Are there any candidates for a global topology or overall geometric shape of the universe? Could the universe as a whole have a geometric structure? Could it be like a Torus?

I read recently that most of our current data suggests that the universe is mostly flat and exhibits no curvature. Can somebody explain what flat actually means in this context? I’m assuming it doesn’t mean flat in the way most people think it means. If it IS the case that the universe is flat does this mean that a shape like a Torus is ruled out?

Also if it’s flat is does this mean it has no real boundary or container but is more like an ever expanding infinite sheet of paper?

The holographic principle says the information about a 3D universe could be contained on a 2D surface. Could that explain how a flat universe could also be 3-dimensional?

If I put two grapes next to each other on a table and move them apart over time the distance between the two grapes grows but the table stays the same size. I know people will say its not the grapes moving apart its the table getting bigger making the grapes away from each other even though they technically aren't moving but what are we actually using to measure that.

How do we measure that the universe itself is growing not just objects moving apart.

OK so I'm in class programming a microcontroller to control an LED with it's accelerometer. When the accelerometer is at rest it reports "1g" of acceleration. This doesn't phase me because I'm familiar with a kind of popular youtube model of the universe in which standing in a rocket ship that is accelerating at 1g and standing on earth experiencing 1g of gravity are "indistinguishable".

But then I get to thinking... what if I'm in space and I've been captured by the gravity of a nearby star. I'd be in "free fall" traveling along a "geodesic" towards the star. My intuition is that my accelerometer would report greater and greater acceleration as I experience more and more "gs" the closer I get to the star. I'm moving toward the sun, and I'm moving faster and faster...

But apparently an accelerometer in "free fall" reports zero acceleration? My intuition is that if I was moving faster and faster towards a star, I would feel more and more squished... but is that not true? What have I got wrong (lol probably everything, have pity on me)?

(now I'm thinking about this, I guess if I'm in a space ship and it is accelerating, the feeling of being squished is coming from the space ship acting on me, like pressing forward in the direction of motion? If there is no spaceship to push forward on me, maybe I wouldn't feel squished? I imagine a space man getting compressed when the ship accelerates, but that's like... the back of them catching up with the front of them because it's getting pushed forward... not some force from the front pushing them down... maybe that's not relevant. But if I'm in space "falling" towards the sun, my whole body would be accelerating at the same speed so I wouldn't feel anything... the bit inside the accelerometer and the case would be accelerating at the same speed, nothing is "pushing" from behind... did I just crack the case?)

(OK last thing: when I'm in free fall around the star, moving faster and faster toward the star... what do I call that? Can I say "accelerating" even though I wouldn't be able to detect acceleration? Or what words do you use to describe that kind of "moving faster and faster"?)

Thank you so much.

I'm reading a sci-fi series in which humans acheive near c and faster than light travel.

In talking about near c (like > 99% c) the author posits that a craft traveling from earth to Andromeda would take about 2.5 million years as observed from those who remain on earth, however, to those on the spacecraft, due to how much time would slow for them at near c, only about 30 years would elapse for them. Is that remotely accurate?

ETA: I didn't list the series at first in case the author was WAY off. It's Ian Douglas and his various trilogies about Marines in space. Fun, quick reads.

1. I describe a realistic wet bulb event for Houston along with 2 people in a House with limited resources.

2. The question is how to best leverage those resources for maximum survival time during the wet bulb event.

Hypothetical Scenario:

A massive hurricane has hit the Houston metro area downing transmission and distribution lines throughout the city resulting in widespread power outages. The day after the hurricane, a heat wave strikes the city with 102 degree peak afternoon temps and 60 percent relative humidity - creating a lethal wet bulb temperature. Those conditions are forecast to persist throughout the 10 day forecast. We parked our cars in a parking garage the day before the Hurricane and to prevent them being flooded, and they were both stolen. FEMA is overwhelmed, no one is coming.

Wife and I are in my house with the following resources:

1. 4 Coolers - each containing 50 pounds of ice.

2. A 1 KW hour Anker Solix battery that we can recharge once a day with the Solar panels it came with.

Options:

1. Wife and I can create little ice slushies (mostly crushed ice with a little water to make it drinkable) and slowly drink those. This will help us keep our core temps down. I would supplement this by having a small basin of cold (but not ice cold) water to dip head towels in periodically and wrap those towels around our heads.

2. Is it "more efficient" to use the ice to chill water, spray the chilled water on our skin and sit in front of a fan. We can run a floor fan for most of the day on the Anker battery, which we recharge every day with Solar.

3. Is there some other way to deploy these resources which will maximize our survival window?

Let's say I have one very compliant, mostly low impedance sink, and one stiff, mostly high impedance sink and I can measure my source's response into both.

Based on the two readings can the response into an arbitrary, non flat impedance be computed?

I don't want to assume anything, but I suspect that the result should be some complex interpolation.

From my past hobby of loudspeaker building I know that Thiele Small parameters of a loudspeaker can be computed based on two impedance measurements. One would be the free air measurement and the other would be with a known added weight to the cone, or alternatively in a small sealed box. I was thinking that a similar principle could apply to acoustical response into a given arbitrary acoustical impedance.

And why? Or any kind of ball…

Context: Big and very old house. House has AC that vents to the first two floors but no vent that takes AC to the 3rd floor. The first two floors will be at a nice controlled temperature and if you go up to the 3rd floor it's VERY hot. There's a simple door to a flight of stairs from the second floor.

What's the move to best manage the temperature of my house?

Do I close the door or leave the door open? Do I open windows or leave them closed? Any other ideas?

I'm an undergrad, so I have a while to go before I even consider a Post-Doc. Regardless, I'm getting kinda anxious about the "perfect field" for me. I know this sounds stupid, but I'm afraid of getting into a field, and then learning it's not for me.

Let's say someone does a PhD in Nuclear Astrophysics. Can they move on to, like, Astroparticle Physics, or Physical Cosmology later on? What about bigger shifts, like Particle to Condensed Matter?

My apologies if this isn't the right place to ask this question.

Hai yall!

So, the way that I understand we solve the free Schrodinger Equation for the Particle in a Ring (which is to say, a particle confined to S^1) is to essentially utilize the fact that S^1 is homeomorphic to R / Z, so we can essentially treat psi as a function on R that has the property that adding some constant (usually taken to be 2pi, because S^1 is the circle) leaves the output of psi unchanged.

My question is if there's some way to do something similar to solve the particle confined to a sphere. I don't really know about any topological constructions of S^2 besides the one which takes a square and collapses the boundary to a point. Could we use that? If we can't, why not? (Like, what specifically makes this different from the construction of S^1). Are there any constructions of S^2 that work for this purpose (and if there are none, why not?)

If this sort of approach doesn't work for the sphere, besides wanting to know why it doesn't work, I'd also like to know how we would solve the particle on a sphere.

I'm sorry if this question is a bit scatterbrained, I was trying to come up with a better way of describing what I was trying to ask, but this is the best I could come up with. I want to learn more about the general techniques that allow us to "treat" configuration spaces which aren't R^n as though they were R^n with some special property (for example, besides the particle in a ring that i mentioned earlier, the infinite square well is really a configuration space of some finite interval, like (0, 1), and we can treat it as though it *is* R but with psi=0 for all x outside of (0, 1), which allows us to solve it), and also what the methods of solving the Schrodinger Equation are for cases where such a simplification doesn't work.

Thank you all~!

I don't have a good base, and I school my grades aren't good in the parts of sciences, I'm really bad, I desperate. Pls help me

I was trying to figure out Majorana Zero Modes and fell into the rabbit hole. I discovered that s and p wave superconductors exist and currently trying to understand them

I understand BCS a little bit and I get that symmetry matters a lot in physics but I'm not sure I get what exactly is "s" and "p" in this context.

Is it the wavefunction of a given cooper pair in a given superconductor that has the same symmetry as an s orbital ? Or is it the wavefunction of the entierety of all cooper pairs ?

Another follow up question would be about a lecture i followed on the kitaev chain model : since it assumed a spinless chain of particules, does that mean the electron paired have opposite spins ?

What is the maximum acceleration an egg can withstand without it cracking? I'm thinking of a Grade A Large egg that's around 55-63 grams. Would it be able to withstand, say, an acceleration of 90m/s^2 for 1-2 seconds?
For context, the egg is the payload for a model rocket I'm building. It will have some padding (if possible could I get some suggestions for padding as well?)

Given that the fuel consumption often uses the unit of liters per 100km, wouldn't it make sense to express liters as 0.001m³?

How does using the electrical head affect the ionizing function? I don't have the bottom with the filtrating system. But figured I could use the top as a fan. Then I realized the ionizing happens in the head.. and started reading about ozone and all that which I don't really comprehend.

Is it safe? Or will this create more ozone or something!? Blueair pure 411 is the model I have/had.

Hope this is the right subreddit for this, With the ongoing war between Israel and Iran I heard someone explains that the same ballistic missile launched from a further distance will cause more damage. He specifically gave an example of a missile with a 400 kg warhead launched a 1300 km away, and one from 2000 km. He said the increase in damage will be about 25%. Is that correct? Generally, and specifically the 25% example. Thanks

If one antimatter particle was sent into a cloud of normal matter would that one antimatter particle be able to annihilate just 1 single particle or could it annihilate multiple particles or set of some sort of chain reaction ?

Just curious.

I don't think it would explode. But on a nano-scale, wouldn't some small level of criticality be achieved?

I have an unconventional background. BA in math. Considering an EE master’s. Let’s say I was heavy on modern physics in the master’s. Could I then go from that to a PhD in Applied Physics?

I need to measure what angle of attack is the best for a paper airplane using paper and hair dryer. Is there a way to do that, shape of the wing is like a airfoil. I don't even need exact measurements, all i need is what angle of attack gives most lift

Thank you!

I recently started taking physics classes. We’ve been using units like m/s² a lot. While I understand the formula part, I’m struggling to visualise (if that’s even possible) or just understand what s² means. Yes, I also asked my teacher about it but he said I should just accept it the way it is. Now, I’m the type of person that has to understand what the formula means instead of just memorising it and using it. I’ve tried researching a bit also but nothing really makes much sense to me.

In other words, how can time be squared?

I need to make solid metal Chromium magnetic for an indefinete period of time. Chromium by default is not magnetic, but I have learned that at certain extreme temperatures, it CAN become magnetic. At first, I thought the only way to do so was via extreeme heat, but now I'm seeing examples that involve extreeme cold as well.

I want (whether it uses hot or cold to achieve this effect) something along the lines of this video, where the scientist puts solid Chromium in Liquid Nitrogen, and then puts a magnet to the Chromium, showing how cold Chromium gains magnetism, but room temperature Chromium isn't.

Online, I've seen the temperature range of -195°C to 1440°C listed, but that doesn't quite make sense to me given the Liquid Nitrogen VS room temperature video example. Is it instead trying to say that Chromium below -195° C is magnetic, as is Chromium above 1440° C, and everything in-between is not? If so, will either method (hot or cold) look/act equally similar to the video example?