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InvisibleEgo Death
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What is light?
    #7567512 - 10/27/07 06:11 PM (16 years, 3 months ago)

Is it a particle or a wave?

Is a wave a particle?

Does emitting light give propulsion, like emitting air would?


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Offlineboingkster
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Registered: 09/28/07
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Re: What is light? [Re: Ego Death]
    #7567604 - 10/27/07 06:42 PM (16 years, 3 months ago)

I think light is a particle [photons] that travel in waves. This was debated for a long period of time before it was agreed that light displayed properties of both waves and particles!

I'm not sure if it would give propulsion that would be useful to humans, but you can achieve acceleration using an ion drive - essentially a magnet driving away an ionised gas to give small but detectable propulsion with no conventional rocket motor. This has been used [or is proposed to be used?] on deep space probes with good degrees of success, accelerating to tens of thousands of miles per hour over the period of a few months [negligible period of time in space-travel terms].

Cheers, hope that can give you something to think over! :laugh:


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A Question Never Asked is an Answer Never Given
[Having said that, use the Search button! Teks too!]


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InvisibleMrKite1
Cosmo

Registered: 03/02/04
Posts: 1,384
Loc: AK
Re: What is light? [Re: boingkster]
    #7567703 - 10/27/07 07:12 PM (16 years, 3 months ago)

Ion propulsion has been used successfully.
http://en.wikipedia.org/wiki/Ion_engine#Missions


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When the going gets weird, the weird turn pro.


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: What is light? [Re: boingkster]
    #7568275 - 10/27/07 10:57 PM (16 years, 3 months ago)

Quote:

boingkster said:
I think light is a particle [photons] that travel in waves.


No, that is not true and is a common misconception. Particle/Wave duality is not particles that travel in a wave like manor. It is when the phenomena (light) is observed in one setting to be a particle traveling in a straight line, and in another setting to be a wave oscillating through space (specifically, perpendicular oscillating magnetic and electric field). Each of these descriptions is needed to explain/predict all that we observe light to do.

What is light really? Who knows... Scientists dont know what anything is really. What is time, mass, light... What is known is that it is connected to electricity and magnetism. So instead of having three unknowns, electricity, magnetism and light... We have one unknown, electromagnetism (which includes light).

Light can and does impart momentum on an object (the Poynting vector). However the momentum of light is very low, and would be difficult to use for propulsion. (Consider that the strength of the light would fall off by the inverse square law, so you would lose power very quickly as you move away from the source) But I have read accounts of 'solar sails' that would use the momentum of light to propel the craft they are attached to.


The coolest aspect of light... It travels the same speed no matter how fast you are going, or the source of it is going. No matter how fast you go you always measure a light beam traveling at the same speed.


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InvisibleAcyl
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Re: What is light? [Re: Ego Death]
    #7568457 - 10/28/07 12:41 AM (16 years, 3 months ago)

For our purposes, light can nver hope to push on anything like a stream of air does. The photon has no mass when compared to oxygen/nitrogen.

Under most circumstances, shining light on matter will simply cause electrons in ground state orbitals to move into higher energy orbitals. This is how photosynthesis, phosphorescence and fluorescence (glow sticks, n shit) works. This also forms the basis of an entire branch of chemistry..

I highly doubt that shining any sort of light, long or short wavelength, would efficiently propel an object.


Quote:



Is it a particle or a wave?

Is a wave a particle?





Invalid questions, really. As DieCommie said.


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:scrambled:

1 ,2


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OfflineSeussA
Error: divide byzero


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Re: What is light? [Re: Acyl]
    #7569381 - 10/28/07 10:40 AM (16 years, 3 months ago)

> I highly doubt that shining any sort of light, long or short wavelength, would efficiently propel an object.

So how does a light-mill work? (I know... just giving you a hard time.)

http://video.google.com/videoplay?docid=-1804589211555222478


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Just another spore in the wind.


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InvisibletrendalM
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Registered: 04/17/01
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Re: What is light? [Re: Seuss]
    #7569390 - 10/28/07 10:44 AM (16 years, 3 months ago)

Yes but a light mill is not driven by light hitting the veins...but by the very small amount of air still inside the chamber. The black sides heat up much quicker than the white ones, and as a result they heat up the air to a higher degree on one side than the other. Hotter air takes up more room, so it gives the veins a little push as it does so.


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Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: What is light? [Re: trendal]
    #7569651 - 10/28/07 01:47 PM (16 years, 3 months ago)

Trendal has the answer to the 'light mill'. Think about this way to understand why it cannot be that the light's momentum is moving the mill....

Look at conservation of momentum---> Black side, light is absorbed so the momentum in (p) from the light equals the momentum the paddle gets (p). But now look at the white side, here the momentum in is (p) and the light reflects off with a momentum of (-p). Sum the momentum before and after and you find that the white paddle must have a momentum of (2p). So if the lights momentum is what is pushing it the white side should be pushed. But it is the black side that is pushed, for the reason that trendal stated. Its not that the momentum from the light doesnt push, its just to small to outweigh the temperature effect.


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InvisibleAcyl
cyanidepoisoning
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Re: What is light? [Re: trendal]
    #7570065 - 10/28/07 03:51 PM (16 years, 3 months ago)

Thats pretty sweet


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:scrambled:

1 ,2


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Invisiblejohnm214
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Re: What is light? [Re: DieCommie]
    #7570892 - 10/28/07 08:27 PM (16 years, 3 months ago)

Quote:

DieCommie said:
I have read accounts of 'solar sails' that would use the momentum of light to propel the craft they are attached to.




You must be refering to the "Cya Bitch" protocol I've been working on. Basically, I'm hopping to attach a giant sheet of aluminum foil to my ex with the aid of scotch tape, and launch her ass to pluto.

If all goes well, I hope to have the schematics finished in a few months, and the finished product by next year. Should make history (as well as my life much more peaceful)


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InvisibleAcyl
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Re: What is light? [Re: johnm214]
    #7570908 - 10/28/07 08:30 PM (16 years, 3 months ago)

haha


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:scrambled:

1 ,2


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OfflinePhanTomCat
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Re: What is light? [Re: johnm214]
    #7570916 - 10/28/07 08:32 PM (16 years, 3 months ago)

Better use myar for he sail and duct tape if you want a rig that will last all of the way to pluto....  :wink:

:tongue:


>^;;^<


--------------------
I'll be your midnight French Fry....  :naughty:

"The most important things in life that are often ignored, are the things that one cannot see...."

>^;;^<


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OfflineQuerjek
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Re: What is light? [Re: PhanTomCat]
    #7582405 - 10/31/07 09:05 PM (16 years, 3 months ago)

Isn't light (as a single unit, the photon) caused by the collision of an electron with a positron (essentially, an electron with a positive charge)?


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tripping eyes and flooded lungs
northern downpour sends its love


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: What is light? [Re: Querjek]
    #7582627 - 10/31/07 10:49 PM (16 years, 3 months ago)

A form of light does get made when an electron and positron annihilate. But that is a highly energetic, invisible form of light known as gamma rays.

'Traditional' light, as in most of the EM spectrum including the visible light we see, is made another way. The basic idea is that an atom somehow absorbs energy which knock the electrons into a high energy state. They then collapse down to a lower energy state and emit that extra energy in the form of a EM wave, or light.

The gamma rays from your situation cannot be made this way because they require more energy then any atom's electrons could provide from a transition to a low energy state.

edit- I think one of the most interesting things in physics is the interaction between light and matter. If you learn a little more about it you can see the beginnings of quantum and relativity theory, which are the best of physics.


Edited by Qubit (10/31/07 10:53 PM)


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InvisibleSilversoul
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Re: What is light? [Re: Ego Death]
    #7582687 - 10/31/07 11:34 PM (16 years, 3 months ago)

Well, we can theorize that light is a particle.  We can model experiments to test if it's a particle, and will prove beyond a doubt that it is a particle.

Then we can theorize that it is a wave.  We can model experiments to test if it's a wave, and will prove beyond a doubt that it is a wave.

God, I love quantum mechanics.  :grin:

Anyone see the recent South Park episode about Imagination Land?


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OfflineSeussA
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Re: What is light? [Re: Silversoul]
    #7582698 - 10/31/07 11:39 PM (16 years, 3 months ago)

> God, I love quantum mechanics

I used to until I took the class(es) and saw how difficult the math is. (Math isn't my strong suite.)


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Just another spore in the wind.


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InvisibleSilversoul
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Re: What is light? [Re: Seuss]
    #7582728 - 11/01/07 12:26 AM (16 years, 3 months ago)

Quote:

Seuss said:
(Math isn't my strong suite.)



*suit

Apparently spelling isn't either. :wink:


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: What is light? [Re: Silversoul]
    #7583153 - 11/01/07 08:05 AM (16 years, 2 months ago)

Quote:

Silversoul said:
Well, we can theorize that light is a particle. We can model experiments to test if it's a particle, and will prove beyond a doubt that it is a particle.

Then we can theorize that it is a wave. We can model experiments to test if it's a wave, and will prove beyond a doubt that it is a wave.




There are some experiments, like the famous double slit experiment, where you need to the use particle and wave descriptions to account for the phenomenon in one experiment.


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InvisibletrendalM
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Re: What is light? [Re: DieCommie]
    #7583166 - 11/01/07 08:12 AM (16 years, 2 months ago)

I think that experiment proves that a photon of light is neither a particle or a wave...not that it is "both".

Light behaves like a wave or particle...but experiments such as the double slit prove light is, in fact, something more.


--------------------
Once, men turned their thinking over to machines in the hope that this would set them free.
But that only permitted other men with machines to enslave them.


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InvisibleDieCommie


Registered: 12/11/03
Posts: 29,258
Re: What is light? [Re: trendal]
    #7583202 - 11/01/07 08:34 AM (16 years, 2 months ago)

Well, if you read carefully what I said (not to be an ass...). I didnt say it is both, only that that we need both descriptions to account for the behavior.

Surely what light 'really' is, is something of the type we cannot visualize and have to use waves and particles to understand it.

And of course, we know that matter exhibits the same duality. Thats a much harder concept to accept I think, and very tripy.


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