There are no fundamental particles, only quantum fields.
In a recent OP, I pointed to a 2010 paper by Richard Campbell and Mark Bickhard in which the authors argue the failure of reductive physicalism (and substance metaphysics generally) on the premise of quantum field theory, pointing out that:
But Campbell and Bickhard do not really mount any rigorous arguments by which to conclude that “there are no elementary particles”. In a 2013 paper published in American Journal of Physics, “There are no particles, there are only fields,” physics professor Art Hobson presents a series of killer arguments for the proposition that the assumption of quanta as independent particles is incoherent in the context of quantum field theory. Quanta are nothing more than epiphenomenal excitations of infinitely extended fields. “ . . . fields are states or conditions of space. [. . . ] According to general relativity, the universe is full of gravitational fields, and physical processes associated with this field occur even in space that is free from matter and EM fields.” Hobson views quantum field theory as a continuation of the process initiated by Maxwell's formulation of electromagnetic phenomena as fields, beginning with a quote from Einstein:
As a simple example of one of Hobson's more succinct arguments for the proposition that there are no particles, only quantum fields:
Hobson engages in a detailed, technical analysis of the two-slit experiment. Non-technically he notes first and foremost that what is observed when both slits are open is most conducive to a field explanation, yet observations when only one slit is open are not more readily accounted for as an effect of particles:
He proceeds to explain that the flashes seen on the screen are multi-atom events caused by interactions of a single quantum (i.e., a field mode excitation) with the screen. “. . .each electron interacts with a portion of a fluorescent film, creating some 500 photons; these photons excite a photo cathode, producing photo electrons that are then focused into a point image that is displayed on a TV monitor (Ref. 51). This shows that a quantum can interact locally with atoms, but it doesn't show that quanta are point particles.” (Analogous arguments apply to the appearance of “particle” tracks observed in cloud chambers and other such observations that are commonly taken as detection of particles.) Thus, the interference patterns seen in double-slit experiments “confirm field behavior and rule out particle behavior, while the small interaction points neither confirm particle behavior nor rule out field behavior. The experiment thus confirms field behavior.” “Localization” is just the high probability of being found in a small region, per personal communication.
Hobson cites two no-go theorems by Hegerfeldt and Malament, explicating the former in greater detail. These theorems demonstrate that if one begins with the assumption that the universe contains particles, then special relativity and quantum mechanics lead to contradictions. Neither theorem is premised on QFT; both merely assume only the requirements of special relativity, the general principles of QM, and broadly inclusive definitions of “particle.” The theorems then, by different methods, derive contradictions, showing that there can be no particles in any theory that obeys the principles of both special relativity and QM.
On the basis of the Unruh effect, Hobson argues that particles do not exist objectively but are observer-dependent. This is precisely what the Unruh effect indicates, predicting that a uniformly accelerating observer will see and experience quanta that are the product of blackbody radiation, while an inertial observer in the same vacuum reference frame will not. This effect is particularly pronounced near the event horizon of a black hole. Hobson asks: “If particles form the basic reality, how can they be present for the accelerating Velma but absent for the nonaccelerating Mort who observes the same space-time region?” It's a heavy question.
Hobson points to the fact of single-quantum nonlocality as indicating that quanta are not discrete particles but, rather, are mode excitations of infinitely extending fields. At the time Hobson's paper was published, he did not have benefit of the experimental demonstration of single-photon nonlocality by Fuwa et al., published in a 2015 paper in Nature. In their abstract, Fuwa et al. explain:
Hobson accounts for single-quantum nonlocality as entailing entanglement between two quantized field modes, one of which is in the vacuum state. The Fuwa et al. experiment demonstrates the reality of the inexorably expanding wave function, not the reality of a discrete particle. As Hobson says in his abstract, the Schrodinger equation describes a space-filling field whose value at any spatial point is the probability amplitude for an interaction to occur at that point.
The above does not summarize all of Hobson's arguments. I must admit that I have long been sympathetic to the idea that fundamental empirical reality does not consist of particles but rather fields. But I had not examined the question thoroughly enough to formulate even simplistic arguments to that end. Frankly I was under the impression that point and spatially extended particles, as distinct from the mere clumping of energy of fields, are somehow necessary for some reason. Unless and until I am confronted with arguments justifying that position, I relinquish it forthwith, as Occam's razor seems to demand. I didn't realize how many physicists (and other scholars) have likewise relinquished the notion of the existence of particles. Hobson references a pile of such physicists.
So, are there any empirical reasons to retain the idea there are particles? Even if so, how does one counteract Hobson's many arguments?
In a recent OP, I pointed to a 2010 paper by Richard Campbell and Mark Bickhard in which the authors argue the failure of reductive physicalism (and substance metaphysics generally) on the premise of quantum field theory, pointing out that:
What our best contemporary physics reveals is that there are no elementary ‘particles’, fundamental events, or some such particulars. There are only processes of various scales and complexity. [. . .] Quantum field theory shifts the basic ontology of the universe from micro-particles to quantum fields.
But Campbell and Bickhard do not really mount any rigorous arguments by which to conclude that “there are no elementary particles”. In a 2013 paper published in American Journal of Physics, “There are no particles, there are only fields,” physics professor Art Hobson presents a series of killer arguments for the proposition that the assumption of quanta as independent particles is incoherent in the context of quantum field theory. Quanta are nothing more than epiphenomenal excitations of infinitely extended fields. “ . . . fields are states or conditions of space. [. . . ] According to general relativity, the universe is full of gravitational fields, and physical processes associated with this field occur even in space that is free from matter and EM fields.” Hobson views quantum field theory as a continuation of the process initiated by Maxwell's formulation of electromagnetic phenomena as fields, beginning with a quote from Einstein:
“Before Maxwell, Physical Reality …was thought of as consisting in material particles…. Since Maxwell's time, Physical Reality has been thought of as represented by continuous fields, ...and not capable of any mechanical interpretation. This change in the conception of Reality is the most profound and the most fruitful that physics has experienced since the time of Newton.”[28] [. . .] QFT puts matter on the same all-fields footing as radiation. This is a big step toward unification. In fact, it's a general principal of all QFTs that fields are all there is (Refs. 10-21). For example the Standard Model, perhaps the most successful scientific theory of all time, is a QFT. But if fields are all there is, where do electrons and atoms come from? QFT's answer is that they are field quanta, but quanta of matter fields rather than quanta of force fields.[46]
As a simple example of one of Hobson's more succinct arguments for the proposition that there are no particles, only quantum fields:
Some authors conclude, incorrectly, that the countability of quanta implies a particle interpretation of the quantized system.[38] Discreteness is a necessary but not sufficient condition for particles. Quanta are countable, but they are spatially extended and certainly not particles. Eq. (3) implies that a single mode's spatial dependence is sinusoidal and fills all space, so that adding a monochromatic quantum to a field uniformly increases the entire field's energy (uniformly distributed throughout all space!) by hf. This is nothing like adding a particle. Quanta that are superpositions of different frequencies can be more spatially bunched and in this sense more localized, but they are always of infinite extent. So it's hard to see how photons could be particles.
Hobson engages in a detailed, technical analysis of the two-slit experiment. Non-technically he notes first and foremost that what is observed when both slits are open is most conducive to a field explanation, yet observations when only one slit is open are not more readily accounted for as an effect of particles:
Consider, first, the extended pattern. It's easy to explain if each quantum (photon or electron) is an extended field that comes through both slits. But could the pattern arise from particles? The experiments can be performed using an ensemble of separately emitted individual quanta, implying the results cannot arise from interactions between different quanta.[52] Preparation is identical for all the quanta in the ensemble. Thus, given this particular experimental context (namely the 2-slit experiment with both slits open, no detector at the slits, and a "downstream" screen that detects interactions of each ensemble member), each quantum must carry information about the entire pattern that appears on the screen (in order, e.g., to avoid all the nodes). In this sense, each quantum can be said to be spread out over the pattern.
If we close one slit, the pattern shifts to the single-slit pattern behind the open slit, showing no interference. Thus each quantum carries different information depending on whether two or one slits are open.
How does one quantum get information as to how many slits are open? If a quantum is a field that is extended over both slits, there's no problem. But could a particle coming through just one slit obtain this information by detecting physical forces from the other, relatively distant, slit? The effect is the same for photons and electrons, and the experiment has been done with neutrons, atoms, and many molecular types, making it difficult to imagine gravitational, EM, or nuclear forces causing such a long-distance force effect. What more direct evidence could there be that a quantum is an extended field? Thus we cannot explain the extended patterns by assuming each quantum is a particle, but we can explain the patterns by assuming each quantum is a field.[53]
If we close one slit, the pattern shifts to the single-slit pattern behind the open slit, showing no interference. Thus each quantum carries different information depending on whether two or one slits are open.
How does one quantum get information as to how many slits are open? If a quantum is a field that is extended over both slits, there's no problem. But could a particle coming through just one slit obtain this information by detecting physical forces from the other, relatively distant, slit? The effect is the same for photons and electrons, and the experiment has been done with neutrons, atoms, and many molecular types, making it difficult to imagine gravitational, EM, or nuclear forces causing such a long-distance force effect. What more direct evidence could there be that a quantum is an extended field? Thus we cannot explain the extended patterns by assuming each quantum is a particle, but we can explain the patterns by assuming each quantum is a field.[53]
He proceeds to explain that the flashes seen on the screen are multi-atom events caused by interactions of a single quantum (i.e., a field mode excitation) with the screen. “. . .each electron interacts with a portion of a fluorescent film, creating some 500 photons; these photons excite a photo cathode, producing photo electrons that are then focused into a point image that is displayed on a TV monitor (Ref. 51). This shows that a quantum can interact locally with atoms, but it doesn't show that quanta are point particles.” (Analogous arguments apply to the appearance of “particle” tracks observed in cloud chambers and other such observations that are commonly taken as detection of particles.) Thus, the interference patterns seen in double-slit experiments “confirm field behavior and rule out particle behavior, while the small interaction points neither confirm particle behavior nor rule out field behavior. The experiment thus confirms field behavior.” “Localization” is just the high probability of being found in a small region, per personal communication.
Hobson cites two no-go theorems by Hegerfeldt and Malament, explicating the former in greater detail. These theorems demonstrate that if one begins with the assumption that the universe contains particles, then special relativity and quantum mechanics lead to contradictions. Neither theorem is premised on QFT; both merely assume only the requirements of special relativity, the general principles of QM, and broadly inclusive definitions of “particle.” The theorems then, by different methods, derive contradictions, showing that there can be no particles in any theory that obeys the principles of both special relativity and QM.
On the basis of the Unruh effect, Hobson argues that particles do not exist objectively but are observer-dependent. This is precisely what the Unruh effect indicates, predicting that a uniformly accelerating observer will see and experience quanta that are the product of blackbody radiation, while an inertial observer in the same vacuum reference frame will not. This effect is particularly pronounced near the event horizon of a black hole. Hobson asks: “If particles form the basic reality, how can they be present for the accelerating Velma but absent for the nonaccelerating Mort who observes the same space-time region?” It's a heavy question.
Hobson points to the fact of single-quantum nonlocality as indicating that quanta are not discrete particles but, rather, are mode excitations of infinitely extending fields. At the time Hobson's paper was published, he did not have benefit of the experimental demonstration of single-photon nonlocality by Fuwa et al., published in a 2015 paper in Nature. In their abstract, Fuwa et al. explain:
A single quantum particle can be described by a wavefunction that spreads over arbitrarily large distances; however, it is never detected in two (or more) places. This strange phenomenon is explained in the quantum theory by what Einstein repudiated as ‘spooky action at a distance’: the instantaneous nonlocal collapse of the wavefunction to wherever the particle is detected. Here we demonstrate this single-particle spooky action, with no efficiency loophole, by splitting a single photon between two laboratories and experimentally testing whether the choice of measurement in one laboratory really causes a change in the local quantum state in the other laboratory. To this end, we use homodyne measurements with six different measurement settings and quantitatively verify Einstein’s spooky action by violating an Einstein–Podolsky–Rosen-steering inequality by 0.042±0.006. Our experiment also verifies the entanglement of the split single photon even when one side is untrusted.
Hobson accounts for single-quantum nonlocality as entailing entanglement between two quantized field modes, one of which is in the vacuum state. The Fuwa et al. experiment demonstrates the reality of the inexorably expanding wave function, not the reality of a discrete particle. As Hobson says in his abstract, the Schrodinger equation describes a space-filling field whose value at any spatial point is the probability amplitude for an interaction to occur at that point.
The above does not summarize all of Hobson's arguments. I must admit that I have long been sympathetic to the idea that fundamental empirical reality does not consist of particles but rather fields. But I had not examined the question thoroughly enough to formulate even simplistic arguments to that end. Frankly I was under the impression that point and spatially extended particles, as distinct from the mere clumping of energy of fields, are somehow necessary for some reason. Unless and until I am confronted with arguments justifying that position, I relinquish it forthwith, as Occam's razor seems to demand. I didn't realize how many physicists (and other scholars) have likewise relinquished the notion of the existence of particles. Hobson references a pile of such physicists.
So, are there any empirical reasons to retain the idea there are particles? Even if so, how does one counteract Hobson's many arguments?
