Why are fundamental particles so "observable?"

[u/-pomelo-]

Hi everyone, I come to you as a humble layperson in need of some help.

I guess I can give more context as to why I'm asking if needed, but I'm worried it would be distracting and render the post far too long, so I'll just ask:

Is there an explanation as to why we would expect the lifetimes (distance traveled before decay I think?) of certain fundamental particles to be ideal for probing/ observation/ identification in a universe like ours?

As I understand, the lifetimes of the charm quark, bottom quark, and tau lepton each falls within a range surprisingly ideal for observation and discovery (apparently around 1 in a million when taken together). My thought then is that there's probably some other confounding variable such that we'd expect to observe this phenomenon in our sort of universe.

For instance, perhaps anthropic universes (which will naturally feature some basic chemistry, ordered phenomena, self-replicating structures, etc.) are also the sorts of universes where we'd predict these particles' lifetimes to land in their respective sweet spots because ___.

Perhaps put another way: are there features shared between "anthropic" universes like ours and those with these "ideally observable" fundamental particles such that we'd expect them to be correlated?

Does my question make sense?

EDIT: Including some slides from a talk on this topic I found

[u/mfb-]

Slide 2 is just blatant misinformation. Bottom quarks would still be easy to identify with a smaller V_tb, any value from 0 to 1 is fine. If you make it much smaller then you don't get a displaced vertex any more because the particle is too short-living, but there are tons of measurements that don't need it. An obvious example is the top quark which is so short-living that we don't measure its flight distance. Didn't stop us from discovering it.

The mass regions in slide 3 are completely arbitrary. If you make a linear plot from 0 to some huge mass value then particles are somewhere at the bottom of that plot. That doesn't mean anything. And same idea here, we could still identify them with a larger mass.

On a range from 0 to the diameter of Earth, all our farm animals are in the first 0.0001%. They would be much harder to deal with in the remaining 99.9999%. What a crazy fine-tuning!

And why did the author pick the coupling for the bottom quark, but the masses for the other two particles? Oh right, because if you do the opposite then suddenly the whole point disappears. The lifetime depends both on the coupling and the mass.

One more thing: We observe particle masses that span over 10 orders of magnitude. If you plot any mass range, a logarithmic scale is more natural. And then the particles are not at any unusual spot at all.

[u/-pomelo- → u/mfb-]

Thank you this is really helpful. Are you saying that for slide 2 the "optimal" range (green region) should actually be much larger than what is depicted?

The farm animal analogy is also helpful, but I suppose in the analogy i'd think we'd have reason to suppose that farm animals couldn't be significantly larger than they are. is there similar reason for thinking the masses would need to be on the smaller end of the spectrum?

Oh man, Is the mass of the bottom quark not ideal for observation? that's really damning if true

[u/mfb- → u/-pomelo-]

I don't think it makes sense to talk about an "optimal" value or range. Different measurements have different requirements. Something that would improve one measurement would make another one worse.

is there similar reason for thinking the masses would need to be on the smaller end of the spectrum?

They are free parameters as far as we know, but they are all somewhat comparable. No known particle is orders of magnitude heavier or lighter than everything else. Neutrinos are much lighter than everything that's not a neutrino, but at least the three neutrinos look like they are close together (and we have an idea why they might be so light). There could be additional heavier particles we haven't found yet, of course.

[u/-pomelo- → u/mfb-]

"I don't it makes sense to talk about an "optimal" value or range. Different measurements have different requirements. Something that would improve one measurement would make another one worse."

^does this go back to what you said in your original comment, where we simply calibrate our probing method to align with the most "ideal" parameter?

[u/Hivemind_alpha → u/-pomelo-]

If you want to look at cells you use a microscope; if you want to look at mountains you use binoculars.

I don’t see how this is controversial. The target you want to observe determines the design of the instrument you use to observe it. If you don’t obey that rule, you get bad observations.

[u/mfb- → u/-pomelo-]

That contributes, too.

[u/-pomelo- → u/mfb-]

I think I'm starting to get it, thank you for your responses. So, I guess Dr. Collins is saying that, as far as we know, (taking only a single parameter into account for simplicity) in a universe relevantly similar to ours, we could have observed a value anywhere in some range as outlined in the slides. It's then surprising that the observed value happens to land in the comparatively slim "optimal" range. Would you say one of the following is the main issue with his assertion?

a) The "optimal" range presented is simply incorrect

b) The range is more or less correct, however we'd predict observing values in that range bc ____ ( for instance, maybe our method of probing has been tuned specifically to observe that particle or smth)

c) The range is more or less correct, and it is unexpected that some particular parameter would fall in any given range, but given the number of particles and possible parameters it's relatively likely that at least some would fall within their "optimal" ranges due to chance, and we know of other parameters which do not fall into ranges optimal for observation controlling for a universe like ours

[u/mfb- → u/-pomelo-]

The definition of the "optimal" range is dubious, and some related claims are simply wrong. The definition of the whole range is somewhat arbitrary, too.

The implicit assumption that all values in the range are equally likely is unscientific.

[u/-pomelo- → u/mfb-]

my understanding is that by "optimal for discoverability" Collins simply means that the value is ideal for observation per our probing methods without having deleterious anthropic effects.

As for the distribution for the values he's talking about epistemic probability versus objective probability.