Ask any question you want about Physics

originally posted by: dragonridr
As for wavelengths I think you are majorly confused no where did we discuss the wavelengths a frog can see. Yes a frog can see green light but hardly what was being discussed or even relevant for that matter.

Correct, we didn't discuss it directly in this thread, but the "532 nano-meters" came from the article I linked to which is the wavelength the experimentalists chose to use for their experiment in determining that frogs eyes could detect individual photons.

The original light source was ultraviolet, (wavelength 266nm) and to get individual photons for the experiment they used a nonlinear optical crystal which converts about one photon in every million into two photons of half the energy level, with wavelength 532nm. It's just a trick they used to get the number of photons down to an experimentally manageable number.

KrzYma somehow managed to read the "532 nano-meters" in the article without realizing that the entire experiment would be impossible if photons didn't really exist.

Speaking of mirrors my crazy idea was that we could see Earth's past if there was a mirror in space we could aim a telescope at that was positioned perfectly so Earth's past light was reflected back from where the earth was to where it is now, not an easy feat considering all the motions of the earth over time, rotating, orbiting the sun which is orbiting the galaxy.

a reply to: Arbitrageur

No joke, that was my original idea.... using mirrors, but i simply thought it was less feasible than just putting a telescope in place of the mirror to begin with... but yes totally impractical and improbable to achieve... cool to think about indeed!

Photons have mass yet travel at the speed of light. Light exhibits wave-form motion. In an experiment light is aimed perpendicular to two parallel planes with perfectly concentric holes of equal size. Light passes through the first opening. Some of the light continues through the second opening, but not all of it. The remainder fans out in a cone shape as a result of having been re-directed by the edge of the first opening. The re-directed light continues at the same speed as before it passed through the opening.

How can mass be re-directed without losing energy? If the photons do slow down, what does light become when it travels at sub-light speed? If it is possible for photons to travel below light speed, theoretically should it be possible for them to travel above light speed as well?

Question to all

I was thinking recently how to picture GR concept and may be have come closer in understanding its premise and principal of gravity. That is from geometry visualisation point of view.

We have axis combination X Y Z somewhere in space. Lets equally make one meter apart markings on all three.
Now, lets position axis set of X Y Z in low Earth orbit in such a way that axis Z is pointing toward Earth.

GR gradient factor in this case simply would mean that markings on axis Z with every repeat will get longer compared
to the other two.
If we are to speak of physical solid body (rubber cube) positioned in such coordinate system, we will get the cube
elongated along axis Z. Physically elongated. Its local center of gravity will move along Z. Since cube is rigid coherent physical
body, molecular, nuclear forces will compensate such a move to maintain over all composure and shape. The thing is that as soon as form gets restored, gradient factor on axis Z again distorts the cube along Z axis.

Gravity in this GR scenario to me is pure geometrical in nature.

And QM fits into this in a way that strong forces of an object inside gravity well finds balance and maintains composure despite being physically stretched along Z axis.

What do ya think?


cheers

originally posted by: Vroomfondel
Photons have mass yet travel at the speed of light.

We say they're massless, meaning if they have any it's too small for us to measure. They might actually have exactly zero mass but we'll never be able to prove that, the best we can do is prove the mass, if any, must be very, very small, which includes zero.

How can mass be re-directed without losing energy?

Not relevant since photons don't have mass.

If the photons do slow down, what does light become when it travels at sub-light speed? If it is possible for photons to travel below light speed, theoretically should it be possible for them to travel above light speed as well?

Photons travel at the speed of light in a vacuum. In substances other than a vacuum, the measured speed of light is slower than the speed of light in a vacuum. Existing theory explains this and doesn't allow for faster than light photons that we know of.

originally posted by: darkorange
Question to all

I was thinking recently how to picture GR concept and may be have come closer in understanding its premise and principal of gravity. That is from geometry visualisation point of view.

We have axis combination X Y Z somewhere in space. Lets equally make one meter apart markings on all three.
Now, lets position axis set of X Y Z in low Earth orbit in such a way that axis Z is pointing toward Earth.

GR gradient factor in this case simply would mean that markings on axis Z with every repeat will get longer compared
to the other two.
If we are to speak of physical solid body (rubber cube) positioned in such coordinate system, we will get the cube
elongated along axis Z. Physically elongated. Its center of gravity will move along Z. Since cube is rigid coherent physical
body, molecular, nuclear forces will compensate such a move to maintain over all composure and shape. The thing is that as soon as form gets restored, gradient factor on axis Z again distorts the cube along Z axis.

Gravity in this GR scenario to me is pure geometrical in nature.

And QM fits into this in a way that strong forces of an object inside gravity well finds balance and maintains composure despite ever running out of shape along Z axis.


cheers

Shape of an object really doesn't have as much effect on gravity as the density of the object. The particles mass doesn't change stretching or bending rubber. So it's center of gravity really wouldn't change but add a second cube and you would see a shift.

originally posted by: Arbitrageur

originally posted by: dragonridr
As for wavelengths I think you are majorly confused no where did we discuss the wavelengths a frog can see. Yes a frog can see green light but hardly what was being discussed or even relevant for that matter.

Correct, we didn't discuss it directly in this thread, but the "532 nano-meters" came from the article I linked to which is the wavelength the experimentalists chose to use for their experiment in determining that frogs eyes could detect individual photons.

The original light source was ultraviolet, (wavelength 266nm) and to get individual photons for the experiment they used a nonlinear optical crystal which converts about one photon in every million into two photons of half the energy level, with wavelength 532nm. It's just a trick they used to get the number of photons down to an experimentally manageable number.

KrzYma somehow managed to read the "532 nano-meters" in the article without realizing that the entire experiment would be impossible if photons didn't really exist.

They picked a green laser because the frog could see it and it was easy for the experiment to manipilate. Has nothing to do with anything about the frogs eye. Only thing it shows is they are much more sensitive to light they we are and can see far fewer photons then we can. Just the fact that they can see something there when we can't jag very significant it means nature made something we had to build.

So i read about the doube slit experiment;

link

Does the world only exist when its perceived? Or is it a click and bait?

a reply to: Arbitrageur

originally posted by: yulka
So i read about the doube slit experiment;

link

Does the world only exist when its perceived? Or is it a click and bait?

For the best answer, see the video in the OP by Sean Carroll.

tl;dr: We don't really know which of our ideas about the true nature of reality, if any, are correct.

originally posted by: yulka
So i read about the doube slit experiment;

link

Does the world only exist when its perceived? Or is it a click and bait?

No it's here all the time just maybe not where we think it is.

a reply to: Arbitrageur

Photons travel at the speed of light in a vacuum. In substances other than a vacuum, the measured speed of light is slower than the speed of light in a vacuum. Existing theory explains this and doesn't allow for faster than light photons that we know of.

This is where the theory and the logic diverge for me. If light slows down when passing through some media, or stops when it encounters something solid, it is behaving exactly like we would expect any moving mass to behave. The waveform motion described in the double slit experiment also indicates mass.

I was always taught that the answer is never to redefine the question. You may have to redefine reality, however.

I have always thought of photons as having mass but an immeasurably small amount of friction. That theory explains the speed but still allows for the observable properties of mass in motion. I find it much easier to define photons as small, fast, and slippery rather than observable non-masses that exhibit fluid properties yet travel at the speed of light...

originally posted by: Vroomfondel
This is where the theory and the logic diverge for me.

The massless photon is based on observation, not logic or theory though it happens to fit our theories. Observation hasn't been particularly friendly to our logic since we discovered quantum mechanics.

If light slows down when passing through some media, or stops when it encounters something solid, it is behaving exactly like we would expect any moving mass to behave. The waveform motion described in the double slit experiment also indicates mass.

Light travels at a constant velocity through a medium like water. This is not how a massive object would behave. If you drive a boat through the water you have to add energy to keep it moving at a constant velocity....not so with light traveling through water. The second sentence makes no sense to me since the double slit experiment tells us nothing about any mass.

I have always thought of photons as having mass but an immeasurably small amount of friction. That theory ...

Why are you still talking about photons having mass when observations show it doesn't? Friction? A wall stops photons of certain wavelengths completely but allows photons of other wavelengths to pass. This isn't how friction works. Again observation is the key to science. When observation shows the photon has no measurable mass (less than 1×10^−18 eV/c^2), it's not productive to continue to hang on to the idea that it has mass.

The key to science:

a reply to: Arbitrageur

What you say makes sense. I had not considered some wavelengths passing through while others do not.

It was the double slit experiment, or something very similar, that led me to believe that photons have mass. I usually hang on to my beliefs until someone gives me good reason to change them. I was not challenging the science, or your explanation of it, but rather my own beliefs.

Thank you for answering my question.

a reply to: dragonridr

As for wavelengths I think you are majorly confused no where did we discuss the wavelengths a frog can see. Yes a frog can see green light but hardly what was being discussed or even relevant for that matter.

DUDE !!! that's from the experiment.
The experiment didn't proved a frog can see a single photon, it proves only that rod cell from a frog's eye react to EM radiation at a wavelength of 532 nano-meters.
The experimental setup with splitting crystal and what not else used in that experiment proves only and only this, nothing else !!

a reply to: dragonridr

The shorter the wavelength the higher the energy and yet the speed of light remains the same for all wavelengths. The constant value of the speed of light in vacuum goes against our intuition: we would expect that high energy (short wavelength) radiation would move faster than low energy (long wavelength) radiation. We can consider light as a stream of minute packets of energy, photons, which create a pulsating electromagnetic disturbance.

I need to split it...

The shorter the wavelength the higher the energy

sure... more change in EM in shorter time period.

yet the speed of light remains the same for all wavelengths

locally.. but yes, same medium for all waves propagating

we would expect that high energy (short wavelength) radiation would move faster than low energy (long wavelength) radiation

I would never assume this, told you, same field density same propagation speed

We can consider light as a stream of minute packets of energy, photons, which create a pulsating electromagnetic disturbance.

kicking out electrons from an material is the property of the material and not a property of the radiation only.
There is an interaction and different materials have different effect.

originally posted by: KrzYma
kicking out electrons from an material is the property of the material and not a property of the radiation only.
There is an interaction and different materials have different effect.

Yes some physicists weren't entirely convinced the early photoelectric effect experiments couldn't be explained classically along those lines, but there wasn't a single physicist left that I know of who could explain this later experiment in 1985 without using photons, emphasis mine:

A New Light on Single-Photon Interferences

We report on two experiments using an atomic cascade as a light source, and a triggered detection scheme for the second photon of the cascade. The first experiment shows a strong anticorrelation between the triggered detections on both sides of a beam splitter. This result is in contradiction with any classical wave model of light, but in agreement with a quantum description involving single-photon states. The same source and detection scheme were used in a second experiment, where we have observed interferences with a visibility over 98%.

There is no scientific debate anymore about the existence of photons, but your thoughts would have fit in about 100 years ago in 1915 when there was some skepticism about Einstein's 1905 quantum predictions.

Now you've got a century of catching up to do.


a reply to: Vroomfondel
You're welcome.

While photons don't have mass, they do have momentum.

a reply to: Arbitrageur

Not only einstine in 1905.but id add the Compton effect and thisjournals.aps.org...

Now of he would like to show how any of these would be possible if light were not quantized I'm all ears.

a reply to: dragonridr
Neils Bohr was the "B" in BKS theory advanced in 1924 which tried to explain the Compton effect without using photons, but more refined Compton experiments later finally convinced Bohr and others to give up their struggle to hold on to the concept that classical electromagnetism could explain observations.

It's interesting to study the history of physics and see how some of the old ideas aren't given up without a fight, and that was one of them, but even Bohr finally admitted he lost the fight, and that some observations couldn't be explained classically.

a reply to: Arbitrageur

A photon is an elementary particle, the quantum of light and all other forms of electromagnetic radiation. It is the force carrier for the electromagnetic force, even when static via virtual photons.

if this is true, radio waves are photons to ???