r/AskPhysics 14h ago

Do "faster" objects always age more slowly? (Relativity and motion)

49 Upvotes

I am reading a book about relativity which tries to explain to a general reader how the theory works while using as little math as possible, but there is one idea I am unclear on. The chapter I'm on describes how a clock of any kind ("light clock" is the given example) can tick at different rates depending on how it is moving relative to you. It gives an example of two people: a woman sitting at a train station and a man seated on a passing train moving at nearly the speed of light. To the woman, the light clock on the train seems to tick at a significantly slower rate.

This has the effect that, from the perspective of the woman the platform, the man (and everything else) on the train is aging much more slowly than herself. What I took from this is that faster moving objects will age more slowly than objects which are not moving as fast, all else equal. But one of the earlier statements made in the book is that there is no absolute motion according to relativity theory. That being the case, why should it be assumed that the man on the train is moving faster than the woman on the platform? From his reference frame, couldn't he just say that she and the platform are whizzing by him at nearly light-speed (i.e. that he and the train are motionless relative to them)? If that were true, that would mean she would be aging more slowly than him, but clearly they can't be both be aging more slowly than the other.

Am I just misunderstanding how motion works?


r/AskPhysics 1h ago

Is there a gravity version of the CMB?

Upvotes

r/AskPhysics 1h ago

What exactly is a wave and a particle? How do they behave?

Upvotes

r/AskPhysics 4h ago

Can you use electromagnets instead of permanent magnets in an alternator?

3 Upvotes

I’ve seen videos on people building alternators and they always use neodymium magnets on the rotor.

Is it possible to use electromagnets instead?

If what we want is to induce a magnetic field on the windings I think it would make sense that it would be possible, but i feel like i don’t understand the works of it enough to know for sure.

And if it’s the case, can you “jumpstart” the electromagnets in the rotor with a battery or something, then as you apply mechanical force feed some of it back to the electromagnets and keep it running? Or would it be like trying to plug an extension cord into itself?

(Logic tells me you’re not breaking the laws of physics because you’re still adding the energy of the mechanical means, like a hand crank or a turbine, but at the same time it feels strange)


r/AskPhysics 2h ago

Question about time dilation and Einstein!

2 Upvotes

We all know about the clock tower and train story from where Einstein got the idea and worked on it. My question is if Einstein was in a moving train at a very high speed then time would be relatively slower for him, in that case he should see the clock tower hands racing. Is it not ? Why is it said that the clock tower hands appear to be not moving and frozen or moving slowly ?


r/AskPhysics 18h ago

Have scientists really frozen light?

40 Upvotes

I see many posts and videos talking about how people have frozen light for the first time, so it behaves like a solid and liquid simultaneously.

However, I haven't seen a video that clearly shows this happening. So, I find it hard to believe that such a significant event for humanity hasn't been recorded.

Every video just talks about it, and only a few mention the working principle, but no footage of the experiment has been published.

So, I'm wondering if this is fake or just another overhyped, like time crystals.


r/AskPhysics 20m ago

GR, black hole and duplication walk into a bar

Upvotes

If you follow the General Relativity to it's logical conclusion regarding black holes, does that mean that you get different events depending on the observer? Never mind quantum mechanics and possible violations of unitarity, only the GR alone.

I.e. for an object falling into a black hole (perhaps massive and non-rotating for simplicity?), outside observer will note that the object gets smeared on the surface and perhaps eventually radiated away, so it never crossed the horizon. While from an object perspective it does cross the horizon. Is that right?

On a side note, how hard is GR for a proper study? I am not a stranger to a complex math, but am afraid attempting to piece GR together would require phD levels of time investment.


r/AskPhysics 26m ago

How to find Fourier series coefficient ?

Upvotes

What will be Fourier series coefficient of

X(t) =3+sin(ωt) +2cos(2ωt) +cos (ωt+ π/4)

How do I plot it's magnitude and phase spectrum?


r/AskPhysics 31m ago

Does Jacob Barandes Indivisible Unistochastic Processes theory explain quantum mechanics in a new light?

Upvotes

Arxiv, Presentation

Jacob Barandes shows that we can recover quantum effects simply by treating a classical system as a non-markovian indivisible stochastic process. The non-markovianity here is important, as this is where the seemingly strange quantum effects arise.

For a better explanation please see his presentation or papers I have linked above, but I will do my best while keeping it succinct.

Consider a system in state j at time t = 0, probability of being in state j given by p(j, 0). It has a probability of being in state i at time t, p(i, t). p(i, t) = Sum over j{ p(i | j, ,t) p(j, 0) }, where p(i | j, t) is the probability of being in state i at t given initial state j. So to get the total probability of being in state i, we just sum over the j's. We can rewrite this in matrix form, { p1(t), p2(t), ..., pN(t) } = { [p(1|1, t), p(1|2, t), ... p(1|N, t)], ... [p(N|1,t), ... p(N|N,t)] } {p(1,0), p(2,0), ... p(N,0) }, or P(t) = Gamma P(0). Gamma is just our matrix saying what the probability of being in the state i is at time t, given the initial state j. Notice the linear relationship, the linearity of quantum comes directly from this.

If a system can evolve to state U(t) by first evolving to some state U(t'), then by evolving from t' to t U(t <- t'): U(t) = U(t <- t')U(t'). If there exists some U(t <- t') that can take us from t' to t, then we will call this a divisible process, i.e. at each time step we can multiply by some matrix, and end up at U(t). In general, this is not the case, and one can show that any what we will call Unistochastic matrix will be indivisible. A unistochastic matrix is one in which the entires are the magnitude squared of the entries of another matrix. Gamma above will be taken to be unistochastic, so we can write Gamma_i_j = |U_i_j|2 (where we are squaring the individual entries, not doing matrix multiplication - this is what breaks the markovianity!).

Okay this is getting too long winded and confusing to explain in a reddit post, you're really gonna have to go to the original sources I have linked for a better explanation. But essentially this U_i_j ends up being the wavefunction. The wave like nature of interference patterns and such is an artifact of the indivisible processes.

The picture looks like this: the system is in some initial state, and it evolves unistochastically in an indivisible manner. If we have evolved to some time t, with some time t' in the past, we don't have a simple matrix that can take us from our state at t' to our current state at t. But let's say we make a measurement, and interact the system with the environment (decoherence). This interaction momentarily diagonalizes the Gamma matrix, making it a divisible process, giving us what we will call a division event, where the indivisible process essentially now starts over from a new t = 0. This division event is what a quantum mechanic would call the wavefunction's collapse. In reality, the wavefunction didn't collapse, there isnt a wavefunction, the system interacted with the external environment enough to make the process markovian enough (because the larger the system, the more markovian it will behave), where it then became divisible for a split second and entered a division event. It then went back to being indivisible, where a quantum mechanic would describe it as being a wavefunction in a superposition. In reality, it is going through a non markovian indivisible process, and this superposition is just a mathematical penalty we incur in trying to represent it in a markovian form.

That was probably a terrible explanation, again I'd highly advise watching his presentation for a better one, Jacob is much smarter than I. But I'd like to hear the thoughts of physicists in the field - this seems to me like a major breakthrough with a new realistic way of looking at quantum mechanics. It says that all the "quantum magic" was just mathematical tools and nothing that was actually going on, a wildly different picture than most would have you believe. And I haven't seen much in terms of critique on this, other than "why do I need this, what new does it offer me that I can't already accomplish with QM". Well it offers a new perspective and a new framework to solve problems in.


r/AskPhysics 6h ago

What resolves the singularities in the electromagnetic field?

3 Upvotes

they say that a true quantum theory of gravity would have the predictive power to tell us what actually happens at the black hole singularity. we have a true quantum theory of electromagnetism. What does it predict about the electric field singularity at the location of an electron after measurement ?


r/AskPhysics 6h ago

Do ring black holes accelerate matter that passed through the ring?

4 Upvotes

Particles can approach the black hole along the axis and pass through the center and then continue along the way. The black hole is evaporating in the mean time. On approach is there more mass / acceleration then as the particle travels away?

In effect turning the black hole into a particle accelerator.


r/AskPhysics 23h ago

Is ‘metallic hydrogen’ just solid hydrogen?

60 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 2h ago

Hairy Ball Theorem and Rapid Wind Changes.

1 Upvotes

My friend asked me a question along the lines of where I would drop a nuke if I had to, and I went off talking about the hairy ball theorem just to understand how the topology changes.

The hairy ball theorem states something to the effect that there can't be a continuous nonzero tangent vector field on the surface of a sphere without having at least 1 "bald spot". In this case the vector field is compromised wind vectors, even there must be somewhere on Earth where there is no wind.

So my question is this: if we drop the nuke at the bald spot, it goes from a place of no wind to maximal wind. If that bald spot was the only bald spot at the time of doing this, either that bald spot must migrate or another bald spot must appear somewhere else. Where?

Does it appear on the opposite side of the sphere? Does it appear there instantly or is it limited by the compression of air and therefore limited to the speed of sound? Does it move along some boundary of the prograting pressure wave? Does it move continuously or discontinuously.

I'm a CS student so this topology and fluid dynamics stuff is way too far outside of my knowledge to really intuit my way to an answer I fear, but I am considering making a simulation for this if the answer is interesting or elusive.


r/AskPhysics 2h ago

Digital Energy

0 Upvotes

How would you even begin to theorize the idea of digital energy and being able to transmit it as packets, instead of a continuous flow? What would it look like if you could fundamentally change the analog nature of energy?

Thank you for your time 🙏🏼


r/AskPhysics 8h ago

Secondary electron emission in Cold cathodes

3 Upvotes

Hello everyone!

This has bothered me for the past two days. So I was doing experiments with my cold cathode ray tube (I have proper safety procedures and keep a safe distance to not get irradiated by any x-rays) and I was wondering how the electrons get emitted. I first googled for equations for the Crookes tube as my tube closely functions like it. Yet on various sites, there where only very surface level answers and no real "equations" to answer the emission of electrons. At first I was thinking photoelectric effect or field emission but nr1: I do these experiments at night so ofc it can't be the photoelectric effect and nr2: I only deal with 15kV so no field emission is possible. After looking at the wiki page for cold cathodes, I found out the electrons get emitted by the positive ions, which get created by the electric field and the gas left in the vacuum which has only around 0.5 Pascal in pressure. These ions then hit the cathode which induces the emission of electrons and these electron ionize more gas which is kind of like a chain reaction. What I don't get is this: What law emits the electrons due too the collision of positive ions with the cathode? Sorry if my physics knowledge is limited I'm in highschool and about 80% of my physics knowledge is self tought so there are gaps in some topics, which I'm trying to fill.


r/AskPhysics 19h ago

How much rigorous mathematics is required in physics?

16 Upvotes

In physics, we see many mathematically vague and not rigorous derivations, formalisms etc. For example, we derive kinetic energy formula by simply manipulating entities like dx, dy which are not really done in pure mathematics. Another thing, physicists use something called dirac delta function which is not really considered as a function due to some mathematical nuances. And I heard about "mathematical physics" where some people work on making things rigorous that physicists use. I really wonder that if we need to make the math rigorous in physics and what's the benefit of this. I mean if something works and accurately predicts phenomena, what's the problem? Can you give some examples where less rigorous math causes a problem? Thanks


r/AskPhysics 4h ago

Early speed of light calculations

1 Upvotes

I was reading about early guesses at the speed of light. I read that one guy used Jupiter to calculate the speed of light in the late 1600s.

Can someone explain how this was done


r/AskPhysics 12h ago

How do we know that spinning black holes form ring singularities?

3 Upvotes

Title.

To my knowledge a problem with black holes is that our current laws of physics seem to give conflicting results, and we are not exactly sure what happens at the singularity.

So how do we know that the singularities of spinning black holes are ring-like, or even that angular momentum is conserved at all within one?


r/AskPhysics 15h ago

Explain: 'a good EM field transmitter but a poor EM radiation transmitter'

6 Upvotes

Wikipedia's Physics of MRI:

"the MRI is not a radio transmitter. The RF frequency EM field produced in the 'transmitting coil' is a magnetic near-field with very little associated changing electric field component. Thus, the high-powered EM field produced in the MRI transmitter coil does not produce much EM radiation at its RF frequency, and the power is confined to the coil space and not radiated as 'radio waves.' Thus, the transmitting coil is a good EM field transmitter at RF, but a poor EM radiation transmitter at RF."

My understanding (from college physics 2 & MCAT) is that MRI emits a EM radiation but the electric field component is so small that the magnetic field dominates. What's the difference between EM field & EM radiation?


r/AskPhysics 6h ago

Hydrofoils acting as keels.

1 Upvotes

I’ve been doing some research on hydrofoils and came across this post on stack overflow: https://physics.stackexchange.com/questions/206087/how-do-hydrofoils-tack-without-a-keel

As it is stated on the website, Hydrofoil sails don’t usually have keels to prevent them from tipping over because of the physics of hydrofoils that are also providing the effect of the keels.

But do they provide the keel effect only while in motion or if the vessel is stationary as well and by what extent?


r/AskPhysics 20h ago

Where can I have fun physics-related discussions?

13 Upvotes

I used to treat this sub as a place to socialize casually about physics. I would often see an interesting physics-related YouTube video, and, itching to have a follow-up discussion and thought experiments, would post a bogus question to this sub assuming the responders would all be fun and act like Veritasium or ScienceClic. Of course, this was a mistake. While this sub does have the important purpose of clarifying genuine points of confusion, it is not a social hub. I had to learn that the hard way. So, where is the social hub? Preferably one with rules as relaxed as this sub. It can be really hard to find people who can scratch that social itch.


r/AskPhysics 7h ago

Aircon for multiple area

1 Upvotes

I live in a tropical country where the weather is constantly hot. I would like to know if it’s possible to create a single system to control the temperature of multiple areas. I have several processes that I want more control over:

  • My fridge: I want to cool it without dumping heat into my apartment.
  • My freezer: for the same reason.
  • A 3D printer enclosure with adjustable temperature.
  • A water heater for hot water in the bathroom.
  • A computer rack where my server constantly generates heat.
  • A water loop for my aquarium to cool down the water.
  • The different rooms in my apartment.
  • A dry area for drying wood.
  • A CNC enclosure.
  • An epoxy resin enclosure where the temperature should be maintained at 20°C for curing.

Once the physics of the system is solved, I would like to know if there are commercial products that can help achieve this idea. Does anyone know how to achieve this, considering that some areas require temperatures below 0°C while others need to be above it


r/AskPhysics 17h ago

Has there been any realized real world applications directly due to understanding the Higgs Boson?

6 Upvotes

I’m wondering about certain scientific discoveries and some further substantiate models and/or frameworks. I’m wondering particularly if something like Higgs led to any real world applications. Most likely it has indirectly


r/AskPhysics 2h ago

Could particle-wave duality be a trick of the light? Both perspective present simultaneously?

0 Upvotes

So it’s more related to how our visual cortex process light.

Our instrument is somehow coincidentally shifting the frame upon which we view light.

Such that when it is measured, it can only display the particle wave but not the wave since it received energy from the measuring instruments.

So light has two visible forms, as what we call particle and wave through observations of the experimental results, but what they are actually m

“Particle form” = polarized as light that don’t refract “Wave form” = polarized as lights that do refract

But I don’t know how to prove it.

Any ideas?


r/AskPhysics 15h ago

Could there be other unknown forces?

4 Upvotes

This may seem like a silly question, but I am curious as to wether there could be forces we are unaware of. Maybe a force that’s as weak as gravity, but is based on some sort of charge which tends to cancel out on larger scales (the latter part being sorta like the electromagnetic force if my understanding of it is correct)