Sabine Hossenfelder does her usual spot on job of navigating through the weeds of what it means in science to say that something exists, using the Higgs boson, quarks, and gravitational waves as examples. An excerpt:
When we say that these experiments measured “gravitational waves emitted in a black hole merger”, we really mean that specific equations led to correct predictions.It is a similar story for the Higgs-boson and for quarks. The Higgs-boson and quarks are names that we have given to mathematical structures. In this case the structures are part of what is called the standard model of particle physics. We use this mathematics to make predictions. The predictions agree with measurements. That is what we mean when we say “quarks exist”: We mean that the predictions obtained with the hypothesis agrees with observations.
She goes on to discuss the philosophical concept of "realism" and to, appropriately, dismiss it as basically irrelevant.
4 comments:
" She goes on to discuss the philosophical concept of "realism" and to, appropriately, dismiss it as basically irrelevant. "
but is it ?
string theorists claim that nature really is 10 dimensional. it's not just a prediction but this is how nature is really like. and that neutrinos and electrons really do exist, and not just predictions that agree with experiment
Yes, it is. String theory's claim is not only a prediction, it is one that that has no evidence to support it and lots of evidence to suggest that it is inaccurate, which has forced string theorists into all sorts of contortions to try to explain why there are really ten dimensions despite the fact we only observe four.
"neutrinos and electrons really do exist, and not just predictions that agree with experiment"
Not really. We've measured phenomena that are consistent with the mathematical structures we call neutrinos and electrons, sometimes to great precision. We've measured the electron mass and fundamental charge to parts per billion, and we know the neutrino masses to a precision on the order of tens of milli-electron volts, which is roughy a ten millionth of the mass of the electron.
But, in perfectly respectable and pedestrian widely utilized quantum field theory, neutrinos and electrons (and all other fundamental particles) are merely excitations of a field, basically standing waves. And, of course, in string theory, hypothetically at least, neutrinos and electrons are just particular vibrational excitations of stings.
For lots of purposes, because our brains are trained and evolved to deal with the macroscopic classical physics world, it is convenient to think about neutrinos and electrons as "real". But, quantum physics doesn't resoundingly support that conclusion.
Quantum entanglement as experimentally established requires at least one of the following to not be true in any given case: (1) causality, (2) locality, and (3) reality. And, there are many circumstances where reality seems like the most plausible of the three to sacrifice.
For example, steams of electrons can interfere with each other in much the way that light waves do, and there are tabletop laboratory experiments in which it seems to be possible for some properties of an electron (e.g. charge) to pass to an end point from a source by a different path than other properties of that electron (e.g. mass).
The Heisenberg uncertainty principle (which is a theoretical limit on observation not just a practical engineering limit on observation), is also really at odds with the notion to electrons and neutrinos as "real" particles, and so is the well documented (but ill understood at a deeper level) phenomena of neutrino oscillation between mass states and electroweak states, which like the electron property separation experiment, involves the electroweak properties of the neutrino and the mass of the neutrino not being perfectly aligned with each other.
if you read on her comments
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Armin6:33 PM, May 22, 2019
I think that there is a potential for a great deal of additional clarity in fundamental physics if the concept of "existence" could be connected to physics in a more direct manner than outlined in this essay, by which I mean a specific criterion for existence *within physics*, as opposed to what might be called the meta-criterion that if a physics framework using certain mathematical structures makes predictions with which empirical data agree, then these structures ``exist''."
"Lawrence Crowell8:27 PM, May 22, 2019
Physics does not deal with existential questions particularly. This is seen with the plethora of quantum interpretations. These interpretations are either meant to confer reality to quantum waves, called ψ-ontic interpretations, or they confer epistemic meaning, called ψ-epistemic interpretations. Quantum mechanics in its stubborn way tends to resist fitting completely in any of these."
"Russ Abbott1:38 AM, May 23, 2019
The core of your position is that "predictions agree with measurements." That raises the question of what you mean by a measurement. Presumably it is the value of an indicator on an instrument.
What then is the theory about what produces the indicator reading? That is, how does the instrument interact with the rest of the universe so that its indicator takes on a value? "
I don't think the philosophy of "realism" is irrelevant if physicists want to say certain entities "exist"
"Quantum entanglement as experimentally established requires at least one of the following to not be true in any given case: (1) causality, (2) locality, and (3) reality. And, there are many circumstances where reality seems like the most plausible of the three to sacrifice."
or understanding of reality needs to be changed, a paradigm shift if you wish
With regard to quantum entanglement "reality" basically means that the mathematical construct of a particle corresponds to an actual physical thing which is a particle that actually takes a physical path of the possible ones.
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