Can red and blue light interfere to make fringes in young’s double split experiment? Supposing in young’s double split experiment, I cover one slit with red filter and the other slit with blue filter. The light coming out from the first slit would be red and the second slit would be blue. Would there be any interference fringes? I tried googling this question but all the answers say that two different monochromatic lights cannot interfere and hence no interference pattern. But, we do know that if we did the experiment using white light, there is a pattern(for a few fringes). So what should be the right answer?
 A: So the concept of double slit "interference" is historical dating back to Young and Fresnel (early 1800s)... and is still the basis for the typical high school/university textbook.  When quantum mechanics came about in the early 1900s some of the most famous scientists (Dirac and others) pointed out that "each photon interfered with itself" which was just their way of saying each photon determines its own path. (But it was complex, subject to argument, and textbook writers were happy with what they had written.)
So photons do not cancel each other, that would be a violation of conservation of energy.  When an atom/electron is excited it is already generating virtual EM forces .... when the EM forces see 2 slits they cause the pattern ... the real photon is eventually released and follows the pattern.
So when you filter the slits the red "to be" photons/electrons/atoms only see one slit ..... so no "interference".
Unfortunately there may very likely be high school textbook problems that want you to calculate an interference pattern based on the fact that the 2 colours have a different wavelength value .... it becomes more of a math problem than a physics problem!
A: You would have two single slit diffraction patterns overlapping on the screen.
The two pattern have different spacings between their fringes. For example the blue spacings are smaller than the red spacings. Like any beat pattern you will find points where bright fringes from blue coincide with bright fringes from red. These points will form a double slit pattern with a color mix of magenta.
