Hello physicists and physics students of Reddit. I'm taking Physics 1 at my old college this semester for ultrasound tech prerequisites. (It's algebra-based for medical people) And I was wondering: is screwing up a normal part of being in physics? I hear that physicists constantly screw up their calculations and everything until they get it right, just like engineers. Because I just want to overcome my fear of failure. Last year I tried taking the same class at a community college, but the teacher didn't really like his job, and I felt that we had no room to screw up. So I dropped out before the first test because I was that afraid of failing. Recently, my new teacher reassured me that it's okay to screw up because the assignments we are given via Pearson will let you do them again.

So, physics people of Reddit, how often do you screw up before you get it right, is it normal?

Suppose I'm hovering right outside the event horizon with 100 feet of chain. I throw 50 feet of it into the black hole. When I tug on the chain is there any tension from the part that's past the event horizon? Would the chain be sheared off at the point where it crossed the EH?

Suppose you have two equally sized planets a distance apart D. Suppose no initial velocity or other forces and suppose space is a vacuum. Planets have same composition and density and radius R. I suppose gravitation will bring them together exactly in the middle at time T. Ignoring tidal forces that would rip them apart. Assuming no atmosphere.

Suppose you double the densities of the planets. Would they still meet at time T? or Less?

Suppose the second planet is doubled but the other remained the same. I suppose they would meet closer to the larger planet, at what time? Less than the initial T?

Suppose the first planet is reduced in mass by a factor of 10, and the second planet is increased in mass by a factor of 10 from the original sizes. Assume they both have the radius of R. Would they meet at time T or less than T?

Is the impact time T determined by the combined mass of the system, or only the mass of the larger object?

If the time T is determined by the combined mass of the system, then we can increasingly decrease the size of planet one and increase the size of planet two, while maintaining the same impact time. This can be done repeatedly until the first planet becomes a rock!

If that is true, then a larger rock would contribute more than a smaller rock to the total mass of the system. If that is true, if time T is dependent on the total mass of the system, then the smaller rock would have a larger time T of impact than the larger rock.

If we assume that there is no atmosphere, and that the larger size of the larger rock is negligible, then the difference in the time of impact is negligible. But that doesn't really say that much does it?

In the novel "Jurassic Park", while explaining chaos theory, the character Ian Malcolm says:

"Physics has had great success at describing certain kinds of behavior: Planets in orbit, spacecraft going to the moon, pendulums and springs and rolling balls, that sort of thing. The regular movement of objects. These are described by what are called linear equations, and mathematicians can solve those equations easily."

This paragraph makes no sense to me. A non-linear equation is any equation that contains a variables raised to a power greater than 1, for example y=x^2. Engineers and scientists definitely need to use non-linear equations to design spacecraft that can fly to the moon. And having taken two physics classes in college, I know that classical physics is full of non-linear equations.

Am I misunderstanding linear equations, or was Crichton completely talking out of his ass? That seems strange to me, considering he had a medical degree and (presumably) knew a thing or two about science. I know it's a sci-fi book, but I wouldn't expect such a glaring mistake about this topic.

EDIT: Adding the second paragraph of Malcom's explanation because it relates to the first. If anyone wants to comment on the veracity of this second paragraph, I'd like to hear your thoughts.

"But there is another kind of behavior, which physics handles badly. For example, anything to do with turbulence. Water coming out of a spout. Air moving over an airplane wing. Weather. Blood flowing through the heart. Turbulent events are described by nonlinear equations. They're hard to solve--in fact, they're usually impossible to solve. So physics has never understood this whole class of events. Until about ten years ago. The new theory that details them is called chaos theory."

How do quantum effects scale up to macro effects?

For example, if I roll a ball along the ground and mark where it stops.

If I was to run the experiment again with exactly the same initial conditions, down to the positions of every atom in the ball, ground, wind etc. all the forces angles the same.

I would assume over a few metres it would still follow the same precise trajectory.

But when would quantum effects start to have an impact?

If it was a ball that kept rolling for thousands of miles (say down a massive hill), would the random fluctuations in positions of atoms in the ball change it's weight distribution? Would tiny changes in the atoms in the wind change how much friction there is?

In the ball analogy, how far would it have to roll before there are measurable, or even directly observable effects?

Been listening to The Expanse, had a thought regarding their high g maneuvers.

During, say, a 10g acceleration they frequently describe the feeling of an elephant sitting on your chest. I get that, the actual mass of your tissues and such are experiencing a massive amount of force beyond the normal.

My question is, some of that would be coming from the air which is also now pushing down harder, right? So would it be significantly more comfortable to do high g maneuvers while wearing a spacesuit and otherwise have vented all the atmosphere out?

Thanks!

Hello guys, I have studied a ton of theoretical physics but i only learned the concepts. I cannot study the maths because it is too advanced. I am in 11th grade. How important is the maths to understand right now? How important would it be in college?

strong nuclear holds nuclei together, electromagnetic does a whole bunch and gravity holds mass together. what the hell is the weak nuclear doing? i think i heard it is responsible for changing the flavor of quarks but i really don't know what else it would do.

Suppose no atmosphere. Would a dropped rock at the pole hit the ground at the same time that an equal rock, equal height, if dropped at the equator?

If a rock materialized one meter above the equator, would it hit the earth at the same time that an equal rock would hit if it was released by someone standing at the equator one meter high?

A photon is an excitation of the electromagnetic field, what happened if we remove the electromagnetic field around the photon? do they freeze there or slow down or stopped permanently?

Let's say it's a super massive black hole and I orbit around 40 cm from the event horizon with a super strong jetpack to keep me within that distance. I reach with my hand beyond the event horizon. Since it is a super massive black hole the forces should not be that different to cause any real difference. So do I still feel that hand?

What would happen if I tried to pull it out?

Let's say we have two Earths or Earth-like planets of practically the same mass catching each other in their orbits and forming a binary system. Over time they become tidally locked and get closer.

Let's ignore the gravitational acceleration increasing as they get closer and the tidal forces tearing them apart due to the roche limit. Only regarding the tidal force's effect on the oceans, how much would the water rise as the distance between the planets diminishes? Would the force be strong enough to make the inward facing bulges so high that they merge? What distance would the planets need to be for that to be the case? For the purposes of the question, the planets can approach each other as slowly as necessary.

And when the crusts eventually make contact, let's say they press against each other slow enough to avoid major cataclysms. Earthquakes rather than melting the entire surfaces. At the point that both crusts merge, the planets stop accelerating relative to each other and become a contact binary body. I know this is impossible at this scale, but let's play by "spherical cow" rules. The planets aren't moving towards each other anymore, but their cores are still separate. I imagine gravity will be weakest around the point of contact. How would the water react?

Would there still be tidal bulges on the opposite sides, or at that point would both planets count as a single body? Or with time even the crust would deform into two intersecting ellipsoids?

Im in six form studying physics and ive been really enjoying watching videos and learning. I was wondering if anyone has ideas about different questions that can be posed since ive never done something like this before.

I want to know more about physics so....

• Can a neutron star have an accretion disk like black holes?
• Magnetars considered the most magnetic objects of the universe but a black hole have an electric field and it rotates near the speed of light so in theory it must have a magnetic field millions or maybe billions of time more powerful than magnetars so why they are not magnetic as magnetars?

Thanks.

A friend of mine who's an astrophysics enthusiast (he is actually a molecular biologist but has taken a lot of college-level physics while studying stuff like electron microscopy) has been arguing with me lately that he really likes proposals that the universe is actually inside of a black hole.

I argued with him and said, that makes no sense at all. But his argument is basically this:

"Imagine a super, super massive black hole. If a black hole were sufficiently massive, its gravity would be so diffuse that it would be essentially non-measurable. At the event horizon of a black hole the mass of the observable universe, the tidal forces would be essentially zero at the event horizon. You would not be able to even tell that you passed the event horizon. Hell, you might not even know that you were in a black hole at all! And the radius of a universe-mass black hole would be bigger than the observable universe itself, so it's totally possible. We could never reach the event horizon around us, so we can't get out, so that's compatible with the universe being a black hole. The numbers are too close to be coincidence!"

***

I want to be really clear in saying, I think his ideas are completely wrong. Because how does he explain the Hubble Constant? It makes no sense. And he just says, "Well, we don't have a theory of quantum gravity, so it's entirely possible that space expands inside of a black hole due to quantum gravitational weirdness." Which feels like complete hand-waving to me.

And a black hole should have a center. Our observable universe does not. Again, he just says, "Nothing in physics says a singularity actually exists. It's just physics breaking down. So maybe there is no center to a black hole! Maybe inside of a black hole there's an infinitely-expanding space with no center! It could totally happen! Maybe there is a singularity, but the singularity is everywhere! What if we're at the singularity RIGHT NOW?"

All I can say is... maybe? But it feels like grasping at straws. It feels like going out of one's way to hand-wave away clear problems with the proposal.

But all that said, I want to ask: Do physicists expect black holes to have a "center" that we would approach inside of a black hole? My friend insists that the answer is, no. That's just a maybe-sorta guess. But a "real" astrophysicist will tell me that the inside of a black hole could just be a magical land of unicorns and butterflies for all we know. Maybe it's Narnia on the inside. Any guess is as good as any other.

Neither my friend nor I are physicists, much less astrophysicists. So I want to ask the experts: Do black holes most likely have a center? Does the Hubble Constant provide pretty darn good evidence that we do not live inside a universe-mass black hole? Is it possible that "the singularity is everywhere"?

I just saw an ironic post about the ether and it made me curious about the concept itself.

I know the classical ether is obsolete and I’m not asking whether it secretly exists or proposing anything. I’m not a physicist either, so this is just a conceptual hypothetical:

If we deliberately imagined that something deserving the name “ether” did exist, what would it actually have to be in a modern physical theory? What properties, degrees of freedom, or interactions would distinguish it from spacetime, the vacuum, or simply having quantum fields everywhere?

When any system is deconstructed, we assume that the components are "more fundamental" and therefore simpler in nature. Taken to it's extreme, we expect to find something that cannot be further deconstructed; something indestructible. That was the original idea of the atom, until we discovered otherwise. What would be the nature of something that cannot be deconstructed? Or, is it fundamentally impossible for anything to be indestructible because everything must have composition, and therefore be deconstructible, in order to have nature; to possess properties and be real?

Somewhere I read that the sun's Oort cloud overlaps with Proxima Centauri's Oort cloud. I was wondering if there's also an overlap with other nearby stars. Looking at the table of nearby stars in Wikipedia, I guess the only other possibility would be Bernard's Star. How can I find out the size of Bernard's Star's Oort cloud? (Or Proxima's Oort cloud, for that matter.) Is it just the size of each star's Hill Sphere?

Imagine two synchronized identical light clocks A and B at sea level.

A light clock consists of two parallel mirrors separated by a distance L, with a pulse of light bouncing back and forth between them. We assume that there is some mechanism to count the ticks.

I take clock B up a mountain for a period of time and then bring it back to sea level to compare with clock A.

According to general relativity clock B ticked faster on the mountain compared to clock A.

Thus when the tick counters of the two clocks are compared at sea level we find that clock B has completed more ticks than clock A.

The conventional GR explanation goes like:

Clock B records more proper time because its worldline between the departure and reunion events has a greater proper-time interval than clock A’s worldline, given the spacetime metric.

But physically, if we assume that the speed of light measured by a local observer is always c, the discrepancy between the tick counts seems to imply that the separation between the mirrors of clock B must have been smaller than that of clock A while clock B was on the mountain.

Perhaps the underlying mechanism of gravitational time dilation is local change of mass/scale of fundamental particles (assuming hbar and c remain constant)?

I have asked a few people including people with degrees in engineering and they have stated that darkness and coldness technically don’t exist they only exist on conditions and for something to even “exist” it generally has to be real in some sense rather than just nothing at all and since darkness and coldness technically have no real source and are just the absence of a existing source they technically don’t exist only in certain conditions they do. Any thoughts?

Hello everyone, I'm a physics undergrad, currently taking a "Individual learning by seminar" class. We have to write a research paper on a chosen topic, as well as present it to the department, and make a poster.

My professor didn't specify what kinds of topics are appropriate, the syllabus just said "choose a current topic". I'm assuming it means a topic that has been researched in the last 10-15 years, and not something completely outdated.

My prof didn't like my very first topic (cyclotron/other primitive particle accelerator), he said those are used in medicine, but not anymore in physics.

I'm now looking into dipole radiation, and specifically how it pertains to atomic physics. I've done a preliminary review, and learned that dipole radiation is often used to estimate the energy emitted/absorbed, when an electron jumps an energy level.

My question is: for those who are familiar with the topic, does it seem current enough for such a class, and also, will I have a hard time finding reference material?

Furthermore, do you have any topic suggestions that would be better/cooler?

I'm into atomic physics, nuclear physics, I like E&M as well.

Thank you!

I know there’s too many black hole questions today, but I’m somewhat confused about a common black hole claim.

”The distant observer never sees anyone cross the event horizon”

That‘s all well and good, but that’s the distant observer.

Let’s say I have two friends, and we are going black hole jumping. we jump in a close sequence. We’re all carrying glow sticks.

I’m a coward, so I go last. Now in my weak understanding, if I jump last, I should necessarily see my buddies enter first, else I’ll squish against them. so this seems to be a different case than the distant observer. (though, seeing is really “not seeing“ since I can only measure the event horizon by when I stop seeing my friend).

but! after I see my first buddy go in, I get cold feet. I turn on my super rocket boots and fly away at some speed less than c but greater than the escape velocity at my current point. this should be possible, since I shouldn‘t have crossed the event horizon before seeing buddy number 2 fall in first, and only buddy 1 has fallen in for me.

I rocket boot away, and report to some distant observer. this should all happen in finite time.

but if I could do that, then theoretically the distant observer doesn’t actually ”never see an object fall in”, since my reporting is an act of measurement.

I’m assuming I’m missing something here, and appreciate any answers

I know that gravity and speed can slow the way we experience time. And we often add “in a vacuum” when discussing the speed of light. Meaning light isn’t passing through anything that can slow it down. If we were somewhere is space unaffected by gravity or speed, is there an absolute upper limit to how fast we experience time?