# reproducing double-slit experiment with sunlight

Is it possible to reproduce Double-slit experiment at home with sunlight probably in a larger scale? Thanks for all the answers (and special thanks to Chris for the effort),so i understand that it could be done with sunlight ,since im not a physicist and i don't know how it really works, i would ask why only thin slits works? and what is the limit? Young's equation explains the relation between wavelength, distance between slits, distance between centers of each line of light on the screen and distance between screen and the slit, but i didn't find anything about thickness of the slits.

• @RedGrittyBrick: I think it's not quite a duplicate because the question is less about "home" and more about "sunlight", as far as I can see. Oct 16, 2015 at 13:59
• I was wondering if it was possible to do this experiment as an architecture feature with natural light, we know sunlight is coherent , so i'd like to know if there is a way? Oct 16, 2015 at 14:00
• @Chris: Its a fair point. Comment and vote removed. Oct 16, 2015 at 14:02
• @coilette I tried to create a simulation which would let you vary parameters to see which parameter ranges would work on a 30m-wide room, but I was unable to get convincing behavior in the obvious cases (e.g. very large slits with large spacing should behave like classical windows) so I don't have any confidence in its result. Yes, hypothetically you could install a grating of slits on a wall and if it were precise enough, it would have some repeated rainbowy type pattern on the ground. The exact determination of what slit pattern does that for you is much harder. Oct 16, 2015 at 17:54
• Very relevant link: physics.stackexchange.com/q/76692/26969 Oct 16, 2015 at 22:22

We know from Francesco Maria Grimaldi that his experiment was done with darkened window and a little hole in the sheet, a mirror outside the window, to redirect the sunlight into the room and - a surprising easy idea in the 16th century - a bird feather.

To make the intensity distribution on the observation screen less blurry, one has to put a transparent colored foil into the sunlight beam. As it is known, the sunlight is a mix of all colors and every color has its own intensity distances and this intensities will overlapping each other.

• Very nice answer! The Grimaldi Wiki has a link to a copy of his book, where he describes the color dispersion he observes: "in extremis autem sit color aliquis, nempe caeruleus in extremo ipsi umbrae MN propinquiore, at rubeus in extremo remotiore". But I couldn't find the passage where he states that he uses a bird feather... Where did you get that information? Oct 16, 2015 at 22:20
• @Floris I hoped to re-find the bird feather as a slit equipment in Rosenberger's "Geschichte der Physik" (History of physics). No matches. Google gives back for "bird feather interference" a link to Newton only. Oct 18, 2015 at 13:21

Yes; it has been done in this Veritasium video with a typical result given at e.g. 3:30.

The incoherentness of sunlight is not 100% complete and it can certainly diffract; it's just a little more blurry when it does because the Sun is a macroscopic angular size and so forth.

It's worth remembering, as pointed out in the comment section of that video, that the full name of the experiment is Young's double-slit experiment, performed by Thomas Young in 1801, over a hundred years before anyone came up with the idea of lasers, and over a hundred and fifty before we had built any. Thomas Young's method was indeed to allow a beam of sunlight to enter a dark room where it hit his two slits.

In terms of how you can build one, my first thought would be that you'd either want to slice two slits in aluminum foil with a sharp knife, or if you need smaller resolution, slice one slit in aluminum foil and then stretch a thread of some sort so that it sits inside the gap. Paper could also be used; see e.g. these Instructables.

• To make the sunlight "more coherent", you put a single slit in front of (and some distance away from) the double slits. You will lose some light intensity, but end up with a more distinct fringe pattern. Oct 16, 2015 at 15:01
• @Floris indeed, and the problem is basically just that the Sun has a nonzero angular width when seen from the slits. Oct 16, 2015 at 17:47

I do these experiments at home all the time using a laser and guitar strings. Usually I use only one string as Thomas Young used only one hair in his original experiment. Coherent photons are projected onto a screen from the two edges of the wire. I have also developed a simulator for single or multiple slits that shows both the calculations and the visual of the interference patterns. If you can direct intense enough sunlight onto a wire in a dark room you can get these results.

I think it is not possible do this at home because it requires accurate and precise instruments.

• And is also wrong, given that, as @ChrisDrost points out, Young used sunlight for the original experiments. Accurate and precise instruments for this experiment are actually quite cheap at Home Depot or the like. Oct 16, 2015 at 14:47
• As far as I'm concerned, it is an answer, and a fairly direct one at that - albeit uninformative. Oct 16, 2015 at 14:52