Two pictures with the same green laser pointer. When shone on red wool, it gives off an orange reflection. When shone on red cotton, it retains the normal green colour.

Why would a green laser give off a different coloured reflection?

Hi folks, I’m an aerospace major but I am interested in going beyond industry and into more experimental research (which might be better with a physics degree) while also keeping an industry backup (which is better with an aerospace degree).

For a while now I was teetering between studying aerospace engineering for the sake of being able to have a good job or studying (astro)physics since the department has more resources and it is what I wanted to do originally, but not so great job prospects. My goal is to try and work in aerospace R&D as I feel like industry work is not quite right for me outside of necessity. Most aerospace R&D positions are quite physics heavy (advanced detectors for instrumentation, plasma propulsion, etc).

I decided to come up with a compromise in staying in aerospace but minoring in physics. I will take a full classical mechanics sequence, a full E&M sequence, and quantum I, while hoping and praying I can get into an applied physics program for a masters to make up for quantum II and thermo/statmech while also exploring aerospace-relevant physics topics like plasmas.

This might also keep doors open for PhDs in aerospace, applied physics, or astronomy (specializing in instrumentation in the latter). This way I can pursue the physics research needed for aerospace R&D while also keeping industry positions open, addressing the weaknesses of both degrees.

Is this a good idea? Would it be better for me to just switch to physics/astronomy and join engineering groups/research?

Thank you

Hi everyone!

I wanted to share a project I worked on as part of my undergraduate physics studies.

We were interested in measuring the beam waist of two lasers using the knife-edge method. As part of the project, we put together an automated measurement setup using a Thorlabs translation stage, an ESP32, an optical power meter, and some custom electronics.

We tested it with a diode laser and a HeNe laser. Our measured beam waist values were:

• Diode laser: approximately 9.8 µm

• HeNe laser: approximately 30.8 µm

I also wrote Python scripts for data acquisition, curve fitting, and beam propagation analysis. I've uploaded the code, experimental data, PCB designs, figures, and our lab report to GitHub.

Repository: https://github.com/turtushig22-blip/thorlabs-esp32-laser-beam-profiler

This was an undergraduate project, so I'm sure there are things that could be improved. I thought I'd share it in case anyone is working on something similar or is interested in the knife-edge measurement technique.

I'd genuinely appreciate any feedback, suggestions, or comments on the measurement approach and analysis.

Thanks for reading!

Hello critters in physics! It has come to the point in my academic journey where i need to choose a graduate program. (Or, at least should start thinking about it) I will be graduating with a BS in physics in Spring of 2028, as well as a BA in history. I currently have a 3.9 GPA, extensive experience in education and outreach, as well as planetarium operation. I have taken up to calc 2 and will be finishing diff equ this upcoming season. I have no doubt in my mind about my ability to succeed in a PhD program. However, I don't know what I want to do! My problem isn't a lack of drive, its just that everything is so interesting! (Hence, the history degree) I love atmospheric physics, I love astronomy, nuclear physics is a tad scary, but still pretty fun! Heck, I love outreach and general physics as well. The only things I don't like are just ones I having tried yet. Do y'all have any advice about good programs, or fields, or even just how you discovered your specialty?

Edit: Forgot to say that I have research experience in physics outreach. I've also TA'd for my university's introductory physics class.

This is a Prototype of a Geometric Diagram that I made in Blender 3D, of what could be a Cross-Section of one of the most Symmetrical forms of a Subatomic Particle that could Geometrically Exist.

I have Fine-Tuned the Radii to represent the Distance that the White Line Passes at the Start of a Positive-Interferencing of All Three Geometries Simultaneously.

In this Version of the Animation, all Three Geometries Intersect Simultaneously at the same 4 Points Cyclically.

This is 2-Dimensional Carbon.

If you Additively changed the Spin Rates of the Line Geometries by the same amount you could represent if it were an Electron Cloud Elementally Connected to others in a Crystal. If you Ever So Subtly Increased the Rates of Spin of Both Line Geometries, the Point of where all 3 Geometries Intersecting would Rotate from the Perspective of 2-D and Beyond.

If you were to add a Second Axis of Oscillation (For the Circular Waveform), you could Fine-Tune it to be Closer To or Further From the Average Center of the Geometries at Different Ratios.

The 3-D Grey Space is the 2-D Equivalent of, what to us is, 4-D Hyperspace. In this context, the Circular Wavelength is the Equivalent to a 2-D Membrane, Curved in 3-D, 4-D, 5-D and Spinning in 3-D. The White Line in this Logic is the Equivalent to a 2-D Membrane Curved and Spinning in 3-D. When they Intersect that is where you Could Detect the Electron. There is a Length of Time where the White Line is Continuously Intersecting the Circular Waveform. During this Timeframe, the More Centered the Overlap is when the Positive Interference is occuring would be Strongest. (A Tapered, Curved Line)

If you interpret this Diagram in the Context of Gradient Charge, this changes the meaning of the Solid Geometries, to being a way of Representing how Mathematically Calculatable the Trajectories of the Electron could be. In this Context the Diagram's "Circular Wavelength" is the Curved Traceable Trajectory of the Electron that is going through it's Big Cycle Equivalent (On average Neutral Charge without the Nucleus, (A Photon) which causes it's Spin. It Inverts Geometrically at the Intersection between the 2-D Area and the Circular Wavelengths Outline. As it does so, it Begins Decellerating with the Inertia from before it Geometrically Inverted and is then Reattracted to the 2-D Area while Orbiting Around the Average Location of the Line Geometries. In this context, the Spinning White Line doesn't Exist, but it could be a Representation of the Degree of Precision of Where the Electron will be could Potentially be Predicted to be Detected at, if you were to able to Time and Aim an Observation of it that accurately.

The Rate of Spin of the White Line is 0.03 and the Rate of Spin of the Circular Wavelength is 0.18. The Rates of Spin are Both a Multiple of 3, and the Symmetry of the Intersections of all Geometries is 4 Rotationally. (4×3=12)

When I work on this, another time, I will Modify Both Lines to have Larger Circumferences to allow the the Duration of the Intersection to Occur over a Greater Curved Distance. I'll also give the 2-D Area an Inverted Light Grey Side, and give the Line Geometries an Inverted Equivalent below the Dark Grey Area just the same. To represent their Underside in 4-D.

The reason there'd be an Inverted form or Underside to Everything is because this Model uses a Form of Energy that, in any Dimension of Reality, can Invert or have an Underside. The Underside of the 2-D Area Equivalent to our 3-D Space would be "Negatively Charged" because this Model Utilizes the Idea of a Finite Universe. In this Diagram, the 2-D Area Extends Incomprehensibly Far in all 2-D Directions that it already is Extending out the "Plane" of, but Eventually forms a Sphere. Because of this, the Underside is Ever So Subtly Warped More which gives it a Geometric Contrast to 2-D Area that is in this Prototype Diagram (Which will stay Situated Above on the Final Diagram's Perspective)

I recently came across dielectric laser acceleration (DLA) and started wondering about potential applications beyond research demonstrations.

Could this realistically become useful for electron microscopy or other industrial applications? What are the main technical hurdles preventing that today and what type of performance milestones would need to be met?

Appreciate your thoughts on this.

Figure 1: A short merger of two black holes, viewed from the side.

Figure 2: The same thing, but zoomed out so you can see the waves.

Figure 3: The same thing, but viewed from the top.

Figure 4: The initial starting spacetime, frozen in time. The camera starts on the plane with the holes, the pans left along phi, and down along theta.

I used the BSSNOK formalism for time evolution, and York-Lichnerowicz for the initial data (using the Bowen-York analytic approach for the momentum constraints). This is the result of about 30 hours of time using four NVIDIA H100 GPUs, and about 80 CPU cores. Its a bit iffy, and some of the rays were cut a bit short because the full simulation hasn't run yet, but I thought the current results were pretty cool!

I am someone who has 10+ first author papers, including multiple single author ones in journals with impact factor > 10. Multiple of my first author papers have 100+ citations. Recently arXiv desk rejected two of my single-author submissions after being on hold for a few days, with no way to appeal before publication. What is happening exactly? The biggest issue is losing visibility and citations since I am applying for new positions. My field exclusively uses arXiv as the preprint server, and this will be hurting my applications since publication can take months.

The papers are not in any new field, they are directly in my field of main expertise. I am completely baffled because all my previous first author papers were submitted to arXiv by me. What has happened to arXiv moderation?

Most people are saying on MotoGP starts, the riders kick their feet back so they can use their chest and torso to "press" more on the front of the bike, therefore increasing weight on the front wheel and preventing wheelies (which is a big no no for starts). I just cant seem to picture how kicking your legs out back puts more weight on the front. First of all, i imagine it acts like a seesaw, the hips being the pivot and the legs weight pulls the torso off the bike like a lever. And second, just simply by distributing weight backwards, theres no way that CG doesn't shift rearward, therefore taking weight off the front wheel.

(The first image is generated with chatgpt but the second slide is a real image of the stance that riders take on motogp starts)

Basically i'm convinced that this stance helps with balance and stabilization, but everyone saying it puts more weight on the front wheel has me absolutely dumbfounded.

Omasheet is a new spreadsheet alternative (runs on any Linux or macOS - Windows soon) built by a physicist with an eye for a more precise way to work with a grid of numbers. Here, things like Delta-V calcs for today's launch are built with typed Quantitys. Uncertainty can be used in ad hoc calculations too.

This is a quote from Robert Emden:

" Why do we have Winter Heating? The layman will answer: ‘To make the room warmer.’ The student of thermodynamics will perhaps so express it: To impart the lacking (inner, thermal) energy.’ If so, then the layman’s answer is right, the scientist’s wrong.”

.

The photo basically argues that the total energy of the air in the room is rather a function of pressure, and since pressure is equal to the outside pressure it does not matter whether you lit the bonfire for heating or you did not the energy inside stays the same.

But can anyone explain this? q

I am in uni and my physics 2 (covering thermodynamics, electricity, a little bit of nuclear physics) class has been taught horribly. It’s an online class and the prof does not do any examples, just reads off of slides. I haven’t learned much, if anything. With 30 days to go until the final exam, I am trying to teach myself all of these concepts so I don’t fail the final.

I have a few questions:

Are there any recommended free sites that are helpful in teaching oneself? Are there any large practice quesiton banks I can access for free?

Are there any tips/tricks for learning physics and retaining it, or is it just practice practice practice? I’m good at math but struggle with thinking spatially.

Why is it, that popular media represents blackhole as point object with an infinite density? Why do we not discuss more on the possibility of the singularity as a probability wave? I am sure there are enough smartypants here who can shed some light on this (pun intended lol)!

P.S.: $G_{\mu\nu}=\frac{8\mu G}{C^4}(\hat T_{\mu\nu})$

I am working on a project where i want to create a simple demonstration of a digger arm similar to the child’s toy for scooping sand in the second image, however, i want it to just demonstrate a looping scooping motion that you can control from a crank.

The desired motion i want is the circle in the first image. Ideally, i would like to create this motion from the rotational motion of a crank from the left side of the mechanism. I don’t know if translating a circular motion through this mechanism, back to finish in another circular motion is possible but thats essentially what i think i have to do. im trying to do it without ropes or sliders. I have tried loads of different combinations on this simulator but cant figure it out.

Please, if anyone has any helpful information, even such as it not being possible, please let me know!

Thank you.

I'm applying to some physics programs and i was wondering what are the best or the top for my interest/ overall just ranking, quality, opportunity, etc.

I'm personally interested in astrophysics, i'm really into cosmology, dark matter/dark energy and Astro particle physics, black holes (high energy physics), theoretical physics, and general relativity/graviation.

I was wondering which schools do you recommend i apply to and why? What are the best programs in canada for physics and my interests? What are the top ones (like whats the top 5 ones) that i should apply too or mainly consider applying to?

Note: My average using English, fonctions, calc, physics, bio and a 4m or 4u course is 89%. Most physics programs so far (at least Queens and Waterloo request these courses and that’s how you calculate your application average, since these are the courses they will look at).

I’m just adding that note incase this helps with your recommendations, but overall I just want to get this post another chance since I posted late at night last time and it didn’t go far.

Also so far i've applied to Queens (Physical and Chemical sciences (physics option)) and waterloo (Physical sciences (astronomy/physics option)).

Note: I understand this post would be better suited under a canadian universities reddit or something, and i have already posted a identical post there, there just tends to be very little responses so i was hoping to see if maybe theres any canadian physicist here or people who would know about some of the canadian programs and could give me some insight. Thank you!

This sub seems to believe that being a physicists will most likely not be replaced by ai but Instagram, YouTube, discord say the opposite? I enjoy physics and plan to do physics degree next year after 12th grade ends. Bachelors+masters+phd+postdoc take almost a decade, i fear ai will replace physicists by the time i complete my phd.

This video particularly scares me a lot as this is a harvard physicist saying math is cooked and all other fields will be cooked soon enough

https://www.instagram.com/reel/DfioTMptCQl/

I’m finishing a teaching degree in Education (Pedagogy) in Brazil and thinking about getting a second teaching degree. I’m torn between Physics, Biology, and Philosophy, and I’d love the perspective of people who actually study or work in physics.

Some background: What I love most about teaching is making students think: question things, reason, challenge assumptions. I’m less drawn to the technical, memorization-heavy side of education. I’m also quite skeptical by temperament. For example, I teach English, but it's not something I enjoy that much, especially the vocabulary part, since it's basically memorization.

My favorite books are popular science, mostly physics and biology. The topics that fascinate me most are the ones with big existential implications: the Big Bang, general relativity, human evolution. I’ve noticed that when I ask questions about reality, or even about human behavior, I’m far more satisfied by answers from the natural sciences than by those from philosophy or the humanities. Even on topics like free will, I find the scientific perspective more convincing, which I know is a controversial take.

Here’s my doubt: I’m not sure whether I like physics or whether I like the feeling of confronting deep questions about existence. Those might be two different things.

• Maybe I love physics itself: the models, the explanatory power, the way theories get tested against reality.

• Or maybe I love the philosophical implications of physics (what is time? why is there something rather than nothing?) and I’d be bored by the actual day-to-day work of problem sets, derivations, and mathematical formalism.

And honestly, I’m currently bad at basic math. I know that’s a big deal for physics, so I want to be realistic about it.

My questions for you:

1. How did you tell the difference between loving popular-science physics and loving actual physics (the math, the problem-solving, the methods)? Was there a moment you realized the two weren’t the same?

2. If what draws me is the conceptual, big-picture side, is a physics degree a good fit? How much of the curriculum is that, versus heavy mathematics and technical problem-solving?

3. Is weak math at the beginning a deal breaker, or can it be built up with serious effort? Did anyone here start out weak and get there?

4. Are there good ways to test my interest before committing to a whole degree (a calculus course, a classical mechanics textbook, open courses, etc.)?

5. For those who teach physics: can it be taught in a way that emphasizes reasoning and critical thinking rather than just formulas and exam prep?

Thanks for reading. Honest answers, including “this might not be for you,” are very welcome.

I need help, in my physics class I am doing well, but the slightest rocky, I’ve been struggling to answer some questions because I always bring up the question to my head like a math question (because it’s all I am used to). I most definitely know that if I grab the habit of thinking like a Physicist or at least approach questions physically it will most definitely help me. I was wondering if any experienced Physicists on here can help give me advice for a student like me.

My daughter in high school asked a question that I really don’t have the physics and math background to answer so hoping someone here can help. So the story goes that Uranus was discovered by using mathematics and as far as I know Newtonian mechanics was used to do it but how does one translate from the values those equations produce to an actual position in the sky. Is there a way to break that down in a way that is understandable by a high schooler taking Trig?

I recently received a Cloud Chamber experimental kit from CERN as a prize in a physics competition.

While unpacking the materials, we found this blue jelly-like substance (see attached photo). It says that the kit is intended for educational physics demonstrations and a citizen science project involving the observation and comparison of particle tracks around the world.

Could this substance be the isopropyl alcohol, or is it something else entirely?

Does anyone recognize them or know what they might be used for?

Thanks in advance!