# All Questions

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### Quaternions and 4-vectors

I recently realised that quaternions could be used to write intervals or norms of vectors in special relativity: $(t,ix,jy,kz)^2 = t^2 + (ix)^2 + (jy)^2 + (kz)^2 = t^2 - x^2 - y^2 - z^2$ Is it ...
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### Why is tunneling not a classical idea?

There is no tunneling in the case of infinite potential barrier, but there is when we have a finite well. In the classical analog, in the first case we have a particle bouncing between to infinitely ...
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### Gravitation as the source of redshift of light beams

According to Hubble's law, light and other kinds of electromagnetic radiation emitted from distant objects are redshifted. The more distant the source, the more intense is the redshift. Now, the ...
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### Since radioactive material decays how is it possible that there is any left after 4.5 billion years?

I was not able to find an answer for this question... Some radioactive elements have half-life measured in thousands of years and some others even in millions, but over 4.5 billion years all the ...
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### Unstable energy levels

Well, reading about "Raman Effect" I saw that when the electron absorb some energy, with frequency $\omega_{abs}$, that is different from $\omega_{n} - \omega_{n-1} \neq \omega_{abs1}$, it go to ...
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### Conceptual problems in nuclear physics for students?

Is there any good reference for conceptual problems for students which learn nuclear physics first time? I am not searching problems that involve difficult calculations. Quite the converse, they ...
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### If there is a meltdown at the Fukushima reactors, would the control rods melt also?

According to the reports, the shutdown procedures at all the Fukushima reactors were successful, and all the control rods were fully inserted. So - if there was a meltdown, would the control rods ...
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### Is Gravity Energy?

This might be stupid, but is gravity a form of energy? And, if so, couldn't we use it for power?