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Scientists hypothesize about how to turn light into matter.

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Scientists discover how to turn light into matter after 80-year quest


Physicists have discovered how to create matter from light -- a feat thought impossible when the idea was first theorized 80 years ago. In just one day over several cups of coffee in a tiny office, three physicists worked out a relatively simple way to physically prove a theory first devised by scientists Breit and Wheeler in 1934. Breit and Wheeler suggested that it should be possible to turn light into matter by smashing together only two particles of light (photons), to create an electron and a positron -- the simplest method of turning light into matter ever predicted. The calculation was found to be theoretically sound, but Breit and Wheeler said that they never expected anybody to physically demonstrate their prediction.


From How Stuff Works the following explanation is excerpted:


A photon is produced whenever an electron in a higher-than-normal orbit falls back to its normal orbit. During the fall from high energy to normal energy, the electron emits a photon -- a packet of energy -- with very specific characteristics. The photon has a frequency, or color, that exactly matches the distance the electron falls.


Curious About Astronomy posits the following:


The simplest answer is that when a photon is absorbed by an electron, it is completely destroyed. All its energy is imparted to the electron, which instantly jumps to a new energy level. The photon itself ceases to be. In the equations which govern this interaction, one side of the equation (for the initial state) has terms for both the electron and the photon, while the other side (representing the final state) has only one term: for the electron.


The opposite happens when an electron emits a photon. The photon is not selected from a "well" of photons living in the atom; it is created instantaneously out of the vacuum. The electron in the high energy level is instantly converted into a lower energy-level electron and a photon. There is no in-between state where the photon is being constructed. It instantly pops into existence.


Philosophically, this explanation is problematic. Popping into and out of existence runs counter to causal law. But if examined from the standpoint of entities coming to be or of ceasing to be, as a process, the orbit increasing with the absorption of a photon, or decreasing by the emission of a photon is descriptive. The atom does not cease to be as a consequence of absorbing or emitting a photon - the electron orbit increases or decreases.


If colliding two photons together do, in fact, produce an electron and a positron, it should be interesting as well to discover if the photons cease to be or continue to persist, albeit, in a determinable different state. Either way, this should help in better ascertaining the identity of a photon.

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  • 2 months later...

I'm not sure where the indication of confusion lies


Philosophy recognizes A is A, for both the philosopher and physicist alike.


Described by the articles cited, is a denoted relationship between the energy level of the electron and the photon. The photon is absorbed or emitted by the electron in conjunction with the energy level of the electron increasing or decreasing. What was of more interest to me is if an experiment colliding two photons together might produce the expected results.


The fact that light travels was not discovered until Ole Roemer discovered the time discrepancies with regard to the distance between earth and the moons of Jupiter depending on the orbital locations. It is not surprising to me that trying to observe what is happening at a fraction of that scale of distance results in a time-frame so short as to be imperceptible with our current instrumentation. *poof* it's there, *poof* it's not, flies in the face of matter (or energy) can neither be created nor destroyed. In this regard, the contention is with the wording of the last citation.

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Robert Grosseteste (1175 - 1253) maintained long before Breit and Wheeler that light is the fundamental stuff of the universe, giving rise in turn to matter.


To follow up on what Skylab72 said, philosophy's job is not to tell us what facts are allowed to be discovered.  I know nothing of theoretical physics, but I suspect that the quandary here arises from an inadequate notion of "existence", identifying it with the physical continuity over time that we observe in macroscopic physical entities.    Even these pop into existence (e,g, by being born, by being amalgamated by heat or pressure, by being manufactured) and out (e,g. by dying or by being demolished).  A single entity rarely pops out of existence and back in, but physical sundering and reassembly is one way such a process might happen.  If even this kind of object can disappear and reappear, then a fortiori so can the objects that theoretical physics studies.

Edited by Reidy
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Scientific method, optics, with traditions established carrying through to Galileo and Newton. Thanks.

"Grosseteste was the first of the Scholastics to fully understand Aristotle's vision of the dual path of scientific reasoning: generalizing from particular observations into a universal law, and then back again from universal laws to prediction of particulars." (Logical Leap?)


You state: "but physical sundering and reassembly is one way such a process might happen."


This reconciles with the notion of a thing coming to be or passing out of existence via a process. It appears between the lines of what I was critiquing is a process - but the wording makes it sound as if the photon bursts forth ex nihilo, at the same time describing something that is there out of which the photon emerges. Given the responses so far, is this just nit-picking?

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"no in-between state where the photon is being constructed. It instantly pops into existence.

Philosophically, this explanation is problematic. Popping into and out of existence runs counter to causal law."


There are many ways to word "popping", but what is being stated is that the release of a photons is not a "continuous" act like waves rolling across the ocean.  Photons are released in discrete quantities (quanta) of energy (see black body).    Furthermore, it's not observable, in a classical sense, until it is released, so math at the quantum level is probabilistic - it absolutely will happen - your computer is a testimony to that.  But because it's modeled probabilistically, all we can say is that it "pops" into existence.

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@New Buddha

The three citations did not bring up the "continuous" distinction, the last citation merely relating mathematically the increase of the electron energy level with the absorption of the photon, and the decrease with the emission. The "How Stuff Works" citation relates the frequency or color of the photon to the distance of the fall [or presumably, rise] of the electron. Leaving aside the probabilistic aspect, this outlines what we know of the event - when it actually occurs.


I've not happened across any updates on the plans of colliding two photons, and a quick Google search does not pop up any new articles relating to it.

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  • 5 months later...

Scientists slow down the speed of light travelling in free space


Scientists have managed to slow photons in free space for the first time. They have demonstrated that applying a mask to an optical beam to give photons a spatial structure can reduce their speed.


Crux of this story:

The team's experiment was configured like a time trial race, with two photons released simultaneously across identical distances towards a defined finish line. The researchers found that one photon reached the finish line as predicted, but the structured photon which had been reshaped by the mask arrived later, meaning it was travelling more slowly in free space. Over a distance of one metre, the team measured a slowing of up to 20 wavelengths, many times greater than the measurement precision.

The work demonstrates that, after passing the light beam through a mask, photons move more slowly through space. Crucially, this is very different to the slowing effect of passing light through a medium such as glass or water, where the light is only slowed during the time it is passing through the material -- it returns to the speed of light after it comes out the other side. The effect of passing the light through the mask is to limit the top speed at which the photons can travel.


Shape affects speed? Who would have guessed? The auto companies have used wind tunnels to develop aerodynamic shapes to improve fuel efficiency for years. (One of the reasons so many cars have similar shapes.)


From what I understand of space, there is not supposed to be a lot of wind resistance. Yet a reshaped photon has now been shown to travel more slowly through the aether. What is this imperceptible to the unaided senses stuff?

Edited by dream_weaver
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