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  • #31
    Originally posted by firstfloor View Post
    I’m glad you brought this up Sparko because it is very surprising and I am enjoying learning about it.

    The speed of light comes out of Maxwell’s equations once a couple of measurable constants (one electrical, one magnetic) and put into the equations. It is simply the speed that the wave goes no matter what energy it has. Nothing to do with impulses or recoils except that the photon has momentum by its velocity and energy.

    When you look at the night sky, photons that have been travelling across space for hundreds and perhaps thousands of years (Eta Carinae on the limits of naked eye visibility is 7500 ly away) are annihilated by interaction with a molecule of the pigment retinaldehyde. Photons are not conserved. They do not age either – the spacetime distance between emission and absorption for any photon is zero (Relativity).

    Why does light go through glass? – There are no energy levels available in glass (the electrons are tightly bound to atoms) to absorb visible light – there are for ultraviolet light – which gets absorbed.
    yep I find it interesting too.

    so what causes the "wave" - in sound, you have the motion of an object back and forth at a particular frequency that pushes the air molecules and pulls them causing compression waves that are pushed outwards. They are physically propelled by the diaphragm. So what causes the light wave and frequency?

    For the sarcastically impaired the following is said in jest


    My theory: Space is a vaccuum and it is dark. The light is attracted to the dark vacuum trying to fill the dark holes (darkons). Vacuum sucks the photons into the darkons. And since even much matter is mostly empty space (vacuum) light can move through and is sucked by the vacuum between air molecules. Your eyes are dark inside, so the light is attracted to them and slams into your retinas allowing you to see.


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    • #32
      Originally posted by Sparko View Post
      So what causes the "wave" - in sound, you have the motion of an object back and forth at a particular frequency that pushes the air molecules and pulls them causing compression waves that are pushed outwards. They are physically propelled by the diaphragm. So what causes the light wave and frequency?
      It's not really a wave so much as it's oscillation + motion. For a photon, the electromagnetic field is oscillating around the photon itself. If the photon were stationary and polarized in the right way, we'd just view it as bouncing up and down around the central point. Since it's moving at a finite speed, it end up behaving like a wave.
      "Any sufficiently advanced stupidity is indistinguishable from trolling."

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      • #33
        Originally posted by TheLurch View Post
        It's not really a wave so much as it's oscillation + motion. For a photon, the electromagnetic field is oscillating around the photon itself. If the photon were stationary and polarized in the right way, we'd just view it as bouncing up and down around the central point. Since it's moving at a finite speed, it end up behaving like a wave.
        what is an electric field made out of?

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        • #34
          Originally posted by Sparko View Post
          yep I find it interesting too.

          so what causes the "wave" - in sound, you have the motion of an object back and forth at a particular frequency that pushes the air molecules and pulls them causing compression waves that are pushed outwards. They are physically propelled by the diaphragm. So what causes the light wave and frequency?
          The diaphragm of a loud speaker does not really push the wave outwards. For example you could generate a loud low note and a soft high note and they would travel at the same speed of sound through the air. What the speaker is doing is determining pitch and how energetic the wave is. The medium determines the wave velocity.

          The Michelson–Morley experiment (1887) was supposed to discover the medium (aether) through which light travelled or at least the speed that the earth was travelling through it. What it discovered was the invariance of the speed of light which counts against the idea of a medium. As far as I can tell, the current view is that light does not require any medium. Why? – Because it is not a mechanical wave. It is made of quantum-mechanical stuff and different rules apply.
          “I think God, in creating man, somewhat overestimated his ability.” ― Oscar Wilde
          “And if there were a God, I think it very unlikely that He would have such an uneasy vanity as to be offended by those who doubt His existence” ― Bertrand Russell
          “not all there” - you know who you are

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          • #35
            Originally posted by firstfloor View Post
            The diaphragm of a loud speaker does not really push the wave outwards. For example you could generate a loud low note and a soft high note and they would travel at the same speed of sound through the air. What the speaker is doing is determining pitch and how energetic the wave is. The medium determines the wave velocity.
            The wave moves outwards. The diaphragm generates the wave by moving molecules back and forth which push other molecules and continue the wave. It creates high and low pressure zones which propagate through the medium (air, wood, water, whatever)

            The Michelson–Morley experiment (1887) was supposed to discover the medium (aether) through which light travelled or at least the speed that the earth was travelling through it. What it discovered was the invariance of the speed of light which counts against the idea of a medium. As far as I can tell, the current view is that light does not require any medium. Why? – Because it is not a mechanical wave. It is made of quantum-mechanical stuff and different rules apply.
            Isn't an electromagnetic field a medium?

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            • #36
              Originally posted by Sparko View Post
              The wave moves outwards. The diaphragm generates the wave by moving molecules back and forth which push other molecules and continue the wave. It creates high and low pressure zones which propagate through the medium (air, wood, water, whatever)



              Isn't an electromagnetic field a medium?
              Certainly, physicists talk in terms of fields and waves. It seems that the electric field is generated by stationary charges and the magnetic field by moving charges (currents) which I take to mean that the field is determined by the distribution and movement of everything electrical that’s in it. And the strength of the field at any point has to do with the probability of there being something there. Presumably, if you could remove all the electrons or other charged particles, there would be no electromagnetic field at all except perhaps for these virtual particles (electron/positron pairs) that we hear about.

              I’m not sure whether that counts as a medium or not.
              “I think God, in creating man, somewhat overestimated his ability.” ― Oscar Wilde
              “And if there were a God, I think it very unlikely that He would have such an uneasy vanity as to be offended by those who doubt His existence” ― Bertrand Russell
              “not all there” - you know who you are

              Comment


              • #37
                Originally posted by Sparko View Post
                what is an electric field made out of?
                How much of quantum field theory do you know?

                The only answer i can realistically give is something i'm sure is a gross oversimplification that will horrify physicists (i'm not a physicist, so i'm good with it):

                Empty space is filled with fields - gravitational, electromagnetic, etc. These fields mediate all the behavior we see at the quantum level. So, electromagnetic phenomena are basically changes in the electromagnetic fields. In that sense, electric fields aren't "made" of anything - they're simply something that exists in empty space.
                "Any sufficiently advanced stupidity is indistinguishable from trolling."

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                • #38
                  Originally posted by Sparko View Post
                  There is no way it can go any measurable distance without hitting some atom in the air or in say a piece of clear glass.
                  There's a lot of space between atoms, even in a solid object. It's also why balloons don't stay inflated forever. Any gas in them will eventually squeeze its way through the rubber until the inside and outside pressure is equalized.
                  "As for my people, children are their oppressors, and women rule over them. O my people, they which lead thee cause thee to err, and destroy the way of thy paths." Isaiah 3:12

                  There is no such thing as innocence, only degrees of guilt.

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                  • #39
                    Originally posted by firstfloor View Post
                    Certainly, physicists talk in terms of fields and waves. It seems that the electric field is generated by stationary charges and the magnetic field by moving charges (currents) which I take to mean that the field is determined by the distribution and movement of everything electrical that’s in it. And the strength of the field at any point has to do with the probability of there being something there. Presumably, if you could remove all the electrons or other charged particles, there would be no electromagnetic field at all except perhaps for these virtual particles (electron/positron pairs) that we hear about.

                    I’m not sure whether that counts as a medium or not.
                    From what I understand, the electromagnetic force is basically transmitted by photons. After all electromagnetic radiation IS photons. But that still doesn't explain what fields are. the Electric field and Magnetic field are 90 degrees out of phase with each other but what they actually ARE I don't think anyone knows. Magnetism is transmitted via photons and Electricity is transmitted via electrons, and moving a conductor through a magnetic field creates electricity, and moving electricity creates a magnetic field. It's all pretty confusing.

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                    • #40
                      Originally posted by Sparko View Post
                      From what I understand, the electromagnetic force is basically transmitted by photons. After all electromagnetic radiation IS photons. But that still doesn't explain what fields are. the Electric field and Magnetic field are 90 degrees out of phase with each other but what they actually ARE I don't think anyone knows. Magnetism is transmitted via photons and Electricity is transmitted via electrons, and moving a conductor through a magnetic field creates electricity, and moving electricity creates a magnetic field. It's all pretty confusing.
                      A field is just some region of space where some influence or other (force) can be felt, say, like the magnetic field surrounding a magnet. Photons are the quantum of the electromagnetic field. It is possible for electricity to give rise to magnetism and for magnetism to give rise to electricity and it is this interplay that is exhibited in electromagnetic radiation (light) that requires no medium.

                      https://www.scribd.com/document/3391...And-Matter-pdf
                      “I think God, in creating man, somewhat overestimated his ability.” ― Oscar Wilde
                      “And if there were a God, I think it very unlikely that He would have such an uneasy vanity as to be offended by those who doubt His existence” ― Bertrand Russell
                      “not all there” - you know who you are

                      Comment


                      • #41
                        Originally posted by firstfloor View Post
                        A field is just some region of space where some influence or other (force) can be felt, say, like the magnetic field surrounding a magnet. Photons are the quantum of the electromagnetic field. It is possible for electricity to give rise to magnetism and for magnetism to give rise to electricity and it is this interplay that is exhibited in electromagnetic radiation (light) that requires no medium.

                        https://www.scribd.com/document/3391...And-Matter-pdf
                        You just said the same thing I did.

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                        • #42
                          Originally posted by Sparko View Post
                          From what I understand, the electromagnetic force is basically transmitted by photons. After all electromagnetic radiation IS photons. But that still doesn't explain what fields are. the Electric field and Magnetic field are 90 degrees out of phase with each other but what they actually ARE I don't think anyone knows. Magnetism is transmitted via photons and Electricity is transmitted via electrons, and moving a conductor through a magnetic field creates electricity, and moving electricity creates a magnetic field. It's all pretty confusing.
                          Fields are just various physical interactions at different points in space-time that can be described by either scalars, vectors, or tensors.

                          There are fields for just about everything in physics. Fundamental forces like Gravity, Electromagnetism, and the Nuclear forces have specific quanta that levitate them: Gluons for the Strong Nuclear force, Photons for the Electromagnetic force, W and Z Bosons for the Weak force, and a hypothesized 'Gaviton' for the Gravitational force. According to the Theory of Quantum Fields (QFT) these fields exhibit both particle like behavior through their quanta, and also behave as classical fields too. The fields I just mentioned are vector fields as they have both a magnitude and direction, whereas fields such as the Higgs field have no direction and can be represented by just it's magnitude -- so just a single number. Part of the reason Dark Matter is so hard to understand (aside from it not being included in the Standard Model) is because it does not interact with the Electromagnetic field.

                          Yes, it can be confusing.

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                          • #43
                            Originally posted by Sparko View Post
                            You just said the same thing I did.
                            In that case you must be right.
                            “I think God, in creating man, somewhat overestimated his ability.” ― Oscar Wilde
                            “And if there were a God, I think it very unlikely that He would have such an uneasy vanity as to be offended by those who doubt His existence” ― Bertrand Russell
                            “not all there” - you know who you are

                            Comment


                            • #44
                              Originally posted by firstfloor View Post
                              In that case you must be right.
                              which means you are right. Welcome to the republican party!

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                              • #45
                                Originally posted by Sparko View Post
                                which means you are right. Welcome to the republican party!
                                I recommend to you “Making sense of Maxwell” in series History 181B available on iTunes.
                                “I think God, in creating man, somewhat overestimated his ability.” ― Oscar Wilde
                                “And if there were a God, I think it very unlikely that He would have such an uneasy vanity as to be offended by those who doubt His existence” ― Bertrand Russell
                                “not all there” - you know who you are

                                Comment

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