41–50 of 67 posts
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All things decay and have half life time. I don't get what's so mysterious about it. Neutrons have some not well understood structure and that structure is unstable in the dangerous waters of quantum turbulence.
Photons don't, for counterexample
Here's a question I was always curious to hear a good intuitive explanation for -- Why does a neutron star not decay, as it is composed of neutrons, and free neutrons should decay in 15 minutes? Is it because the neutrons are in an energetic "well" and to decay out would actually require energy? In collapsing under gravity to neutron degeneracy, did the neutrons say, radiate away their ability to decay any more?
This is the best answer I've seen: https://physics.stackexchange.com/a/63387 which to my layman eyes basically seems to match your theory.
Here's a question I was always curious to hear a good intuitive explanation for -- Why does a neutron star not decay, as it is composed of neutrons, and free neutrons should decay in 15 minutes? Is it because the neutrons are in an energetic "well" and to decay out would actually require energy? In collapsing under gravity to neutron degeneracy, did the neutrons say, radiate away their ability to decay any more?
"Magnetic fields at the bottom of the bottle prevented the neutrons from touching the surface," So you can control neutrons with magnetic fields??
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Photons don't, for counterexample
I'm wary of such absolute statements. I'd put photons near protons in terms of stability: they just don't show signs of decaying.
However, in relativity a photon cannot decay: because it travels at the speed of light and has infinite time dilation, it does not subjectively experience the passage of time in which the possibly of decay could exist.
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From skimming the review paper from OP (the "source:" in the caption on that error-bar chart), the neutrons in the beam experiments are thermalized, to a mean velocity of ~2,200 m/s. So, slower than 1e-5 c. https://doi.org/10.3390/atoms6040070 (Thermal meaning the neutrons scatter lots of times against atoms in a solid material, until they reach thermal equilibrium. ~km/s is a typical Boltzmann velocity for atom-size…
How does the scattering affect the neutrons? When do we start the clock for their lifetime anyway? It sounds like they could absorb + reemit sometimes when being scattered.
If you have a bunch of neutrons and put them in a box, and look again 10 minutes later, you will see that you have only half of them.
If pick all the neutrons that survived for 3 minutes, and put them in a box, and look again 10 minutes later, you will see that you have only half of the neutrons that survived for 3 minutes.
If pick all the neutrons that survived for 7 minutes, and put them in a box, and look again 10 minutes later, you will see that you have only half of the neutrons that survived for 7 minutes.
If pick all the neutrons that survived for 42 minutes, and put them in a box, and look again 10 minutes later, you will see that you have only half of the neutrons that survived for 42 minutes.
When the time is too long, you need to create a really big number of neutrons initially, so enough survive until you start the experiment.
So ... the waiting time until the experiment start doesn't matter.
It's easier to understand with a discrete model with coins. You have perfectly balanced coins with 50% chance of head and 50% chance of tail. Each minute you flip all the coins at the same time and remove all the "heads". So you can repeat this, and each time you have less coins. You start the experiment, flip the coins 10 times (and remove the heads), and you get 1000 coins that survived. How many additional times should you flip them to remove half of them and have only 500?
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is the annoying answer "if it were really that much shorter we probably wouldn't exist"?
https://en.wikipedia.org/wiki/Anthropic_principle
Then I thought his notion likely balmy or eccentric, now I've no opinion as my brain tends to overheat whenever I think about it. ;-)
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Nobody knows
is the annoying answer "if it were really that much shorter we probably wouldn't exist"?
Reckon that stands to reason, same goes for the physical constants, c, µ, ε, α, etc.
But why remains the question.
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I'm wary of such absolute statements. I'd put photons near protons in terms of stability: they just don't show signs of decaying.
I understand the wariness. However, in relativity a photon cannot decay: because it travels at the speed of light and has infinite time dilation, it does not subjectively experience the passage of time in which the possibly of decay could exist.
And what would happen in some theoretical meta material where say, values for say µ and ε were lower than their vacuum counterparts?
OK, it's a red herring, but interesting to contemplate.
The question I want answered is not why a neutron takes so long to decay - that seems understandable as it's mitigated by the weak force - but why is that time of ~14.63 minutes the actual time it is? When the W- boson decays into an electron and antineutrino it happens millions of times faster than the life of the neutron itself. What makes that trigger point happen when it does?
Generally decay rates scale with the energy release (Q) which is relatively small here compared to the W decay. Decay is a tunneling process so less Q generally means a slower decay since there are fewer final states available (but the details are complicated). Fermi's Golden Rule in principle allows you to calculate the decay rate. In practice we dont know how to calculate all the relevant quantities since QCD is ha…