Discussion in 'Science & Technology' started by The Imp, May 4, 2010.
That's what Michkov said, basically. And uppi.
Some questions, in Quantum Mechanics:
Primary: Is the photoelectric effect ever observed to be modified by the type of elemental metal involved? Similarly for metal alloys of multiple elements?
Secondary: If so, is there a relationship between say the atomic number of the metal element involved (i.e. do protons in the atom influence or modify the photoelectric effect?) ?
Secondary: Again, if so, is there a relationship between the electronic structure of the metal element and the photoelectric effect?
hmmm how about a winch to Jupiter, by a carbon fiber?
Or a concerted rocket motor (like maybe we turn one continent completely volcanic, as a kind directed planetary core tap) ?
A sort-of orbit-centered question:
-Is there any (known or theorised) celestial object which is estimated/guessed as running a non-elliptic orbit around another? (planet or star, etc).
From what i read on comet orbits, they are bound to break off the local star once they reach a parabolic course (and i suppose soon having a hyperbolic course next to the old focus point).
I am not sure how much actually is established on what happens in the not charted out parts of a parabolic or hyperbolic course, but it seems an interesting issue; afaik Kepler did not originally try to assign ellipsis as the orbital type of the known moving planets, and i was wondering if in astronomy there have been attempts to theorise on other orbital types (set parabolic, or any kind of hyperbolic)
There are lots things which can happen.
Small asteroids experience some change of their orbit by radiation pressure.
If an object is not much smaller than it's orbital radius, this will result in a different motion. This might for example happen if you put a long rope into orbit. The end motion is usually chaotic.
The Saturn moons Janus and Epimetheus exchange their orbits every four years due to mutual interaction.
Celestial objects can be Trojans of bigger objects, occupying their Lagrange points L4 or L5.
The Newtonian elliptical orbit can be strongly altered by effects of General Relativity. This is common for orbits around black holes or neutron stars, but the effect is already measurable on the Mercury orbit.
Yes, the minimum energy required to extract an electron from a metal (called the work function) depends on the type of metal.
Yes, there is a relationship between the number of protons and the work function. For example, for alkali metals, the work function decreases with increasing number of protons. But there is no general description of that relationship, because, yes, the electronic structure (mainly the ionization energy) does play a role.
There are also other effects, especially surface effects, which further modify the work function. So predicting the work function for any given metal is quite hard.
For a two-body systems, the laws of physics require the orbits to be elliptical. So to get a non-elliptical orbit you would have to go to a multi-body system. In a three body system you can get a horseshoe orbit for example, and some asteroids are know to have such an orbit.
For a weak influence of General Relativity like for Mercury, the orbit is still an ellipse and there is just a slow precession of that ellipse. I don't know how orbits look like around neutron stars and black holes, but I would guess they would still be mostly elliptic.
Thank you both for the replies!
I saw this earlier: http://www.cnn.com/2014/06/12/tech/innovation/warp-speed-spaceship/index.html?hpt=hp_t2
Will time dilation still be an issue? If so, will we ever figure out a way to bypass time dilation? Because I would still rather be able to warp to, say, Deneb, and then be back in time for dinner, instead of finding everyone I know and love six feet under.
If I understand, it's a complete solution.
We have to be careful. There's a difference between "particles theorized to exist, because of math" and 'invented particles". Theoretical physics has a strong history of predicting particles - we're now entirely sure that 'dark matter' exists, for example. An engine that required Dark Matter could, I guess, exist at some point.
The alternative is unicorn horns.
As far as I can tell, this thing needs 'exotic particles'. We have no reason to think they might even exist.
As the ship itself can be at rest and it is space that is moving, I would suspect that this would circumvent time dilatation. But that would cause issues with causality. Unfortunately I am not good enough at General Relativity to find out.
In my opinion, this 'exotic matter' here falls on the unicorn horns side of the line.
Hmmm can we really say there is material evidence of dark matter, as in de novo creation or isolation of it?
I thought that is one goal of LHC, but hmm, I don't find any explicit claims by CERN / authorities.
There's nothing to say the idea is bad, and the idea is a logical inference made from observation, and there is more indirect evidence (excess positrons finding) yet. But there is not direct evidence in the way that you can process iron into steel and then analyze the process, as proof that steel exists.
The experiments (AMS) are still running.
The game of Duck Duck GOOSE
Absolutely appalling plan. Thee environmental impact paperwork would cost, like, billions, and the project still wouldn't get approved. Tree huggers!
And then there's the insurance costs, which would be ... well, prohibitive.
I prefer a "close pass" strategy, where a passive objective gives the earth a gravitational nudge. So, it takes awhile.... You have to do it repeatedly, but that means you can charge repeatedly for the service! And as you only *risk* destroying civilization you can skip both the environmental studies and, with a little finesse, the insurance.
Hmm ... devices making use of particles whose existence hasn't been *dis-proven* could be fertile ground for submarine patents.
BTW: I was the first to theorize that neutrinos are actually the size of beach balls and are the cause of spontaneous human combustion.
I just want to make sure I understand black body radiation properly.
A black body is an [ideal] object which absorbs all possible radiation it receives. Thus, the observation that radiation was still detected coming from it created a crisis which "broke" Newtonian physics and required the invention of quantum mechanics in order to solve. However, the radiation a black body emits comes only from emission, which is heat transfer, not reflection (because it absorbs all that light). Thus the hotter it is, the more energy it emits in an effort to reach thermal equilibrium with the environment. This explains why its radiation passes from invisible infared light at room temperature into the visible spectrum starting with the reds, as the temperature increases.
For each material, the pattern of this color shift is different. Thus, you can tell what material it is if you know the temperature, and examine the light (radiation) it emits. Correct? And this is related to spectral lines...somehow.
Now, assuming the above is correct, where I really struggle is the relation of all this to the particle-wave duality of light. Presumably the black body problem demonstrates both aspects of this duality. Is this because Einstein conceptualized the emission of light as "packets of energy," aka photons, and thus the problem with this paradox is that the idea of a photon as a "particle" is a false attempt to think of it as equivalent to electrons, protons, etc. which were being discovered around the same time? Or is it because, as de Broglie demonstrated, all matter can be described as energy with a given wavelength, which would again make the photon "particle" a distinction without a difference? That would render the duality question useless.
So all that remains is, why are separate aspects of this duality observable at different times, but not simultaneously?
The first paragraph is correct, but there is some confusion in the second: The black body radiation only depends on temperature (and to some extent on the "blackness" of the body), but not on the material. So by looking at the spectrum of a black body you can determine its temperature, but not its composition.
Spectral lines are very narrow absorption lines in the broad black body spectrum at those frequencies the atoms or molecules in the body are resonant with. They depend on the material of the body and modify the black body spectrum, but have a different origin. When identifying the material a body is made of, you rely on identifying spectral lines.
To put it short: Black body radiation results from the properties of light, spectral lines from the properties of matter.
I don't think the black body problem is well suited to demonstrate the aspects of the so-called duality. It was only the first problem where the quantization of energy was required (and introduced in a quite ad hoc fashion) to solve the problem. Only later it was realized what an important step that was and how fundamental the two constants introduced by Planck were.
As we have discovered, all particles can behave like a wave, so I would agree when you call the distinction useless. In my opinion, the answer to the question whether light is a particle or a wave would be: neither, it is a quantized field. The concepts of "wave" and "particle" are only approximations to the behavior of quantized fields in certain situations. So the so-called duality is just our decision which one of the - by design - mutually exclusive concepts we use to explain a certain observation. As both of those concepts cannot describe the whole picture, they will fail at one point, so we can try to apply the other concept.
Actually I would argue, that we can do experiments where we can observe particle-like and wave-like behavior at the same time - or as an alternative description: where the wave and the particle concept both fail.
Really? There are situations where both models fail simultaneously? I wasn't aware of that.
Have any of you made a cloud chamber using an inverted fishtank, dry ice, and alcohol?
I've be meaning to try this for a few years, but there are always other things that take command of my spare time. This summer I really hope to do this when I'm visiting my cousin's kids. I just wonder if there are things I should keep in mind to maximize success...
We have a cosmic ray detector in a hall at the university, but IIRC it is a wire chamber.
This is ofcourse an interesting thread and all, but maybe we need more questions along the lines of:
"What would be needed to realistically bring life to a Golem, using any even tenuous parallel between placing a letter on its forehead and working with known phenomena studied in Physics?".
And so on. Would spice things up
I agree, I don't see enough moronity.
Link to video.
Do helicopters really work in Mars' atmosphere?
They shouldn't. There's so little air, there would be nothing to push against.
The air isn't thick enough on Mars. The highest anyone has ever gotten a helicopter is under 41,000 ft. And that was specially modified for the occasion. A common copter like the Blackhawk can only reach 19,000 feet.
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