/r/AskPhysics

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/r/AskPhysics exists to answer questions about physics.

  • Questions should be relevant, and answers should be on-topic and correct.

  • We don't condone cheating on school work, and homework questions should be handled according to these guidelines.

  • Incivility will not be tolerated.

  • If your question isn't answered in a day, you can post it in the Tuesday thread in /r/Physics (unless it's homework-related).

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[;i\hbar \frac{\partial}{\partial t} \Psi = \hat H\Psi;]

/r/AskPhysics

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1

According to our current understanding of dark matter, has it been detected in the "voids" that are inbetween the cosmic web, and if so can matter exist outside the dark matter halos?

To expand, the cosmic web is comprised of gigantic clouds of dark matter that binds visible matter into clusters of galaxies. The cosmic voids are spaces inbetween those clusters that contain very very low densities of matter (I need a reference for that claim). So I ask has the dark matter been detected in those voids? Or is it exclusevly clustered in the cosmic web that forms the shape of the superstructure of the universe?

Because I came up with a hypothesis that goes like: The visible matter is ALWAYS surrounded by the dark matter halo. No matter the size or mass of the particle. Meaning, if that's true, and if we really have wandering particles in the voids of space inbetween galaxies, there must be wandering dark matter aswell that follow them, or the other way around.

0 Comments
2024/06/12
21:19 UTC

1

Question about neutrino flavor oscillation, mass and speed

I understand the physicists here would prefer a question on the speed of light or black holes rather than neutrinos, but I will ask anyway lol. I am a scientist but not a physicist and am having difficulty understanding flavor oscillations (this part I get), the differing mass of neutrinos and thus differing speed as they oscillate (this part I don't get). I read this in wikipedia:

"As a neutrino superposition propagates through space, the quantum mechanical phases of the three neutrino mass states advance at slightly different rates, due to the slight differences in their respective masses."

So is this saying as neutrinos oscillate that they slightly speed up or slow down due to the changes of the three mass states? How would this occur? Or am I misunderstanding the concept here and "advance" means something other than speed?

0 Comments
2024/06/12
21:05 UTC

1

What textbooks should I use?

Hey everyone, I have upcoming (Complex Variable) & (Vector Analysis and Tensor Calculus) courses in my sophomore year, alongside (Modern Physics I) and (E&M). I think I'm lost a little, how do I start? Is there a somewhat right order for studying them? Or should I just starts with whatever and it doesn't matter? Also, what textbooks would you recommend for each one?

P.S: So far, I took the introductory courses (math I&II, waves and optics, electricity and magnetism, thermo, mechanics)

0 Comments
2024/06/12
20:21 UTC

2

Microwaves?

So, I’m not sure if this is the right place to ask this, but I was wondering if there is a substance that you could microwave that would protect the contents of a container from getting hot.

I understand the concept of a faraday cage, but I don’t believe you can microwave one due to the metal components.

Any suggestions?

2 Comments
2024/06/12
19:36 UTC

1

How to consider rotation when finding the centre of mass?

0 Comments
2024/06/12
19:32 UTC

4

Does nature "want" to maximize entropy, & also "want" to minimize energy usage? If so...

In my understanding, the 2nd law of thermodynamics says that the closed system of the universe, or nature, "wants" to maximize entropy. In other words, its physical processes always unfold so as to increase its entropy. It is also my understanding that the principle of least action says that nature "wants" to minimize its use of extraneous energy. In other words, the path that provides the least resistance for a system to get from point A to point B is the one that is selected. Is my understanding of these two concepts basically correct?

If so, why would minimizing extraneous energy usage be a factor in the universe? Shouldn't the universe be burning energy like coal if max entropy is its goal?

12 Comments
2024/06/12
19:31 UTC

1

How could you find a time when two objects in different circular motions aer next aligned?

https://imgur.com/a/mxETEL7

I have solved part a, where I had T = 24.5, wb = 35/6 and wa = 14/3.

I am at a loss to how to approach part b.

I began with w = 2pi/t and found the time period of each particle, but I am not to sure on how to progress from here.

Appreciate any assistance!

6 Comments
2024/06/12
19:03 UTC

2

Does time “speed up” when observing something far away that you are traveling to?

If aliens were 80 light years away and observed us, they would see WW2, if they travelled at high speeds towards us would they observe time passing on earth sped up until they reached us and observed modern day earth? Also how would they look from our perspective, also sped up?

2 Comments
2024/06/12
18:51 UTC

3

thermodynamics

Question: on dissolving a compound X in water at room temperature, solution feels hot to touch. Under which of following cases, dissolution of compound X will be most rapid?

(A)Crystals of compound X in cold water

(B) Crystals of compound X in hot water

(C)Powdered form of compound X in cold water

(D)Powdered form of compound X in hot water

1 Comment
2024/06/12
18:47 UTC

1

Does light polarization change as it interacts and bounces off as surface or pigment?

background:

I am looking to do a Cosplay where is am using a LCD screen to create a character who has a tv for a head. I created a transparent LCD by removing the backlight. When the LCD is set to white it is clear and see through. my plan is to have my head in the box with the LCD and LED lights and want to be able to see out of the box when the lights are on I am looking to move to step two. Here is the design and I want to make sure my assumptions about polarization hold.

  1. Remove one of the polarizers from the LCD panel inside of the box and instead polarize the light coming from LEDS in the direction the removed filter was.

  2. create polarized glasses that are aligned with the polarizer film still on the lcd.

  3. The orientation difference between glasses and light in the box should mean it is filtered out while light the LCD should be transparent and I should be able to see out of it. People looking from the outside will see bright lit image.

This hinges on the light not changing polarization as it bounces off the sides of the box and the white mask I will be wearing to give contrast.

So Does light polarization change or can I rely on it to make a sick cosplay?

1 Comment
2024/06/12
18:12 UTC

1

Is the potential at the surface of a metal conductor inside an external electric field is 0 even if metal is charged or not?

I don't understand the freedom to set V = 0 for the equatorial plane in problems.

2 Comments
2024/06/12
17:46 UTC

4

is there an event that would make all watches in a whole city mismatch?

to day; I woke up to find the watches in my house were mismatched, including phones and smartwatches. I asked my family and some friends and there watches and phones were also mismatched, there friends also told them the same thing, for all that I know, the watches in whole city were affected.

I live in a hot area so my first thought was that my city got attacked by some neighboring country, but I figured that such Attack would not be reasonable Since my city don't have critical military bases or strategic targets.

so my second thought was, that there is some solar storm effecting electronics, but my search showed that there isn't one today, but There's a chance of minor solar radiation according to spaceweather.com.

so what is the possible reason for that mismatch?

16 Comments
2024/06/12
16:20 UTC

0

what is "normal contact force" ?

got gcse physics paper 2 on Friday. I'm no good at physics and will be dropping it as soon as the exam is over, but I don't understand what 'normal contact force' is? is it just the pushback from an object when you touch it? like I touch the wall and feel pressure from the pushing back

idk guys please help

2 Comments
2024/06/12
16:09 UTC

1

Thought experiment: Relationship between speed, gravity, and time

I've often heard of black hole singularities described as an inevitable point in your future, if you were inside the event horizon and moving toward it, and that spacetime ends once you reach it. It led me to a thought experiment.

We know both speed and gravity have relativistic effects at sufficiently high amounts. Speed has a limit, c. We know that as something approaches c, its clock slows down, and stops completely at exactly c. This made me wonder if gravity also has a maximum finite limit where time completely stops. If gravity is simply based on mass, then this limit would be all the mass in the universe in one spot. As far as we know, this state only existed at t=0, the Big Bang. If this truly represents the gravitational limit, it seems to mean that this would also mean stopped time, which makes intuitive sense because how can you have time before the Big Bang?

Which leads me back to black hole singularities. If time was only truly stopped/non-existent before the Big Bang, how can black hole singularities also represent the end of time/spacetime if they have less mass than the entire universe? This makes my head hurt.

Afterthought: Would this also make intuitive sense by the fact that, if ALL mass in the universe is at one point, then you could only exist in its vicinity as a photon or other massless particle, and necessarily not experience time?

4 Comments
2024/06/12
15:56 UTC

10

What are, in your opinion, the must have of a physics books collection

I am creating my physics home library, since now I added some divulgative books that brought me there such as seven brief lessons on physics, surely you're joking Mr feynman and the stephen hawking's George saga.

Then I have the textbooks I'm studying or I've studied on, such as the Landau-Lisfits collection or Griffiths introduction to electrodynamics.

Now I would like to add some more historical books, such as Galileo's dialogue or Newton's principia, and for that category I'm looking for something else to there.

What are in you opinion in this three categories books that must be on a personal library?

12 Comments
2024/06/12
15:20 UTC

23

Can humans really create the quantum computer they expected?

In recent years, there have been a lot of reports and discussions about the manufacture of quantum computers at many academic conferences around the world, in various languages, and on the Internet。From these articles and reports, it seems that the quantum computers should come out soon。However, so far, it can not be seen。This phenomenon let many people doubt whether or not the mankind can make the quantum computers。From these reports and paper, they mainly focus on reporting the progress of engineering research and manufacturing of quantum computers (certain hardware and software)。Few articles analyze the feasibility of quantum computer research and manufacturing。

The purpose of this question is to try to ask the feasibility of the manufacture of quantum computers, that is, whether humans can finally successfully manufacture quantum computers that can be put into practical use, thereby pushing human social civilization forward。Because if humans invest a lot of money and time, but fail to manufacture quantum computers in the end, then quantum computers will become the second "perpetual motion machine" in human history, which will be another huge loss for mankind。

35 Comments
2024/06/12
15:06 UTC

2

Negative energy for a tau neutrino

In the decay of a pion into a tau particle and a tau neutrino, I’m calculating that the tau particle has more energy than the original pion and that the neutrino has a negative energy. I did this calculation in the rest frame of of the pion. Energy is still conserved according to what I have calculated.

Is this a mistake or is it ok because energy is conserved. If it is ok, how can negative energy be interpreted?

3 Comments
2024/06/12
14:57 UTC

0

What if

What if were to make a vehicle that travels even a little bit faster than light. Would we be seeing the vehicle in the past if we were to be able to just track it. I’m pretty sure I know the answer to this but I would like to double check

4 Comments
2024/06/12
14:33 UTC

1

Help! Need mechanical advantage advice

I have a physical test for a job coming up and have to pull 110 lbs of tension and hold it via a single rope from a tension scale up through a pulley then angled downward for me to pull. Here’s the issues, I’m only 125 lbs, I can’t stand directly under the pulley and hang on it, and as far as I know I won’t be able to add any additional pulleys to improve my mechanical advantage. So here’s my question to y’all, how can I improve mechanical advantage using only the single line rope itself? Is it even possible for me to get improvement from that?

2 Comments
2024/06/12
14:27 UTC

2

Why is the integral of current density is independent in surface?

9 Comments
2024/06/12
13:06 UTC

0

Physics experiment worksheet help

Hey everybody, I’m wondering what other errors are possible for this experiment on optics. Any ideas on what they could be?

https://imgur.com/a/tNnuXaB

0 Comments
2024/06/12
12:07 UTC

6 Comments
2024/06/12
11:51 UTC

0

In this video at 0:58 when Peter starts jumping really high on those buildings is he violating Newtons Third Law of Motion?

2 Comments
2024/06/12
10:08 UTC

5

Does gravity affect the outcomes of dice rolls?

Instead of just painted dots, some dice have circular indents that represent the numbers. So for these dice, I'm wondering if there would be a slight tendency to roll a 6 since it's the lightest side because it has the most matter removed from it. Given that, then the least likely outcome should be rolling a 1 because it's the heaviest side.

Am I correct in thinking this, or does the constant of gravitational acceleration negate this?

11 Comments
2024/06/12
09:57 UTC

4

How come during an eclipse you can still sort of see the rest of the moon that isn’t lit, does this mean some of the suns light is reaching it somehow?

9 Comments
2024/06/12
09:33 UTC

30

Is the age of the universe relative?

The age of the universe is said to be 14 billion years (give or take). I imagine this is from the perspective of Earth (per relativity). Is this age different at the epicenter of the Big Bang? Apologies if this is a dumb question; I'm new to relativity (and physics generally).

27 Comments
2024/06/12
09:12 UTC

3

Is there anyway to tell which side of the CPT mirror where in?

This comes from the extension of the question of why we're not made if antimatter. My layman understanding is this: if antimatter scientists exist, they'd be asking why we're made of antimatter. Then I fell into a rabbithole of CPT parities. Its the last symmetry to not be broken.

Is there anyway tell if we're +CP going forward in time or if we're -CP going back? Is it even a falsifiable question?

4 Comments
2024/06/12
09:03 UTC

3

Forgot all my physics, looking for a physics textbook

Hi r/AskPhysics,

I did the APP1 exam last year, and scored a 4. I used Flipping Physics and Khan academy, and I finished the Khan academy APP1 course 100%. But honestly, I didn’t think I understood the content in depth enough (even while I was doing the exam).

A couple months back, I did the F=ma exam (the USAPhO prelim thing) and I scored worse than a monkey guessing. Across 5 units (dynamics, Circular motion, energy, momentum, simple harmonic motion, rotational motion) my foundation honestly feels quite shaky. It doesn’t help that I’ve also taken a bit of a break from physics since then 💀

I’m looking for a textbook (or two) to rebuild and retain a solid foundation on physics. Like, I’m not really looking to cheese with an AP exam prep book. For my goal this year, I want to learn enough physics to qualify for and take on the USAPhO. I want to dedicate about 7 hours every week this summer, and 4 hours per week after school starts. For the math prerequisites, this year I’ll be concurrently taking Calc BC.

Bonus if the book includes the content needed for APPC E&M

2 Comments
2024/06/12
08:37 UTC

3

What does d(psi)/dx represent?

I was studying the derivation for transmission of a particle through 1D rectangular potential barrier and while applying the 2nd boundary conditions ie. At x=0 and x=a, d(psi)/dx should be finite I realized I don't really know what d(psi)/dx represents. I know it represents psi changing with time, but is that all?

4 Comments
2024/06/12
08:19 UTC

0

What if Dark matter came from Blackholes?

Could dark matter come from blackholes?

So while at work an idea came to mind. So my idea is that that dark matter is either makes up a black hole or comes from it. And due to the fast rotation of the black holes and energy released from the electromagnetic jets. Parts of the blackhole/ dark matter is made or released into space

This is just my idea, and I'd like to know if there are any papers that prove or disprove this idea.

13 Comments
2024/06/12
08:02 UTC

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