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Physics, Astronomy & Cosmology / Re: What Really is a photon?

« on: 10/08/2006 08:18:33 »

quote:Originally posted by Soul Surfer

... This can be proved by setting up a classic two slit intereference pattern which causes the light to form interference fringes where parts are brighter than the other.  These intereference fringes can be shown to exist even if ONLY ONE photon is inside the apparatus at any one time so there is no doubt that both the particle and the wave actually travel between the source and the detector (revelator).

We have an electromagnetic wave that hits the shield with two (or more) slits, then it hits the revelating shield. Without the concept of a flying photon, I can easily imagine a low intensity wave that hits this last shield, making it "clicks" only in some precise point of it and only once every minute: the low intensity wave means low probability of interaction. The fact that THE INTERACTION is particle-like, doesn't mean that a particle travels from source to revelator.

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Physics, Astronomy & Cosmology / Re: What Really is a photon?

« on: 10/08/2006 08:05:43 »

Quote, from another someone:

"I am curious as to how a laser can emit a single photon.

Is not the acronym LASER implicitly telling you that the light is amplified, and thus must be greater than the minimum intensity, otherwise if it is merely at its minimum intensity, what is it amplified from?"


It's an intelligent observation another someone!

However, other important features of a Laser beam are coherence, monocromaticity and parallelism: the first is a precise phase correlation among the waves in the beam; the second is a single, precise wavelenght of the beam; the third...you understand perfectly (important for writing-reading devices, as in computer drives). Coherence, for example, is necessary to make holograms

You can make a Laser emit one single photon at a time reducing enough its intensity, for example putting a filter in front of it.

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Physics, Astronomy & Cosmology / What Really is a photon?

« on: 08/08/2006 16:29:57 »

Hello to everyone,

I hope this subject hasn't already been covered; if so, I ask you to forgive me.

A Laser emits a weak beam of low frequency (I will explain later why low frequency) light, so that a revelator "ticks" once every, let's say, minute. Most physicists explain: "one single photon is emitted from the Laser every minute, travels to the revelator and it's revealed".

Question: How can we say that, in this case, a spatially localized particle travels from the source to the revelator? A way to prove it would be to put...another revelator in the middle of the route, so destroing the photon (here is why low frequency and hence low energy); so we are left with the same question: What is the photon from the source to this new revelator?

From my point of view, and I've thought a lot about it, the "photon" doesn't really exist from the source to the revelator; the "photon" actually is "The Tick of The Revelator".

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Chemistry / Re: What is the best way to make powdered aluminum?

« on: 09/08/2006 20:05:54 »

quote:Originally posted by Mr Andrew

I think it might be possible to precipitate aluminum in a powder form in a double replacement reaction.  Pour sulphuric or hydrochloric acid on your aluminum chunk and collect the aluminum salt produced (you can also light the hydrogen gas on fire and make a large fireball if you want--loads of fun!![]).  Next take the aqueous aluminum salt and add a more reactive metal than aluminum (try magnesium, it's not hard to come by).  The aluminum metal should precipitate and another metal salt will be be formed (aqueous of course).  Filter out the aluminum metal (which should be in the form of a powder[?]) and dry.  Do not heat the powder to aid in evaporation as the powder will ignite!!!  That is a bad idea.

Are you sure it would work? I doubt a lot. When the first atoms of Al are produced, they will immediately react with water. The reason Al doesn't normally react with water is that the particles are covered with Al oxide; but this happens when you already have Al particles. Infact, "naked" Al particles react immediately with oxigen or water in the air. Very fine Al particles without the protective layer of oxide are piroforic (=they ignites on contact with air), as a lot of other very fine powdered metals (Fe, Mg, Ni, ...)

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Chemistry / Re: Help with writing a FLASH POWDER combustion rxn??

« on: 09/08/2006 19:41:38 »

Sulfur, in black powder and in flash powder, is used for many reasons. Some of them are:
to catalize the reaction; to increase flame, friction and shock sensitivity, to make the powder less hygroscopic, to make the combustion more homogeneuos. So the speed of reaction increases, the ignition temperature decreases. The heat released is not higher, however, but lower.

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Physics, Astronomy & Cosmology / Re: The Band Of Stars..The Milky way ?

« on: 09/08/2006 17:48:33 »

When we have the possibility to see such wonderful things, in complete silence (outside and inside), if our soul is strong enough, we can have the most beautiful and strong emotions of our life. Please, next time you have such an experience, remember: we all comes from the stars. We have always lived there, we will always live there, forever.

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Physics, Astronomy & Cosmology / Re: An interesting pattern

« on: 09/08/2006 16:58:57 »

quote:Originally posted by Mjhavok

Is an answer going to be provided to this question by thebrain13?

Steven

Yes.

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Chemistry / Re: Thermite

« on: 09/08/2006 14:12:04 »

quote:Originally posted by DrDick

quote:Originally posted by pyromaster222

there are many different thermites such as CaSO4/Al. this is a very high temperature thermite, more so than iron oxide i believe. it's also castable but is extremely hard to light. There are also thermites with copper oxide which burn very fast (like medium grade gunpowder)

Are you sure you don't mean CuSO4/Al?  To convert a metal cation to the elemental metal, you need a more active metal (one that wants to be in the cationic state even more) to perform the conversion.  Al is more active than Fe, so Al metal will react with oxidized Fe but Fe metal won't react with oxidized Al.  Likewise, Ca is more active than Al, so oxidized Ca won't react with Al metal.  However, Cu is a pretty inactive metal, so oxidized Cu will react with Al metal.

You are right when you say that CaO cannot be reduced from Al; you could be wrong when you believe that, in CaSO4, Al must reduce CaO: it could reduce SO3; I have never tried this thermite, however.

About 3CuO + 2Al = 3Cu + Al2O3, I have tried it several times. If powders are very fine, the reaction is almost as quick as flash powder! Delta H of formation of CuO is much lower (in absolute value) than that of Fe2O3, for example, so the heat of reaction is Very high. Probably, some of this heat decomposes CuO producing oxigen gas, and this makes the reaction explosive. Don't confine this thermite at all!

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Chemistry / Re: Practical Jokes

« on: 09/08/2006 12:38:55 »

A joke: mix very well equal amounts of aluminium fine powder and iodine powder (no more than a few grams); put a little piece of very cold ice on it (so that it doesn't melt immediately). When the ice starts melting, the water reacts with the mix, producing a little flame and violet fumes of iodine and aluminium triiodide. Be careful not to breath those fumes!

Al + 3I = AlI3

By the way: those equations with H2O2 and NaI are wrong. This is what happens:
(1) H2O2 + 2NaI = 2Na+ + I2 + 2OH-
(2) H2O2 = H2O + 1/2 O2
Probably, (if pH is >7) there is also the formation of some IO3-:
3I2 + 6OH- = IO3- + 5I- + 3H2O

You can easily see the iodine (I2) produced from the reaction, because the solution becomes brown.

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Physics, Astronomy & Cosmology / Re: faster than light communication

« on: 09/08/2006 12:11:35 »

quote:Originally posted by thebrain13

Could someone tell me what information means in physics?

information is related to entropy: the entropy of a physical system is proportional to the maximum amount of information it can contain.

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Physics, Astronomy & Cosmology / Re: solar furnace

« on: 09/08/2006 12:07:17 »

Sun is seen from earth as ~ a blackbody with a temperature of ~ 6000°K. At this temperature, most of the energy emitted is in the visible spectrum (around 550 nm = yellow-green colour).

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Physics, Astronomy & Cosmology / Re: About electrons

« on: 09/08/2006 11:46:17 »

However, even if classical physics is completely inappropriate to describe the behaviour of an electron in an atom, there is a simple classical answer to the questions: "What makes electrons spin around the nucleus at their speed? Where is the force that makes them do this? Why don't electrons fall into the nucleus?"

The answer is: centrifugal force. The same reason for which earth doesn't fall into the sun.

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Physics, Astronomy & Cosmology / Re: An interesting pattern

« on: 09/08/2006 08:08:23 »

Maybe it's Awareness?
If anything (mass, space, time, energy) existed without Awareness, who could prove it would exist? No one.
You can get rid of everything, but the last thing you are left with is...Awareness.

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Physics, Astronomy & Cosmology / Re: Can the sun reflect light?

« on: 08/08/2006 17:03:25 »

I have a friend in astrophysics research. He states that sun is considered as a good blackbody, at least in the visible spectrum. So the answer to the question if sun reflects light (by the way, not a naive question) is: no. Soul Surfer is right.

The fact it's a good blackbody can be deduced from its spectrum of emission, it's not necessary to send light to it and look for a reflection! Physics is fascinating, isnt'it?