# Interference in time

1. Jun 29, 2004

### anuj

What do we mean by interference in time? Is it possible to make two light waves interfere in time instead of interference in space, as we all know?

2. Jun 30, 2004

### turin

It's kinda the same thing. They really interfere according to their relative phase, which is of course determined by both time and space.

3. Jun 30, 2004

### robphy

Do you mean like "beats" as in "beat frequency"?

4. Jul 1, 2004

### anuj

Yes, It will be something like "beats" as in "beat frequency".

But, I suppose, Its more important to know the physics behind this effect.

Any interference observed in the time domain would also mean that there is diffraction in the time domain. That would mean the spread of the wave function in the time domain instead of space domain. We all know from the quantum mechanics that a wave function spreads from -infinity to +infinity in the space domain and this wavefunction propagates in space as a function of time. We never talk about the spread of the same wave function in time.

If there is diffraction and interference in time, that would also mean that the wavefunctions do spread in time.

What is the general comment here....

5. Jul 1, 2004

### anuj

For further discussion on this topic, please visit the GENERAL PHYSICS, THEORY DEVELOPMENT CATAGORY of Physics forums.

6. Jul 2, 2004

### Chronos

Unclear how you would detect time interference or diffraction. It would only exist in the observer's reference frame.

7. Jul 2, 2004

### anuj

You should be able to detect (record) the intensity of two interfering light waves at a point on a screen. Remember, the intensity will change rapidly as a function of time. Treat the time as your screen in this case.

8. Jul 7, 2004

### Reflector

Or conversely, light passes a room one minute, ten minutes later, light again passes the room. Do the lights exist in the same time? Why not interfere? Because the space has changed (earth rotating).

9. Sep 28, 2005

### anuj

For further details, please visit this site
https://www.physicsforums.com/archive/t-33217_Interference_in_time.html

The question I posted under this tread was

Is it possible to interfere two light waves in the time domain? Does anyone has come across an experiment like this?

1. Treat time as the fourth dimention of space.
2. Consider two slits of time duration T1 seperated by
time delay T2.
3. Make sure the wavefront emerging from the two time
slits do undergo diffraction (time domain).
4. The two emitted wavefronts will broaden in time
domain and hence interfere in the overlapped time
region.
5. What do we expect: A beat pattern of varying
intensity in the time domain if the slit widths and
gap are appropriate(?). The pattern may be simmilar to
the one we observe in double slit experiment in the
space domain.

Last edited: Sep 28, 2005
10. Oct 7, 2005

### anuj

11. Oct 7, 2005

### George Jones

Staff Emeritus
I don't like item 1., but 2. has been performed expermentally, and 5, was observed. This has been noted in threads in other forum(s) (Quantum Phyics, I think). I wrote an expository blurb on a crude model of this which may be pure BS, but which, in any case, I've attached. References to the experiment are given at the end.

Again, I'm not sure this is the right forum for this.

Rgards,
George

#### Attached Files:

• ###### slits.pdf
File size:
89.2 KB
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44
12. May 31, 2006

### michaelr

the true meaning of interference in time can only be calulated
in the amount of time between life and death

13. Jun 1, 2006

### gptejms

Anuj,
I had forgotten what I had written there,so have just checked back to refresh my memory.In referring to Zeilinger's paper,I had mentioned diffraction due to an edge in time--where a particle has a finite probability of covering distance d from the edge to the screen in time less than d/v,where v is its velocity.Now if we apply the same idea to a photon--what happens?--finite probability of superluminal propagation?

The answer is no--can anyone tell me why?I leave this as a riddle.

14. Jun 3, 2006

### gptejms

Nobody seems to have attempted the riddle(so far)--so let me give the answer.A photon may be regarded as a wavepacket---but a wavepacket with all the Fourier components moving with same velocity i.e. all the Fourier components satisfy $$\omega/k=c$$.So there is no dispersion and no interference in time.

Interestingly,one may derive the wave equation for a photon using the square of the above relation $$\omega^2/k^2=c^2$$.So,the (e.m.) wave equation is also the (Schrodinger (relativistic)) wave equation for a photon.

Another question:-why can't we use the relation $$\omega/k=c$$ as such i.e. obtain $$\frac{\partial \psi}{\partial t} = -c \frac{\partial \psi}{\partial x}$$(1-d case) as the equation?

Last edited: Jun 3, 2006