Ask any question you want about Physics

a reply to: mbkennel

That doesn't make sense, and at least regular fluids can't support transverse forces like magnetism. E&B are the fields. The late 19th century was looking for all sorts of mechanical and fluid like models for electromagnetism until Einstein & the Michaelson-Morely experiments. The mechanical properties necessary were so strange and unlikely that it didn't make sense.

that's why I've said fluid like

Imagine E and B more as an phenomenon or occurrence in one higher field.


Here is a very nice talk about QM. Good to understand for people not so familiar in this field...

If you watch his explanation why an EM wave is an particle because of dots on the screen...
9:30 some till 13:30 some


well... I have a different explanation for the dots on the film or whatever detector you use..
The EM wave "hits" the whole area on the detector, but is so week that it interacts with few atoms only, or even with only one, on the film it triggers the chemical reaction only in few spots.
Because you can't measure E directly, only its interaction with detectors.

A reflection or diffraction of light is also not the same incoming wave just going in other direction,
its a new wave with same or different length, dependent on the status of electron that reproduces this wave spherical in all directions.
If the E modulation can't be accomplish because my referring proton also just get displaced by som "high" E,
my emitted wave length will be different from that I'm ridding on

EM is not quantized, your detectors are.

originally posted by: KrzYma
If you watch his explanation why an EM wave is an particle because of dots on the screen...

well... I have a different explanation for the dots on the film or whatever detector you use..
The EM wave "hits" the whole area on the detector, but is so week that it interacts with few atoms only, or even with only one, on the film it triggers the chemical reaction only in few spots.

People used to think light was a wave before 1900, but there were problems with the wave theory of light not explaining certain observations, like the photoelectric effect.

According to classical electromagnetic theory, this effect can be attributed to the transfer of energy from the light to an electron in the metal. From this perspective, an alteration in either the amplitude or wavelength of light would induce changes in the rate of emission of electrons from the metal. Furthermore, according to this theory, a sufficiently dim light would be expected to show a lag time between the initial shining of its light and the subsequent emission of an electron. However, the experimental results did not correlate with either of the two predictions made by this theory.

Instead, as it turns out, electrons are only dislodged by the photoelectric effect if light reaches or exceeds a threshold frequency, below which no electrons can be emitted from the metal regardless of the amplitude and temporal length of exposure of light.

Your explanation does not explain why the photoelectric effect is not dependent on intensity but only occurs if the threshold frequency is exceeded. If your idea was right, you should be able to just increase the intensity of the light to dislodge electrons, but that's not what happens.

originally posted by: Arbitrageur

originally posted by: KrzYma
If you watch his explanation why an EM wave is an particle because of dots on the screen...

well... I have a different explanation for the dots on the film or whatever detector you use..
The EM wave "hits" the whole area on the detector, but is so week that it interacts with few atoms only, or even with only one, on the film it triggers the chemical reaction only in few spots.

People used to think light was a wave before 1900, but there were problems with the wave theory of light not explaining certain observations, like the photoelectric effect.

According to classical electromagnetic theory, this effect can be attributed to the transfer of energy from the light to an electron in the metal. From this perspective, an alteration in either the amplitude or wavelength of light would induce changes in the rate of emission of electrons from the metal. Furthermore, according to this theory, a sufficiently dim light would be expected to show a lag time between the initial shining of its light and the subsequent emission of an electron. However, the experimental results did not correlate with either of the two predictions made by this theory.

Instead, as it turns out, electrons are only dislodged by the photoelectric effect if light reaches or exceeds a threshold frequency, below which no electrons can be emitted from the metal regardless of the amplitude and temporal length of exposure of light.

Your explanation does not explain why the photoelectric effect is not dependent on intensity but only occurs if the threshold frequency is exceeded. If your idea was right, you should be able to just increase the intensity of the light to dislodge electrons, but that's not what happens.

We can show individual photons easy now. We have digital cameras instead of photo paper. This is done in physics classes with a camera and a filter. If light was a wave putting basically sun glasses in front of the camera would decrease the frequency of the entire wave. But that isn't what happens what we see is a bullet effect on our camera with each dot having its own amount of energy. So there is no doubt photons exist and following this line of questioning is in direct contrast with observarions. The wave theory was shot down when Einstein figured it out up until that point they were blaming ozone for observations ect.

originally posted by: KrzYma
well... I have a different explanation for the dots on the film or whatever detector you use..
The EM wave "hits" the whole area on the detector, but is so week that it interacts with few atoms only, or even with only one, on the film it triggers the chemical reaction only in few spots.

OK, but some of that has to be quantum mechanical, right? What is causing the 'trigger of the chemical reaction only in [a] few spots'?

Because you can't measure E directly, only its interaction with detectors.

A reflection or diffraction of light is also not the same incoming wave just going in other direction,
its a new wave with same or different length, dependent on the status of electron that reproduces this wave spherical in all directions.

Sure, but 'new' vs 'old' is a human distinction, not a physical distinction.

If the E modulation can't be accomplish because my referring proton also just get displaced by som "high" E,
my emitted wave length will be different from that I'm ridding on

EM is not quantized, your detectors are.

It's been proven by delicate experiments in quantum optics that both E&M and the atoms it interacts with in detectors are quantized.

You're talking about a 'semiclassical' approximation which is often quite good in some limits (use QM in atoms, treat E&B classically and often with perturbation theory) and used in first semester QM, and is much easier to compute. But the full QFT of E&M is more correct.

originally posted by: Arbitrageur
Your explanation does not explain why the photoelectric effect is not dependent on intensity but only occurs if the threshold frequency is exceeded. If your idea was right, you should be able to just increase the intensity of the light to dislodge electrons, but that's not what happens.

True that's not what happens but still to explain the base experiment you could come up with a hybrid non-classical theory where the electron's allowable energy states & dynamics are quantized and the transition matrix element has the dependence on the incoming wave's frequency.

As it turns out, of course, the conceptually simplest and logical theory is that E&M is quantized as well. Einstein's hypothesis simultaneously explained the photoelectric effect and the Planck black-body spectrum, where the allowable modes of E&M in thermal equilibrium really are quantized.

In experiments with quantum optics with low photon numbers one could distinguish semiclassical from full quantized E&M explanations conclusively.

With SR, photons, GR, and even solid state physics Einstein had extraordinary physical insight and intuition, well before conclusive experimental evidence.

BTW, Bohr thought Einstein's idea of stimulated emission, and hence the laser, was nonsense.

a reply to: Arbitrageur, dragonridr, mbkennel

I'm not saying what we observe is not true, I just see it from a little different point of view.

I think the misleading point is this "wave" we're talking about.
You guys know nothing really travels from one charge to another, right?.
I mean saying that, there is nothing that moves between them, right?

How much is the potential difference between an electron that oscillates and a second one some "time later",
I mean far far away comparing to the second one and his nuclei "holding" him ?
I don't think it really matters, not for the B as well...

the field also does not "transport" any energy. All it does is pointing a direction.
EM wave, when it passes a charge, it does not move the charge or transfers anything to it.
It's giving the information about the direction to the charge only.
There is a second part, the density part, but I think you guys don't believe in scalar waves, right...

Of course one need a certain frequency to break a bond between "free" electron and nuclei in a metal structure.
They themselves have "stable" frequencies holding them together.

so what's so quanta in this except the jumping electrons ?


I said something about riding on a wave in my previews post, and called E field week,
what it means is... week means small directional change, and riding means getting the direction.
Sorry for the misleading words

originally posted by: KrzYma
the field also does not "transport" any energy. All it does is pointing a direction.

I found it interesting to learn just how much energy the field does transport. High voltage power lines transport most of the power in fields outside the wires.

Here's an interesting video demonstrating how fluorescent bulbs near power lines can light up from the power in the surrounding field:

Under high voltage power transmission lines fluorescent light bulbs light up without having any electrical source.

That video claims something about the fields around power lines being hazardous, but I don't think there's any clear evidence to show that living near a power line is either dangerous or completely safe. Personally I'd prefer to be at least a short distance away until more research is done, but I've never seen any proven hazard. However the fluorescent lights do indeed light up, there's no debate about that. How can they do that if the field isn't transporting any energy?

a reply to: Arbitrageur

sure, cool, so what's so special about it ??
You have a gas in a tube, are you saying they get powered by the line ??

Isn't it resonance and gas and molecule collisions that produces the light in the tube?

what do you think ? is there any energy transfer ?

a reply to: KrzYma

There's no direct connection with the power lines, so they aren't powered directly from the lines.

If you set up those tubes away from the power lines they don't light up by themselves.

So it's the EM fields around the power lines that cause them to light up.

In fact people have stolen power from the fields around the power lines and have been prosecuted for it. Their defense is often that they didn't touch the power lines, but it's still illegal.

message.snopes.com...

originally posted by: KrzYma
a reply to: Arbitrageur, dragonridr, mbkennel

I'm not saying what we observe is not true, I just see it from a little different point of view.

I think the misleading point is this "wave" we're talking about.
You guys know nothing really travels from one charge to another, right?.
I mean saying that, there is nothing that moves between them, right?

How much is the potential difference between an electron that oscillates and a second one some "time later",
I mean far far away comparing to the second one and his nuclei "holding" him ?
I don't think it really matters, not for the B as well...

Of course it does. Lienard-Wiechert potentials.

the field also does not "transport" any energy.

Sure as heck does. Momentum too.

All it does is pointing a direction.
EM wave, when it passes a charge, it does not move the charge or transfers anything to it.
It's giving the information about the direction to the charge only.
There is a second part, the density part, but I think you guys don't believe in scalar waves, right...

Experiment shows Maxwell is right.

My question about physics is- what is the future of quantam physics?

originally posted by: KrzYma


well... I have a different explanation for the dots on the film or whatever detector you use..

How about the nozzle of the source light emitter? In the device that creates EM radiation to be propagated toward the screen we can imagine that fundamentally as always, when the charged particles are accelerated, the EM field which is attached to the charged particles is moved, and its movement can be termed a wave. So this occurs inside a device. In order for this occurrence inside the device to get outside the device, it must pass through some opening. Is it not possible that the EM wave created in the device via charge particle acceleration is 'cut' when forced through the nozzle, and due to the relatively short distance in these experiments (in terms of light speed, very short distance) when the wave created in the device is broken, or channeled, by the nozzle, it is shot out in such a way, that in only pierces an area relative to the size of the nozzle, not relative to the size of the true wave, the true wave of which would be created if the charged particle was accelerated any where any time, though not when the result of the charge particles acceleration is channeled through a small opening, and then detected a small distance away?

originally posted by: dragonridr

originally posted by: Arbitrageur

originally posted by: KrzYma
If you watch his explanation why an EM wave is an particle because of dots on the screen...

well... I have a different explanation for the dots on the film or whatever detector you use..
The EM wave "hits" the whole area on the detector, but is so week that it interacts with few atoms only, or even with only one, on the film it triggers the chemical reaction only in few spots.

People used to think light was a wave before 1900, but there were problems with the wave theory of light not explaining certain observations, like the photoelectric effect.

According to classical electromagnetic theory, this effect can be attributed to the transfer of energy from the light to an electron in the metal. From this perspective, an alteration in either the amplitude or wavelength of light would induce changes in the rate of emission of electrons from the metal. Furthermore, according to this theory, a sufficiently dim light would be expected to show a lag time between the initial shining of its light and the subsequent emission of an electron. However, the experimental results did not correlate with either of the two predictions made by this theory.

Instead, as it turns out, electrons are only dislodged by the photoelectric effect if light reaches or exceeds a threshold frequency, below which no electrons can be emitted from the metal regardless of the amplitude and temporal length of exposure of light.

Your explanation does not explain why the photoelectric effect is not dependent on intensity but only occurs if the threshold frequency is exceeded. If your idea was right, you should be able to just increase the intensity of the light to dislodge electrons, but that's not what happens.

We can show individual photons easy now. We have digital cameras instead of photo paper. This is done in physics classes with a camera and a filter. If light was a wave putting basically sun glasses in front of the camera would decrease the frequency of the entire wave. But that isn't what happens what we see is a bullet effect on our camera with each dot having its own amount of energy. So there is no doubt photons exist and following this line of questioning is in direct contrast with observarions. The wave theory was shot down when Einstein figured it out up until that point they were blaming ozone for observations ect.

What light being a particle means, is that the entire universe is full of light particles, and that when light is created it is like Newtons cradle, and the detector detects the last particle hit?

a reply to: Arbitrageur

Ok does space really have to be expanding in order to accomodate the galaxies all, but a few, moving away from each other?

Now I hear that closer up galaxies move faster than the ones further away. It used to be the other way around, right?

Why o why don't I ever hear about the double slit experiment done with molecules? www.livescience.com...
The weirdness applies to all matter as long as the net interference with it is zero.

originally posted by: Mousygretchen
My question about physics is- what is the future of quantam physics?

Nobody really knows for sure but one common aspiration is to develop a "quantum theory of gravity" if such a thing is possible, to bridge the gap that now exists between general relativity and quantum mechanics.

originally posted by: QueenofWeird
a reply to: Arbitrageur

Ok does space really have to be expanding in order to accomodate the galaxies all, but a few, moving away from each other?.
Now I hear that closer up galaxies move faster than the ones further away. It used to be the other way around, right?

Galaxies moving through space is not the same thing as galaxies appearing redshifted because of expanding space. The apparent motion of the former is limited by the speed of light, while the latter is not, and in fact numerous distant galaxies have apparent recessional velocities greater than the speed of light, as a result of the expansion of space. This is simply not possible with closer galaxies moving through space.

Why o why don't I ever hear about the double slit experiment done with molecules? www.livescience.com...

Because you're not watching the right videos on youtube? I recall several that talk about performing the double-slit experiment with buckyballs which is a molecule with 60 atoms of carbon in a ball shape. That experiment was done at least 16 years ago:

sci.tech-archive.net...

Number 453 (Story #2), October 19, 1999 by Phillip F. Schewe and Ben Stein

WAVE PROPERTIES OF BUCKYBALLS have been observed in an experiment at the University of Vienna. Physical objects from quarks to planets have wavelike attributes. The quantum nature of a bowling ball, unfortunately, is not manifest since its equivalent quantum (or de Broglie) wavelength is so tiny that interference effects (for example, the left part of the ball negating the right part of the ball) cannot be detected in a practical experiment. However, the wave properties of some composite entities, such as atoms and even small molecules, have previously been demonstrated. Now Anton Zeilinger at the University of Vienna (zeilinger-office@xxxxxxxxxxxxxxxxx) has been able to perform the same feat for fullerenes, the largest objects (by a factor of ten) for which wavelike behavior has been seen.

The weirdness applies to all matter as long as the net interference with it is zero.

They have gone a little larger than buckyballs as your article states, but don't expect the double slit experiment to succeed with bowling balls. I rarely say something is impossible but I'm pretty sure it's impossible with bowling balls. It will be interesting to see how much larger they can go, but they may be getting close to a practical limit already, long before the size approaches bowling balls.

a reply to: QueenofWeird

in witch way exactly have they propelled the molecules again ?

originally posted by: Mousygretchen
My question about physics is- what is the future of quantam physics?

It's moved in, rearranged the furniture, drank the beer, stil smoking the weed, spewing all sorts of crazy stuff that somehow keeps on being right, and it ain't moving out.

originally posted by: ImaFungi


What light being a particle means, is that the entire universe is full of light particles, and that when light is created it is like Newtons cradle, and the detector detects the last particle hit?

In the end, yes. Pretty much all that technology is about light hitting an electron which was more, or less attached, to an atom or a collection of atoms in metal (so that the electrons are in a crowd), and then that starts moving as a current.

a reply to: Arbitrageur

Question for you Mr Arbitrageur (apologies if this has been asked).

I understand the dark matter theory was advanced to explain the flat rotation curves of stars orbiting a galaxy. The outer stars ought to be traveling slower than inner stars because the gravitational influence of the central black hole is weaker for them. But because the velocity is roughly the same for the outer stars, you need more matter to explain the apparently extra gravity.

Why isn't the same true then for outer planets orbiting a star system?

They DO travel slower than the inner planets, and dark matter - which is everywhere - doesn't influence them.

a reply to: CJCrawley
That's one of the best questions in this thread and no it hasn't been asked, so thanks for a great question.

Some of the common ideas about dark matter such as "wimps" would seem to suggest that they should be plentiful and create observable effects in our solar system, yet if the authors of the following paper are correct, their research supports what you say that there doesn't seem to be much effect if any from dark matter in our solar system:

Constraints on Dark Matter in the Solar System

We have searched for and estimated the possible gravitational influence of dark matter in the Solar system based on the EPM2011 planetary ephemerides using about 677 thousand positional observations of planets and spacecraft. Most of the observations belong to present-day ranging measurements. Our estimates of the dark matter density and mass at various distances from the Sun are generally overridden by their errors (σ). This suggests that the density of dark matter ρ dm, if present, is very low and is much less than the currently achieved error of these parameters.

This doesn't bode well for the idea that dark matter is mostly in "wimps", but that's not the only idea on the table about dark matter. A dark matter scientist on ATS posted this graphic showing many possible sources of dark matter, some of which I understand and some of which I don't so I can't even explain them all to you, but the main point you should take away from looking at this graphic is that there are many different ideas about what dark matter could be:

www.abovetopsecret.com...

originally posted by: ErosA433
As for what it is, there are as many theories as you can think of, and an interesting interplay between what the theories are and how they behave. There is a great image that shows this...

That is not my picture, I grabbed it from a blog after I saw it presented by a theorist in a conference.... To say that dark matter theory is closed minded is to deny that theory didn't put all its eggs in one basket but actually many baskets hehe

Common thoughts are that the dark matter can't have more than a small contribution from baryonic matter, meaning objects like Earth that we would generally have a hard time seeing at any significant distance. However gravitational microlensing observations claim to rule out an abundance of dark baryonic objects from half the mass of Earth and up. So could there be a lot of objects out there, maybe less than half Earth's mass, that wouldn't show up in microlensing experiments? Some say big bang nucleosysthesis models rule that out but I'd have to learn more about those models to comment on them. In fact I'm still trying to figure out what some of the potential dark matter sources on that chart above are. Maybe if the dark matter scientist who posted that chart sees your question he can share his thoughts with us on possible answers to your question.

When we say we don't know what dark matter is, we really mean that. At least one astronomer is still pushing for a modified gravity explanation despite most of the astronomical community being persuaded by bullet cluster observations that modified gravity can't really be the only answer either. It seems like every answer we try to come up with has some problems with it, so it's a great mystery. The answer may be that it's not any one thing, but many different things, some of which may already be listed on the chart above. There's also a possibility it could be something we haven't thought of yet.