The SMALLEST particle, Human can ever see

[Ashish]

So according to Quantum Theory, if light consists of a photon then photon will be the smallest particle towhich human can observed because human eye can see any thing if a light rays get reflected from any object or matter

[Klaynos]

http://www.scienceforums.net/forum/showpost.php?p=427827&postcount=4

 

Holds your answer.

 

It's a wave effect, so the quantisation doesn't matter much...

 

Photons don't really have a physical size.. But I recall there is some evidence that the human eye can detect a single photon.

[Sisyphus]

Well really, photons are the only things we can ever see.

 

However, they don't have a size, and they don't reflect off one another.

[John Cuthber]

The post Klaynos refers to gives the limit of resolution for the eye, but that's not the smallest thing you could see. A brightly lit speck of dust smaller than that limit would still be visible against a dark background.

[Klaynos]

The post Klaynos refers to gives the limit of resolution for the eye, but that's not the smallest thing you could see. A brightly lit speck of dust smaller than that limit would still be visible against a dark background.

 

But you couldn't resolve it... you can see an individual photon caused by an electron dropping down an energy level in an atom does that mean you can see the atom? What does the op mean by to see...

[John Cuthber]

What does the op mean by to see...

 

Good question.

Imagine a couple of small specks of dust an inch apart and both very brightly iluminated (perhaps by a laser). You would be able to see them provided that they scattered enough light in the direction of your eye. You would be able to point at them and estimate the distance between them. You wouldn't be able to say anything about them apart from the fact that they were bright dots (and how bright they were).

If the 2 spots were close enough together they would look like just one spot. That distance is the resolution that the post above gives.

[TheDrBraniac]

Yes, you can see a photon if you can ever slow it down to human-like speeds. The slowest light has travelled is 38 miles/hour. They used laser cooling to slow down and freeze the photons.(Slightly.) The photon was not anything physical; it was just a little dot.

[swansont]

Yes, you can see a photon if you can ever slow it down to human-like speeds. The slowest light has travelled is 38 miles/hour. They used laser cooling to slow down and freeze the photons.(Slightly.) The photon was not anything physical; it was just a little dot.

 

IIRC the 38 mph is right, but the rest is varying degrees of wrong. Laser cooling reduced the temperature of the atomic vapor; the light was slowed because there was a sharp transition nearby which caused a rapid change in the refractive index and group velocity depends on the slope.

[Leader Bee]

IIRC the 38 mph is right, but the rest is varying degrees of wrong. Laser cooling reduced the temperature of the atomic vapor; the light was slowed because there was a sharp transition nearby which caused a rapid change in the refractive index and group velocity depends on the slope.

 

Didn't we conclude in this thread that photons always travel at C?

http://www.scienceforums.net/forum/showthread.php?t=51142

 

How is it possible to slow down?

 

Edit: sorry, just sat and re read your last post and realise it is due to photons taking a longer path.

[swansont]

Didn't we conclude in this thread that photons always travel at C?

http://www.scienceforums.net/forum/showthread.php?t=51142

 

How is it possible to slow down?

 

Edit: sorry, just sat and re read your last post and realise it is due to photons taking a longer path.

 

Really it's the distinction between "light slows down" and "photons slow down." Light slows down because photons interact with the medium (which takes time), but the photons travel at c. The "slow light" is a very strong interaction, over a very narrow frequency range.

[mannzzu]

do you mean to say photons vibrate at c speed over a very small range? due to which light appears to slow down! then normally photons can interact with atmosphere which has to slow down light in earth's atmosphere. does it happen so? if yes then how come expt to calculate speed of light be accurate?

[Leumas13]

When a photon intereacts with a medium it's not really going less than c? It's simply being absorbed and emitted so its like it's traveling over a longer distance. It's not actually, but my point it that it's still moving at c