Photons & Quantum World

[chandragupta]

WHY PHOTONS ARE THE ONLY QUANTUM PARTICLES WHICH ARE VISIBLE TO THE NAKED EYE ? Any thoughts?

[swansont]

WHY PHOTONS ARE THE ONLY QUANTUM PARTICLES WHICH ARE VISIBLE TO THE NAKED EYE ? Any thoughts?

They aren't. Photons interact with molecules in our eyes which send an impulse to our brain, so what you mean by "see" the photons is not so simple. But you can get the same result from an interaction with charged particles — astronauts reported seeing light flashes which were caused by cosmic rays. We did not evolve to be perceptive to these, though — charges have a limited range, especially in a fluid like an eye, and it's not a very useful trait. Ionizing radiation tends to cause damage, too.

[Anders Hoveland]

And photons have a rather large "size" for a subatomic particle.

 

Red light, for example, has a wavelength of 0.7 millimeters. An object that size is just vissible to the human eye (well, it depends who's eyes). If I look closely, I can see some details on a tiny grain of sand that is that size, but I have really good vission. For most people, an object that size looks like just a little black speck. Because of this, it is more difficult to see fine details in red light than in blue light, because the larger wavelength of the red light obstructs things. For example, I probably would not be able to see any details on that tiny grain of sand I was looking at it only under red light.

 

I have also read somewhere that if a grating is made with the right size of holes, blue light can pass through but red light cannot.

[swansont]

Red light, for example, has a wavelength of 0.7 millimeters.

No, red light has a wavelength of around 700 nanometers, which is 0.7 micrometers. You're off by a factor of 1000.