/sci/ - Science & Math

>>6490565
Ok so this is a weird question. We can define non-integer derivatives such as the half derivative and so on, I had the random thought a week or two ago about whether or not one can define a complex ordered derivative?

>>6496002

I understood OP's post to be in the context of quantum fluctuation, which is certainly a manifestation of the HUP, these are generally what laypeople speak of when discussing "virtual particles". Insofar as the virtual particles one realizes when considering the interior lines of a Feynman diagram, I agree with you that they are more so a computational tool than a physical manifestation of a particle.

>>6495953
https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment

>doesn't a photon, when generated by a stationary atom by an electron dropping to a lower orbital, have to accelerate to c over some distance and time? This distance and time has never been shown to exist. If a medium exists, then the photon is just a disturbance in the medium whose velocity (and other properties) depends on the medium's properties.

No. It is "created" travelling at c.

> how do we explain the different velocities of EM waves in different mediums like space, air, water, etc.?

EM waves interact with the medium they are travelling in in a manner dictated by Maxwell's equations. In an ideal vacuum there will be no interaction and the wave travels uninhibited.

> how does empty space have properties like permittivity and permeability?

Changing magnetic field makes a changing electric field makes a changing magnetic field makes a..... These parameters simply define how "easy" that process is in a vacuum.


>how can we explain the magnetic field being generated by a moving charge? If we assume a medium, couldn't the field just be simple currents in the medium?

"What led me more or less directly to the special theory of relativity was the conviction that the electromotive force acting on a body in motion in a magnetic field was nothing else but an electric field." -Albert Einstein.

This might interest you: https://en.wikipedia.org/wiki/Relativistic_electromagnetism#The_origin_of_magnetic_forces


> how can we explain virtual particles coming into existence from nothing? If we have a medium, we at least have a material for these particles to be "born" out of.

This is derived from the Heisenberg Uncertainty principle. Energy and time are two quantities you can't know with total certainty. In a vacuum you are saying that energy (E=mc^2, remember) is explicitly zero so that simply cannot be true.

>>6494228
I love it! Are you looking to go into RadOnc? Or something entirely separate? Did you finish the medical school requirements like orgo and all as an undergrad or while in your PhD program? Why did you switch?

Calculus, linear algebra and group theory for math background would be a must. Any time you have the availability to take a class on linear algebra you should.

>>6491747
Medical physics is, loosely and plainly speaking, any application of physics to medical technology or practice. Most medical physicists work in radiology, either imaging (CT, PET, SPECT) or radiation oncology.

Most tumors, especially those in the abdomen and thorax move a good deal and we really don't like to miss with our radiation beams during therapy so I'm coming up with a method to do real time PET/CT imaging during therapy so that we either can lead the tumor like a quarterback leads a receiver so we know we're only hitting what needs to be hit. Most people assume radiation oncology is a 3D problem (ie hit the tumor in the right spot in the body) but it turns out a lot of cancer moves a bit as your heart beats and lungs expand and deflate so we are coming up with techniques to punish it more accurately. A lot of people start freaking out during their therapy and the stress will exacerbate this motion.

Main problem is that a PET/CT scan involves a decent chunk of radiation suffered to the patient so I'm also involved in some longitudinal analyses of whether or not it is worth it.

>yfw nothing is at rest regardless

>yfw when babby's first relativity

I'm a PhD student in medical physics. I study 4D radiation therapy and intend to go into treatment planning. Any questions about the field?

>>6482780
The number I've always seen quoted for the maximum theoretical resolution of modern MRI technology is 100 micrometers. That said, MRM imaging--which has not yet been feasibly scaled up to "human size"--offers nanometer resolution

Yes, it is because of the U(1) symmetry. There wouldn't be a way to break the electroweak symmetry into two independent symmetries if that wasn't there.

The ubiquity of Euler's constant and pi was probably the first thing that got me truly interested in real math as a kid.

They do something they can reasonably convince an employer requires the kind of critical reasoning and abstract thinking a math major develops.

The scope of opportunities you have with a math major is narrow if you can't pitch why that degree will help you in a field. That said, you ought to be able to explain away why majoring in math will help you enter most fields. If you couple a degree in math with economics, finance or computer science you will have endless opportunities ahead of you. I major in math and physics and was recruited for two jobs in banking, which I have literally no experience in.

>>6482149
Not a single person in my family would read an article that included the word "eigenfunction" in the headline.

>>6481507
I do so just because I've found that doing so helps me stay focused in some way. I'm also a firm believer in having pride in your work.

>>6482154
I also glanced over your blurb about an upcoming co-authorship and possible independent publications. That easily glosses over a slip up freshman and sophomore year. If this were an analogous physics application I would be confident in saying you could get into a respected graduate school

>>6482154
I have genuinely no idea what the grad school stats and standards are like but I'll say a few things as a guy who once pulled a lot of hair out over getting into a PhD program:

I was explicitly told that my performance in junior year was the only part of my transcript they were particularly thrilled with (I had decent grades, over a 3.0 every semester but I had a flat three in two semesters in my first two years, nothing special). It was when I took my most challenging courses and those which could reasonably be called applicable to medical physics and I had a 3.8 and a 3.9 that year. An upward trend is critical; your performance in a senior sociology seminar is going to be a lot more important than your performance in SOCL101 or PSYC101, if it isn't consistent my adviser has told me a C from you in some subject like computer science would be entirely irrelevant.

Onto your second point, regarding your depression; the fact that you were diagnosed is great because they know you aren't bullshitting them. They are sociologists and are probably going to be among the most sympathetic academics out there. That said, it isn't good that you got D's for a year and a half, but you get to write a personal statement and including that information is entirely appropriate. It sounded like this happened freshman year, I'd say it matters as little as it possibly could.

Have you been published?

Medical physics, particularly radiation oncology.

I am a PhD student doing research in 4D radiation therapy.

The ChemE people I know at grad school basically describe it as PhD level thermodynamics. If that sounds fun then do it.

>>6482009
Spatial or temporal resolution?

>>6481990
No, plainly speaking the field encompasses any applications of physics to medicine. The most common field to go into these days is radiology, which I think 80% of medical physicists work in.

Designing particle detectors, particularly x-ray detectors and gamma cameras is a huge part of the field as well. Many medical physicists are also directly involved in the consultation or practice of radiation oncology, radiosurgery and laser ablation; these physicists go through a graduate school program that is a bit more like medical school these days, residencies are required and only specifically licensed PhD/MSc programs can lead to a residency. My thesis pertains to 4D radiation oncology. I'm working on algorithms to "lead" the tumor with the radiation beam in the same way a quarterback leads a wide receiver with a pass. Tumors--particularly those in the thorax--move a good deal during treatment due to breathing and blood flow and we are currently working on real time analysis of PET/CT and SPECT/CT scans to accurately hit the tumor without missing due to its motion.

Any questions for a medical physics PhD student? Anyone else in the field?

The best explanation of Schrodinger's cat that I've ever been able to give a layman is that it's just how we express 50/50 in quantum mechanics...

If I flip a coin, it isn't both heads and tails while its in the air, but we can obviously reason out why .5H+.5T wouldn't be the dumbest way to write out the math behind what is going on here. I don't know why it gets so damn impressive when a cat is involved.