4 ms·

But in the Standard Model each “generation” of particles is so much heavier than the previous one, and in practice there is a limit on the power of the accelera

by vl 6y ago

But in the Standard Model each “generation” of particles is so much heavier than the previous one, and in practice there is a limit on the power of the accelerator we can build. Even then there is no reason to believe that there is infinite number of subatomic particles.

TeMPOraL 6y ago
But what happens if you add more energy? Do we know that past some point, new particles will stop appearing?
- at_a_remove 6y ago
  "Know" in the sense that we can be certain, one hundred percent, never doubt? No. In the sense that you would have to convert the Milky Way's entire mass into a particle accelerator large enough, over the course of millions of years, to get that much energy to probe even further, ain't nobody gonna do that. You could go out even more, why not convert the Local Group? At some point you must accept that we're not going to undertake a billion year engineering project to do that and so it is irrelevant. "More" will run out as a useful strategy eventually. However, there are other clues, which largely live in symmetry. How do we "know" that there are three families of leptons and quarks? Even in the 1990s, there were certain cosmological-level hints that the universe would look very different if there were five; four was just barely allowable if you squinted very hard. Don't get me wrong, you can slam together a lot of energy in one place and get funny things, but they won't be funny things that are new fundamental particles, which are governed by different symmetries, which you will see if you begin browsing the, ah, "zoo" of subatomic particles. For a particle, an anti-particle (even if it is itself), as a symmetry example. And so you would need new symmetries to explore, which brings us back to the possible axion of the article, which was suggested by a symmetry. In general, new particles are suggested either by symmetry or in some cases, simple conservation, like the humble neutrino, which was originally a placeholder particle to say, "Where is the spin in that reaction going?"
  - AnimalMuppet 6y ago
    > Even in the 1990s, there were certain cosmological-level hints that the universe would look very different if there were five; four was just barely allowable if you squinted very hard. Could you (or someone) be more specific here? Or give a pointer to where to learn more?
    - at_a_remove 6y ago
      Short of me digging through boxes of old college textbooks and such, I must wave my hands about as I struggle with memory. Here goes: essentially the number of particle "generations" (with the first generations of leptons being the electron, the positron, the electron neutrino, and the electron anti-neutrino) has an effect on the abundance of the "light elements" like Helium-4 during the early phase of the universe. This was pointed out as a dependence in roughly the 1960s by Hoyle (yes, that Hoyle) and Tayler. Each generation would increase the density of the early universe, causing it to expand faster, and in turn the earlier the transmutations of light elements would have stopped, leaving excess neutrons to go around. This means more Helium-4. So, measure the Helium-4 abundance and you can set some error bars on the number of generations. So the tau particle, in generation three, was predicted around 1971 and finally detected about six years later. Of course the Nobel for this discovery wasn't awarded until much later but everyone was on tenterhooks: could we find a fourth generation? Could it exist? But we didn't have the measurements of the early universe nailed down at the time. Measurements of the abundance of these elements around the late eighties or early nineties is in line with the number of generations being three, but it could be four at the "couple of sigma" level of confidence. Indeed, originally it was thought that four was an upper limit in the 1980s. And so here we are. For a fourth generation, the equivalent of the electron mass would be >> 45 GeV/c². Simply enormous. My guess is that further observations have pushed the confidence of "three" much much higher since then, but I haven't been paying attention. Of course, the generations aren't confined to leptons (the "lightest" particles), but also to the quarks. So the first generation has its mirror in the up quark, the anti-up quark, the down quark, and the anti-down quark. Again, one of those symmetries I brought up.
- RhysU 6y ago
  Add allll the energy? Big bang. One particle. ducks

by vl 6y ago

TeMPOraL 6y ago

But what happens if you add more energy? Do we know that past some point, new particles will stop appearing?

at_a_remove 6y ago
"Know" in the sense that we can be certain, one hundred percent, never doubt? No. In the sense that you would have to convert the Milky Way's entire mass into a particle accelerator large enough, over the course of millions of years, to get that much energy to probe even further, ain't nobody gonna do that. You could go out even more, why not convert the Local Group? At some point you must accept that we're not going to undertake a billion year engineering project to do that and so it is irrelevant. "More" will run out as a useful strategy eventually. However, there are other clues, which largely live in symmetry. How do we "know" that there are three families of leptons and quarks? Even in the 1990s, there were certain cosmological-level hints that the universe would look very different if there were five; four was just barely allowable if you squinted very hard. Don't get me wrong, you can slam together a lot of energy in one place and get funny things, but they won't be funny things that are new fundamental particles, which are governed by different symmetries, which you will see if you begin browsing the, ah, "zoo" of subatomic particles. For a particle, an anti-particle (even if it is itself), as a symmetry example. And so you would need new symmetries to explore, which brings us back to the possible axion of the article, which was suggested by a symmetry. In general, new particles are suggested either by symmetry or in some cases, simple conservation, like the humble neutrino, which was originally a placeholder particle to say, "Where is the spin in that reaction going?"
- AnimalMuppet 6y ago
  > Even in the 1990s, there were certain cosmological-level hints that the universe would look very different if there were five; four was just barely allowable if you squinted very hard. Could you (or someone) be more specific here? Or give a pointer to where to learn more?
  - at_a_remove 6y ago
    Short of me digging through boxes of old college textbooks and such, I must wave my hands about as I struggle with memory. Here goes: essentially the number of particle "generations" (with the first generations of leptons being the electron, the positron, the electron neutrino, and the electron anti-neutrino) has an effect on the abundance of the "light elements" like Helium-4 during the early phase of the universe. This was pointed out as a dependence in roughly the 1960s by Hoyle (yes, that Hoyle) and Tayler. Each generation would increase the density of the early universe, causing it to expand faster, and in turn the earlier the transmutations of light elements would have stopped, leaving excess neutrons to go around. This means more Helium-4. So, measure the Helium-4 abundance and you can set some error bars on the number of generations. So the tau particle, in generation three, was predicted around 1971 and finally detected about six years later. Of course the Nobel for this discovery wasn't awarded until much later but everyone was on tenterhooks: could we find a fourth generation? Could it exist? But we didn't have the measurements of the early universe nailed down at the time. Measurements of the abundance of these elements around the late eighties or early nineties is in line with the number of generations being three, but it could be four at the "couple of sigma" level of confidence. Indeed, originally it was thought that four was an upper limit in the 1980s. And so here we are. For a fourth generation, the equivalent of the electron mass would be >> 45 GeV/c². Simply enormous. My guess is that further observations have pushed the confidence of "three" much much higher since then, but I haven't been paying attention. Of course, the generations aren't confined to leptons (the "lightest" particles), but also to the quarks. So the first generation has its mirror in the up quark, the anti-up quark, the down quark, and the anti-down quark. Again, one of those symmetries I brought up.
RhysU 6y ago
Add allll the energy? Big bang. One particle. ducks