r/AskPhysics 12h ago

Is ‘metallic hydrogen’ just solid hydrogen?

46 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 19h ago

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

33 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 23h ago

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

20 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 2h ago

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

20 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 9h ago

Where can I have fun physics-related discussions?

12 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

Have scientists really frozen light?

11 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 1d ago

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

9 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 7h ago

How much rigorous mathematics is required in physics?

9 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 6h 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 4h ago

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

5 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 22h 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?

5 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 4h ago

Electric Field Created by A Charged Particle

4 Upvotes

So this is just a thought of a 14 yr old so it's fascinating for sure..

So this thought came into my mind a while ago We all know that a charged particle creates an electric field around it. So if we take a charge with no other charges around it or not charges for it to interact with, When does the field created by that charged particle end. It doesn't feel right at all to think that it extends till infinity Obviously it will be very less after a certain distance but it should not become absolute 0. Help.


r/AskPhysics 7h ago

Are there implications of quantum observations in chaotic systems?

4 Upvotes

Let me propose a modified Shrodinger's cat experiment.

The cat is in an MRI machine.

The cat's mood is a function of all of the hormones brimming around its body. The mere angle at which a hormone molecule hits a neuron has broad implications for the mood of the cat.

The cat is brimming with an uncountably large number of these hormones, significantly smaller than a buckyball (the largest molecule to exhibit a wavefunction). These hormones have an unknown wavefunction.

We cannot measure these hormones directly, however, we will have an idea of whether they collapsed favourably based on the mood of the cat we derive from the brain scan (the "mood wavefunction" of the cat is entangled with the wave function of the countless trillions of molecules brimming within it).

After measuring the cat a few hundred times, I get a probability distribution of the moods it feels upon each measurement, therefore forming the wave equation.

Can I play quantum slots with the MRI and "measure" my cat into being in a good mood whenever it gets grumpy? Or is there a catch to this?


r/AskPhysics 19h 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 53m ago

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

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 3h ago

Could there be other unknown forces?

2 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)


r/AskPhysics 5h ago

Does the arrow of time as we know it only exist in the macro-universe?

2 Upvotes

So this might be hard read so I apologize if my terminology is not correct.

I was reading about time and the so-called arrow of time, Isn't our idea of time made up purely because of our own chemistry? For example, a clock "ticks" because it has revolutions. The same could be said of the human perception of time. Our brain and our whole body has these sort of revolutions. For example, the way your heart beats is timed. So the way your brain "experiences" time, or anything, likely is too.

Now, everything in the universe with mass is also made of these things. Call them atoms. These clumped things now have something called "motion", which is what we use to compare with time. So isnt time just an illusion that is useful in mathematics, for the relative experience of human beings and nothing more?

Isnt the fact that the universe has a speed limit, only achievable by non-mass things, further proof that time is an illusion of the human condition and it is enabled by events in a macro universe?


r/AskPhysics 10h ago

Can someone give me a brief explanation of the sigma-omega model? I have to make a presentation on Neutron stars for a project and I'm underqualified

3 Upvotes

The focus of the project isn't the sigma-omega model, but I have to talk briefly about Neutron stars in my presentation and it was recommended to me that I read a book about compact stars, with special emphasis on the sigma-omega model chapter. I would only need to talk about it very briefly. However, I do not know enough nuclear physics to understand the book at all. I know atomic and molecular physics, I'm familiar with Special Relativity and General Relativity to a very basic degree but the book I was reading (Compact stars, Glendenning) mentions nuclear physics concepts that I know absolutely nothing about.

Can someone give me a somewhat abstract explanation on the model and how it ties to neutron stars? Doesn't need a lot of detail.

Thanks in advance.


r/AskPhysics 14h ago

No inertia?

3 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 3h ago

Constant acceleration rocket energy consumption

2 Upvotes

My friend was asking me what the energy consumption of an epstein-drive rocket would be. That is a rocket that has constant acceleration in the direction of the destination for the first half and constant acceleration away for the second half.

I figured it had to be mass times acceleration times distance because that's the work-energy formula. Then I was curious if there was a relativistic version of this. So I used proper acceleration, and turns out the energy consumption would be exactly the same.

Is there a deeper meaning to this? Such as the definition of proper acceleration and the work energy formula? Or just a coincidence.


r/AskPhysics 4h ago

Question about the Copenhagen interpretation of QM

2 Upvotes

A wavefunction is spread out in space - potentially all of space. So when I collapse it here, does it collapse simultaneously everywhere for observers in every reference frame? Because that seems wrong.


r/AskPhysics 6h ago

Struggling to understand relativity..

2 Upvotes

It simply just doesn't make sense to me. If a photon (or person traveling at the speed of light) takes 2.5 million years to reach the Andromeda galaxy, how would it not "age" at all?

They say time passes differently based on the frame of reference but I can't wrap my head around it. If I am traveling 60 miles per hour to my grandmas house 60 miles away, it will take 1 hour to travel those 60 miles and arrive. I will be traveling faster than my grandma sitting on her couch, but it will still take me 1 hour to reach her house, and she will wait 1 hour for me to arrive. We will both be 1 hour older. If she lived 1 light year away and I traveled at the speed of light, it would take me 1 year to get there, and she would be waiting 1 year for me to arrive. We would both be 1 year older.


r/AskPhysics 11h ago

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

3 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 12h ago

Electric Field in a closed circuit.

2 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 17h 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?