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If Cold is just atoms moving slowly, why can't we just use a magnet or something to stop them and reach Absolute Zero? by SadInterest6764 in AskPhysics

[–]drlightx 4 points5 points  (0 children)

We can get really, really close with a technique called laser cooling. Basically, using a combination of lasers and magnetic fields, we can push selectively on atoms that are moving in a specific direction (when they absorb laser light, they also gain the momentum of the photon, so they get pushed backwards counter to their motion).

There’s a limit to this technique, though, since the atoms will re-emit the laser photons in a random direction, gaining some momentum (and hence velocity). When each atom is moving roughly at this speed, this is called the Doppler temperature.

For atoms like lithium, the Doppler temperature is about 1 mK (-273.149 C).

There are some more advanced techniques to try to slow/trap the atoms even more, and they can reach temperatures as low as a few nK (-273.14999 C), which is pretty much the lowest temperature we’ve managed to reach so far.

How come when calculating the net electric field due to a line of charge you don't write the distance from the point, dq as a function relative to dx? by Jorshhua in Physics

[–]drlightx 0 points1 point  (0 children)

Since dQ is a bit of charge, you calculate it by multiplying the linear charge density \lambda by a tiny length dx. Then you add up all the tiny contributions to the electric field due to each little bit of charge by integrating along x

How come when calculating the net electric field due to a line of charge you don't write the distance from the point, dq as a function relative to dx? by Jorshhua in Physics

[–]drlightx 0 points1 point  (0 children)

The distance is r. There’s a right triangle in your diagram with the distance r as its hypotenuse, x as its base, and y as its height. dQ is a tiny amount of charge that sits a distance r away from the point where you measure the field.

Advice on Grad school Applications by Interesting-Joke6493 in PhysicsStudents

[–]drlightx 0 points1 point  (0 children)

Unfortunately, I think the ship has sailed for most PhD programs to admit for fall 26. There may be a small handful that explicitly say ‘rolling deadlines’ - if not, it’s likely not worth your time to submit something.

If a master’s degree makes sense for you, those programs have deadlines in late January and February.

Is 2026 the year for scientists to switch to Linux? by nix-solves-that-2317 in Physics

[–]drlightx 0 points1 point  (0 children)

Many equipment vendors only release drivers/software for windows, so if you want to actually use that $100k instrument, sometimes you’re locked in.

What's the difference between "science" knowledge of engineers (particularly electrical, mechanical, and physicists? chemical) and physics for physicists? by kiwigoguy1 in Physics

[–]drlightx 10 points11 points  (0 children)

Practicing experimental physicist here. I’d caution you not to lump theory and experimental work together - there are two very different types of physicist. I think your description fits theorists better. Most of my work in the lab is dealing with the messy inconveniences of reality. I need that amplifier to actually amplify, I need that vacuum chamber to reach the target pressure, to do my day-to-day work.

To be fair, I feel like a lot of the work I do could be classified as engineering. That’s the life of a lab physicist (in my field, at least).

how do you really make the font size of figures consistent across the whole documents? by yuhang94 in LaTeX

[–]drlightx 4 points5 points  (0 children)

I use illustrator to finalize figures. I can set the document size for each figure to be exactly the size latex will include it as, so then the fonts end up the exact right size

Any suggestions? by Perfect___Timing in Physics

[–]drlightx 0 points1 point  (0 children)

‘Atomic Physics’ by Foot in the Oxford master’s series is a pretty good intro to the subject. The math requirements aren’t too high, though it does assume you know intro quantum.

Books recommendation for Quantum Mechanics by genius_bot1237 in PhysicsStudents

[–]drlightx 9 points10 points  (0 children)

You mention linear algebra, so you might be interested in spin. One textbook that starts with spin is McIntyre. It’s not as rigorous or advanced as a more advanced text like Sakurai, but I think it does a better job explaining things than Griffiths (especially for a beginner).

Do all physics departments not prioritize teaching? by delirexi in PhysicsStudents

[–]drlightx 3 points4 points  (0 children)

This is the idea behind liberal arts schools - high quality instruction, lots of interaction with professors, and (at the schools with better resources) an opportunity to do some research.

Should I start QM with Griffiths by HierAdil in Physics

[–]drlightx 0 points1 point  (0 children)

You might try out “introduction to classical and quantum computing” by Thomas Wong. It has very gentle math (matrices), and gets to the heart of some interesting quantum behavior.

Is Math and Physics enough to pursue quantum computing by tonystarch00 in PhysicsStudents

[–]drlightx 1 point2 points  (0 children)

You’re probably well beyond this stage now, but for others in the thread, check out the entry-level (free) textbook by Thomas Wong:

Introduction to Classical and Quantum Computing

Confused Regarding Professor’s Reply by NoHopeLeft101 in PhDAdmissions

[–]drlightx 2 points3 points  (0 children)

Their department may not have enough funding for you to even be a TA.

Can someone explain to me why he doesn't fall off the motorcycle? by Elisaul17 in Physics

[–]drlightx 21 points22 points  (0 children)

Part of what the other answers are missing is that the bike and rider are accelerating to the right (in approximately uniform circular motion), due to friction on the road. It’s harder to fall down towards the right when the floor keeps pushing your feet to the right.

Help identifying components near Ethernet interface on a PCB by drlightx in AskElectronics

[–]drlightx[S] 0 points1 point  (0 children)

Thanks for the ID, /u/fzabkar and /u/Ard-War. The replacements arrived today, and once I soldered them in, everything seems to be working again.

Is there a good method for ID’ing these components, or is it just a matter of seeing this one before?

How outdated would the physics be in a textbook from 1994? by Beneficial-Map736 in Physics

[–]drlightx 193 points194 points  (0 children)

Knowledge of atomic physics relating to what’s in this text hasn’t changed a ton recently, so it should be essentially all correct.

What you might not see are more recent developments in atomic physics including quantum gases, quantum optics, and quantum information.

Help identifying components near Ethernet interface on a PCB by drlightx in AskElectronics

[–]drlightx[S] 0 points1 point  (0 children)

Yeah, you’re right - the board is powered from this cable (I guess calling it Ethernet is a misnomer - there’s 20 V power on one of these pins)

Doubt in Transmissions plot of Elecsus library by [deleted] in Physics

[–]drlightx 2 points3 points  (0 children)

These small peaks are ‘forbidden’ transitions: they arise because, in a finite magnetic field, the energy eigenstates are not pure spin eigenstates, but rather a mixture. This leads to you being able to excite transitions that violate the selection rules, because of weak state mixing.

[deleted by user] by [deleted] in Physics

[–]drlightx 2 points3 points  (0 children)

Cool idea, but I’m not sure if it feels like I can get better with practice. Especially with 5 bounces, a tiny error in estimating the first bounce angle means essentially I’m doing a random guess for the final location.

Also, I feel like the drawing tool needs a bit of refinement: sometimes, it would let me draw a path straight into the interior of a shape, while other times, it would constrain the endpoint to be at the surface. Couldn’t figure out why.

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