AskPhysics

In The Two Towers, the elf Legolas, at a distance of five leagues, observed once, “there are one hundred and five [riders on horses]. Yellow is their hair, and bright are their spears. Their leader is very tall.” In 2014, a viral video made the claim that this was impossible, based on the equation θ≈1.22λ/d, where θ is the angular size of the Airy disk produced by a point source of light, λ is wavelength, and d is the diameter of the pupil. My idea is that, in a material with a high refractive index, λ would be proportionally less than it is in air, resulting in a smaller θ, and with it an image with better resolution.

(This post’s image and alt text are not my work; Wikipedia user Inductiveload released them into the public domain.)

cross-posted from: https://lemmy.blahaj.zone/post/27093935

Are these three statements true:

(1) We can observe where A hits (thereby seeing A as a particle instead of a wave) before B’s path determines the availability of information?

(2) Measuring where A hits, (even if done with thousands of previous data points of A sorted by B hits showing the interference patterns) has no predictive power over whether B’s whichpath information will be erased or not?

(3) Whether or not B’s whichpath information was erased, has predictive power over where A landed?

Whenever I leave sugar in hot water, it always form a distinct transparent layer from the water above. After I stir it, the remaining sugar will form a less distinct layer. Why don't the layers diffuse onto eachother? Can anyone explain this?

There are the 3 considered outcomes for the universe - continued expansion, reaching a static astrophysical plane or gravitational collapse. No matter the outcome, if there is a standing wave the length (why would you have 1.5 times or anything other than 1 !?) Then under the expansion, statis and contraction scenarios, only one of these would ever reach stasis, all other scenarios have a standing wave in flux.

In ATR FTIR (attenuated total reflectance Fourier transform infra-red spectroscopy) evanescent waves penetrate outside the medium to complete the Quantisation rule. Would the same occur if we did try produce a 1.2 times wave?

Let's suppose we have a wish granting genie that gives us a working Alcubierre drive. The drive is turned on and the bubble is staying stationary to our frame of reference (so, it's turned on on our imaginary helipad and it's just sitting there). What could an outside observer expect to see when they look at the bubble? I.e. would light get redshifted or distorted, since it has to pass through space that's expanding faster than the surrounding space? If I shine a laser pointer directly at the bubble, does it lens around the bubble and stroke the far wall, or will it pass through and strike what's inside? Further, could one expect any ill effects from approaching or passing through the bubble, or would that even be possible? Would an Alcubierre drive in motion create a gravitational wave or something very much like it, since it works by distorting space?

Couldn't the camera sensor be turned on and off at will?

Edit: Thank you for your answers everybody!

If we look into a far off distance at an object travelling towards Earth, shouldn't we be able to see both the light from the object at some time t plus the light at some later time (t + delta t)?

Let's also assume that the object is traveling fast enough that it is discernable. This point might be moot, since I'm not sure if such a situation is possible. I know that Rayleigh's criterion could give us a lower bound for how far the images of the object has to be, though I'm not sure how complicated it would be to throw redshift into the mix.

This seems like one of those "Whoa this feels see weird causally but it's just a natural consequence of things we've observed thus has little repercussions as to what limitations physicists actually work around." Actually, I could see perhaps long exposure photos (or the telescope equivalent, if it exists) could run into issues.

cross-posted from: https://lemmy.ca/post/33867210

Here's a little physics riddle. It's really meant as a moment of self-reflection for physics teachers (I invite you to compare what answers you'd give within Relativity Theory).

We're in the context of Newtonian mechanics.

There are three small bodies. In the inertial coordinate system (t, x, y, z), we know the following about the three bodies (at a given instant of time):

• The first has mass 3 kg
• The second has velocity (1, 0, 0) m/s
• The third has momentum (2, 0, 0) kg⋅m/s

Now consider a new coordinate system (t', x', y', z') related to the first by the following transformation (a Galileian boost):

t' = t, x' = x - u⋅t, y' = y, z' = z with u = 1 m/s

Questions:

• What is the mass of the first body in the new coordinate system?
• What is the velocity of the second body in the new coordinate system?
• What is the momentum of the third body in the new coordinate system?

Can you give definite answers to these three questions, and motivate your answers with simple physical principles? Note that by "definite answer" I don't necessarily mean an answer with a definite numerical value.

I had an idea in a dream where a pressure vessel had a buoyancy valve at the lowest point. The idea was that a ball would sit in a hole and water that may condense inside the vessel would lift the ball allowing the water to drain after which the pressure of the vessel would seal the ball back into place. That made me wonder about the possibility of a pressure based buoyancy valve and whether the physics were there.

Just musing here, I've been a proponent of new ether theories the past few years and so there's some assumptions that go into this.

1. Spacetime is a fixed grid with planck-length-cubed voxels.
2. Information can travel through the grid at 1 planck-length per planck-second.
3. Particles evolve from this grid to perform some function, typically related to self-propagation.

I would posit that the big bang theory makes no sense. A tiny spec of everything which may or may not be finite just kinda gesundheit's itself into existence for no particular reason and then sputters out over trillions of years.

Nah I'm with Max Tegmark, we're an information set, since everything in physics really boils down to information anyhow. What makes more sense to me is if the big bang is instead a white hole, spewing information from some source of random information, possibly the digits of pi or some such.

Back to ether theory, the Permittivity of Free Space can be looked at as the inverse and called the "Electric Tension" [Roychoudhuri 2021]. This is the fundamental resistance of space to accept new information, and conducting Roychoudhuri's experiment (Michelson/Morely in hard vacuum) could verify that this is indeed the bedrock of reality.

So back to a graviton, what would it need to do?

1. Undetectable. The graviton must be smaller than a photon and much smaller than an electron. The diameter of an electron seems to be 10^20 Planck-Lengths.

2. Emitted from all massive particles.

3. Carries information about where the massive particle that emitted it is.

4. Collides with larger particles, with the negative direction vector being the source of the emission.

So what about the particles? Well an electron is ~~(10^20)^3~~ 10^20-cubed voxels, so there is room for extremely complex structures in there, and I would posit that massive particles (and photons) exhibit intelligence and try to survive. What would they use gravitons for?

1. Emitting gravitons causes the particle to decay. Absorbing gravitons prevents this decay, therefore it is advantageous for the particles to move close together, as this increases the absorption of gravitons.

2. The direction vectors of incoming gravitions are summed up and the direction with the most mass is where the particle tries to go.

So what do you think? Do gravitons exist? If they do they're basically the particles shooting spit balls at each other. We can talk about time dilation next.

I just wrote this article and I would like your comment:

The Universe Will Not Die a Heat Death

We assume that the universe is expanding according to the Lambda-CDM model with a fixed Lambda constant.

Imagine a central star, like our sun. Two artificial satellites are orbiting this sun in circular orbits in opposite directions. As the universe expands, the orbits of the satellites are elevated, and the satellites thus gain mechanical energy (the sum of potential and kinetic energy). This energy can be released by causing the satellites to collide or by simply having them graze each other. As a result, some of their kinetic energy is converted into heat, which can be radiated away as thermal radiation, and the satellites descend to lower, more inward orbits. The process can then begin anew.

Im in the process on building something similar with the rack you see in the picture.

What I want to know is if its possible to determine the optimal length of the tube on the frame and on the rack to allow the max load under stress without the rack breaking/bending on a spot that its not mounted on the frame, and what would be the max load?

and if it is, how to calculate it? :)

things that i know:

• number of tubes
• length
• diameter
• thickness
• bending tube angle
• stainless steel type

worth saying that this is more of a learning exercise.

My understanding is that "what happened to the antimatter?" is a bit of an open question. How sure are we that all of the matter we can see is in fact matter, and not antimatter?

Antimatter has the same mass, electromagnetic spectra, falls down, etc. Do we have a way of determining which version of matter distant objects are made of?

I think I need to rephrase the question. I'll post again in a few days.

The replies so far have generally been very polite, given the subject. I was nervous about that. Thanks everyone!

... Hear me out, okay?

Back in 2000 I took my first solo, out of state trip, to meet an online friend. When I got off the bus, she greeted me, and let me know that we had to go stop by her friends house on the way back.

She was Wiccan and needed some Spiritual guidance because the night before she saw a black portal open up in the corner of her room that was giving her really bad vibes.

It wasn't my thing, but I never discounted it. Maybe it was real, and if nothing else it's just how her mind is rationalizing things.

But I guess my question is: Does the Scientific Method rule out the possibility that a "real" portal appeared in her room?

Taking wave function probability into account and the absense of data from the room, is it fair to say that the scientific method doesn't rule out the black portal being real?

Looking for black and white answers if possible, but I'd also love to hear your reasoning~

Is it possible to determine the percentage of the gravitational force at a specified distance using only the geometry of the planet?

Example: The ISS at ~420km altitude "weighs" about 90% of what it would on the Earth's surface.

Is there an equation using only geometrical values that would give you this info?

Sorry if this is a naive question (I am in high school), but why do we always talk about ‘ideal’ stuff in physics? The conditions are not possible in real life so why bother with them, won’t the numerical values not accurately represent real life situations?

Edit: I assume we’d at least have to take intended acceleration and the mass of the spacecraft into account, at least, right?

All blades have the same size, 36cm long, aerodynamically well shaped. But. The first weighs 120g, the second 125g… And the third one 210g… This is a small problem. So what are my options now? Making a new blade would be the last option, but do I have any other options?

Pressire acts on all directions, which means that pressure has a direction to act upon, allbeit plural. A scalar quantity is a force that has no direction to act upon. How is pressure a scalar quantity? Shouldn't it be a vector quantity?

In school, I was taught that the speed of light is constant, in the sense that if you shoot a laser off of a train going 200 km/h, it still just goes at a speed of c=299,792,458 m/s, not at c + 200 km/h.

What confuses me about this, is that we're constantly on a metaphorical train:
The Earth is spinning and going around the sun. The solar system is going around the Milky Way. And the Milky Way is flying through the universe, too.

Let's call the sum of those speeds v_train.

So, presumably if you shoot a laser into the direction that we're traveling, it would arrive at the destination as if it was going at 299,792,458 m/s - v_train.
The light is traveling at a fixed speed of c, but its target moves away at a speed of v_train.

This seems like it would have absolutely wild implications.

Do I misunderstand something? Or is v_train so small compared to c that we generally ignore it?

Electricity is in the form of electrons, which have mass. Everything that has mass is influenced by gravity. Therefore, why doesn't electricity fall down to the ground due to being influenced by gravity?

The reason planets orbit stars is due to gravity. The reason stars glow is due to heat. What's the reason for gravity existing?

What are your plans for this community or is it abandoned?