Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I've seen a documentary, whose name I don't remember but I'm curious because it suggests that subatomic particles are able to "foresee the future".

I'll try to describe it here:

Some particles are shot through two slits in a plate, if the particles are not interfered by trying to measure its trajectory, they form an interference pattern on a wall where the beam is being projected, otherwise they just hit the wall in a single point according to the measured trajectory.

The following image depicts what is described above:

enter image description here

The dotted red lines are where waves are canceled, blue ones are where waves overlap.

Then, they modify the experiment, so that they sort of turn on the detector after the particles have crossed the slit, where particles have allready being "forced" to behave as waves or single particles, to see if they change its behaviour after the measurement, just to find that the particles were measured as if they always knew that they would be measured, and they crossed the slit as particles and not waves.


This is the link to the documentary, it's titled "Microscopic Universe", is part of this TV series. They describe the experiment about 17 minutes in.

share|cite|improve this question
Would you be able to be more specific? Possibly include a link to the documentary or a related article about the experiment. – Argus Dec 19 '12 at 15:17
This sounds like the quantum eraser experiment. No actual foreseeing of the future takes place in it. – Peter Shor Dec 19 '12 at 16:07
@PeterShor: That's what I thought as well. But it's a bit vague--if he can be more specific, I'd reopen this question.. – Manishearth Dec 19 '12 at 16:30
@Manishearth: sounds good. – Peter Shor Dec 19 '12 at 16:33
@rraallvv: If you can be more specific about the experiment you heard of, ping me/another mod (Use @Manishearth in a comment or flag the post for ♦ attention) and I'd be happy to reopen it for you :) – Manishearth Dec 19 '12 at 16:37
up vote 2 down vote accepted

The answers given by @annav and @ChrisCharles, got me to the answer that the documentary possibly refers to the most recent experiment of the Wheeler's delayed choice experiment, because it's called the first "clean" experimental test of Wheeler's ideas, and one posible interpretation of the experimental data is that they were able to change retroactively the particle/wave behaviour.

Also this page has a pretty good description of the experiment, and explains its interpretations.

This is the abstract of the article on Science Magazine, the full text is free upon registration.

As a personal note: Maybe the subatomic particles behave as both, waves and particles, and by meassuring we just change the image projected onto our perceived reality of some hiper-particle that in essense remains basicaly unaltered in the hiper-space.

share|cite|improve this answer

In the wiki link provided also by @ChrisCharles there is a paragraph on a more recent experiment where the interference pattern appears even if the experiment is set up in such a way that the slit through which the electrons passed is known.

enter image description here

It is a clear demonstration that one is talking of a quantum mechanical probability distribution and not of an electron matter "wave". The "waviness" is in the mathematical wave function the square of which gives the probability of finding an electron on the (x,y) of the screen, when there are two slits through which it could pass.

Usually a measurement disturbs the boundary conditions which define the solution of the quantum mechanical problem. In this experiment care was taken to minimize the disturbance and still know from which slit the electron passed. In this sense the measurement above contradicts the usual narrative, that if one measures the path the interference disappears, it should be if one measures badly and disturbs the electron path the interference disappears.

Now in the video they are exaggerating for impression the effect of "bad measurement", imo.

Every experimental setup establishes boundary conditions that really pick up which solution of the quantum mechanical equations refer to the experiment. To go on and say that the setup projects backwards in time is wrong. The set up picks up the whole solution which does have solutions for -t, but it is the setup that does it, nothing mysterious. In a similar way one knows that the train that arrives at the station was moving on the tracks ten minutes before, so is that backwards in time or an extrapolation of the solution : "train at station" ?

share|cite|improve this answer

double slit experiment Wiki link

share|cite|improve this answer
I am not downvoting, but you got down votes because the rule in answering here is not to just give a link but give your opinion and at least clarifying quotes from the link – anna v Dec 20 '12 at 16:23

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.