ohwilleke

Yet, this is precisely what happens. The reason your intuition is failing you is that you expect particles to be the size of the smallest particle you can perceive, a mote of dust perhaps. But, photons are very, very small, and stars produce a huge amount of light.

First, the problem of a moving platform is easily solved. Under Einstein's Theory of Relativity, you can choose any spot you want as an inertia reference frame, and define all other motion in reference to you. This does result in some pretty ridiculous seeming implications, such as the fact that time moves at different rates in different places. But, experiment supports Einstein in this. For example, particle accellerators wouldn't work if they didn't (because they are designed on the assumption that particles accellerated in them decay more slowly in the lab's frame of reference than they would at rest, because time slows down when the particle is moving quickly relative to the lab).

The experiments used are clever and don't rely on the speed of the electricity in wires.

A fundamental principal of quantum mechanics instead of asking "why" simply posits that all particles act like waves and visa-versa. One way of thinking about the wave-particle duality in photon (not mathematically rigorous, but conveying the right idea) is to visualize an individual photon as a tiny arrow spining about its center as it moves in space, rather than a round dot. When two photons pointing the opposite direction hit the same spot, they cancel out. When two photons pointing the same direction hit the same spot, they merge into one big photon. Viewing photons as a wave is a convenient way of explaining the average behavoir of numerous photons acting in this way.

When light hits something it does one of three things. It goes betweeen atoms, it bonks from the electrons around atom to another in a chain reaction producing a new photon at the other end, or it bounced back. What happens depends on atomic structure.

Sidian

Thank for the info/links. I'm learning alot which of course provokes more questions.

What happens to photons? All the photons from the last 2345623452435 billion years are bouncing (in huge numbers which i have a problem with =( ) around in the galaxy? Or do they get "absorbed" into say black paint and transfered into heat energy?

Can a photon become heat? I understood heat to be molecular activity. I concluded (with absolutely no scientific evidence...sorry) that heat from light was maybe collision based or else my molecules being pulled and pushed by waves from light sources.

Also where did we get measurements on the energy of one photon? especially to a -19 power of accuracy?

Also, when they do these lightwave experiments looking for interference, how do they know their distances between mirrors are perfect? Visible light surely has very short wavelengths (nanometers?), it would seem difficult to credibly validate measures without USING light interference to line up the mirrors. Isn't that a circular type of experiment? Interferometers are going to tax my mind for a while.

Farther out from the north star(I picked this one for it's fame) aren't there stars about the size or smaller then our sun which we can see with telescopes? How many photons have to be fired from THAT star (with lower lumination then our sun) to reach all the way to our telescopes? And can we assume those are widespread?

I'd like to add that i'm a peon who works nights and has a high school grad education. I like math a lot and this stuff pops into my head when I'm bored staring at the wall(on the clock of course =) ). I'm definately not highly educated, just good with what it is i HAVE learned. I found this board a long time ago doing some other self answering and figured I'd pop some more questions on you guys.

I'm not trying to insult any scientists past or present. Stuff like this pops into my head and won't leave me alone. It still doesn't seem to come together well for me. More time and thought to invest staring at the wall =)

tronvillain

Well, to start with your age of the universe is a little larger then current estimates, by a factor of around a hundred million. Anyway, all the photons ever emitted are either still around (for example, the cosmic microwave background radiation) or have been absorbed by matter. When photons are absorbed by matter, the energy of that matter is raised, and it either retains that energy or emits some or all of it again as a photon.

Now, the more distant a star of a given brightness is, the fewer photons from it reach us. In other words, more distant stars are harder to see. Other than that, I'm not sure what you're asking.

Tim Thompson

Photons from Polaris

<a href="http://www.astro.uiuc.edu/~kaler/sow/polaris.html" target="_blank">Polaris</a> is 431 light years away (<a href="http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/hipparcos.html" target="_blank">Hipparcos</a> parallax 7.56 milli-arcseconds). It is (or was) a <a href="http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/cepheid.html" target="_blank">cepheid variable star</a>, an overtone pulsator, with an average absolute magnitude of -3.50, which means that its visual magnitude would be -3.50 if it were 10 parsecs (32.6 light years) away.

From the absolute magnitude, we can compute the true average luminosity of Polaris, and it turns out to be 2070 times that of the sun, or about 7.92x10^36 erg/second. The distance 431 light years translates into 9.4606x10^17 cm, and a sphere with that radius has a surface area of 1.12x10^37 cm^2. Divide the total luminosity by the area of that sphere, and you get 0.704 erg/sec/cm^2, the energy flux delivered to Earth by Polaris.

The energy of a single photon is Planck's constant times the frequency (E = hf). The frequency of a typcal visible photon will be about 5.45x10^14 Hertz where the normal eye is most sensitive, and Planck's constant is about 6.626x10^-26 erg-sec. The product hf is therfore 3.61x10^-12 erg. That's the energy of a single visible photon. Now just divide the total energy (0.704 erg/sec/cm^2) by the energy per photon, and you get the total number of photons per square cm per second that are required to deliver that energy. The number is 1.950x10^11 photons/cm^2/sec. That's one hundred and ninty five billion photons per square centimeter per second, delivered to Earth, by Polaris. In millimeters, that's 1.95x10^9 photons per square millimeter per second.

The pupil diameter for your eye varies from about 1 to 8 mm. At one millimeter, its smallest size, its area is 0.785 mm^2, and it would see 1.53x10^9 (1.53 billion) photons per second. However, under a dark night sky, your pupil should be wide open, much closer to 8 mm, in which case its area of 50.3 mm^2 will see 9.80x10^10 (98 billion) photons per second, just from looking at Polaris.

Now, armed with the real numbers, we can revisit the question, whether or not there is something strange about being able to see Polaris as you move around, as illustrated in the earlier long post. We see that it is not at all surprising. What probably is surprising, and unexpected, is the huge number of photons actually arriving at Earth, from Polaris, even though it looks like just a tiny light in the sky. But in fact, the number is really that big. The sun, which delivers about 1.367x10^6 erg/cm^2/sec to the top of Earth's atmosphere, therefore delivers about 3.787x10^17 (3.787 hundred thousand trillion) photons per square centimeter per second.

Also note that the idea that many photons are required to stimulate vision is incorrect. The rod cells in the retina are sensitive enough to trigger off of a single photon, under optimum conditions (it takes about a half hour to reach fairly decent dark adaption). So we can see things that are much fainter than Polaris.

Can a Photon Become Heat?

Absolutely. Just stand in the sun. Photons are absorbed by your skin, and are transformed by the act of absorption, into heat. The so called "greenhouse effect" is another example. A gas molecule in the atmosphere absorbs a photon, and as a result now has more energy than it used to. It will wait a while ("while" being a tiny fraction of a second, the specifics of which depend on the molecule), and then emit another photon to get rid of the excess energy. However, if that molecule collides with another molecule before that "while" is up (and it almost certainly will in the troposphere), then it loses the energy in the collision instead of emitting a photon. So the photon has been turned into heat, which we feel as the kinetic energy of the molecules bashing into us.

Particle & Wave

"Particle" and "wave" are ideas that come to us from common experience. We can easily see and interact with particles & waves, and we can describe them with lots of sophisticated mathematics. But there is no fundamental reason to believe that such concepts, derived from the world of "common sense", should be constraining to nature on scales of the very small, where we have no common experience, and therefore no "common sense".

We don't know for sure what light "really" is, but we do know that it will act like a wave, or act like a particle, depending on circumstances. We also know that tiny particles, like electrons, do the same thing. A simple Young's double slit experiment offers conclusive proof that light is a wave. A simple photoelectric experiment offers conclusive proof that light is a particle. The conundrum is satisified only by realizing that "wave" and "particle" are just too limited to describe the reality of whatever light (and everything else) really is. For further reading see "<a href="http://www2.ncsu.edu/unity/lockers/users/f/felder/public/kenny/papers/quantum.html" target="_blank">Quantum Mechanics & The Young Double Slit Experiment</a>".

ohwilleke

Only have time for a partial answer here:

Visible light wavelengths are roughly speaking 400 nanometers (violet) to 700 nanometers (red).

Also, you are asking good questions, reasonable scientific questions, as opposed to unreasonable questions you know can't be true, but believe anyway. Nothing wrong with that.