This class was extremely difficult I would recogmend not taking it with him. This class is also technically skippable. If you must take this class take it with a diffrent professor.
He is a great guy, funny, and lectures well. But his exams can be astronomically difficult.

Regan doesn’t know the material, and doesn’t want you to know it either. 17 is supposed to be an introduction to atomic phenomena and some elements of quantum mechanics. He refuses to make a class that is in itself supposed to be easy actually digestible, by including as much content as possible, and presenting it as superficially as he can. He mentioned geometric algebra (cause I cannot use the word “taught”), only to not use it again in the remainder of the course. He usually starts using some physical concepts under the umbrella of “I’ll make it clear later” and then forgets to define it properly until everyone is utterly confused. He spent an entire lecture talking about fermion and boson statistics, which required attention to the effects of spin-coupling. He used the word “spin” about 30 times that entire lecture, without defining spin once. The first question he was asked after the class was “What is spin?” He went out of his way to give the most rigid, abstract, confusing, and mind-boggling presentation of one feature (the turning of a playing card), instead of defining it for the means of a lower division class. The student was visibly confused. They were speechless. Regan smirked and moved on. He didn’t even ask the student if it made sense. He just moved on. That happened to me too. He just doesn’t know the material profoundly enough to actually answer questions, or teach for that matter. And he enjoys confusing his students. Otherwise, he would not smirk so visibly when someone doesn’t know something.
His homework is unreasonably difficult. He always taught the concepts needed for 80% of an assignment the day it was due. Since his lectures lacked any conceptual insight and were nothing but regurgitations of formulas, the assignments felt demoralizingly difficult. And the grading was harsh and lazy. His homework problems had a lot of subsections, and if you had one typo for one, your score for that problem started from 75%. It didn’t matter if everything but your answer for one subsection out of say 5 was perfect, you still got a 75% for the problem.
His exams require literal memorization of problems, instead of conceptual understanding. Preparing for exams was a witch hunt of “What could Regan decide to test us on?” He didn’t teach what a blade in geometric algebra was. He briefly described it in some typed lecture notes on his website. We got that on our exam. And he shamed us publicly for not knowing it in the lecture notes.
Regan is too concerned with trash talking other physicists to actually do his job. He builds his personality on the hate he has for the textbook, the constants in physics, or different historical concepts. No human being should build a personality on what they hate. That is not just counterproductive, but harmful. As a physics major, I want to be encouraged by my professor’s love for physics, not their hate for what they perceive to be “stupid.”
Don’t take his class. Just don’t. As a physics major in college you deserve a professor that is knowledgeable, passionate, and sincere. Regan is none of those things.

This class for most of the quarter was quite difficult and had me questioning my major. There were two midterms, a final, and a bunch of homework. The homework was very doable and Regan would almost always extend the deadline. The midterms were difficult but overall I would say they were fair. The final was also fair in my opinion. Some tips for future people taking this class: 1) Don't freak out if you start off the quarter not knowing wtf is going on in the class. The first lecture petrified me and I didn't think it would get better from there, but it does. 2) KNOW THE HOMEWORK. It seems that Regan really liked pulling questions from the homework to put on the midterms/final. If you really know the homework and the ideas that were covered then you will do fine on the exams. 3) Don't freak out if you do poorly on the first (or maybe second) midterms. Since Regan curves, as long as you stay near the average you should do fine. I was below average by a lot on the first midterm, around average on the second midterm, but I crushed the final, so I ended up with an A-. For me, Regan's lectures weren't that helpful, but they were entertaining. I found myself mostly self-studying for the course. Overall, study the homework/textbook really hard and don't freak out and you should do fine.

Notorious for a reason. Ask around the department and they can provide you a thorough synopsis. His class is the only one I've ever happily and excitedly attended.
Iconic and difficult professor, worth it for the experience IMO

Modern physics was a cool experience! Regan definitely added his flavor to the course, which made the first 3 weeks feel a little rocky because the material taught didn't run very parallel with the textbook, but by week 9 it all came together and wrapped up super nicely. Side-note: He has a mad passion for physics, which made each lecture that much more enjoyable. The lectures are spent motivating and deriving some of the main ideas/equations that are relevant to whatever is being discussed that day. Something that i thought was awesome is Regan provided typed-up lecture notes on BruinLearn(also recorded lectures), so throughout the quarter I felt free to sit and tune-into a lecture, without feeling the need to write down everything as he lectures. Also, having a thorough understanding of the homework problems is important, as he tends to pick similar problems for the exams, so with that said, re-working old problem-sets is a great way to prepare for exams. Doing a lot problems/exercises in general is the other secret!! - solve as many problems as possible(solve them honestly!), it'll help a ton(this is probably general advice for physics/math, but it helped a lot in this course). Another thing with hw, he almost always extends the deadline, which was super nice. The exams are curved, so staying near/above the average is what really counts(obviously you want to work and shoot for the stars, but keep this in mind if things don't go so well). I was around avg on the first midterm(54%), nicely above avg on the second midterm, and did well on final. SO even if that first midterm doesn't go so well, just learn from it, figure out what went wrong and keep at it. Tbh, this class does require a lot of work, but the effort is worth it! Goodluck !!

This class took away any doubt I had about majoring in physics. Regan started off at a hundred miles an hour with geometric algebra and stat mech but backed off quite a bit after the first midterm. The first 3-4 weeks were absolutely terrifying, especially since his lectures moved incredibly quickly. Don't try to take notes during lecture unless you already have some understanding of what he's talking about - he complained a lot about the textbook but ended up following it pretty closely, so try to at least skim the section before lecture. The class slowed down a lot after midterm 1 when we got into the background and very basics of quantum, which was by far the easier part of the class.
He assigned a lot of homework but was very forgiving with deadlines and his exams were very fair. Learn the homework well and you should be fine for the exams, many of the problems were similar or identical to ones we had already seen. Also, don't expect to get much homework/content help from office hours - Regan would always start off trying to answer questions but would quickly get distracted and go off on tangents about his own interests. This ended up being my favorite part of the class and I would highly recommend going, he brought up so many little things that made me even more interested in physics. He has a thing against the cross product as well as hbar and other "fundamental" constants like c and the Boltzmann constant and prefers to describe everything in terms of frequencies but he won't force that on you in exams. In summary - Regan is a little crazy and makes you feel like you have no idea what's happening but taking it with him is absolutely worth the extra effort, at least it was for me.

The professor drops a lot of formulas throughout the class. While he often does not give explanations as to where they come from, he will explain them in his office hours. Reused questions from the homework for midterms and questions from the midterms for the final. Going to class is essential.

Professor Regan is a great lecturer and makes his passion for physics (as well as his hatred for arbitrary constants and units) very evident. He'll clarify a lot of the language and fluff that cloud the overarching concepts behind basic stat + quantum mech. Things may feel a bit confusing in the beginning but once you reach the end of the quarter it should click.

The problem sets are generally doable with what you learn in lecture and he's pretty generous with extensions if you guys ask. Make sure you really understand the homework well because he can (will) use similar (identical) problems in the midterms/final. Pay especially close attention to the problems your TAs emphasize in discussion or office hours and you'll do well on the exams.

TLDR: Lectures > textbook. Put effort in problem sets. c = 1. The Planck and Boltzmann constants, among others, are sacrilegious.

I feel that Regan has a lower rating than he deserves because his exams are difficult. He really does care about students doing well in the class, which is why he curves so much.

HOMEWORK: Some questions are hard, some are just plug and chug. I really like the questions Regan writes, and I wish he wrote more of the homework questions because they usually take a while, but I come out of it with a deeper understanding of the topic of the question. They were graded on correctness, but I feel they graded pretty easily, and the TAs were nice with regrades.

EXAMS: Honestly, they were all reasonable in my opinion. There were definitely difficult questions, but a lot of the problems were straight off the homework, or straight from a derivation he does in lecture that he makes sure we know is important, so make sure you understand those. Also, when I say some questions are straight off the homework, I don't mean the plug and chug problems. I mean the problems that really get us to think about the concepts at a deep level. Sometimes, he will even tell us that a certain topic is definitely going to be on a midterm/final.

OFFICE HOURS: Sometimes they're helpful and sometimes they're not. He will go over homework problems if you ask him about them, or at least get you started on them.

COURSE CONTENT: Although I personally didn't hate how Regan structured his class, it isn't for everyone. His lectures focus more on what he thinks is important for a physicist to know, which I actually like. However, his homework is mainly questions from the textbook, and he often doesn't talk about the content covered in the homework until the lecture on the day the homework is due. Because of this, the homework is often self-taught. The tradeoff is that you are able to learn certain things that other professors would not have taught. For example, I don't think statistical mechanics is usually covered in this course, but Regan talked about it for 2ish weeks before we did any quantum. Regan also curves the class at the end rather than each test, so it's hard to tell what grade you have during the quarter. This is a big factor of stress for students, but I feel that Regan acknowledged that this quarter and is trying to make easier tests now so the averages aren't super low.

Overall, I would recommend Regan because he is a very entertaining person, and he does care about students learning the content.

I think this professor has unrealistic expectations for what should come obvious to students. I think the materials in the class (textbook, homework, aside essays, tests, etc..) are fair and help one learn what they are supposed to for this class. This class was very fast paced in content but also had a manageable workload. Although I found prof. to be a very entertaining lecturer and great at explaining concepts, I found myself uncomfortable asking any questions for the fear that they might be seen as trivial or obvious. I would have appreciated more explanation for where many of his lecture derivations come from.