A remarkable phenomina.

Orionaut · 20 Aug 2015 at 20:57

Was reading recently a description of an interesting experiment that you can actually try at home.

Pick a dark room with a single light source (say a table light)

Close one eye and hold your hand up at arms length so that you are looking at the light through the gap between your first finger and your thumb.

Bring your finger and thumb closer together.

Now, it takes a bit of practice, but if you get it right there will come a point where, in the gap, there will be a dark band with light on each side of it.

This is not some sort of mere optical illusion. You are actually looking at the consequence of interference patterns cancelling out the light!

I just find it remarkable that it is actually possible to demonstrate optical diffraction effects using only your fingers, a convenient light source and the Mk1 eyeball! :cool:

adolf hamster · 20 Aug 2015 at 21:04

You mean a version of youngs double slit experiment?

Thekwango · 20 Aug 2015 at 21:05

Who has a dark room with only one source of light? Are you a murderer, or a practitioner of torture??

dacads · 20 Aug 2015 at 21:05

demnons?

touch · 20 Aug 2015 at 21:08

adolf hamster said:
You mean a version of youngs double slit experiment?

I thought the double slit thing only worked with a laser? Isn't a normal bulb too random at spitting out light for this to work?

Amp34 · 20 Aug 2015 at 21:08

Thekwango said:
Who has a dark room with only one source of light? Are you a murderer, or a practitioner of torture??

Or currently in a cell awaiting murder or torture?

Thekwango · 20 Aug 2015 at 21:15

Amp34 said:
Or currently in a cell awaiting murder or torture?

In a cell waiting to be murdered or tortured??? What the hell is wrong with people on OcUK?!

p.s. I take it you meant awaiting trial for murder or torture.......least I hope you did!!

adolf hamster · 20 Aug 2015 at 21:15

touch said:
I thought the double slit thing only worked with a laser? Isn't a normal bulb too random at spitting out light for this to work?

Nope, just a point source (so that when split the 2 beams have the same phase and wavelength), lasers are better but not essential.

You can do it with a bulb and a box with a pinhole/slit to provide the point source, iirc young originally did it with daylight through blackout curtains

lunar · 20 Aug 2015 at 21:18

touch said:
I thought the double slit thing only worked with a laser? Isn't a normal bulb too random at spitting out light for this to work?

With a laser (monochromatic light) the bands produced will be only the colour of the laser and black fringes. With white light you still obtain interference patterns, but the colour bands are rainbow colours with blue closer to the central fringe. I have performed the double slit experiment many times in a lab. Electrons also display diffraction/interference patterns when targeted at a graphite crystal. Hence, electrons are waves!

robfosters · 20 Aug 2015 at 21:21

Thekwango said:
Who has a dark room with only one source of light? Are you a murderer, or a practitioner of torture??

Amateur photographer?

Thekwango · 20 Aug 2015 at 21:22

robfosters said:
Amateur photographer?

Always has to some smarty pants with a sensible answer.

rubberduck · 20 Aug 2015 at 21:26

The double slit works with electrons too. Even if you fire them individually they still create an interference pattern which implies they act as a probability function and go through both slits and interact. However if you try to observe which slit trey go through they go back to acting like a particle and don't create an interference pattern. I don't think this has much to do with the OP though

Amp34 · 20 Aug 2015 at 21:30

Thekwango said:
In a cell waiting to be murdered or tortured??? What the hell is wrong with people on OcUK?!

p.s. I take it you meant awaiting trial for murder or torture.......least I hope you did!!

No, I meant the former. Just whiling away his hours in a semi dark cell, slowly going mad...

robfosters · 20 Aug 2015 at 21:32

Amp34 said:
No, I meant the former. Just whiling away his hours in a semi dark cell, slowly going mad...

How would he be posting on the forums?

Amp34 · 20 Aug 2015 at 21:36

Maybe we are a figment of his worsening mind?

Remind me never to go see a film with you!

The double slit experiment and the whole wave/particle situation always bemuses me.

robfosters · 20 Aug 2015 at 21:38

Amp34 said:
Maybe we are a figment of his worsening mind?

Remind me never to go see a film with you!

The double slit experiment and the whole wave/particle situation always bemuses me.

Now you're in Arthur C Clarke territory. That means it's getting dangerously close to abandon thread time!

Orionaut · 20 Aug 2015 at 21:38

rubberduck said:
The double slit works with electrons too. Even if you fire them individually they still create an interference pattern which implies they act as a probability function and go through both slits and interact. However if you try to observe which slit they go through they go back to acting like a particle and don't create an interference pattern. I don't think this has much to do with the OP though

If you are a follower of the multiple universe concept, the single electron/photon diffraction experiment implies a whole lot more!

robfosters · 20 Aug 2015 at 21:40

Amp34 said:
Remind me never to go see a film with you!

I know when to leave my brain at the door.

I'm indoors now, so I can't really do that, or I wont be able to put my socks on tomorrow.

lunar · 21 Aug 2015 at 00:47

Amp34 said:
Maybe we are a figment of his worsening mind?

Remind me never to go see a film with you!

The double slit experiment and the whole wave/particle situation always bemuses me.

And so it should.
I think it was Richard Feynmann who said 'if you understand quantum mechanics then you do not understand quantum mechanics.

Tefal · 21 Aug 2015 at 01:02

One question, how can it be a double slit with interference patterns with only one gap?