breckenridgeback t1_jadno0v wrote on February 28, 2023 at 6:08 PM

A subatomic particle is just a particle "smaller than" an atom (hence sub + atomic). The three you're familiar with are the three component particles that make up atoms: protons, neutrons, and electrons. It turns out that protons and neutrons (but not electrons, so far as we know) have further internal sub-structure; protons and neutrons are each made of three smaller particles called quarks. The only other example you "see" in everyday life is the photon, the particle of light. Others exist, but none of them are long-lived or seen in everyday life under normal conditions.

What they "really are" is more a matter of philosophy than it is of physics. Physics is interested in describing how they behave. And in modern physics, we model the behavior of particles through quantum mechanics.

It turns out that the way we tend to think of particles in our minds - tiny little spheres bounding around and exerting forces on one another - just doesn't correspond to the way particles actually behave.

In quantum mechanics, the underlying "reality" of a particle is something called its wavefunction. Rather than a particle "being in one position", a wavefunction takes every possible position and assigns a single number to each of them. These numbers are complex numbers (that is, they look like something like 0.2 - 0.4i), and the Schrodinger equation tells us how they evolve over time.

Exactly how we interpret these wavefunctions as corresponding to any of the things we observe day to day is a topic of some debate. In a sense, the ultimate underlying reality is always the wavefunction, and the Universe as a whole has one wavefunction that has just been evolving according to the Schrodinger equation since the beginning of time. But since we often want to consider particles in isolation so that we can talk about an electron without talking about the whole Universe, we have to think about how we can "cut off" the electron from the cosmos. In this sense we try to talk about "the electron's" wavefunction, but in reality, even the existence or non-existence of the electron is a statement about the wavefunction of the entire Universe, so by talking about "an electron" at all we are going to introduce some weirdness.

We do this by thinking in terms of probabilities. The electron, if measured, will appear to be in one of several locations, and the probability of it being in each of them is equal to the square of the magnitude of the number the wavefunction assigns to that location. For example, if a position has wavefunction value 0.1 - 0.4i as mentioned earlier, the electron will be in that location with probability (0.1)^2 + (0.4)^2 = 0.17. Since the wavefunction has non-zero values at many points, in this sense the electron "can be in more than one place at once", or more properly, could be measured to be in any one of several different places at random.

Exactly how this corresponds to our conventional notions of position, velocity, etc is a topic of considerable debate, but this approach to modeling particles works well and describes our world accurately (and no non-probabilistic model can do so).

frustrated_staff t1_jadqzgk wrote on February 28, 2023 at 6:29 PM

They're not "really" in two places at once. But, since we can't know their position and momentum at any given moment (only one or the other), we say that they have equal probability of being in multiple locations at the same time. There will be talk of a collapse of the wavefunction, which is what happens when a particle interacts with an observation, fixing its location for a time. In that instant of observation, it has a 100% probability of being where it is observed, but before that and after that, it can be anywhere in its' probability cloud. And that's what it is, too: a cloud of various probabilities for a particles location, some of which defy belief, but are nonetheless possible.

MrHeavenTrampler OP t1_jadumrj wrote on February 28, 2023 at 6:52 PM

Thanks for the explanation, it was easy enough to understand. Now, is this why the Kaluza-Klein theory eveolved into string theory? Because the particles behaved more like vibrating strings than floating spheres rt?

How does the Higgs boson come into play here? Is it merely hypothetical or has it been widely accepted as something that exists? I recall several years ago there was a lot of hype because it was "observed" in CERN or something like that. What I can remmeber, it was the particle responsible for granting all sorts of matter their mass.

Doing some diving into wikipedia there are tons of things like gravitons and fermions and whatnot that make it seem like it's a massive iceberg out there. My question is, what is the most widely accepted theory for quantum mechanics and what subatomic particles have been proved to actually exist?

My very last questions:

Is it theoretically possible to split a subatomic particle? If so, how much energy would it release?
Is it true that many subatomic particles are believed to interact with parallel universes (like basically exist in both simultanoeusly)?

breckenridgeback t1_jae0wpw wrote on February 28, 2023 at 7:31 PM

String theory is an attempt to explain the phenomena of current physics as emergent behavior of some underlying objects. The details are beyond my understanding of physics.

> How does the Higgs boson come into play here? Is it merely hypothetical or has it been widely accepted as something that exists?

The Higgs was hypothetical for a long time, but was observed by the LHC in 2012. It's now generally accepted that it exists.

> What I can remmeber, it was the particle responsible for granting all sorts of matter their mass.

More or less, yes. Specifically, it's (among other things) why the W and Z bosons have mass but the photon doesn't.

Recall that mass and energy are two different expressions of the same thing. Potential energy stored in one of the physical fields underlying the universe is mass, and in fact about 99% of the mass of the objects around you comes from the potential energy of quark-quark attraction, not in the bare mass of the quarks themselves. The Higgs mechanism gives some particles mass by effectively "tangling" the Higgs field (one of the underlying physical fields) with the field underlying the weak interaction (one of the four fundamental physical forces) in such a way that neither of them can settle into the zero-energy state that they "want" to settle into.

Again, the details here are extremely complicated.

> Doing some diving into wikipedia there are tons of things like gravitons and fermions and whatnot that make it seem like it's a massive iceberg out there. My question is, what is the most widely accepted theory for quantum mechanics and what subatomic particles have been proved to actually exist?

The basic accepted theory of particle physics today is the Standard Model, which contains the following particles:

Six quarks, two of which (the "up" and "down" quark, no relation to everyday directions) make up protons (two up, one down) and neutrons (one up, two down) respectively. The others (the charm, strange, bottom, and top quarks) are unstable under normal conditions and are only observed briefly in particle accelerators.
Six leptons: the electron and its two heavier cousins, and the three types of neutrino. The muon and tau (the two heavier cousins of the electron) are unstable. The three neutrinos are sort of stable, but they actually oscillate (change from one type of neutrino to another) as they travel. Neutrinos are rarely important to everyday events because they interact very weakly with the matter humans are made of.
The bosons, particles that carry the underlying physical forces of the Universe. These are the photon (carries electromagnetism), the W+, W-, and Z bosons (which carry the weak interaction), the eight types of gluon (which carry the strong interaction), the Higgs boson (which carries the Higgs field, or more properly one component of it), and the still-unobserved graviton (which carries gravity).

Of these, only the graviton has not been observed.

The Standard Model is, however, known to be incomplete. It can't explain some physical phenomena, and it's incompatible with relativity in conditions where both gravity and quantum mechanics become relevant. Theories like string theory are attempts to expand the standard model in ways that cover these gaps.

> Is it theoretically possible to split a subatomic particle? If so, how much energy would it release?

Subatomic, sure, but not fundamental. The only subatomic particles currently known not to be fundamental are protons and neutrons, and you could in principle split them apart...

...but the properties of the strong interaction make the behavior of such a split a bit weird. Instead of seeing free quarks, you'd see new protons and neutrons!

The reason is that the strong interaction (in its full form, not to be confused with the residual strong force that holds the nuclei of atoms together) doesn't fall off with distance the way that electromagnetism or gravity do. The potential energy of two separated charges in electromagnetism, for example, is -1/r, but the potential energy of two separated strong-interacting particles is, roughly, just r. So once quarks get very far apart, it's actually energetically-favorable to just spontaneously produce new quarks from the void to bind them up into protons and neutrons again.

In any case, protons and neutrons are very tightly bound, so you wouldn't release energy by splitting them (you'd have to input a huge amount of energy). The same is true of nuclei, by the way, it's just that sometimes splitting a nucleus results in more tightly bound nuclei.

> Is it true that many subatomic particles are believed to interact with parallel universes (like basically exist in both simultanoeusly)?

This is speculative and depends on your interpretation of quantum mechanics. Unless you're doing the math, this sort of question is more "whooaa duuuuuude" stoner speculation than science.

Nowhere_Man_Forever t1_jadyhvd wrote on February 28, 2023 at 7:16 PM

My recommendation is that if you want to even begin to understand stuff like string theory, you really need a solid background in the basics of physics and calculus. I took two courses in college with a large quantum physics component (College level physics II and physical chemistry) and I will say none of it made any sense at all until I just put aside my intuition and just followed the math, and that was just the basic stuff. I still can't understand shit like string theory even though I got pretty good at basic quantum physics, but I can at least follow some of the discussion because I have that foundational knowledge.