Light

[faizdwolf]

How modern physics defines dual particle nature of light, what justification it gives?

[Klaynos]

Experimental evidence I think is the main justification.

 

The normal experiment given, the first to really describe this is the photoelectric effect, which won Einstein his nobel prize. If you monitor the current produced by incident light on a metal, you need to remove electrons here so you need to provide enough energy called the work function, you have monochromatic light and no matter how much you increase the intensity you do not see any effect, but you then change the frequency of the light and suddenly at a very specific frequency you get a massive photoelectric effect. This can only be true if light is particles.

 

So we can now produce individual photons at a time. We can send these photons threw slits, if we have two slits very close together and fire individual photons at them we see an interferance pattern build up on a detector array behind the slits, this pattern can only be formed if light is a wave.

 

So, we've two experiments conducted independently of each other one shows light is particles the other shows it is a wave... what is it? The answer lots of people give is "it's both" I don't like that very much, it exhibits the properties of both, sometimes, but it seems better to me and to cause less problems if we say that it's neither.

[faizdwolf]

So what would we say to that "neither" state of light?...because in elementary or high school we always listen to that both state concept.

[Klaynos]

I don't quite know what you mean?

 

People are taught that it is both because that is slightly easier to explain/understand, if people are told it is neither than they say things like "what is it" and there is no macroscopic explanation for what it is, but it has the properties of both a wave and a particle depending on the situation.

[faizdwolf]

Thanks for the reply....anyway can u help me to understand Dark matter?

[Klaynos]

Of course, but there are significant limitations to what I can tell you about dark matter as we know very little about it.

 

When we observe galaxies spinning their speeds, and the distribution of the rotational speed doesn't match to the amount of mass from normal matter we observe in those galaxies. So we assume there has to be some other mass, which doesn't interact with the EM force very strongly at all, what this is we don't really know, there's several different options out there. We've actually generated maps of distributions of dark matter based on our observations of gravity...

[swansont]

We have a number of threads on dark matter, which you can find with the search function