Consider a power station set up in the middle of a town with cold winters. In the first example it burns has, drives a turbine and cycles water back after some form of basic cooling loop.

In the second example the waste heat (after driving the turbine) is connected to a distributed heating system throughtout the town that heats buildings and pavements and so on. In this case the return loop is much lower temperature, say just above freezing.

In order to do work you need a temperature gradient, although I'm not sure if that is relevant here. On the one had there will be a bigger gradient between the boiled and cooled water, but on the other hand you need to use more energy to lift the temperature from the cooling loop to boiling.

How does the efficiency for purely energy generation compare in these cases?

I.e. what is the loudest can?

Sorry in advance for a potentially nonsensical question. But I've been thinking of this and couldn't get a decent answer.

Assume spacetime is a quantum field with the propagation speed greater than c (let's call it c1). All other fields we know of are at c (we're assuming gravity is quantum too).

Coordinates on the spacetime field and standard model fields correlate. However, information travels faster on the spacetime field than the SM fields.

Assume the spacetime field expands. When it does so, due to c1 being higher than c, SM fields feel a lag for this expansion. Thus, they act as if spacetime is smaller than it actually is.

This means, SM fields seem uncharacteristically stronger than they're supposed to be. This effect becomes more apparent as speed of expansion of spacetime grows (lag increases, SM fields operate as if spacetime is its actual size minus lag).

Let's look at the Chandrasekhar limit. With this effect, it changes over time. When gravity becomes stronger temporarily, it lowers. Because it lowers, we need less mass to trigger a type la supernova. This reduces brightness than expected.

Thus, a standard candle isn't as bright as we thought it to be. Also, its brightness changes with this changing "lag" between spacetime and the SM fields.

In our models, we incorrectly believe that standard candles are further away than they actually are (because we think that they are brighter than they actually are). This results in us calculating a higher expansion rate of spacetime.

While this effect would apply to the CMB, it would be less apparent as the universe was expanding at much lower speeds. This is the "real-er" value.

The above effect also means that galaxy formation would occur earlier than predicted (stronger SM fields).

Note: To clarify, the assumption is that gravity is a quantum field and that it is separate from this spacetime field. The propagation speed of gravity is the speed of light. It is NOT the speed of propagation of the spacetime field.

cross-posted from: https://sh.itjust.works/post/52943342

Hey everyone!

I’m forming a team for a citizen science project called IASC — International Astronomical Search Collaboration and I’m looking for teammates! Interested?

It's nothing too crazy and the process can be underwhelming. I'll say that just so you don't expect anything extraordinary.

Basically, what we'd have to do is analyse images that will be sent to us from these two observatories in Hawaii called Pan-STARRS 1 and 2. And we'd have to look for moving possibily unidentified objects and send an report to IASC (the organization behind it).

It's super quick and simple, and it really shouldn't take more than 20 minutes per pack out of your day and you'll have an entire month to sort through the packs. So, time really isn't an issue and you can do things on your own time.

This is a great way to be part of hands-on science. You're helping scientists track objects and identify new ones. This is very relevant, especially on a planetary defense level. You can't protect yourself from a threat you don't see coming.

They offer certificates to all participants, and the certificates are pretty neat.

Requirements/preferences:

• Willing to commit some time to analyzing telescope images
• Preferably located in the Americas, Europe, or Africa (similar time zones are a plus)

Relevant links: https://science.nasa.gov/citizen-science/international-astronomical-search-collaboration/ http://iasc.cosmosearch.org/

If you want in or have questions, lmk below :)

(Sorry if this isn't allowed mods. I couldn't find anything that said I couldn't do this in the rules T-T)

cross-posted from: https://lemmy.world/post/39777765

So, I was reading about the Unruh effect. In short, if I understood correctly, it is about a constantly accelerating observer finding particles in vacuum that an inertial (non-accelerating) observer wouldn't, and relatedly, measuring a higher temperature there than an inertial observer would. This is due to a combination of quantum and relativistic phenomena. There even seems to be recent empirical support for this, but as I was reading about it, I accidentally stepped into some pseudoscience, which left me in an emotional state where I find everything suspicious.

Anyway, even though I technically am a physicist, this is far from my area of expertise. I came up with a thought experiment and would like to ask a couple of questions related to it.

Let's imagine a spacecraft that does a little trip where it goes into open space accelerating enormously, then stops and comes back. My first question is this: would it be (theoretically) possible for the spacecraft during the acceleration to capture some of those particles that from an inertial perspective don't even seem to exist, store them and bring them back as a very concrete evidence of the Unruh effect? If not, why not?

Another question or two: is my intuition correct when I think that if those collected particles were converted into energy, it would in no situation be possible to gather more energy this way than would be spent in the process of accelerating the spacecraft etc? If yes, could one in some sense say that the energy put into the acceleration is what created those particles in the first place?

I've seen lot of theory about how it works.
But how do they get to that conclusion?
As far a i know, you can see that it's air vibrating bc when there's a loud noise you can feel the floor vibrating or if i drop something in a table and i place my hand on it i can feel the table vibrating as well. But how do they know it in more detail. How do they know about the pith and that it's a wave?

[Edit: no. The λ in question is the wavelength of the light before it reaches the pupil because that wavelength is what determines how many more wavelengths light has to travel from the source to reach one side of the pupil than the other. The lens and vitreous humour focus the light onto the retina by ensuring that the light from a point source travels the same amount of time to reach the corresponding point on the retina, regardless of which point on the pupil it passes through. Because all the light travels the same amount of time from the source to the corresponding point on the retina, the light waves’ maxima all arrive at the same time, so the light waves interfere constructively at that point and produce a bright spot. Near that point, the light travels almost, but not quite, the same amount of time, so the point source illuminates a region around the point slightly less than it illuminates the point where it is focused. When light comes from two sources close to each other, the difference between the amount of time the light from one source takes to reach one side of the pupil and the amount of time the light from the same source takes to reach the other side of the pupil is close to the difference between the amount of time the light from the second source takes to reach one side of the pupil and the amount of time the light from the second source takes to reach the other side of the pupil. And there is nothing that the lens or vitreous humour can do about that.]

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.