The double beam experiment

A bit of optics fun and a little riddle: two coherent light beams of equal intensity and opposite phase meet up. They interfere destructively in the center, thereby creating a continuous plane of zero EM field (and so of zero intensity). The question is: how can the energy in either beam cross and area of zero intensity? Leave a comment if you want to show off your intellect ;-).

The experiment in the last 20 seconds of the video shows the cross section of 2 laser beams that meet up and part again. For the experiment I used a single coherent source (HeNe-laser), because that is the only way this experiment could work. It requires a fairly high degree of coherence. Basically it's just a 50% beam splitter and an adjustable mirror under 45 degrees, that create 2 beams of equal intensity, initially spaced 4mm apart, 1mm in diameter and are under an angle of 0.1 degrees with respect to each other. I moved the camera sensor over a distance of 6 meters and recorded 40 images around the area where the beams were crossing paths.

BTW: officially, I think there is no such thing as the "double beam experiment", I just made that name up...

[juliusfucik]

Intensity is the sum of all contributions. You are observing the sum, not the separate contributions.

Is there no gravitational pull in a Lagrange point? Of course not. The forces just add up to zero.

[Drawliphant]

Waves don't change properties after interacting, but that doesn't feel like a satisfying answers. How do standing waves transfer energy through "nodes"? A point of zero intensity doesn't mean a point of zero energy. The EM field is being stretched and squished by the nearby intensity.

Edit: a transverse wave can transfer energy through nodes by rotating the nodes back and forth. Light is a transverse wave so there must be some energy in having zero intensity but having an oscillating slope.

[xenontesla]

My intuition might be wrong, but it makes me think of mechanical waves. Energy can still travel through nodes of a string even though they don’t move.

[dutchflyingviking]

The sine and cos beam meet each other at a very small angle (sin + 1/2 angle) ( cos - 1/2 angle ) the true direction of powerflow for each beam is straight and only a part of the beam is destructive interfered and moves from one side to the other side of the beam over time. When masking one path of the other beam and we see the behavior. The 2 beams seem to pass an area of no light only because our brains interpret the small angle differently. As referencing to one beam: Sine wave propagation direction + 1/2 angle and the path 90 degrees on this is 'seen' as the observers reference frame.
Best greetings John

[hamdaniyusuf_dani]

The use of reflecting/transmitting beam splitter causes a phase inversion in one of the resulting two beams (the reflected beam). That's why when they interfere after traveling the same distance, the result is a destruction interference.
You can try to use a polarizing beam splitter such as Wollaston prism, and you'll get no destructive interference.
You can also try to use a diffraction grating, and isolate the beam going to the left and right of the same order. You'll get a constructive interference in the center instead of destructive interference.

[aaronsj]

So what happens if you put a physical divider between the two sides where there is zero light energy?

[think]

Correct me if I am wrong. But here is my current understanding:

Light interacts with other light WITHIN the EM field BEFORE it interacts with other fields. Within a single field, we use wave computations. BETWEEN fields, we need discrete computations. The mistake is thinking that the energy within the EM field is carried as photons. It isn't. The photons ONLY happen at the very end: when the EM field interacts with electrons in some atoms inside your eyes. Our model of photons freely zipping through space without a target is wrong. The illusion arises because of the "cast time" of light being dependent on distance between emission and absorption. But photons don't exist per se as objects. Rather, they are phenomena of energy transmission between fields that give that illusion (but only somewhat).

I now see photons as their worldines. You can think of them as straight threads (though they follow the curvature of spacetime). They tie two spacetime points in two different fields together. In this case, since we are talking about photons, points between the EM field and the electron field.

Not two space points together, but two spacetime points. Once you realize that, you stop thinking of them as free moving particles zipping through space over time, and instead see them as threads--wormholes of sorts--between points in the fabric of reality.

In the context of this experiment, there are threads between all the points in the interference pattern that are "lit up" and your eyeballs. There are no such threads between the "dark" patches and your eyeballs. The interference pattern can be thought of as a negotiation between the field and itself. The conclusion of that negotiation is then presented as photons to your eyeballs at the last step, as mentioned earlier. What you see, in the end, is a time traveled signal of the negotiation presented through discrete packets which I think of as threads.

What is weird is that there are certain energy levels required for those threads between spacetime points to exist at all. If we think of them as wormholes, it's almost as if to keep the wormhole open, we need certain specific energy levels.

[tanvach]

I think of it like a guitar string with a standing wave. There are points with zero amplitudes due to interference, but the guitar string is still vibrating. The wave momentum / energy still moves through the string. Similarly, the electromagnetic field extends through the line of deconstructive interference even though there are points with zero amplitude.

[ssisok]

The result of minimum intensity from desconstructive interference of the 2 light waves does not collapse into one resultant wave (an analogy used to analyse the resulting interference pattern by superposing the coherent antiphase waves), but energy is still transmitted across the space beyond that said path where constructive / deconstructive interference occurs

[russellking]

Should I point out that observing the boundary means collapsing the wave function? In RF theory light only interferes at the receiver, not in transit to it. You'd only observe the interference pattern by putting something in at the junction.

[BlahVideosBlahBlah]

When it comes to fundamental physics I just toss my hands in the air and say "because the math matches the observations"

[jonaoconnor]

beams bounce! Although they are just quantum fluctuations, their properties are available alongside the whole beam. Because of the' quark grid' we can't see outside a certain interval!!! Im glad you've asked me ! This eventually will explain black holes!! You're welcome

[james]

The observed emission pattern is an emergent property and not a fundamental one. There is plenty of energy transfer happening between the two sides. The the overall effect on the macroscopic system is that there is a dark low or no emission part but that has nothing to do with what's actually going on fundamentally

[Hailfire]

The waves don't just know about the values of the E and B fields, but also their derivatives. Just becajse the E and B fields are zero doesn't mean their derivatives are, so the waves still know that they exist.

[HaziqArbab]

The energy thats supposed to be there instantly reappears in the areas of constructive interference where the waves meet and then is distributed over the wave again as the wave moves along

[Astrochronic]

You are seeing scattered light, not the direct light of the lasers, where they phase each other out, they scatter no light but the beams are still intact. Sound waves are different because the waves are dependent on the medium they are traveling through, and when they interfere they cancel the energy in that medium. Light is radiant. Sound is not.

[marino]

In my point of view there is a basic misconception.
In the event of a vacuum situation, the paths of the two beams are not 'visible' and there is no interference.
In the presence of air (or dust) the beams become 'visible' and the interaction with them results in the visibility of the beams with interference

[HannesHille]

I love this!

For an unconventional but I think valid interpretation - no energy crosses the "barrier". As the beams are indistinguishable, the result remains the same whether we imagine the beams "bouncing" off each other, or swapping sides.

If we try to cheat the experiment to distinguish the beams, e.g. by varying the frequency of one of them, then the node in the middle disappears.

Are there other examples where energy is transferred across a point of zero intensity? I'm not sure there are. In the nodes of standing waves, there is also no energy being transferred.

[richardtatorship]

It is the cancelation effect that occurs when any frequency meets its equal.

[jfmaster]

(From my understanding and please correct me if I'm wrong?)
First, direct from the source, emitted light is subject to resonances and particles of the medium.(including structured light vorteces like our two subjects) .despite popular beleif formed from "bells theorum "
All observable light is permeated by a hidden variable that includes asterism within the medium from a external source not in the observable spectrum .there is no such canceling interference..this is a error..only merging into higher energy state and out of the observable spectrum..
Thirdly, and most in regards, the two structured vortex beams in question already have higher energy states within its matrix before the aperture..when vortices kinetic impacts the structured mater(aperture) it is changed into a higher energy state of turoidal vortex pulses of color in the observable spectrum .
Lastly, structured light beams have a exterior layer (alot like cohesive water surface tension)to stop the beam from permeating. This outer layer makes a bond in a higher energy state not observable in the visible spectrum..when two beams outer layer come in contact they form a bond to allow permeating..the wavelenghts don't cancel each other out. This is most inaccurate description...I have a experiment most profound to human history..we need to know..and it involves light.are you interested? Could make history?