Fantastic!

excellent

Brilliant

Loved it!

Noice!!!!

Excellent

Very Nice

excellent

Awesome!

Great!

AWESOME

Great!

cool

Great

goood

great

good

Wow!

Good

Yo

R

f

A

I’ve enjoyed this course, which I’ve been following during the UK’s Covid 19 lockdown. It’s kept me happily occupied and, thanks to Larry Lagestrom’s generally careful and enthusiastic exposition, I’ve finally got my head round the relativity of simultaneity and its role in explaining the ‘pole in the barn’ paradox - something I never quite managed when introduced to special relativity as a physic’s undergraduate more than 50 years ago. So, a big thank you to Prof Lagerstrom.

I’ve a few reservations. First, the treatment of Einstein’s second postulate seems to be needlessly confusing. Starting in week 3, and then repeatedly throughout the course, the lecturer maintains that, by the phrase ‘the constancy of light’, used to describe the second postulate, Einstein means that light is a wave, implying, drawing an analogy with, say, sound waves, the the existence of a ‘supporting’ transmission medium - the luminiferous ether. It’s then maintained that, somehow - I can’t follow the argument - Einstein combined this interpretation of the constancy of light with the principle of relativity to deduce that the velocity of light is constant for all observers. I’ve read the relevant bit of Einstein’s 1905 paper several times, and I just don’t think this is what Einstein is saying at all. What it actually says is: ‘Llght is always propagated through empty space with a definite velocity c, which is independent of the motion of the observer’. There’s no recourse to any sort of argument, instead, it’s simply stated as a fact - just what you’d expect for a postulate. From some of the posts in the discussion forum, it would appear I’m not the only one having difficulties with this issue.

My second reservation - following on from the first - is that there’s too much time and effort devoted to the Michelson-Morley experiment. There’s no ether, the experiment was doomed to failure and all that time and effort deriving expressions for possible phase shifts - using highly questionable assumptions about the speed of the local ‘ether wind’ - could have been better spent.

It’s a small point, but my last reservation is with the derivation of length contraction, which I found hard to follow. The alternative approach - using a light clock sending pulses longitudinally along a train - seems much more straightforward and follows on nicely from the transverse clock used to explain time dilation.

Where I think the course really scores is in the derivation of the Lorentz transforms and the use of space-time diagrams. If you can work your way past possible early confusions and press on to these key topics,; you'll be amply rewarded for your troubles.

Alongside the course I’ve read Larry Lagestrom’s book, ‘Young Einstein: From the Doxel Affair to the Miracle Year’. It’s a good read and is particularly good at explaining the content of all Einstein’s 1905 papers.

Lecture delivery: Very engaging, in general. I do appreciate the historical background material. Difficulty: Way too easy. The professor seems to assume that the audience is weak in Math & Physics. The prerequisites for the course should include at least elementary Mechanics and Vector Algebra. Near the end, one problem should have been presented in 3D [t, x, y, z] to reinforce that the the previous problems were based on holding 2 of the 3 space dimensions constant. Leaving the details of the vector algebra as an exercise for the student to verify is justified with a change in the prerequisites. There was way too much explanation of algebra manipulation. Much should have been left as an exercise to the student! The mass/energy issue with respect to the speed of light should have been presented. This was skipped and could have been presented in a general sense with accompanying Internet GR references for derivations (E.g. DrPhysicsA on YouTube.com). Problem sets should not be optional! These are good student reinforcement opportunities. A presentation which needs to be revisited IMO: "The Twin Paradox" part 3.