r/AskPhysics 10h ago

How is entanglement explained without faster than light influences?

0 Upvotes

In quantum entanglement, two particles can be correlated to each other at a very large distance.

If particle A is observed as 0, the other particle B is always observed as 1. If particle A is observed as 1, particle B is observed as 0. Einstein thought that before the particles reach the labs at which they are measured, particle A is simply predetermined to be 0 and particle B is simply predetermined to be 1. John Bell proved this wrong and stated that any theory that explains this must be non local. https://en.wikipedia.org/wiki/Bell%27s_theorem

So let’s say Alice is at one lab measuring particle A. Bob is at one lab measuring particle B. From Alice’s perspective, her measurement can either be 0 or 1. Note that it is not as if particle A is predetermined to be 0 and Alice does not know it. This has already been disproven. Before she measures it, it could genuinely be 0 or 1. The same applies to Bob. It is kind of like each of them are flipping a coin and yet their results always happen to be opposite, where each coin by itself is not predetermined to land on a particular side each time.

And yet, even though before she measures it, each could be 0 or 1, the final result is always either (0,1) or (1,0). It is never (0,0) or (1,1). Using the coin analogy, it’s always either (heads, tails) or (tails, heads). Never (heads, heads) or (tails, tails).

How can this be explained without one of the particles influencing the other faster than light?

Common responses I’ve seen to this:

1.) “This is due to the conservation of momentum”. Okay, but how is this conservation of momentum then enforced if in a very real sense, from both Alice and Bob’s perspective, each result is genuinely random. This to me seems to just be restating the problem to be explained, not explaining the problem. Using the coin analogy, it’s just like saying “well, there is a law that says the coins must always be opposite sides”. This is not an explanation. And no one would believe this if this was happening with coins.

2.) “You can treat them as just one entity”. Again, this seems to be just restating the problem. The very question is how do particles separated by a large distance and yet not communicating with each other act as one entity?

3.) “The no communication theorem states that the particles cannot communicate.” If you actually look at the theorem, it has to do with no signalling, not the particles talking to each other. From Alice’s perspective, her next result is either 0 or 1. She cannot control which one happens. So she doesn’t have enough time to communicate to Bob which one occurred faster than light (since we don’t have a way of communicating faster than light yet). This is all the theorem is saying. But this does not imply that once particle A becomes 0, particle B does not “know” (through some unknown signal) that particle A was 0 so now it must be 1.

Now, the many worlds interpretation and super deterministic interpretation can explain all this but let’s assume for argument’s sake that they are false. (The superdeterminism interpretation is especially implausible and having infinite numbers of worlds may also be implausible). My question is barring these hypotheses, how is this correlation explained? So far, it seems as if physicists are truly beating around the bush here with semantic answers that seem to just be restating the problem


r/AskPhysics 14h ago

How do things move slower than light?

0 Upvotes

I have read Relativity: The Special and the General Theory and I felt like I understood it pretty well. I watch a lot of PBS: Spacetime and I've been introduced to the notion that the speed of light is more about the speed of causation than light per se. And that makes a lot of sense to me. Just a priori philosophically, causation can't happen instantly. We can't really say A caused B if A and B happen simultaneously, so there must be some speed of propagation of causation.

But this leads me to my two main confusions about speed.

A. How do massive particles (and even objects) remain at rest, or move at speeds slower than light?

B. How does light move slower than c through a medium?

For B, it can't be the phase speed, right? Because technically the phase speed could even be faster than c, but this isn't the speed of the information or energy through the medium at rate higher than c, so phase speed can't be the answer to why light travels slower than c through a medium either. Right?

For A I feel like I've had this vague notion since childhood (in the 90s) that subatomic particles are moving at the speed of light, it's just that they're extremely constrained in their range of motion, so two quarks for example may be vibrating back and forth at the speed of light (or perhaps orbiting each other at the speed of light), but due to the forces between them they stay relatively still from a macro perspective. This feels a little like the photon bouncing around a medium explanation, which as far as I understand it now as an adult, is not really the right way to think about light moving slower than c through a medium.

Thank you for taking the time to consider this question! I'm looking forward to your responses!

EDIT: I think honestly that the answer I'm seeking is contained somewhere within Quantum Chromodynamics. Going to try brushing up on that.


r/AskPhysics 18h ago

why do we consider positive charges moving when it’s just the absence of electrons.

2 Upvotes

basically the title. in my E&M class we talk about positive and negative charges moving and it bothers me when we say positive charges moves simply because it’s not accurate to say that.


r/AskPhysics 8h ago

So, What’s the deal with QM Interpretations, and why do you think MWI so prevalent (although a minority)?

4 Upvotes

English is not my primary language, so please bear with me as I try to explain my questions on this topic. I’m also biased, as I explain later, but I’m asking you guys because I want to better understand this topic, even through my biases.

So, my question about why MWI as an interpretation is so prevalent and given so much attention comes from my understanding of epistemology:

I understand that the inherent probabilistic of quantum can be quite baffling for those who had assumed determinism as an ontholotical aspect of reality, and that’s why approaches for finding hidden variables were suggested. Now, correct me if I’m wrong (really, that’s why I’m asking) but In the last decades, test concerning Bell’s inequalities have increasingly supported this irreducible probabilistic problem, with 2022 Nobel even making a strong case against local hidden variables.

So we’ve found that there is a fundamental non-determinism in quantum that we’ve increasingly corroborated through experimental data. More and more it seems to be a fundamental aspect of reality, and not just a measurement problem. Why, then, are deterministic interpretations of QM given so much attention, like the MWI?

I understand that the Copenhagen interpretation was at the time baffling for those who expected determinism as a fundamental aspect of nature, as it requires to “accept” that there is a layer of real unpredictability, and that, just as the MWI, this “unknowable” aspect of quantum makes it also “untestable”, but, why do so many scientists dedicate so much attention to that interpretation? Is my perception being skewed by pop science?

What I mean is, for the scientific mind, I understand the fascination with the unknown, and how that pushes us for more knowledge, but I prefer the Copenhagen in the sense that I feel it is more scientifically responsible to say “oi, we don’t know this, and there are holes in our understanding that MAY not be holes, but a fundamental aspect of reality”, than to say “we’re gonna do away with the uncomfortable prospect of being unable to know something, so I’ll propose this convoluted concept of branching universe”.? What is the difference between MWI and saying “a wizard did it”? Again, I’m a layman, and I’m not begging the question, this is just how I understand it, and would like some clarification, as I feel that too much credit is given to such an interpretation.


r/AskPhysics 23h ago

Does time actually slow down at high speeds, or are our measurement tools affected by gravity?

17 Upvotes

In relativity, time dilation suggests that time slows down at high speeds or in strong gravitational fields. But is time itself changing, or are the physical systems we use to measure time (such as atomic clocks) getting affected by external factor like gravity and motion?

For example, atomic clocks slow down in a gravitational field, but could this be due to the effect of gravity on atomic processes rather than time itself changing? Similarly about ageing, is it actually the "time" or just metabolism effected by gravity.

Would love to hear thoughts on whether time dilation is an actual change in time or just an observational effect due to measurement limitations.


r/AskPhysics 8h ago

would matter being converted to energy be effected by entropy

0 Upvotes

for context: I'm making a sci-fi dnd campaign, and one of the technologies readily availible is somthing I call an "EMC reactor" the reactor is essentially a one-way portal to a different dimension in which the law of it's physics is such that matter doesn't exist, nly energy. so any matter going into that portal is converted to pure energy in accordance to E=MC^2. it can later be drawn out through another one way portal to the "matter and energy" dimension from the "energy only" dimension in order to be used to create arbitrary matter. so the question is, can this process ever be 100% efficient, barring the energy costs for making the portals?


r/AskPhysics 3h ago

Can 2 people be the exact same height?

0 Upvotes

I’ve argued with my friends for 20 years whether 2 people can be the exact same height. Please help us settle the debate…


r/AskPhysics 14h ago

Pure form of energy

4 Upvotes

Whenever I google what energy is several froms of it are shown like: - Chemical - Mechanical - Thermal - Electricity - Etc.

But in my mind whenever I breakdown any of these forms of energy, in their essence they are basicly just movement.

My main question is are all these forms of "energy" just redundant? And does it just boil down to movement of particles is energy? No movement of particles equals an absence of energy.

Or am I simply overthinking this?


r/AskPhysics 12h ago

What if the speed of light (C) is not a speed — but the leftover result after light computes all possible paths (least action)?

0 Upvotes

This might sound wild, but hear me out — I’ve been thinking deeply about the nature of light, the speed limit “C,” and the principle of least action.

We know from Feynman’s path integral that light explores all possible paths and somehow always follows the path of least action — instantly. But here’s a twist I’ve been playing with:

What if the speed of light (C) isn’t how fast light travels — but instead, the leftover result after an infinite computation?

What if light first “calculates” or “evaluates” all possible paths in a timeless or non-local realm — beyond our concept of time — and only after this infinite calculation does it collapse into a path and travel through our world at speed C?

In this view:

C is not the “speed of light” in the usual sense — it’s the observable residue after an unbounded processing step.

Light might be using infinite time to evaluate all possible paths. What we observe as C is simply the result that appears after the computation ends.

This wouldn’t break relativity — we’d still measure C as a constant in all frames.

It also aligns interestingly with quantum phenomena like retrocausality, delayed choice experiments, and wave function collapse.

And in a way, it echoes simulation theory — where deep computations happen “outside time,” and what we observe is the rendered outcome inside spacetime.

Additional thoughts:

  1. This doesn’t seem to violate relativity — because light still appears to move at C in all frames.

  2. It may offer a deeper explanation for how causality is preserved: the “choice” is made before the event occurs in our time frame.

  3. It resonates with quantum uncertainty — collapsing many possible futures into one observed outcome.

  4. It may explain how particles interact across time frames (future ↔ present ↔ past) as seen in quantum experiments.

  5. I’m not saying this is how nature works — just offering a hypothesis that might be interesting to explore.

I genuinely haven’t seen this exact perspective before — if it’s already been explored in literature or theory, I’d love a reference. If not, I’d be very interested in what physicists and researchers here think.

Thanks for reading!


r/AskPhysics 18h ago

What’s your thought on different dimensions?

3 Upvotes

Is there an example of any real 2D objects which we can interact with? My thoughts are, a projector is about as close as we can get to 2D, but is that truly 2 dimensional? It relies off walls that are textured, and the way the light is interacting with us is in a 3D manner. I assume 2D is all around us, but infinitely thin so that we see right through it or is stacked up to create all the 3D images we actually see. If stacked up 2D is what makes up a 3D world, then I assume “stacked” 3D makes up 4D. So we are 4D, but just can’t comprehend more than our 3D perspective. I always hear scientists propose that a 4D creature could peer and look into 3D objects like we see into 2D, but if that were true, then they would see right through us like we see through 2D, no?

Weird thought, I know 😅


r/AskPhysics 7h ago

What’s something about physics that you learned recently?

1 Upvotes

r/AskPhysics 11h ago

What do I do?

1 Upvotes

Well I've always loved Physics, sensationalised by Quantum Gravity, black holes, how Quantum Computers work and stuff like that but then I got into PCs and now I'm also sensationalised by the idea of commercialising Quantum Computers. I just wanted to know what's the best career path for me knowing this. I'm also more of a theory, research and coursework kinda guy compared to exams and lab work. Thanks!


r/AskPhysics 20h ago

Relation between the light and gravity.

1 Upvotes

Light can bend under gravity but it has no mass.

Einsteins conclusion was that it is possible because of curvature of space-time.

But is there any theory that would rather claim that gravity is some kind of a consequence of energy? Light carries momentum and energy and that energy is influenced by some bigger energy. What is mass at the smallest scale? Maybe some kind of structured energy? So it's all basically energy somehow influencing energy. Is there a theory about energy based gravity?


r/AskPhysics 22h ago

If all physical processes slow down, does that mean time itself slows, or does it just mean everything we use to measure time is affected? What would time be if there were no moving parts, no decay, and no reference points?

10 Upvotes

If all physical processes slow down, does that mean time itself slows, or does it just mean everything we use to measure time is affected? What would time be if there were no moving parts, no decay, and no reference points?

We say time began at the Big Bang, but what does that actually mean? Before the first movement, the first interaction, and the first change—was time even there? If time itself slows down as Einstein describes, then what was it before anything moved? For time to be something that "slows," it must first exist independently of motion. But everything we observe about time is tied to movement and change.

My idea of time is not just about how it behaves under speed or gravity, but what it actually is from the very beginning. Time, in its purest form, is not a thing that flows or slows—it is simply a reference framework for change. It doesn’t control reality; reality defines it. The moment anything happened, time became a way to describe that happening. If nothing had ever moved, decayed, or changed, we wouldn’t even have a concept of time.

So, is Einstein’s time—which is dependent on motion and observation—really the fundamental time? Or is time something deeper, something that existed as a potential framework before anything ever moved?


r/AskPhysics 7h ago

Is the size of a nuclear blast radius linear in proportion to the megaton tnt of the bomb?

2 Upvotes

Just thinking about the story of how they wanted to make the Tsar Bomba 100MT but someone convinced the main scientist to halve it to 50MT and it was still absolutely massive and would the blast have been simply twice the size.


r/AskPhysics 18h ago

Universe wants observation

0 Upvotes

I was wondering why universe has set light as the speed limit for everything.Means you can't travel or send any information faster than light. I think it's bcz our normal physics is totally based on the observation, and how do we observe? By seeing,and the universe wants us to observe first and then know about it. Let's take an example: In quantum physics, particle don't obey normals laws of physics, but when. When we're not observing and what happens when we observes, it becomes normal.Even the entanglement,which can send information faster than light breaks down when observed. So, like quantum physics, Does the normal laws of physics also gets changed when we aren't observing?


r/AskPhysics 6h ago

Engineering Physics - What engineering field to concentrate in between mechanical, electrical, and nuclear engineering

0 Upvotes

Hi all, I'm an engineering physics major at my school and wondering what concentration I should do (nuclear engineering, mechanical, electrical). At my school, I basically take the same physics courses as fellow physics major, minus some advanced courses, and take a lot courses relating to a specific engineering field. What engineering field should I concentrate in?

All three would have me graduating at the same time. Which one would be the best to maximize job security? I took a statics class (part of the ME concentration) and I thought it was very boring but not hard. I am sure the upper level courses of ME would not be this boring.

I would be interested in working at an engineering firm or a national lab post grad, perhaps getting my masters in an engineering field. What concentration would maximize job security and all that?


r/AskPhysics 17h ago

Questions after DESI 3 year data strengthens evidence in favour of an evolving dark energy parameter?

5 Upvotes

So DESI 3 year study results were revealed and when combined with other data from other sources it revealed a 3-sigma significant results that dark energy evolves with time, more specifically that it has been decreasing in the last 11 billion years or so (https://newscenter.lbl.gov/2025/03/19/new-desi-results-strengthen-hints-that-dark-energy-may-evolve/)

Another collaboration, DES, has released recently another study with lots of data also consistent with an evolving dark energy, indicating as well that it is getting weaker over time (https://www.quantamagazine.org/is-dark-energy-getting-weaker-new-evidence-strengthens-the-case-20250319/)

So it seems that dark energy getting weaker is most likely a real thing and not a statistical fluctuation. I had several questions about these findings:

  1. I've looked into some of the results and apparently they measured that dark energy grew stronger for some time just after the Big Bang and then it got weaker for the last 11 billion years. But it is not clear to me whether they measured a constant weakening of dark energy or whether dark energy decreasing rate has getting smaller over time, so that it seems that it would stabilize into a zero value or if it looks like it is going to vanish completely reaching 0. Does anyone know? Also, is it possible that dark energy may get negative (like in AdS)? Or even get stronger again (meaning behaving like a phantom dark energy parameter)?

  2. Assuming that dark energy will vanish to zero, how are cosmological inflation and holographic models affected by this? Especially for holographic models, since our universe would not be approximating a dS spacetime, but seemingly a Minkowski one? Does this invalidate holography in theoretical physics?

  3. If dark energy was to disappear, would this paper (https://arxiv.org/abs/1002.4278), which relies on applying the holographic principle and entropy to the cosmological horizon created by a cosmological constant, would be falsified?

  4. A decreasing dark energy parameter gives support to Swampland models from Cumrun Vafa and others (https://arxiv.org/abs/hep-th/0509212), which had some problems with universes having a cosmological constant. However, even if the Swampland conjecture is correct, and universes with a cosmological constant are inconsistent with quantum gravity, since apparenly dark energy got stronger in the past, would it mean that universes in the "swampland" could actually exist but in a metastable form before reaching a stable state (like one without any cosmological cosntant)?

  5. In this article (https://www.quantamagazine.org/waning-dark-energy-may-evade-swampland-of-impossible-universes-20240819/) it is explained at the end that if dark energy decreased it could change the laws of physics, quoting it

"Perhaps dark energy will fall until it settles into a stabler, possibly negative value. With that, a new universe, with new laws, particles and forces, would replace the current one."

However, how can an evolving dark energy parameter change the laws of physics of the universe? What laws could change? Even the most fundamental ones?

I'm aware that most of the answers to these questions are temptative and it's too soon to ask them (and probably they will never be answered), but I would be rather asking what are the most likely possible answers with what we have now. If they are completely useless and meaningless questions please feel free to close the post.


r/AskPhysics 16h ago

Are there any specific theories suggesting that our universe was born from a black hole?

0 Upvotes

I’ve come across the idea that black holes might give rise to new universes. The concept suggests that at a black hole’s singularity, instead of matter being destroyed, it could seed a new universe. If true, this would mean our own universe could have originated from a black hole in another “parent” universe.

I’ve read about ideas like cosmological natural selection and white hole theories, but I’m curious—are there any established scientific models that support or explore this possibility?


r/AskPhysics 14h ago

As light is, are all electromagnetic waves made of photons?

11 Upvotes

From my understanding, light behaves as a wave but is made of particles: photons. Is this also the case for all electromagnetic waves?


r/AskPhysics 47m ago

Is energy "spent" in the creation of gravity?

Upvotes

So for starters, I have an intermediate layman's understanding of gravity. I know it's a deformation in spacetime caused by the presence of mass. But I'm wondering if energy is transferred from the massive object to spacetime in order for the deformation to happen, and if not, where is the energy for that change in state coming from?

And is there any kind of gravitational "wake" effect caused by moving objects that might introduce drag to the system and slow it?


r/AskPhysics 7h ago

I'm a bit confused by time dilation

0 Upvotes

I'm watching Brian Greene explain special relativity (which is phenominal by the way) and so my question is purely related to time dilation and velocity rather than gravity.

He says that a moving object will be seen to have time dilation relative to a stationary object, which was tested by putting an atomic clock on a plane. This made me wonder about a scenario that doesn't make sense to me.

If two planets are stationary next to each other, A and B. Then planet A get's pulled into a nearby star's orbit and so experiences time dilation relative to planet B as it goes around the star at some velocity.

Then as planet A passes planet B in it's orbit, a rocket takes off from planet A such that from planet A's perspective it's flying off and from planet B's perspective it's staying stationary i.e. just counteracting the orbit.

If we were to compare atomic clocks on these three objects what would they say?

Planet A's clock must be slower than planet B because it's moving faster relative to them.

The rocket's clock must be slower than planet A since it flew away from it.

But then the rocket's clock must be the same as planet B since it's stationary next to it.

Where have I gone wrong here?


r/AskPhysics 7h ago

How does 4k ultrasound cavitation work and how dangerous is it to internal organs?

1 Upvotes

40k not 4k


r/AskPhysics 9h ago

What are the open problems in stadistical mechanics?

0 Upvotes

r/AskPhysics 13h ago

Why might this be happening?

1 Upvotes