[itistoday]

Originally posted by kidtexas:
No, an electron and a gamma ray aren't the same. electron is an electron Its a particle in the classical sense. A gamma ray is a high energy (short wavelength) electramagnetic wave. past UV, past x-rays. Sure sure, quantum mechanics, photons, particle-wave duality, but in the classical sense, electrons are particles, gamma rays are waves.

Well, as you've said, they do kinda act like particles, and don't they have mass? If not, then please explain what a wave is. If even gravity exists in the form of a "graviton" particle then shouldn't something as evident as gamma rays be contained in particles too?

[BlackGriffen]

Originally posted by itistoday:
Well, as you've said, they do kinda act like particles, and don't they have mass? If not, then please explain what a wave is. If even gravity exists in the form of a "graviton" particle then shouldn't something as evident as gamma rays be contained in particles too?

Yes, gamma rays are particles. So is ordinary, everyday light. Even the radio signals are carried by photons (light particles).

The three biggest differences between an electron and a gamma ray are:

electrons have mass, gamma rays do not
electrons have charge, gamma rays do not
electrons are spin one half, photons are spin 1

Gamma rays are really just extremely high energy light. Electrons are different because they don't travel at the speed of light.

So, they are very different beasts. I don't have time to elaborate any further right now, though.

[kidtexas]

Originally posted by itistoday:
Well, as you've said, they do kinda act like particles, and don't they have mass? If not, then please explain what a wave is. If even gravity exists in the form of a "graviton" particle then shouldn't something as evident as gamma rays be contained in particles too?

one big difference between classical particles and classicle em waves is mass. yes particles have wave like characteristics, and em waves (light for short) has particle characteristics. when light behaves like a particle, we call that a photon. Think of it like this - light isn't a continuous stream like water from a hose. the energy it carries is quantized (in discrete little packets). In other words, for a given wavelength, as you bring down the intensity of light, you theoretically could get to the point where you are 1 unit of energy that the light can deposit - read up on the photoelectric effect. to go the other way around, particles behaving like waves, look at the following progression of pages. it goes from Young's double slit experiment, which showed the wave nature of light. Then with quantum mechanics, it can be seen that a single particle (including a photon) can interfere with itself in the double slit, much like a wave. particles have wave like attributes.

http://www.qmw.ac.uk/~zgap118/2/yds.html
http://ophelia.princeton.edu/~page/single_photon.html
http://www.colorado.edu/physics/2000...two-slit3.html

One might think that particle-wave duality means that light can always be considered a particle, and that particles can always be considered waves. that is a bit far - for all intents and purposes, in everyday life, particles are particles and light is a wave - this is the realm of classical mechanics.

photons don't have charge. photons (light) travel at the speed of light. particles with mass can't reach the speed of light without an infinite amount of energy - think about that for a bit. photons also don't have charge.

So to answer your question, yes gamma rays do have a particle correspondance (photon, just like all other em waves). I don't know about gravitons. that is a particle that transports the gravitational force about, but at this point, we haven't seen evidence that the exist. i don't do that research and really haven't studied that at all.

if you want to know what a wave is, think ocean waves and sounds waves (transverse and compressional). or if you prefer otherwise, waves on a string vibrating and a slinky compressing (also transverse and compressional). with the exception of light waves, waves need a medium to transfer their energy. light waves don't follow this rule, but to explain more, you should bone up on some e&m.

[itistoday]

Originally posted by kidtexas:
one big difference between classical particles and classicle em waves is mass. yes particles have wave like characteristics, and em waves (light for short) has particle characteristics. when light behaves like a particle, we call that a photon. Think of it like this - light isn't a continuous stream like water from a hose. the energy it carries is quantized (in discrete little packets). In other words, for a given wavelength, as you bring down the intensity of light, you theoretically could get to the point where you are 1 unit of energy that the light can deposit - read up on the photoelectric effect. to go the other way around, particles behaving like waves, look at the following progression of pages. it goes from Young's double slit experiment, which showed the wave nature of light. Then with quantum mechanics, it can be seen that a single particle (including a photon) can interfere with itself in the double slit, much like a wave. particles have wave like attributes.

http://www.qmw.ac.uk/~zgap118/2/yds.html
http://ophelia.princeton.edu/~page/single_photon.html
http://www.colorado.edu/physics/2000...two-slit3.html

One might think that particle-wave duality means that light can always be considered a particle, and that particles can always be considered waves. that is a bit far - for all intents and purposes, in everyday life, particles are particles and light is a wave - this is the realm of classical mechanics.

photons don't have charge. photons (light) travel at the speed of light. particles with mass can't reach the speed of light without an infinite amount of energy - think about that for a bit. photons also don't have charge.

So to answer your question, yes gamma rays do have a particle correspondance (photon, just like all other em waves). I don't know about gravitons. that is a particle that transports the gravitational force about, but at this point, we haven't seen evidence that the exist. i don't do that research and really haven't studied that at all.

if you want to know what a wave is, think ocean waves and sounds waves (transverse and compressional). or if you prefer otherwise, waves on a string vibrating and a slinky compressing (also transverse and compressional). with the exception of light waves, waves need a medium to transfer their energy. light waves don't follow this rule, but to explain more, you should bone up on some e&m.

Thanks for the great post and the links. But I'm still a bit fuzzy on what exactly a wave is. A slinky and ocean waves have metal and water to do the motion, are "light waves" simply photons traveling in curved paths? I don't really understand what is meant by waves; how it looks like, and what is doing the waving.

Oh, and just in case you didn't see my other questions (or anyone else would like to answer them) here they are again:

And what's the difference in terms of high energy/low energy particles in terms of strings?

What seems skeptical about the theory though is that they've supposedly answered how the Big Bang happened but in doing so simply created another problem: where do membranes come from?

And are membranes simply a single stretched out string?

And what exactly was the big bang then? Did it in fact create our universe or was it simply a big explosion on the surface of a membrane?

[tie]

What a refreshing thread! I don't know anything about this, but have picked up a few intriguing pieces:

I like the idea that different group symmetries are broken, energies split, at lower energies.

I like the idea that an extra dimension of small radius could give a tower of widely separated effective masses.

I like the idea that gravity could be stronger at small length scales, but weakens at lengths above the radius of that extra dimension. Also, or alternatively, that gravity is weaker because it propagates off this brane. And that E&M might come out of this! Just crazy.

I've "learned" a lot of hand-waving physics recently. Another interesting thing was a very good explanation of the expansion of the universe, and CMB. I used to wonder where the CMB was coming from, but I guess it is just an expanded causality region in a large, apparently isotropic universe (not yet large enough to detect any curvature). Can someone explain why the isotropy implies that light must have expanded faster than the speed of light just before the CMB emission? (Because it's synchronized? Aren't there better possibilities?) Also, what the deal is with (lack of) low frequency harmonics in the CMB? I read that famous book on the first few seconds a long time ago, and didn't really understand. Would that explain these questions or is it now dated?

[voyageur]

I'm reminded of a funny typo that appeared in the title of a lecture at a local university:

"The Moon: A Heavy Electron"

Now there's a big particle. Was meant to read "muon".

[wataru]

Originally posted by itistoday:
Thanks for the great post and the links. But I'm still a bit fuzzy on what exactly a wave is. A slinky and ocean waves have metal and water to do the motion, are "light waves" simply photons traveling in curved paths? I don't really understand what is meant by waves; how it looks like, and what is doing the waving.

Oh, and just in case you didn't see my other questions (or anyone else would like to answer them) here they are again:

You're right, no one (well, maybe someone; I didn't read everything in this thread) has mentioned what light is a wave of. It is actually two transverse waves, one a electrical and one magnetic.

A changing electric field produces a magnetic field (example: two wires that have current running through them will be either attracted or repulsed depending on the relative directions of the current) and a changing magnetic field produces an electric field (one kind of electricity generator turns mechanical energy in the form of moving permanent magnets into an electric current). These transformations are described classically by Maxwell's equations, discovered by James Clerk Maxwell near the end of the 19th century (I think). This discovery is what makes TV, radar, radio, WiFi, etc. possible.

What do these waves travel through? Nothing. Err, in other words they don't need a medium to propagate, unlike many other kinds of waves. It used to be thought that the universe was permeated with a substance called "ether" through which light travelled, but all experiments to detect Earth's passage through the ether have found nothing. It is now known that electric and magnetic fields just propagate on their own.

[kidtexas]

Originally posted by itistoday:
Thanks for the great post and the links. But I'm still a bit fuzzy on what exactly a wave is. A slinky and ocean waves have metal and water to do the motion, are "light waves" simply photons traveling in curved paths? I don't really understand what is meant by waves; how it looks like, and what is doing the waving.

Oh, and just in case you didn't see my other questions (or anyone else would like to answer them) here they are again:

Well... to answer your other questions... I know ****all about string theory. All I really know about it is what i read in Kaku's book Hyperspace, and that was about 5-6 years ago. One thing to remember about string theory is this: yes it is a big topic in physics - its the cutting edge. It looks like it might be the answer to some of the difficulties we've had in uniting the fundamental forces of nature in a unified theory. But, there is a lot left to be done on this, and we don't really have any way to test this physically at this point. So as far as what caused the big bang, etc, its all theorizing at this point. I'm an experimentalist, so I have my bias, but a theory, no matter how elegant and great, needs to have it demonstrated that it does in fact correspond to how the world works.

back to the wave business. most waves need a medium to travel in. you are 100% right about the slinky and water examples. Which is exactly why for quite some time in our scientific past, there were many who believed in the "ether". Light was demonstrated to be a wave by Young:

Thomas Young performed a very simple experiment using natural sunlight,
back in 1801, which provided support for the wave nature of light.

Many of Young's contemporaries, on the other hand, held the competing
view, championed by Newton, that light was a stream of particles that obeyed
his laws of mechanics. The different colors of the rainbow were simply due
to different particles of light that had different masses and has different
values of the momentum (mass time velocity, with velocity being the same for
all the colors).

The wave view point was championed by the Englishman Robert Hooke and was
the Dutch physicist, Chrisitaan Huygens, both contemporaries of Newton.
Huygens developed the mathematical aspects of the wave theory, in 1678, and
showed how the then known laws of reflection and refraction could be
explained readily on the basis of the wave theory. The ratio of the sines
of the angle of incidence to the angle of refraction could be related to the
speed of the light wave as it travels from one medium (say air) into another
(say glass or water). However, because of Newton's great authority and
prestige, the wave theory found very little support during his lifetime.

Young's experiment, however, seemed to prove conclusively that light must
be a wave. Even today this experiment cannot be rationalized on the basis
of the particle theory of light. In the middle of the 19th century,
Foucault showed, quite convincingly, that the relative values of the speeds
of light in air and water was exactly as predicted by the wave theory (and
inconsistent with the conclusions of the particle theory, and Newton's
predictions).

http://www.youth.net/eratosthenes/030923/0002.html

So, it was proven that light must be a wave (remember, this is before quantum mechanics - light couldn't be both a wave and a particle). Since all waves travelled in a some medium or another, light must have a corresponding medium. The ether. Lots of theorizing went on about how to detect the existence of the ether. I forget most of them, but an (the) important one was performed by Michelson - don't know were the morley comes in the name. He (they?) tried to measure the ether by measureing the speed of light super accurately, and came to the conclusion that the speed of light was set and that there was no ether. blah blah blah, enter einstein and theory of special relativity. read more about michelson morley and more background and details here:
http://galileoandeinstein.physics.vi...michelson.html

So what light actually is is a series of ... ahh wataru just answered that

[itistoday]

Originally posted by wataru:
You're right, no one (well, maybe someone; I didn't read everything in this thread) has mentioned what light is a wave of. It is actually two transverse waves, one a electrical and one magnetic.

A changing electric field produces a magnetic field (example: two wires that have current running through them will be either attracted or repulsed depending on the relative directions of the current) and a changing magnetic field produces an electric field (one kind of electricity generator turns mechanical energy in the form of moving permanent magnets into an electric current). These transformations are described classically by Maxwell's equations, discovered by James Clerk Maxwell near the end of the 19th century (I think). This discovery is what makes TV, radar, radio, WiFi, etc. possible.

What do these waves travel through? Nothing. Err, in other words they don't need a medium to propagate, unlike many other kinds of waves. It used to be thought that the universe was permeated with a substance called "ether" through which light travelled, but all experiments to detect Earth's passage through the ether have found nothing. It is now known that electric and magnetic fields just propagate on their own.

Thanks so much for clearing that up.

[itistoday]

Originally posted by kidtexas:
So what light actually is is a series of ... ahh wataru just answered that

Hehe yeah, but thanks for your post too; lots of in depth detail.

[tie]

Originally posted by itistoday:
Thanks for the great post and the links. But I'm still a bit fuzzy on what exactly a wave is. A slinky and ocean waves have metal and water to do the motion, are "light waves" simply photons traveling in curved paths? I don't really understand what is meant by waves; how it looks like, and what is doing the waving.

No, there is a very significant conceptual difference. We call a photon a "particle." This is because photons (can) occur one at a time; if we take a light, and slowly turn down its intensity, then sensors will register individual, discrete "clicks" or single photons. (However a photon isn't a particle like a piece of sand; it isn't localized in space.)

Okay, but one way to think of the photon as a wave is to imagine each photon carries with it an arrow (like the hand of a clock) which rotates at some specific speed. Higher energy photons have faster clocks (blue faster than red). The weird thing is: these arrows add up! If there are two paths a photon can take, it takes them both and the arrows for the two paths then add up. (If the paths are exactly the same length, then the clocks will have rotated exactly the same amount, so the arrows will add. If they are different lengths, then the arrows could be in opposite directions, and so cancel each other out.) This explains for example, why a thin sheet of oil on water creates rainbows, or why you see rainbows in a soap bubble; the different thicknesses are just enough so, e.g., the arrows for red light add up while the arrows for blue light (which rotate faster) cancel. An excellent and very readable book on this (with no math) is Feynman's "QED" (up to the last chapter).

Does someone know how many photons it takes to trigger a sensor in our eyes? And how many to trigger a typical digital sensor?

[kidtexas]

Forgot to add this:
http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html

good comprehensive site on physics. I think you might be interested in the quantum part - read the first couple parts there about failure of classical physics.

[itistoday]

Originally posted by kidtexas:
Forgot to add this:
http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html

good comprehensive site on physics. I think you might be interested in the quantum part - read the first couple parts there about failure of classical physics.

Will do, but right now it's a little too much for my brain to handle after sitting here in front of the monitor for so long. surprised I haven't gotten eye cancer yet like that guy from Simone...

[BlackGriffen]

More generally, a wave can be described as energy moving coherently. This is to be distinguished from heat, which is energy moving diffusively. The important thing is that it is the energy that is moving, anything carrying the energy pretty much returns to where it started.

The only thing energy needs to travel as a wave is an elastic medium (that is, something that when stretched or compressed will attempt to return to some rest state - like a spring or rubber band). It just so happens that the electromagnetic field is an ideal elastic medium.

The only hitch to treating light just as a wave is that quantum mechanics steps in and says "The energy you can put in to making this wiggle is quantized." That is, the medium only accepts energy in discrete amounts, given a desired frequency you want to wiggle it at. That discreteness is what makes light a 'particle.'

There is, of course, more to it than that, but that should be enough to get the concepts down.

BlackGriffen