Recent content by Shing Ernst

If you know the basic calculations of SR, then I would highly recommend Spacetime Physics by Wheeler and Taylor

Thanks everyone! Indeed, my problem is that I learn nothing technical. (merely a practice of scientific inquire. that's important, but I am not sure the committee of MIT, etc will care... they simply assume you have?) And in hindsight, I think I should have looked for my professor actively to...

A friend of mine, a PhD in Caltech, told me: as long as GPA > 3.1, your GPA will not make a difference to the committee. However, this information is literally 10 years ago...

Should I include my no-result "research experience" into my personal statement for graduate physics school? My undergrad research experience is basely: 1.) My professor suggested a field - dark matter - to me. (Back then, he was working on mostly Earth science observations, so I did...

I actually asked this question here, but got duplicate. however, the other site's answer doesn't satisfy me at all.

Would you mind elaborating a bit more?

this is obvious in hindsight. but imagine we live in a time before Newton, and want to figure it out by dimensional analysis - we know nothing about G. While in dimensional analysis, we usually assume no dimensions for the proportional constant.

Not exactly... I mean if we know absolutely nothing about Newton's gravitational law, and we want to find gravitational law by dimensional analysis. however, this seems impossible to me (as I wrote in my 1st post)

Pretend that we do not know gravitational law at all, and want to investigate the gravitational law by dimensional analysis: Let's suppose the gravitational force are proportional to both masses, distance, hence: F \propto m_1^am_2^br_{12}^c But obviously, there is no way to equal the...

Thank so much for your suggestions! I would like to ask: I have taken one year quantum mechanics last year; however, it did not cover perturbation theory. (also the uncertainty principle still confuses me) Am I prepared well to read Sakurai's modern quantum mechanics?

Thanks for reply! Is my understanding correct? Given the hydrogen atom is in a superposition of energy eigenstates, so it may or may not emit photon(s). but when it does, ( after reading the detector) we can be sure what eigenstate it is after the detection. And is this whole process what we...

The hydrogen atom is in vacuum and well isolated. No one is measuring it (except for some detectors waiting there for photons, which have no interaction with it). However, I think I wrote the potential term already indicated it is isolated. (please point it out otherwise) I think the confusing...

Thanks for your reply! I would like to know the non-relativistic case with the potential is simply -e2/r. but it sounds strange to me if we measure hydrogen's energy. Surely it doesn't emit a photon when we measure the energy (it has no way of knowing we want to measure it) So I assume it...

I have some confusions, and I would like some help: What states will hydrogen atom be before it emits a photon? Will it possible be superposition of its eigenstates? (If so, then by measuring the energy of photon, we measure its' energy causing its wavefunction collapse, am I right?)...

In that case, then in your field, background knowledge at that level is a must. unless you have a very good reason (e.g. I already taught myself the freshman stuffs), professors will hardly be convinced to change their mind. Another approach is to ask as many professors as possible (their field...