Ask any question you want about Physics

originally posted by: delbertlarson
Feynman perhaps didn't like philosophy because neither he nor anyone else of his time had a satisfactory solution for what is going on. He was in good company, as the best minds for decades wrangled with the issue. The whole Copenhagen philosophy was a dodge. However, just because this problem has simmered for so long doesn't mean it isn't important.

I don't think you understand what Feynman says about philosophy and you didn't understand his example of gravity in the video I posted in your other thread, this one:



He described three different philosophical approaches to describing gravity which sound completely different, but they end up making the same predictions. Then you made some comment about something completely different from gravity which showed you didn't even seem to understand he was talking about gravity. He does care about different philosophies because he thinks one approach might give a theoretical physicist insights that he might not get from a different approach, even if they end up being equivalent. But his advice for the theoretical physicist as far as I can tell is to not get married to one philosophy, rather consider all of them, which by the way is exactly what I try to do with the subject of the interpretation of quantum mechanics discussed in the OP.

Feynman elaborates a little more on how he thinks is a good idea to keep all the different philosophical approaches in mind in this video:



He asks if approach "A" and approach "B" result in the same consequences (observations or experimental results), how are we going to decide which one is right? "No way, not by science". So far that's more or less the case with the quantum mechanics interpretations which predict the same consequences, which is why we can't use science to pick one, at least not until someone devises an experiment to distinguish between them which I think some researchers are trying to do. This is the point I was getting at in my prior reply; if they are experimentally equivalent, why would I try to pick one when it's scientifically impossible to do that (pending further experiment if that may show a difference).

1:45
"psychologically we must keep all the theories in our head, and every theoretical physicist that's any good, knows 6 or 7 different theoretical representations for exactly the same physics, and knows that they are all equivalent, and that nobody is ever going to be able to decide which one is right at that level, but he keeps them in his head hoping that they'll give him different ideas for guessing".

So Feynman does care very much about the approaches for that reason, but that's not saying he picks one when it's impossible to do that scientifically, he tries to consider them all for their different insights.

Speaking of theoretical physicists, I thought of you when I watched the question and answer session at the end of this video from the Perimeter Institute, where some theoretical physicists work.



1:35:15
Q: "Do you have any advice to offer to students considering a career in theoretical physics".

1:36:30
A: "When you go into it... you're taking on the most difficult, challenging, impossible problems. You're trying to challenge Einstein, I mean, good luck, hahaha"...."The people in this institute are playing with statistic agent math, fancy computers, you name it...every day. You're with other people who are as crazy as you, and want to challenge Einstein, and want to discover the next big thing." He makes it sound like there's a whole building full of physicists trying to challenge Einstein; i wonder if any will succeed. The main problem I have with Einstein's model is the description of an infinite density singularity in a black hole; there just has to be a better description than that using quantum mechanics, but nobody has figured that out yet and even if they do figure it out theoretically, how are we ever going to confirm the solution with observations? Even if someday we could send a probe into a black hole, I don't know how we will ever send the observations out. Maybe someone can figure out some clever trick using Hawking radiation or something.

a reply to: KrzYma

As I recall, i gave you a lengthy description of how one such detector worked... you brushed it off and said something along the lines of "You don't know how it works, its all just EM waves" without actually being coherent in your reasoning why.

Single photon counting is a well established and understood process. You have previously claimed light propagates from a source and previously have stated that light sources propagate in a spherical wave front. We pointed out soon after that lasers don't behave at all like you described. You never got back to me on that one either.

Let me give you an example. In my current work, we are characterizing the performance of single photon counting devices at deep uv wavelengths, around 170-190 nm now, this is the wavelength. We use a broad band flashlamp that produces light from around 160 to 1000nm (Xenon flash lamp) Due to the atomic structure of Xenon, the emission spectrum has lots of peaks in it, and a long underlying continuum caused by the rather large amount of energy levels and electrons the Xenon atom has.

So, we are only interested in the 180nm region so we use narrow band filters. These filters are made from tuned layers of different refractive index materials, typically in a 1/4 - 3/4 layer structure, where one layer is 1/4 wavelength thick, and the next ontop is 3/4 nm thick, and so on, and so on. So wavelength does appear to be a real thing. It is both a reflection of energy, but also takes some geometrical form too.

The flash lamp produces many many photons, the optical power is around 5 Watts at maximum pulse frequency (whole spectrum) We filter this using optical components as described above and we focus the light onto a device. By applying 4 filters, collimation, focusing and mirrors we can reduce this signal down to single photon level.

The device we are testing is a pixilated geiger mode APD, and contains a shallow junction. Why? well because photon absorption by silicon is very high in the UV, meaning that technically UV gets very readily absorbed, and you will only see a signal from the device if the photon penetrates deep enough to generate charge carriers (electrons - Holes) near to the junction such that they trigger an avalanche process in the device.

The device has some interesting features. The sensitivity of the device is directly related to the wavelength of the light imparted on it. And the signal intensity is related to the amount of photons. The way you describe things, your explanation for these effects is simply that the only property here is that of waveform intensity, and that its all about electrons not being 'at the right place?' You realize how illogical that is? How many electrons do you think there are? I can tell you that, it is quite a lot.

By your own reasoning you seem to suggest that, if it is a geometry affect 'being in the right place' depending on the waveform, we could test this by using a polarized laser, this allows us to control the polarization of the waveform and the wavelength very precisely. And let me tell you that... single photon counting in a device as discussed above, behaves in a Poissonian manner, meaning the signal being generated is due to a discrete quantized source. This behaviour does not change using a polarized laser source.

So if you take planck equation and do a similar calculation as you have seen in above posts, you can, given a light source wattage, calculate the number of photons for a given wavelength. You can apply neutral density filters to reduce the amount of light at all wavelengths by equal amounts. SO if you take a source that is producing of light at a single wavelength and apply lets say neutral density filters that give you a factor of 10000x reduction in signal, resulting in what theoretically should be 10 photons emerging (on average) from the filter, you measure this using a device with independently calibrated and it says, "I see a signal equivalent to 10 photons" the wavelength of your source is 500nm.

Now, you switch the source for a different one... this time it is at 200nm, you apply the same 10000x reduction and your detector has calibrated efficiency meaning its efficiency is equal at 200nm as 500nm. So what is your signal? By your own logic you state that single photons are not a thing, so you expect your signal to look the same regardless of wavelength. What you actually see is your detector telling you that you see 4 photons. Why?

Well because E = hc/lambda, at 500nm the photon has a theoretical energy of 2.47eV, so your 10 photon signal is 24.7 eV worth of energy. Now the other light source, at 200nm each photon is about 6.2eV but the source power is the same right? well the number of photons is actually not the same, despite the power being the same.

The above experiment isn't fantasy, iv done it, you can do it too, (though you'd need equipment that is expensive and not really worth buying to just do that experiment) and i can confirm the above behavour... and not what you seem to suggest which is that 1) single photon counting isnt a thing and 2) wavelength/wattage relations are also not a thing.

Lol looks like a case of GIGO. But be my guest and believe as you please.
While you are at it chk out some videos of astronauts on the moon and gauge the speed of their speech.

a reply to: Arbitrageur

I watched the Feynman three-ways-to-do-gravity video again. I looked for it in my absolute and real thread but did not see it there - perhaps I scanned too quickly or perhaps it was in some other thread. While I didn't find my response, I do recall that it had to do with the magnetic dipole interaction, which has a different force fall off than 1/r*2. That response came about because at 10:01 of the video, Feynman states something about how nature is so exquisitely balanced, and I thought he was going beyond gravity at that point in the discussion to refer to something more general. I thought so because at 10:10 he refers to the "laws of nature" (plural) not the "gravitational law" or "law" (singular). Also, at 10:44 he refers to modifying the laws, again in the plural. Coulomb is also 1/r*2, and I believe that much of his arguments about gravity also pertain to Coulomb, so I thought he was making a general statement about all physical laws at the end. (F = dp/dt is the same for gravity and Coulomb too, as well as for all laws.) But some forces (like the magnetic dipole) are not 1/r*2, so I thought that was relevant to the discussion.

I may still be missing your point concerning the Feynman gravity video. I thought your point was that we could look at physics from different points of view, and that until experiment can decide between those points of view, we must admit that different views are possible. If your point is/was something else, please let me know.

The main issue for me philosophically is realism. I believe that once we give that up we've given up any grounding whatsoever. We can throw down whatever math we want to model experimental results, but I think we lose a lot when we do so. If we aren't attempting to describe a real, objective, reality, then what are we trying to describe?

Thanks for your further clip from Feynman, as it shows that he did value different philosophical approaches. It also in a way supports my view, since the Mayan astronomer was just using math, but the person with the realist interpretation behind the math had an important contribution. But of course, we can't question Feynman now, we can just reply to each other, and I was replying to this:

Until I see some problem with the approach that time is what atomic clocks measure, the definition seems to work as far as i can tell. I have yet to see any experimental results that show a problem with that approach, and I'm not much interested in philosophical nuances personally, though I know some people have an interest in that. As Feynman said, more experience should cure people of the disease of getting too hung up on specific philosophical approaches, and I think he had a point

The main point is this:

Both the quantum collapse problem and the cosmological constant problem can be addressed if we set relativity aside and return to absolute theory. Those are the experimental results that show a problem with treating time as what atomic clocks measure. Quantum collapse can be easily understood as an instantaneous collapse once absolute simultaneity is recovered by proposing absolute time (moving atomic clocks run slow), and using Absolute Quantum Mechanics instead of QFT goes a long way toward solving the cosmological constant problem.

a reply to: Arbitrageur

What I was trying to get across to kryzma is that if you use analogies from water flow and hydraulics to explain electricity for example there will always be a point where the analogy breaks down and won't give accurate results.

I think that could be the issue he is having.

On another note, thank you for writing the explanations that you did. You answered questions i had always had about radio and radio signals. I'm still processing what you said and reading links, but I'll come back a ask questions at some point I'm sure.

This is probably the dumbest question ever, so you have my apologies.

Is it theoretically possible, when looking up at the night sky, to actually see a star explode?

If so, how long would such an event appear in real time?

originally posted by: Steffer
This is probably the dumbest question ever, so you have my apologies.

Is it theoretically possible, when looking up at the night sky, to actually see a star explode?

If so, how long would such an event appear in real time?

These have been observed on some occasions and the event lasted several weeks. You may find some links on the net for these events

originally posted by: roguetechie
a reply to: Arbitrageur

What I was trying to get across to kryzma is that if you use analogies from water flow and hydraulics to explain electricity for example there will always be a point where the analogy breaks down and won't give accurate results.

See I understand what you said there just fine because I know all about that analogy and like all analogies it does break down at some point just as you say. However I still have no idea what analogy you were referring to in your prior post because it definitely wasn't that one. Photons are rather unique little things and don't lend themselves to analogies of objects we are familiar with very well.

I think that could be the issue he is having.

Well maybe he is looking for macroscopic analogies and there aren't any good ones and he finds that frustrating (I think imafungi was having that issue), but understanding the exact quantum mechanical properties of photons was never required for our evolutionary survival, so there's no reason they need to seem as intuitive as larger objects which we did need to understand for our survival.

On another note, thank you for writing the explanations that you did. You answered questions i had always had about radio and radio signals. I'm still processing what you said and reading links, but I'll come back a ask questions at some point I'm sure.

You're welcome.

originally posted by: Steffer
This is probably the dumbest question ever, so you have my apologies.

Is it theoretically possible, when looking up at the night sky, to actually see a star explode?

If so, how long would such an event appear in real time?

It's not a dumb question but it does require clarification. I will assume that you meant "with the naked eye" though you didn't specifically say that. It's a somewhat rare event to see supernovae as they are called with the naked eye. The last one to have been unquestionably observed was Kepler's supernova in 1604 so I'm pretty sure none of us were around then to see it.

Kepler's Supernova: Recently Observed Supernova

Kepler's Supernova or (SN 1604) was a supernova which occurred in the Milky Way Galaxy in 1604. It's the last supernova that was observed from Earth in naked eye

Before that I've read of maybe a half a dozen in recorded history. Chinese astronomers kept some good records which is some cases were corroborated by other records documenting earlier observations. In some of those cases we think we know where the remnant of the event is.

What's really amazing is even though 1604 was a long time ago and generations since have never seen one, we may actually see one in 2022 if astronomers have made an accurate prediction:

How to See a Star Explode in 2022

Five or so years from now, you may be able to witness a new "star" appearing in the night sky, a cosmic gem that should glitter in the northern wing of the constellation Cygnus, the swan, for a good portion of a year.

For the first time, astronomers are confidently predicting that a specific stellar system will explode within a defined period of time, becoming more than 10,000 times brighter than it is now. The explosion will be visible from Earth with the naked eye, and it could be about as bright as Polaris, the north star.

With the good telescopes we have now, we can observe them all the time and SN1987A even showed up in our neutrino detectors, which as the name implies was observed in 1987. That was the closest supernova since the one in 1604 and maybe, just maybe if you went to the middle of nowhere with no city lights anywhere you might have just barely been able to see that one at peak luminosity without binoculars, but in most places with stray lights around you needed binoculars to see it.

I've heard of people in modern times seeing things that they reported as like explosions in the sky. I don't really know for sure what any of them saw, but here's my best guess. We've probably all seen "shooting stars" that have shot across the sky. Sometimes those can be produced by small objects the size of a grain of sand entering the Earth's atmosphere. But that's different than what people called the "exploding star" they saw, right? Well it's certainly different in that one streaked across the sky and one didn't, but if that's the only difference, maybe it's really the same kind of event. In other words, a brief flash that doesn't "streak" across the sky could be the same thing except it's heading right toward you, and that's why you don't see any "streaking". That would certainly be visible and could look like an "exploding star" descriptions I've heard except not really because those meteors are short-lived events lasting less than a minute, where as an exploding star or nova can have a visible signature that lasts a much longer period of time, such as the predicted event in 2022 that may be seen for a "good portion of a year".

Also depends upon the type of exploding stars and how rare they are.

Astronomers have mapped light curves of any supernova that has been detected (on time) so data is a little scattered. Typically we see the events either too late, or see them comparatively after time has already passed.

So example, a telescope might make observations of one area of sky, for another purpose, say, looking at a variable star and taking spectra. And then might come back to that same area a week, a month, even a year later and do another observation, again for totally other reasons. Astronomers will do comparisons with old data and see that there is a new object in the frame, or a star that has changed luminosity by a significant factor. Then goes out the call to figure out if any other telescopes have relevant data etc.

Catching one in the act, is rare, but not impossible. In 2011 astronomers observed a Type 1A supernova from start to finish, mapping its behaviour. Type 1A is a very specific type of explosion in that it involves a stellar remnant, a white dwarf that is accreting material from a neighbour... once it goes over the Chandrasekhar limit (maximum mass limit an electron degenerate star can obtain before it collapses). When it does this, the star initiates a runaway fusion process and obliterates itself. The light curve of such events can last a month or so... and by last, i mean, they will produce a large spike and a long tail back to normal or the magnitude limit of the telescope

a reply to: ErosA433
Yes it takes a lot of luck to catch the very beginning of a supernova, so that's rare.

The Zwicky Transient facility run by CalTech started using an incredible imaging system in 2017 that can image the northern sky (in 8 hours according to the first video below) down to 20.5 mag, so they can compare tonight's images to last night's images and it's not more than a day old at that point, but they could have already missed the first day or some fraction of the first day of the event, but they could also get lucky and see an event that's only happened within the past few hours.

www.ztf.caltech.edu...

By scanning more than 3750 square degrees an hour to a depth of 20.5 mag, ZTF will discover young supernovae nightly and search for rare and exotic transients. Repeated imaging of the Northern sky (including the Galactic Plane) will produce a photometric variability catalog with nearly 300 observations each year, ideal for studies of variable stars, binaries, AGN, and asteroids.

www.caltech.edu...

A new robotic camera with the ability to capture hundreds of thousands of stars and galaxies in a single shot has taken its first image of the sky, an event astronomers refer to as "first light." The recently installed camera is part of a new automated sky-survey project called the Zwicky Transient Facility (ZTF), based at Caltech's Palomar Observatory located in the mountains near San Diego. Every night, ZTF will scan a large portion of the Northern sky, discovering objects that erupt or vary in brightness, including exploding stars (also known as supernovas), stars being munched on by black holes, and asteroids and comets.

"Each image is more than 24,000 x 24,000 pixels, and 4 terabytes of data will be collected each night."
That's a lot of pixels and a lot of data!


The astronomy professor at the beginning of that video says a star explodes somewhere every second, but I expect most of those we can't see even with the Zwicky imager because they are too far away (even the more sensitive imager only goes down to 20.5 mag) or in a part of the sky not visible from that location. But later in the video he says they hope to find dozens of exploding stars every night, so that's nowhere near one per second, but it's still a lot compared to what they used to be able to find, and they can hopefully even find some events that only last a few hours. Astronomy seems like very time-sensitive work now, since astronomers want to make more detailed observations on some of these transient events as soon as they are detected.

Ques: If I may
Assuming gravitational waves do exist, how would LIGO go about determining the direction from which, they emanate?

originally posted by: Hyperboles
Ques: If I may
Assuming gravitational waves do exist, how would LIGO go about determining the direction from which, they emanate?

You can get a general location by looking at the times it takes to hit each detector. The other thing they can use to get direction is directly over the detectors will have the stronger signal so they can look at signal strength at each detector as well to help estimate location. As they add more detectors you could get very specific because it becomes algabra and you trace back where signals intersect. Guessing id say 5 detectors spread out over the globe should do it.

As Drangonridr said, basically the detectors have an L structure, and are most sensitive to gravitational waves come directly from above, the detectors are more sensitive, if they come off axis, like lets say down one of the straight sections of the L, then they are not as sensitive.

Couple this with the use of multiple detectors separated by 100s of KM, then you can do a combined sensitivity and 'Time of flight' analysis and determine a rough region on the sky in which the wave originated from. It isn't exact. They have since added another detector and are probably buying a 4th, each detector will only add to the sensitivity and accuracy of the system as a whole.

nice write up here : www.thephysicsmill.com...

They can then forward their information on to other scientists to search within the most probable area of the sky to see if there was anything interesting happening at the time.

a reply to: Hyperboles
a reply to: dragonridr
a reply to: ErosA433
They are trying to determine not only direction, but also polarization, so a good array of detectors is needed to determine both.

What I found interesting in the neutron star merger was that with multiple detectors, when one of them got almost no signal, that meant the event happened in one of its "blind spots" which helped narrow down the direction of the event. I found a better video some months ago explaining this and I can't find it again, but this one should be satisfactory with the explanation at 1:50



When searching for that video I stumbled across one from the electric universe cranks saying gravitational waves don't exist. I try to be open minded and look at all sides but the other electric universe videos I've watched have been so vastly ignorant that I don't know if I can bear to watch any more.

Here's a bit of nostalgia about gravitational waves. Decades ago many people didn't believe in them or that they could be detected, but the man in this photo (Joseph Weber) pictured with the first attempt at a gravitational wave detector tried to change all that:

physics.aps.org...


It turned out that he was a little overconfident in his measurements, kind of like the guy measuring his antigravity machine with the Garfield sticker on it, and other people tried to explain why he wasn't getting good measurements but he apparently wasn't very receptive to the criticism. While nobody ever believed his "signals" that I know of, his enthusiasm for measuring gravitational waves spread, so that better detectors were eventually built and thus he's still credited as being the father of gravitational wave detection even though his gadget was trying to do the impossible, measure a change in size that's only a fraction of the size of a proton. We still can't meaningfully do that on this device, so we ended up making the detectors a lot bigger so we don't have to.

I'm sure the device changes in size by more than the size of a proton all the time, so it's really a signal to noise issue. All that noise is as big or bigger than the signal so it was hopeless to try to find the signal with such a small detector.

Thanks for all the replies.
So even with multiple ligos the signal if it exists still cannot be accurately computed.
Lol so the dude with Garfield sticker, would be the father of anti gravity?

originally posted by: Hyperboles
Thanks for all the replies.
So even with multiple ligos the signal if it exists still cannot be accurately computed.

I wouldn't phrase it quite that way. The source of the neutron star merger was computed to have originated within a portion of the sky equivalent to the size of 144 full moons. That's only a small fraction of 1% of the sky (maybe about 1/20 of 1%? I didn't verify that calculation), and it turned out the source was found visually within that 1/20 of 1% region so it was calculated accurately to that extent.

Maybe what you're saying is they didn't get the search area to less than 1/20 of 1% of the sky and that's true, but that region will only get smaller with more detectors due to measurement uncertainty. There are always measurement uncertainties.

Lol so the dude with Garfield sticker, would be the father of anti gravity?

Did he inspire anybody to search for anti-gravity using better anti-gravity detectors? Not that I know of, and I don't know of any valid theory of anti-gravity.

Gravitational waves had a theoretical foundation in general relativity, which had already been found to be consistent with other observations, so there was a solid theoretical underpinning for them which is probably why it was easier for Joseph Weber to get people excited about those.

I doubt anti-gravity will be discovered but if it is, I think the man most likely to be credited as the "father" of the field is Thomas Townsend Brown. He too made errors in interpreting measurements and thought an observed effect in electrohydrodynamics was demonstrating a relationship between electricity and gravity, but it really wasn't. There are still some amateur inventors around inspired by Brown who think he really discovered anti-gravity and don't understand how these ionic lifters really work, but this video explains how they really work, which shows it's no more "anti-gravity" than a helicopter though the lift comes from a different and interesting effect:



They may not be anti-gravity but they make really cool science fair projects which aren't too hard to build and have a definite "wow" factor, much more than the Garfield sticker thing that never gets off the ground.

However I've never seen an ionic lifter get its own power supply off the ground either, which makes it of limited usefulness.

One other possibility is antigravity could have a "mother" instead of a "father", if Ning Li's research going dark is any indication that she's been successful, but as the above examples show you really need a lot of peer review in cutting edge measurements to weed out flawed interpretations, and I think it's just as likely someone working in the dark without such peer review could be making the same kind of mistakes, misinterpreting their measurements.

Silly question.

What would happen if somehow the atmosphere became suddenly unstable and all of the clouds fell to Earth?

Would there be violent weather on land or would it just be a tremendous amount of fog everywhere?

a reply to: Steffer
Not just silly but in some sense self contradictory.

It portrays a scenario which to some extent defies the laws of physics so in an "ask any question about physics" thread the context becomes how can you use the laws of physics to describe outcomes in a physics-defying event.

However there are real and dramatic events called microbursts that have been attributed to at least 9 fatal plane crashes. Here's an animation of a microburst which looks somewhat like a cloud falling:

What is a Microburst?


To try to answer your question one would have to spend a lot of not very productive time further defining exactly how you propose the laws of physics are to be violated and then use the laws of physics to try to describe the aftermath, and I don't see the point.

For example, you'd have to define what you mean by a cloud and what you mean by cloud falling. Does the cloud refer to just the condensation part, or does it also include the intervening regular air molecules that give the cloud its density? If you include all the air molecules then it's along the lines of moving a mass of air toward the ground and not unlike the microburst except maybe on a larger scale since microbursts are somewhat localized. However there are problems with that since on a small scale you can see how air that was near the ground is displaced in the microburst animation, but on a larger scale the air that was near the ground might have a hard time getting out of the way to make way for the air mass falling from above, if it say covered an entire state like Pennsylvania. So again you can end up trying to use physics to explain things that can't happen and that's not what physics is for, in fact the physics tells you why that scenario is a problem, how does the larger air mass covering Pennsylvania get out of the way to make way for the larger air mass of clouds falling from above? I don't think it could work on that scale the same way as the microburst.

originally posted by: Steffer
Silly question.

What would happen if somehow the atmosphere became suddenly unstable and all of the clouds fell to Earth?

Would there be violent weather on land or would it just be a tremendous amount of fog everywhere?

Lol you would get another of Noah's flood, which is overdue

a reply to: ArbitrageurWe see what we see, the Garfield video may be showing sorcery or magic, so peer review is moot. Tho what if it is real, then the dude becomes the father of anti gravity.
Other contenders could be podkletnov and ning li for the same title