of light would have to remain constant. So it would have to speed up to match the expanding space, but that would negate the very explanation for redshift, that it takes light longer to cross this space. (Coel, I’m still waiting for a reply.)

    It’s been my contention that back in the 90’s when the financiers wanted mathematicians to create all their leveraged derivatives, etc, they went to physical theorists out of MIT, rather than use their own accountants, because the theorists think entire universes pop out of every thought bubble, while accountants know too much funny math will get you in trouble.

    All I can say is that if you won’t drink their Kool Aide, good luck!

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  3. Thomas Jones

    Massimo, bon voyage. I look forward to your observations upon your return. You say “two weeks” and so I assume you’ll be in the US for Thanksgiving. Happy Thanksgiving! I’m thinking I’ll suggest to my wife that we have some sort of seafood as an entree instead of the usual fare. Maybe some oyster dressing on the side.

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  4. ejwinner

    Tangentially, I admit that I find it odd that some think it necessary to posit multiple universes to explain this universe, when it is difficult enough to use this universe to explain how Republicans get elected to Congress….

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  5. SocraticGadfly

    EJ, that’s because this universe IS the alternative universe!

    Thomas, you can also go with another fowl besides turkey. Duck? Goose? (Goose is an old German Christmas tradition.)

    Or, you’re in Texas like me.

    Either deep fry that turkey, or find someone who shot a wild hog. I’d still like to try deep-fried small wild hog, with the Cajun butter injection marinade.

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  6. Coel

    Hi ejwinner,

    I admit that I find it odd that some think it necessary to posit multiple universes to explain this universe, …

    Perhaps your comment wasn’t meant seriously, but the basic point is this:

    If we have a physical mechanism that will create a star, then that mechanism occurs trillions of times producing trillions of stars (perhaps an infinite number).

    If we have a physical mechanism that will create a planet, then that mechanism occurs trillions of times producing trillions of planets (perhaps an infinite number).

    If we have a physical mechanism that will create a Big Bang, then the entirely natural things is to suppose that that mechanism will occur trillions of times and produce trillions of Big Bangs (perhaps an infinite number).

    Really, the far weirder thing would be that a physical process occurred once and only once, and thus that there was only ever one Big Bang. Why would that be?

    The idea of a multiverse really is rather prosaic. The idea of a single Big Bang is weirder.

    [NB, here I am talking about a cosmological multiverse, based on the “chaotic inflation” model of the Big Bang, which is the currently preferred variant. Other multiverse conceptions, such as that from string theory (which is as yet speculative and unproven, as every string theorist admits) is a rather different kettle of fish.]

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  7. Coel

    brodix,

    So it [light] would have to speed up to match the expanding space, but that would negate the very explanation for redshift, that it takes light longer to cross this space. (Coel, I’m still waiting for a reply.)

    My reply, as previously, is that you still have not given any reason (at least, none that is comprehensible to me) why you think that light would have to speed up in an expanding universe.

    And no, as per previous replies, it is not the case the “explanation for redshift” is that “light takes longer to cross” the space.

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  8. Massimo Post author

    Philip,

    “I suppose a pragmatist’s point of view would be that the goal should be to find the “use”ful theory, not the “truth”ful theory.”

    Well, that would get participants into a discussion between scientific realism and antirealism, with the latter playing the role of a pragmatic philosophy. Problem is, I suspect most scientists are realists about scientific theorizing…

    As for your latest link, that sort of claim has been made before, and it turns out there usually are other, more mundane, explanations for the alleged evidence of another universe. But time will tell.

    brodix,

    “As you profess to be a skeptic of the mathematical universe theory, I can only wonder how far down the rabbit hole you are willing to tread”

    I draw the (fuzzy) line at what can be empirically tested, either now or in the foreseeable future. The MUH is clearly out, and contra Coel, I think also the multiverse and very likely string theory, though for different reasons.

    Liked by 1 person

  9. Coel

    Hi Massimo,

    I draw the (fuzzy) line at what can be empirically tested, either now or in the foreseeable future.

    OK, how about this.

    Given the finite age of the universe, there is an “observable horizon”, being the light-travel distance in that finite time, from beyond which we cannot obtain empirical evidence. We can see pretty much out to that observable horizon, and we know what the universe looks like out to there.

    Beyond that point, the “default scientific model” would presume that there is “more of the same”. That’s because there is no evidence for anything different, and any “edge” would be a rather radical concept that, as disciples of Occam, we would not advocate absent any evidence for it.

    As a scientist, I’d say that the presumption of “more of the same” extending to infinity is a “scientific” statement (bearing in mind the provisionality of all scientific conclusions).

    As a philosopher of science, would you agree, or would you regard any “more of the same” statement as being beyond the remit of science?

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  10. brodix

    Coel,

    “why you think that light would have to speed up in an expanding universe.”

    When it was originally discovered that redshift is proportional to distance and that there was no lateral action, the effect resulting in that we appear as the center of this expanding universe, it was concluded that this wasn’t just galaxies flying away, but an expansion of space itself, based on the premise of “spacetime.” Yet the premise of spacetime is that the speed of light remains constant to the space, so that in a accelerated or gravitational frame, while the distance shrinks, the speed of light also slows, so that they remain Constant. Remember Constant? Well, if space/the universe expands, such that it takes light longer to cross and thus it is redshifted, then the speed of light is not Constant to the space!

    So I don’t particularly care whether the speed of light speeds up in an expanding universe, but it is counter to using the premise of spacetime to explain redshift.

    “And no, as per previous replies, it is not the case the “explanation for redshift” is that “light takes longer to cross” the space.”

    Is there some other magical/mathematical explanation for why the light would be redshifted, other than a doppler effect of the source moving away?

    The usual answer I get is that “light is only measured locally.” The speed of my car driving down the road is also only being “measured locally,” but if it takes one hour to drive from point A to point B and I am driving sixty miles an hour, then they are sixty apart. Now if it were to take two hours, then either A and B are 120 miles apart, or I’m only driving 30 miles an hour.

    So why not say the light is slowing? Aka, tired light theory? Basically the metric defined by the speed of intergalactic light is being compared to the metric defined by the redshift of the spectrum of intergalactic light. Therefore one is the denominator and one is the numerator. If you say the speed of light is the denominator, then the question is as to why the galaxies are moving apart. If you say the redshifted spectrum is the denominator, then the question is as to why the light is being slowed. The consensus is that the space is expanding, not that the speed of light is slowing.

    Of course, if redshift is actually an optical effect, like gravitational lensing, then it would be quite logical that we would appear as the center and it would also serve as Einstein’s original Cosmological Constant; An intergalactic effect to balance the galactic contraction of gravity.

    Instead we now have Inflation and Dark Energy to patch more holes in the theory.
    One can only wonder if endless generations of theorists will accept their fate of exploring the multiverse, or will there be some reconsideration/revolution.

    Massimo,

    “I draw the (fuzzy) line at what can be empirically tested, either now or in the foreseeable future.”

    Keep in mind that epicycles were quite precisely “empirically tested,” given the cosmos followed very predictable patterns. That is the job of the scientists. It’s the job of the philosophers to keep asking the embarrassing questions.

    Kool Aide, or Hemlock.

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  11. SocraticGadfly

    Brodix, per your comment to Massimo, I’m sure that he gives Occam’s Razor healthy use when a new theory that is just as empirically verifiable is offered to fit the same data.

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  12. brodix

    Socratic,

    Then again, Popper doesn’t apply to cosmology, because every time theory and observation don’t match, they assume another enormous new force of nature, from inflation to dark matter, to dark energy, rather than falsifying the theory, because the theory is not wrong.

    Now if redshift were an optical effect and it compounded on itself and thus went parabolic, that would explain the curve in the rate of redshift, rather than dark energy.

    Then the Cosmic Microwave Background Radiation would be the solution to Olber’s paradox, the light of infinite sources, shifted off the visible spectrum into the microwave and we would have one, infinite universe.

    On the other hand, it is much more logical that the entire universe began as a dimensionless point, 13.8 billion years ago, that expanded out so rapidly and so fast that it only appears as overall flat space.

    Only us delusional cranks would dare question such wisdom.

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  13. Alan White

    Something that has struck me for many years is the empirical equivalence of the first law of thermodynamics with the conclusion of Aquinas’ third way likewise empirically constricted: mass-energy may change in form contingently, but its universal amount may not change, necessarily. So the first law intelligibly expresses a form of empirical necessary existence as constrained to this universe. This may show that all instantiations of empirically contingent existence may be thus interdefined as lawlike transformations of this mass-energy into various forms, living and non-living. Now whether this can be parsed to non-empirical theses about the necessary existence of mass-energy that transcend extensional reference to this universe into multiiverses and the like, I have no idea. But the first law of thermodynamics may be an insight into what is possible in the larger senses of logical possibility, since the intra-world necessity of the existence of mass-energy may have inter-world significance. Hope that sketch is clear enough to be suggestive as a thesis.

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  14. Philosopher Eric

    Sounds like more good fun for you Massimo. Yes I’d second the advise of Philip Thrift at the top to focus upon what’s “use”ful rather than “truth”ful. I don’t take you to disagree of course, though this theme should still be helpful to keep central. Physicists have actually developed NO theories that are known to be true, though some theories do seem quite useful nonetheless. (Don’t get me started on theories which have supposedly been “proven.” I use the term “evidence” over “proof” every time.)

    I personally don’t mind placing theory which has not been corroborated with evidence, squarely under the label of “science” — though I do still look strangely at those who place much stock in such theory. Just as Shakespeare’s “Hamlet” probably never happened, I’m sure that there are all sorts of stories that may be written in the language of mathematics.

    Hi Coel,

    When you used the term several times above, I wonder if you meant to write ? Otherwise it would seem that the next “Big Bang” or whatever, would be the occurrence. I personally don’t like to use this concept at all, unless I’m referring to something such as “one divided by zero.”

    Liked by 1 person

  15. Philosopher Eric

    Let me try that again:

    Hi Coel,

    When you used the term infinity several times above, I wonder if you meant to write “infinity”? Otherwise it would seem that the next “Big Bang” or whatever, would be the infinity + one occurrence. I personally don’t like to use this concept at all, unless I’m referring to something such as “one divided by zero.”

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  16. Robin Herbert

    Hi Coel,

    “Really, the far weirder thing would be that a physical process occurred once and only once, and thus that there was only ever one Big Bang. Why would that be?

    The idea of a multiverse really is rather prosaic. The idea of a single Big Bang is weirder.”

    Yes, in fact when I first heard about the Big Bang when I was a kid. I just assumed it was one of many and was somewhat surprised to find later that most people didn’t think that.

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  17. Robin Herbert

    Hi Eric,

    I’m not sure why you would have a problem with the concept of adding one more thing to an infinite collection of things.

    Always room for one more in Hilbert’s Hotel.

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  18. Coel

    brodix,

    Well, if space/the universe expands, such that it takes light longer to cross …

    OK so far …

    and thus it is redshifted, …

    No. The redshift is not the result of light “taking longer to cross” space.

    … then the speed of light is not Constant to the space!

    I still have no idea what you’re trying to say. What do you mean by “Constant to the space”? The word “to” there seems weird.

    If space expands, such that there is twice as much space, then it will indeed be the case that light takes twice as long to cross it. You have not explained why you think that is a problem.

    Yet the premise of spacetime is that the speed of light remains constant to the space …

    The premise is that the speed of light remains constant. I’m not sure what you mean by adding “… to the space”. Light, travelling at a constant speed, does indeed take longer to cross space when space expands.

    Is there some other magical/mathematical explanation for why the light would be redshifted, other than a doppler effect of the source moving away?

    The redshift is NOT “a doppler effect of the source moving away”!

    Space is elastic. Draw a wave on some elastic. Then stretch the elastic. The distance between wave crests will have increased. That is the redshift.

    Thus the redshift is caused by the stretching of space itself. It is NOT, as you seem to think, caused by “light taking longer to cross” the space.

    [Even if the redshift *were* a Doppler shift, that would still not mean that the redshift were caused by “light taking longer to cross” the space, since a Doppler shift arises from the relative motion of transmitter and receiver, not from the travel time between the transmitter and receiver.]

    So why not say the light is slowing? Aka, tired light theory?

    Tired light cosmologies have been considered extensively, since being originally suggested by Zwicky. They don’t work; see the wiki page for a primer.

    It really is not the case that cosmologists have all blundered, overlooking some basic inconsistency in their models, that you, with your far greater insight, are now pointing out. All of this has been studied extensively, and the fact is that the standard cosmology does an excellent job of not only explaining, but also *predicting*, observations such as the fluctuations in the microwave background and all sorts of other things. If you think you have some alternative cosmology, then, as a starter, please predict what your scheme says the fluctuations in the microwave background should be.

    Only us delusional cranks would dare question such wisdom.

    For all your sarcasm, your posts show that you don’t even understand the very basics of the topic.

    Eric,

    Otherwise it would seem that the next “Big Bang” or whatever, would be the infinity + one occurrence.

    Infinity + one = infinity. (And yes I did mean to use the term “infinity” in my previous comment.)

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  19. Philip Thrift

    Another problem with scientists: Many use “infinity” so informally as to be useless. The issues involved and approaches to the countable and uncountable (cardinality vs. ordinality, hyperarithmetical sets and iterated Turing jumps: the hyperarithmetical hierarchy, infinite time Turing machines; Blum-Shub-Smale computability; Sigma-definability; computability theory on admissible ordinals; E-recursion theory; local computability; and uncountable reverse mathematics, Malament–Hogarth spacetimes, … ) is, well, a big set anyway.

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  20. brodix

    Coel,

    “If space expands, such that there is twice as much space, then it will indeed be the case that light takes twice as long to cross it. You have not explained why you think that is a problem.”

    Because, as I see it, that is distance, not space. If I walk across the room, I’m not creating space, but moving through it. The units of the ruler do not change, only more are added. So if “space is what you measure with a ruler” and there are more units of measurement between the points, then it would seem to me that their relative movement is not creating space, but moving through it.

    “Space is elastic. Draw a wave on some elastic. Then stretch the elastic. The distance between wave crests will have increased. That is the redshift.

    Thus the redshift is caused by the stretching of space itself. It is NOT, as you seem to think, caused by “light taking longer to cross” the space.”

    Isn’t this in contradiction with your prior point, that light is taking longer to cross the space? If light were a static wave, then yes, it would be stretched as the space it is measuring is stretched, BUT why does it then take longer to cross it? The speed of the light would also be “stretched.” There would not be more lightyears between points, only stretched lightyears. The ruler itself would be stretched with the space. But as you said above, the light does indeed take longer to cross the space.

    ” a Doppler shift arises from the relative motion of transmitter and receiver, not from the travel time between the transmitter and receiver.]”

    As the transmitter and receiver move apart, or come together, it is the wave having to travel the increased/decreased distance which creates the shift. For instance, the train moving away stretches the sound waves of the whistle, because the source is moving away and each peak/trough of the waves have longer to travel. Which does take more time, since the speed of sound is relatively constant.

    Hopefully I can keep up the conversation through the day. It is supposed to rain all day and my satellite connection doesn’t always work in such conditions.

    Frankly, I just like the conversation. If you prove me wrong, well, it would be like a tennis match, I lost.

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  21. Coel

    brodix,

    If I walk across the room, I’m not creating space, but moving through it.

    The cosmological (general-relativistic) expansion of space is not a classical effect, and is not comparable to you walking across a room. Anyhow, that paragraph made no sense to me.

    Isn’t this in contradiction with your prior point, that light is taking longer to cross the space?

    Nope.

    The speed of the light would also be “stretched.”

    Why? You keep asserting that that would be the case, but not once have you given a reason (at least, not one comprehensible to me) for why that would have to be the case.

    Imagine a long piece of elastic, and imagine an ant walking along the elastic. You then pull the two ends, stretching the elastic. That creates more “space”. That means that it takes the ant longer to get to the other end. But, the walking speed of the ant (judged relative to the elastic directly under its feet at a given time) is not changed.

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  22. SocraticGadfly

    This is like saying the murderer being a left-handed Albanian is weird, but one being a left-handed Albanian AND wearing pink tennis shoes is less weird.

    No, I think the Big Bang is less weird.

    Also, with Massimo and Steve Gould, I see a lot of contingency in the “tape of life”

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  23. Robin Herbert

    What I don’t get is the philosophical distinction between Smolin’s ideas in physics and something like superstring theory. Smolin has an untested and possibly untestable theory in development. How is that different from string theory?

    And Smolin’s idea is still, effectively a multiverse, it is just a serial multiverse. If time is fundamental and real then it can’t have had a beginning. If the laws of physics evolve then they must have been through infinite evolutions before this and so there will have been infinitely many universes already.

    Incidentally, that appears to suggest that thee was never a first time the rules of chess were formulated, but that is a different discussion…

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  24. Coel

    Hi Socratic,

    This is like saying the murderer being a left-handed Albanian is weird, but one being a left-handed Albanian AND wearing pink tennis shoes is less weird.

    Bad analogy, it’s the *single*-universe model that has the extra thing to explain.

    Single-BB model requires: {mechanism for a Big Bang} + {reason it only happened once}

    Multiverse model requires: {mechanism for a Big Bang}.

    The multiverse model is more parsimonious in terms of the information required to explain it.

    By the way, what’s your suggestion for why a Big Bang would only have happened once?

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  25. Massimo Post author

    Coel,

    “As a philosopher of science, would you agree, or would you regard any “more of the same” statement as being beyond the remit of science?”

    I’m sorry I gave you the impression I’m a radical empiricist. That would be you 😉

    Yes, of course I think extrapolations are within the bounds of science, but the more one extrapolates the more problematic such extrapolations become. I submit that extrapolating from a partially visible universe to an infinity of ones is the motherload of all extrapolations.

    brodix,

    “Keep in mind that epicycles were quite precisely “empirically tested,” given the cosmos followed very predictable patterns. That is the job of the scientists”

    Besides the fact that one can argue that Ptolemaic astronomy was proto-scientific, not really science in anything like the modern sense of the world, epicycles are perfectly acceptable for an antirealist, since they claim that the objective of science is not to find truth, but to produce empirically adequate theories. But, again, most scientists are not antirealists, and they do see their goal as that of producing true (or near-true) theories of how the world actually is. That means no epicycles, and at the moment no strings or multiverses.

    Eric,

    “Physicists have actually developed NO theories that are known to be true, though some theories do seem quite useful nonetheless.”

    But truth, in philosophy of science, comes in degrees, and I think scientists would agree. While neither Newtonian mechanics nor, likely, Einstein’s relativity are “true” in the sense of being a completely accurate description of the world, I think you would be hard pressed finding either philosophers or scientists who would deny that Einstein got closer than Newton. If you deny that, then you also deny that there is any progress in science, a hard conclusion to swallow, unless one is a hard core postmodernist…

    “Just as Shakespeare’s “Hamlet” probably never happened, I’m sure that there are all sorts of stories that may be written in the language of mathematics”

    Interesting comment, which goes to the heart of the issue: yes, you are right, but science isn’t mathematics. The former is in the business to pick which of the many “stories” can be written that is actually true, or as near to true as we can get it. The rest is mathematics.

    Robin,

    “Smolin has an untested and possibly untestable theory in development. How is that different from string theory?”

    Well, for one he thinks it is testable. I do not have sufficient expertise to argue that point, so I’ll leave it at that. But more broadly his point is sociological: the fundamental physics community has put most of its eggs into one basket for decades. This, he claims, has resulted into severely cutting other avenues of research, to the detriment of the whole enterprise. I don’t know whether he is correct in this assessment, but that’s the argument.

    “And Smolin’s idea is still, effectively a multiverse, it is just a serial multiverse. If time is fundamental and real then it can’t have had a beginning”

    Again, he claims testability, whether correctly or not it’s a different matter.

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  26. Philosopher Eric

    Hi Robin,

    I guess my problem with using the term infinite (endless) rather than “infinite” (endless to us), or at least regarding the natural, is that it’s not an actual number. I presume that when one is added or subtracted from something which is physical, that it then gets bigger or smaller. But adding or subtracting from the infinite changes nothing whatsoever to this concept. So if there is indeed an infinite number of anything in the physical world, then this does not seem natural to me, but rather supernatural. I personally don’t believe in the supernatural, though many obviously do.

    I think Philip was referencing this above, with various examples that were beyond me. I can see how a computer programmer would be quite sensitive to this issue, since in practice if you treat infinity as a number, then your program will have a problem. This is why our calculators give us something like an “ERR” sign went we divide one by zero. Here we do need to know that we’re no longer dealing with a number.

    I’m sure that Massimo is aware of all of this, but as I say, it is good to keep what’s “useful” rather that “true” in mind, since we humans are really just idiots regarding reality in the end.

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  27. Robin Herbert

    Hi Philip,

    I do hear physicists sometimes say “effectively infinite” or worse “close to infinite”, but in general I think that physicists have a particular and valid meaning of “infinite”.

    Although, of course, my understanding of physics is limited. From Tegmark’s description of inflation theory, it seems to imply that the universe is infinite, unless there are faster than light particles.

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  28. Philip Thrift

    Robin, outside of the presence of “infinity” (in a particular sense) in an interpretation (model) of mathematical theories, to jump from its meaning in mathematics to its physical realization is problematic.

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