Neat demonstration of interference patterns

[Strange]

 

 

 

 

[John Cuthber]

Nice

[StringJunky]

cool

[steveupson]

Sweet!

[druS]

Fabulous.

[Dalo]

This is certainly a nice video. But, as you might expect, I have some questions, the most important one being:

are the dark parts still water?

[Strange]

9 minutes ago, Dalo said:

are the dark parts still water?

what do you think they could be?

The dark parts are the (self) shadowed sides of the waves.

[Dalo]

Just now, Strange said:

what do you think they could be?

I would find it very strange if it were anything else. But since we are talking about negative interference, it would seem that it only concerns the light waves. Water waves are unaffected by it. There is no "absence of water" as there is "absence of light". That means that we are observing a pure optical phenomenon.

[Strange]

2 minutes ago, Dalo said:

I would find it very strange if it were anything else. But since we are talking about negative interference, it would seem that it only concerns the light waves. Water waves are unaffected by it. 

It is interference in the water waves. Why would you think they do not interfere?

3 minutes ago, Dalo said:

There is no "absence of water"

It is absence of waves.

[Dalo]

4 minutes ago, Strange said:

It is interference in the water waves. Why would you think they do not interfere?

It is absence of waves.

Yes, that makes perfect sense. But applying the same principle to light seems out of the question. We could not say that there is simply an absence of waves but light is still present, as the water is.

Also, the water color is different of what it is there where there are still waves, and from what it was, before the experiment started.

Edited November 25, 2017 by Dalo

[Strange]

11 minutes ago, Dalo said:

We could not say that there is simply an absence of waves but light is still present, as the water is.

Indeed. Where the waves cancel there is no light.

The difference is that the water is the medium for the waves but the light is the wave (the medium is the electromagnetic field).

[Dalo]

Just now, Strange said:

Indeed. Where the waves cancel there is no light.

Also very interesting. We see the absence of light.

[Strange]

2 minutes ago, Dalo said:

Also very interesting. We see the absence of light.

Yep. We do that everyday with, for example, shadows.

[Dalo]

 

2 minutes ago, Strange said:

Yep. We do that everyday with, for example, shadows.

the problem is that blind people do not see shadows. We need vision to see them. 

take two lights in a dark space, some distance from each other.

The only way to keep both lights apart, is to register the dark space between them. We have, as it were, "to see darkness". If we did not, the dark space between the light would disappear, and we would see only one (bigger) light.

Darkness is different from the absence of light. Closing your eyes is different from looking at darkness, Those are two different sensations.

Also, the mind can create all kind of images when our eyes are closed, as in dreams, hallucinations and so on. 

I would certainly not deny that the absence of sunlight leads to darkness.

I would like to point to the fact that light in physics, can be "invisible" to the naked eye.

The absence of light, strictly speaking, would mean the absence of all wavelengths of light, visible and invisible. We do not know what that is. It would mean absolute vacuum.

The idea that light can disappear and still leave a visual impression is somehow contradictory.

 

[swansont]

25 minutes ago, Dalo said:

the problem is that blind people do not see shadows. We need vision to see them. 

!

Moderator Note

Stick to the topic, please.

 

[Strange]

2 hours ago, Dalo said:

Darkness is different from the absence of light. 

No it isn't.

Quote

Also, the mind can create all kind of images when our eyes are closed, as in dreams, hallucinations and so on. 

How is that relevant? That has nothing to do with light.

Quote

I would like to point to the fact that light in physics, can be "invisible" to the naked eye.

Light is only visible if it arrives in the eye. But as an "expert" on the visual system, presumably you now this already.

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The idea that light can disappear and still leave a visual impression is somehow contradictory.

It depends what you mean (as usual, that isn't clear). If the "visual impression" is darkness, then that isn't in the least bit contradictory. It is what is technically called "bloody obvious". If you mean something else, then it is probably just another example of you not knowing what you are talking about.

[Dalo]

1 minute ago, Strange said:

It is what is technically called "bloody obvious".

of course.