Light
- Thread starter Fidget
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First things first. No force is needed to "drive" anything in free space. Newton's first law of motion says that an object will continue to travel in a straight line at constant speed forever, unless slowed down or sped up by a force. In other words, forces are only needed to change motion (speed), but not to keep it going.
Now, photons of light, from the moment they are created (in the sun or wherever), travel at the speed of light. They never change speed, so no force is required to "drive" them.
Now, photons of light, from the moment they are created (in the sun or wherever), travel at the speed of light. They never change speed, so no force is required to "drive" them.
Thanks for the reply. But don't i remember something about an object will remain at rest until etc etc.
So, photons are they called? I suppose that's the particle or wave?
I think you may have ducked the question. Sure after creation they travel at the speed of light and never change speed. But during creation and before the speed of light starts, what gets it going?????????????
I don't want to seem difficult, but I've been told scientists know what propels light, but they seem a bit tight liped.
Yes. That's Newton's first law again. An object at rest will remain at rest unless acted on by a force (because a force is needed to change the speed of an object).
Photons of light are never at rest. They always, from the moment of creation, travel at the speed of light.
A photon is a quantum entity that acts like a particle or a wave depending on exactly how you choose to observe it.
Well, the energy to create the photon in the first place must come from somewhere. One common way to create photons is to shake atoms around, or collide them together in some way, or to hit them with energy of some kind (light, radio waves, electrons, whatever). The atoms then goes to an excited energy state. But they soon spontaneously return to their normal (ground) energy state, releasing photons.
Nothing propels light (photons). Photons are created travelling at the speed of light, and they never change speed.
There is one general principle that's relevant here: photons have no rest mass. And it turns out that anything that has zero mass always travels at the speed of light, all the time. So, it's actually impossible to have a photon that is not moving, or moving slower than the speed of light.
Fidget: a useful analogy is a rubber mat. Pick it up and shake it around like those atoms are being shaken around, and you get a ripple running down the length of the mat. It doesn't have any mass, but it travels at a certain speed and conveys energy. Alternatively think of an oceanic swell wave. It's a bit like that ripple in the rubber mat, and it conveys energy. But it doesn't have any mass because the water has the mass. Then if you flew above the swell-wave in a helicopter, it would look like a "lump" rather than a wave, so it would look more particle-like than wave-like. Electromagnetic waves or photons aren't quite the same, but it should give you a rough idea.
Farsight, thanks. Yes I can imagine all that, but it didn't get down to my question as someone has to shake the mat, and something starts waves moving. What I was wondering is what caused light to travel.
I can accept it moves itsself somehow if it can't be explained to a layman.
Constant speed is also a worry if a weak torch emits a beam at C and goes for ever.
I think my biggest problem is not realising the strange nature of light.
Tried to post a link to a site that had a few examples of experements, including a video and photo of a light particle/wave, Young's double slit etc
but broke some rule that I didn't see in the rules.
I can accept it moves itsself somehow if it can't be explained to a layman.
Constant speed is also a worry if a weak torch emits a beam at C and goes for ever.
I think my biggest problem is not realising the strange nature of light.
Tried to post a link to a site that had a few examples of experements, including a video and photo of a light particle/wave, Young's double slit etc
but broke some rule that I didn't see in the rules.
How are photons created?
Lots of different ways.
One example, given earlier, is when an excited atom loses internal energy. Energy is conserved through the emission of a photon.
freziggity
Registered Member
Well what about gravitation? Could gravity be the force that propels the photon? Think of a super dense star. Imagine the immense pressure at the center of a mass like that. There is a certain Principle founded by one Wolfgang Pauli (The Pauli Exclusion Principle), This principle states, to paraphrase, That two states cannot occupy the same space. And since Newtonian law rules, for every action there is an equal and opposite reaction. Compressing two atoms together will case an emission of energy. Some of that energy would be of the visible wavelength. I think this explains the propulsion of quanta. The speed of light may have something to do with the enigmatic Higgs Background. The hypothetical energy field that applies the equal and opposite force to the compression of gravitation. I believe that the residual energy left over from infinite decay of infinite particles in infinite space/time are what composes the Higgs background, and the reason light can travel smoothly through space is because it is slicing through the particles both propelling them and being degraded by them.
Photons don't need a force to propel them.
That law is only about forces, you know.
Not always. Sometimes energy is absorbed, depending on the atoms.
Not always.
Huh? How can you apply a force to the "compression of gravitation"? Compression is an effect, not an object.
Why do you believe that?
Strange things these photons. The above quote explanes some misconseptions I had in Gemology 101. I.e. That as light exits a gemstone it immediatly speeds up to it's original c.
Well that threw me. I figured it must have it's own power source.
Then this, from a Gem book; Speed of light in air 300,000 km/sec.
Speed of light in a diamond 124,120 km/sec.
I.e. 2.4 times faster in air.
So in science forums I've read light doesn't slow down. I guess it reflects or something, around a transparent stone, which would seem to slow it down in effect.
So I'm fairly happy. Photons are interesting.
It's essentially the same for light. Some applied force essentially shakes an atom and it makes waves that travel through space. See what I said earlier about wave/particle duality. There's no friction at all, so they keep on going just like the earth keeps on going round the sun.
It's simpler than you might think. The key is to focus on the original Maxwell in say On Physical Lines of Force and home in on displacement current. As a photon passes you by there's an electromagnetic field variation, but there's no charged particle present. Instead it's "displacement current" passing you by, and it's effectively alternating because the field variation goes this way ↑ then that way ↓ in line with the typical sinusoidal waveform. For myself I think the best way to think about it is as a "pulse of displacement", or "a pulse of spacewarp".
Note that the quantum nature of light comes from Planck's constant of action, the h in E=hf. Action is basically "kick", and applies to waves rather than billiard-ball particles. Most people have a problem with photons because they think of them as little solid things rather than little pulses of spatial action.
As farsight pointed out, the original Maxwell equations demonstrate how the speed of light can be measured (frequency * wavelength) and James R highlighted Newton's first law of motion stating that a force is not needed to "drive" anything in the vacuum of space. Both examples hint that a photon will always move at a constant rate from the moment it is created. This velocity maxes out at 299,792,458 m/sec in a pure vacuum and there have been experiments preformed that show, in certain mediums, a photon can "stand still". This brings us to post #13 where you bring up the refraction index of diamond.
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An important thing to note is that the photon leaving a diamond medium is not the same photon that entered it. Here's what's happening. The moment a single photon enters an atomic structure, like diamond or air, it immediately becomes absorbed by certain electrons that "orbit" the nucleus of an atom (electron shell). When an electron absorbs the photon's energy it gets "lifted" out of its ground state and then, just as fast, releases that absorbed energy in the form of a newly produced photon. This allows that electron to "snap back" to its natural ground state which is determined by it location from the atomic nucleus. Diamond happens to be the hardest (densest) natural molecular structure known to man. The reason diamond has such a high refraction index is because its carbon atoms are so tightly packed together. The energy being carried by a photon can move through certain mediums without being totally absorbed. The number of times a single photonic energy pocket gets absorbed and then re-emitted will alter its wavelength (not the frequency). This is what we observe as the "slowing of light" I.e. Change in the angle of incident.
freziggity
Registered Member
:shrug:
So, how are they created when two nuclei fuse?
Agreed.
http://www.news.harvard.edu/gazette/1999/02.18/light.html
Do you mean stand still relative to the earth's motion?
Does that mean it stands still in the vacuum of space or relative to the earth's motion?
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Fidget:
What happens to light in a medium (such as diamond or water or glass) is that photons travel between the atoms at the normal speed of 300,000 km/s. However, their interactions with the atoms in the medium lead to a delay in propagation. The details of the interaction in a transparent medium are complicated - it's not quite the same as absorption and re-emission (which also take time and cause delay) - but the effect is similar.
Jack_:
When two nuclei fuse, the resulting nucleus is typically not in its lowest possible energy state. It loses the residual energy by emitting one or more photons.
freziggity:
:sleep:
What happens to light in a medium (such as diamond or water or glass) is that photons travel between the atoms at the normal speed of 300,000 km/s. However, their interactions with the atoms in the medium lead to a delay in propagation. The details of the interaction in a transparent medium are complicated - it's not quite the same as absorption and re-emission (which also take time and cause delay) - but the effect is similar.
Jack_:
When two nuclei fuse, the resulting nucleus is typically not in its lowest possible energy state. It loses the residual energy by emitting one or more photons.
freziggity:
:sleep: