Twin Paradox with radioactive twins

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SUMMARY

The forum discussion centers on the application of the twin paradox to radioactive decay, specifically comparing two identical radioactive samples, one stationary on Earth and the other traveling at high speed. The traveling sample exhibits a higher radioactivity upon return due to time dilation affecting its half-life, which is expressed mathematically as $$N_A = N_0 \ \exp\left(-\dfrac{\Delta t_A \ln 2}{\Delta t_A 1/2}\right)$$. However, the discussion reveals a critical error in the interpretation of half-lives and time dilation, emphasizing that the half-life of particles like muons remains constant regardless of their motion. The correct relativistic decay law is $$N=N_0 \ \exp\left(- \frac{\ln 2 }{t_{1/2}}\int d\tau \right)$$, where proper time must be consistently applied in calculations.

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  • #31
PAllen said:
I’ve always considered that many muons are created at much lower altitude than 10 km, where the atmosphere is denser. However, looking at the density as a function of altitude, it does appear 10 km would be a reasonable median creation altitude. But there is also the question of muon energy. I think many are created with ##\gamma## greater than 5, some much greater (even over 100).
Actually, I just checked and found the average muon energy at creation is well over 4 GeV, which is a ##\gamma## of over 40. Thus, my statement was correct. For some reason, hyperphysics is using a plausible creation altitude, but a way too low energy. There are even substantial numbers of muons created with ##\gamma## of 40,000 or more.

[edit: as a further aside, I note that the cosmic ray muon spectrum is regularly measured out to 100 TEV, which corresponds to a ##\gamma## of 1 million. For such a muon, it would appear only 1 cm of atmosphere passed by before the ground hits.]
 
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  • #32
PAllen said:
Actually, I just checked and found the average muon energy at creation is well over 4 GeV, which is a ##\gamma## of over 40. Thus, my statement was correct. For some reason, hyperphysics is using a plausible creation altitude, but a way too low energy. There are even substantial numbers of muons created with ##\gamma## of 40,000 or more.

[edit: as a further aside, I note that the cosmic ray muon spectrum is regularly measured out to 100 TEV, which corresponds to a ##\gamma## of 1 million. For such a muon, it would appear only 1 cm of atmosphere passed by before the ground hits.]
And this page of hyperphysics has the correct number - no idea why the muon experiment page uses misleading numbers:

http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/muonatm.html
 

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