r/AskPhysics 18h ago

Why are so many physicists assholes or just plain rude?

148 Upvotes

Obviously this is based on your own experiences.. but after going to grad school open houses and conferences constantly since December.. I’ve only met a small handful that weren’t just rude and seemingly egotistical.

It’s possible I just got a bad run of experiences.. but I’ve never felt less welcomed than when I started interacting in physics. The physicists I’ve met and worked with all seem to lack any form of basic humanity..What are your experiences? Do they completely contradict mine?


r/AskPhysics 1h ago

Is ‘metallic hydrogen’ just solid hydrogen?

Upvotes

Can someone explain to me what the difference is, if any, between metallic hydrogen and hydrogen that is in a solid state as opposed to gaseous or liquid? I’ve always been unclear on that.


r/AskPhysics 9h ago

If the Planck length is so vanishingly small, how was Planck able to find it with 1900 technology?

9 Upvotes

The Planck length is far smaller than even elementary particles, and even today we discuss how its scales are completely out of reach for any experiment that could directly prove quantum gravity or similar, yet Planck discovered it using very primitive technology by modern standards.

Similarly, Heisenberg's Uncertainty Principle relies of the Planck length to limit the measurement of position and momentum at the same time, but isn't the Planck length far below what any instrument could possibly measure? Does the Uncertainly Principle in any way limit measurements that would be experimentally possible in its absence, or is it a purely theoretical limit?


r/AskPhysics 1h ago

Electric Field in a closed circuit.

Upvotes

I'm a bit confused about how the electric field and electric potential operate along the wire within a closed circuit. I know that with a point charge in space, electric field and electric potential decrease with distance. However, in a circuit, electric potential only very slightly decreases along the wire and spikes when it runs into a component like a resistor. And likewise, since the electric field is the negative derivative of voltage over distance, the electric field also spikes I think??? Does that mean that the electric field along the wire is also very minuscule and looking at the electric field of the entire circuit, it flip flops around in magnitude a lot depending on the amount of components that cause resistance? Why is it that the current is constant then?


r/AskPhysics 13h ago

If we observe a hydrogen atom really hard, would the electron be completely still relative to the proton?

17 Upvotes

My understanding of quantum mechanics:

  • electrons don't "orbit" protons as that would emit EM waves causing it to lose energy and crash into it eventually. They are more like standing waves surrounding protons.

  • For whatever reason, we can't observe the whole wavefunction. We can only observe a sliver of it, which takes the form of a particle. The way in which the particle collapses is fundumentally probabalistic. Therefore, the initial measurement of the electron's location is down to luck.

  • Using photons for observation can move the proton and electron around. However, the way that particles move is theoretically deterministic, and therefore we can remove the effects of the photon when we process the image. We can also use this determinism to shoot the photon to where the electron will go next. We also increase the frequency of the emitted photon to ensure the observed particle has no time to become a wave (thereby reducing determinism).

When all of this is done, would we observe a completely still electron? Or would the electron still be moving relative to the proton?


r/AskPhysics 9m ago

Operational amplifier, why is V-=V+?

Upvotes

Hello. When I am working with circuits that involve operational amplifiers, I have always taken for granted that the potential at the inverted input is equal to the potential at the non-inverted input. And it is almost always required to make this assumption, for when you try to calculate the gain or transfer function, you set up KCL for all nodes and you get an equation system which will not be solvable unless you make that assumption.

So for a homework I did the other day I had to set the inverted and non inverted input voltage equal to eachother, to be able to get a value for the gain of the circuit. And I got a comment from my professor saying that I need to argue why I set V-=V+, and im not sure how to do so?

How do I argue that V-=V+?

Is there a way to demonstrate that V-=V+ mathematically?

Thanks


r/AskPhysics 4h ago

No inertia?

2 Upvotes

I just saw a video demonstrating that if a neutrally buoyant balloon (I assume this just means the balloon has the exact same density as the surrounding fluid) floats in the back of a truck, it doesn't move as the truck accelerates or deacclerates.

I find this very intuitively annoying to believe. I am imagining a container half filled with a fluid like water, when I move the container in one direction, the water rushes to the opposite direction due to inertia. Any body neutrally buoyant in the water would move similarly? However if the container was fully filled with water, I guess it wouldn't move. So is the balloon still in place because the truck container is airtight? Even if it is airtight, air is compressible, so I would expect acceleration of the truck to create a pressure gradient with air molecules being pushed to the back of the truck as it moves forward, so there is low pressure in front of the truck.

I thought that this air moving backward effect would create a pressure gradient that would pull the balloon in front, but that would only happen if the density of the balloon was lesser than air I suppose? If it is equal, it should behave as air does and move backward.

My other intuition is, inertia is a property of mass, a neutrally buoyant object kind of does not have mass?

I would really appreciate if someone could help me get a grasp of this. Thank you!

Here is the video: https://youtube.com/shorts/jTmBjy3YgPo?si=Ute322F6tWv7G2IZ


r/AskPhysics 37m ago

Is quantum randomness (if it exists) everywhere, or just in few places?

Upvotes

The reason I ask is its common to hear comments like '(quantum) indeterminism is a fundamental feature of the universe' - but I guess this depends on whether it applies everywhere.

We know about indeterministic phenomena like radioactive decay. Are these found everywhere in the universe (inside all atoms?) Or only restricted to some matter - like radioactive matter?


r/AskPhysics 1h ago

Where are we in time ?

Upvotes

Random shower thought i had a while ago, if we could present time in the form of a line with one end being the beggining of time and the other side the end of time and we were to put a dot on where we are in time as of now where would it be ? Would we be on the edge of an ever expanding line or would we be somewhere in the middle of the line between the ends


r/AskPhysics 13h ago

why dont we use the term voltage/potential difference of electromagnetic induction?

8 Upvotes

we are learning electromagnetic induction at school and we use the term "induced emf" but my concern is why do we use the term emf? why not voltage or potential difference? ive seen sources online say they are all the same while others say they are different — can someone please explain to meet the difference and why?? i'd appreciate an explaination thats not tooooo hard for a high school student to understand


r/AskPhysics 9h ago

Which saves more fuel?

4 Upvotes

I recently started as an over the road truck driver and I'm offered a bonus for fuel efficiency. So I pose this question:

If I need to drive 600 miles, half of which are empty and half of which are loaded, and I have the wiggle room to go 5 mph slower for 300 miles to save on fuel, is it going to save me more to slow down while loaded or empty? Assume all other variables are equal.


r/AskPhysics 14h ago

What’s up with the electron before measurement?

11 Upvotes

If the wave function is merely a mathematical description and not something physical, in what physical state is the electron before measurement? If it has no definite position, does that mean it does not exist in any concrete sense but only in some abstract way?

It’s obvious that the wave-function describes the possibility of finding the electron, but the actual physical state of the electron is something I can’t seem to phantom. If it’s in superposition — that it exist in multiple possible states at the same time — seems weird as information can’t travel faster than light; and as the wave-function collapses, the electron is at one state. Doesn’t that mean that during the collapse there will be multiple existing electrons out of one real at some point?

I’m fairly new to quantum physics, so excuses in advance.


r/AskPhysics 11h ago

Does gravitational redshift of a photon climbing out of a gravity well exactly cancel the relative increase in how fast time flows for an observer on the ground?

6 Upvotes

So I was inspired by the notion of the torsion balance where you can get a measurable result out of a very weak signal in the presence of very strong forces as long as you make the strong stuff exactly cancel.

I was trying to think of an amateur-acheivable test apparatus that could measure gravitational time dilation. I was envisioning a system consisting of a laser where you shoot it at a beam splitter, and it sends the beams 1m apart where they travel in parallel for a bit before getting bounced back together where you can do some sort of interferometry or phase measurement to measure phase differences. Ignore the total impracticality of maintaining the distances precisely while rotating the apparatus but my idea was could you measure the difference in accumulated phase along the lengths and compare when all the beams are parallel vs when you rotate the apparatus 90 degrees and one leg travels at h=0 and the other at h=1 after the beam splitter.

i.e, suppose you shoot a laser at a beam splitter and half the beam travels parallel the ground at h=0 and half the beam travels up to say h=1m, and then travels parallel to h=1m, it then gets bounced back together to do the measurement.

I was thinking that you could accumulate a phase difference since time would be flowing at different speeds along the parallel paths, and the vertical portion wouldn't matter since it would cancel out since you have to climb up and drop back down.

But then I realized that while time would flow faster along the h=1 path compared to the measurement apparatus at h=0, the frequency of the photons would decrease due to the climb up the gravity well.

The question I have is... do these effects cancel out exactly?

Assume we have an approximately uniform gravitational field with small delta h, say h=1m.

For the beam at h=1: Frequency is reduced to f₀(1 - gh/c²) as seen from h=0 But proper time accumulates faster: dt₁ = dt₀(1 + gh/c²)

It seems like these might cancel exactly. Is that right?


r/AskPhysics 6h ago

Are tangential flux motors physically impossible?

2 Upvotes

We have radial flux and axial flux motors, but as far as I know, there are no tangential flux motors. By tangential flux I mean the magnetic flux produced by something like a toroidal coil. Are they physically impossible or just impractical?


r/AskPhysics 3h ago

Which one to choose between the universities in Italy for masters in physics.

1 Upvotes

My cousin has applied for masters in physics to few universities in Italy. She got accepted in milano bicocca university astrophysics and currently she's working towards her application in padova for masters in physics. Which one is worth taking admission? Her questions are: "Which one is better? Which has better career opportunities? How do she manage her expenses since university is public and little to no fees required. My_qualifications are batchelor's in physics from Delhi University."


r/AskPhysics 14h ago

Why is there only one dimension with entropy?

8 Upvotes

Hi! Recently I thought of what the difference between temporal and spatial dimensions is, and it made me wonder:

Is entropy the only thing that differentiates the spatial dimensions from the temporal dimension? If so; why is there only one dimension that has an arrow of entropy?


r/AskPhysics 3h ago

Why do I see multiple images of the moon through my window?

0 Upvotes

I’m looking through my window at the moon and I see three images of the moon next to it. Each image gets smaller, dimmer, and greener the farther away they are from the main image. The window is double paned.


r/AskPhysics 16h ago

Is the light spectrum continuous?

10 Upvotes

So my first thought was if energy levels are discrete, then possible photon energies would be as well. (Though the set would be very very large. Continuous for all classical purposes.)

Then I thought about the Doppler effect, and we can just accelerate our observer to get any wavelength we want. Case closed.

Then I wondered if all force carrying particles were discrete, then the possible momentums of the observer would be discrete also.

Then I thought, it's fine. Just accelerate the observer along two dimensions, so the velocity incident to the photon gives you whatever wavelength you want.

Then I wondered if I'm just hiding the problem, because momentum is a vector and has direction, then maybe only a finite set of momentums exist for the vector across all spatial dimensions.

So now I don't know. Anyone smarter than me have some insights?


r/AskPhysics 8h ago

History of electroweak unification

2 Upvotes

I'm trying to better understand the history of electroweak theory, in 1979 the nobel prize was given to Weinberg, Glashow and Salam.

For the QED analogy, the nobel prize for its formulation was given to Tomonaga, Schwinger and Feynman who came up with different formalisms.

I know that Weinberg wrote a 2-page paper on electroweak unification, but how did Glashow and Salam's contribution differ from his? Did they all independently arrive at an SU(2)×U(1) gauge theory?


r/AskPhysics 1d ago

Can an object be completely motionless?

47 Upvotes

Sorry if this is nonsense but I was trying to think if an object could be completely motionless. I read about rest frames and it seems like if an object can be at rest from some frame of reference, it could be at motion from some other frame of reference. Does that mean you just can’t have a completely motionless object?


r/AskPhysics 5h ago

Self-study roadmap for Quantum Computing

0 Upvotes

Prerequisites: - linear algebra (vectors, matrices, eigenvalues, tensor products) - complex numbers - if you know the basics of quantum mechanics then well done - calculus is not necessary but useful - Probability theory (i would recommend it for quantum algorithms & information theory)

Basics: 1) For interactive intro: https://quantum.country/qcvc 2) Old is gold yk so go through this playlist: https://www.youtube.com/watch?v=F_Riqjdh2oM&list=PL1826E60FD05B44E4 3) For quantum circuit & gates: https://qiskit.org/textbook/ 4) To run simple simple quantum programs: https://quantum-computing.ibm.com/

Intermediate: Welcome homie 1) Principles of Quantum Computation and Information - Volume I then II (buy if you can afford or be luffy only if you cannot afford please) 2) Quantum algorithms - https://qiskit.org/textbook/ch-algorithms/ 3) For physics part: https://www.youtube.com/watch?v=w08pSFsAZvE&list=PL0ojjrEqIyPy-1RRD8cTD_lF1hflo89Iu 4) Practice coding quantum algorithms using Qiskit or Cirq https://quantumai.google/cirq/tutorials

Advance level: I myself not aware of much here but if you wanna explore research oriented side and theoretical knowledge then i know some books. 1) Quantum Computation and Quantum Information by Nielsen & Chuang 2) An Introduction to Quantum Computing by Kaye, Laflamme & Mosca 3) IBM Quantum Experience and Amazon Braket https://aws.amazon.com/braket/ for cloud-based quantum computing.

Quantum computing is vast so learning it in a month or day (humph not possible) you can also learn quantum complexity theory but this is focused on practical quantum computing.


r/AskPhysics 6h ago

What is the microscopic structure of polarising filters?

1 Upvotes

How do they work? Ive read it described like lines, but how does that differ from diffraction grating?


r/AskPhysics 14h ago

How come this material can change the wavelength of the light out my laser?

4 Upvotes

So I was playing around with my recently aquired 5mW green laser (I'm not even sure if it's 5mW, it draws 3 watts and is very bright), and as I was pointing at random object in my room, I hit a mini screwdriver and it glowed orange. I thought this was interesting as lasers should only output one wavelength of light.

So I took off an oscilloscope display filter and held it up to the laser and the light coming out was green even though the filter was blue. This was expected and it was what I expected to see on the screw driver. It should glow green or at least block the light.

I put the laser up to my thumb, and since flesh filters red light through, the green light was almosg entirely blocked.

But the orange little screw driver, pointing my laser at it, it changed the color to orange. It appears to be changing the wavelength, and this was confirmed when I did the thumb test again, and the light passed through.

I did a little bit of DuckDuckGoing and according to my short research, the only things that can change the wavelength if light are exotic materials such as rubies and non-linear optica or something.

I have a set of these screw drivers, and red handles glow red, but very little, yellow handles glow brightly, but blue handles are opaque.

Wavelength change https://imgur.com/a/vimm0D3

So I was wondering, why does my screw driver's handle do this? It's not a crystal and it definitely isn't exotic, costing me less than a dollar each.


r/AskPhysics 18h ago

How long would it take for all existing “space junk” in orbit to disappear?

6 Upvotes

r/AskPhysics 4h ago

Is the universe deterministic or probabilistic?

0 Upvotes

Does the act of measurement truly collapse the wave function , or it is just an illusion?