Recent content by Philip Land

Yes this is exactly what I ment and this was very helpful. Thank you very much.

The RW metric reads $$ds^2 = -dt^2 + a^2(t) \Big( \frac{dr^2}{1-kr^2} + r^2 d\theta^2 + r^2 sin(\theta)^2 d\phi^2 \Big)$$ The value of k determines the model is flat/open/closed. But say if we have a model on a completely different form, with no explicit k-dependence. How would I determine if...

I see, thanks for clearing this up!

I simply use the equation above, and the eigenvalus whish yield: ##\hbar^2 [ s_1(s_1+1) + s_2(s_2+1) + m_1m_2 + \sqrt{s_1(s_1+1) - m_1(m_1+1)}\sqrt{s_2(s_2+1) - m_2(m_2-1)} + \sqrt{s_2(s_2+1) - m_2(m_2+1)}\sqrt{s_1(s_1+1) - m_1(m_1-1)}## Very straight forward. My issue is that I don't know...

Well, the electrons will occupy parabolic bands, but that's true for many band structures, all through the are not free electron gases, so there must be something else than that simple argument allowing me to by looking at a plot see if its a free electron gas, such as no splitting between bands?

How can I see, by looking at a band structure if the substance in question can be viewed as a free electron gas (FEG) or not? What characterizes a FEG in a bandstructure plot? Thanks in advance!

Thanks a lot for this!

Yes, I have derived the relation between E and K for free electrons in metals. I have also used Brillouin zones to draw 2-d Fermi-surfaces. Although I just began with condensed matter, I think understanding the Bandstructure diagram would help me a great deal. For example, here the say "The...

Hi! I never really understood band structure diagrams. I think they represent the energy of an electron, with the given circumstances, at a k vector. Are the electrons only allowed to be on the lines here? Or can they also be in areas enclosed under/between certain lines? What are some...

Hi! When calculating ##(\hat{a} \hat{a}^{\dagger})^2## i get ##\hat{a} \hat{a} \hat{a}^{\dagger} \hat{a}^{\dagger}## which is perfectly fine. But how do I end up with the ultimate simplified expression $$\hat{ a}^{\dagger} \hat{a} \hat{a}^{\dagger} \hat{a} + \hat{a}^{\dagger} \hat_{a} +...

Thank you very much. That was very helpful :)

Because it's well known perhaps don't mean they respect it as much :)

Yes, not famous. Of course, people in the industry know very well about Uppsala University, but it doesn't have a prestige such as Oxford of course.

Hi! I'm currently applying for a masters program in theoretical physics, more specifically in String and Quantum Field theory. I will apply for Oxford, Kings college, Imperial college and Perimeter Institute among other universities and institutions. However, I also want to go to Uppsala...

Hey! Let's say we have an electron and proton colliding head-on. We will have ##|p| \sim E## Where ##p_1=(E_1, \vec{p_1})## &##p_2=(E_2, \vec{p_2})## If we want the available energy. We can calculate ##\sqrt{s} = \sqrt{(p_1 + p_2)^2}## We get $$s= p_1^2 + p_2^2 + 2p_1p_2 = m_e^2 + m_p^2 +...