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Light as a signal in physics, and signal response theory

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Considerations of light theory in other sections of this site show that physics taking light as waves or as particles fail to satisfactorily explain all of its various behaviours, and neither does the currently popular theory that light is somehow both. But physics has generally not yet tried taking light as being simply a signal, in the way that it commonly is taken in signal theory.

So it may be of some interest to now examine the possible consequences for physics of treating light as being just a signal, starting from some consideration of the basics of signal response theory.

The basics of signal response theory

The basics of signal response theory can be taken as being that any body can be a signal, relative to some observer body that can respond to it. And that any body can be an observer, relative to some signal body to which it can respond. Response is to some property or properties of a signal that can be taken as carrying data or information, and signal responses may or may not reflect the basic nature of a signal. The simplest signal is exist/non-exist (on/off or 0/1) and even that can carry complex data or information in its eg temporal and/or spatial arrangement.

In signal theory signals are basically anything to which some signal detector can produce some response, so that there are two separate related phenomena being signal and response. If light is taken as being a signal, then different physical systems might be expected to show some different responses to light. This appears to be the case with at least some light-related phenomena like reflection and refraction. It has even been shown that punching holes in thin plates can increase OR decrease the amount of light that appears to penetrate a plate. Physics World

The nature of light itself

In any physics that does not take light as being a signal, light impacting different physical systems may be taken as being different behaviours of light itself. This leads to taking reflection, refraction, diffraction, photoelectric emission, Compton emission etcetera as being light behaviours. And some of these apparent light behaviours can be taken as evidence for light itself being an ether wave, a quantal particle or whatever.

But in a physics that does take light as being a signal, light impacting different physical systems can be taken as evoking different detector responses. This leads to taking reflection, refraction, diffraction, photoelectric emission, Compton emission etcetera as being responses to light signals. And some of these being responses can be taken as giving no evidence for light itself being of any specific nature if the nature of responses is not fully determined by the basic nature of the signals involved.

Responses to signals

Generally in signal theory the nature of responses is not fully determined by the nature of signals, but reflects only some one property or few properties of a signal. Hence some detectors can give digital quantal responses to some continuous signals, or give analog continuous response to digital signals. See eg Digital to Analog Converter or Analog to Digital Converter - though these sources may not be the best.

Modern 'signal processing' is predominantly electronic and often involves systems using extrapolation calculation methods in producing signal responses, but other physical systems can respond in various ways to different signals using only basic physical responses. And it is perhaps that kind of non-calculation signal response that is of more fundamental relevance to physics. Hence mechanical clocks can respond to an analog spring pressure with ratchet-gear digital responses. (And even computational physics can be basically simple resting on 0/1 or On/Off states, so that eg atoms for some phenomena involving one signal may have two states allowing two different responses. Some have even proposed a physics on that basis like the New Kind of Science of Stephen Wolfram.)

Responses of light or responses to light

The observed speed of sound in a given direction in moving air, like the speed of a bullet, reflects both the velocity of sound in air and the wind velocity in the given direction - also the observed speed of sound reflects any source and/or observer relative motion. But the observed speed of light is claimed not to show any such effects.

There are many interesting light phenomena and Isaac Newton offered one possible signal theory or 'attraction theory' explanation of light reflection and of light refraction, though involving the response of light itself to signals. (Newton light-attraction could also explain light diffraction etc - see our Newton's Principia.)

Two other interesting types of light-electron interactions that might suggest different types of signal response to light are the 'Compton Effect' and the 'Photoelectric Effect' :-
1. The Compton Effect involves light deflecting electrons in proportion to light energy, seemingly in an analog manner or to multiple photons with no threshold-frequency.
2. The Photoelectric Effect involves atoms emitting electrons seemingly in a digital manner in response to single incoming photons of some above-threshold frequency. (however an additional lower-level of photoelectric response is also produced, apparantly when two below-threshold photons are received simultaenously as Sipila et al 2007 )

The Compton Effect may indicate atoms or sub-atomic particles being able to add-up consecutive digital signals over time until some target figure is reached to trigger response - or that some time-spread signal property of a continuous signal triggers response. The Photoelectric Effect may indicate atoms or sub-atomic particles responding to each single case of a digital signal - or that some short-time signal property of a continuous signal triggers response. In both of these light phenomena a signal theory can allow of light showing either digital or analog effects without requiring the current physics duality contradiction of it being both itself.

Some other light behaviours that are commonly taken as being responses to light, rather than properties of light, include light slowing and induced transparency - and these cases involve variable response.

Light as a signal for physics

A signal view of light would have some significant consequences for physics. One thing it would throw doubt on is Einstein's conclusion that photoelectric emission is evidence of light being actually quantal, but it could also cast doubt on other claimed evidence for light being also actually a wave. Waves and particles have substantially different mathematics that do not seem to be simple transforms of each other, so it seems that wave and particle theories cannot be compatible image theories of each other. But in fact a signal view of light could perhaps allow of both quantal and wave type responses without any contradictory 'duality' requirement of light itself. Digital signals can give digital or analog wave responses, and analog wave signals can give analog wave or digital responses. Contradictory appearances do not have to indicate contradictory realities.

Information in physics

Signal theory generally locates information, intentional information or unintentional natural information, in signals - but physics tends to trying to locate information either in physical bodies themselves or in ill-defined 'observers'. So a range of issues can arise such as ;
1. physical bodies either do or do not carry some natural information before an observer observes ?
2. signals either do or do not carry some natural information before they are detected ?
3. physical bodies either do or do not carry some natural information before they emit signals ?
4. signals either do or do not carry natural information reflecting the full nature of their source ?
These and other related issues have not always been properly addressed by physics theories to date. A signal physics may seem better able to handle this, though no doubt non-signal image theories of a signal theory would be compatible also.

All forces as signals

It is of course possible that forces like magnetism, electricity and gravity may also work by signal response as proposed first by William Gilbert, and so allow of a signal physics 'theory of everything'.

Responses to signals can involve issues like signal thresholds, response times, signal noise, excitation states, conditional response and signal summation. Depending on the particular signal response parameters involved, signal response systems may also be capable of looping or of hanging. And for some signal response systems a numbers of factors may vary the probability of some signal giving some response. Avoiding the use of signal theory, current physics struggles poorly to explain much, such as exactly what is light slowed and shrunk !? (see Slow Light.)

Such signal theory physics goes right back to 1600 when William Gilbert explained magnetism as response to emitted signals he termed 'effluvia', and took electricity and gravity as working similarly, and this signal physics was developed further by Isaac Newton in his using 'attraction theory' as one explanation option in his blackbox theory of gravitation. Of course unintentional natural signals might include direct emissions from objects or events, as masses emitting gravitons or causing space-curvatures, or be indirect signals as from some external interaction with the object or event, with experimental interactions being intentional replicatable attempts to elicit natural signals. A signal theory physics might still have some usefullness for gravity, for light and maybe more.

The physical nature of signals

Signal theory allows that anything that can convey information can be a signal. Hence all human senses are concerned with signal detection, as in hearing, sight and touch. From this it is clear that some natural signals might take the form of waves in a medium, and others might take the form of particle objects.

Any single object's speed or velocity is simply the rate of change of its position with time in a specified direction. But waves in a medium, and sets of multiple moving objects, can have a group velocity and a phase velocity so that talk of their speed can be ambiguous. Claims that a single object is somehow a wave can involve ambiguous assumptions regarding its speed. There can also be issues with wave mathematics assuming a medium to be continuous rather than particulate.

A light beam is likely either a continuous-medium wave or a set of multiple photon objects, or just maybe something else. But when discussing medium-wave or multiple-object motion, 'speed' should always be clearly specified as being either the group velocity or the phase velocity. Some things to consider when considering the question of whether a light beam is more likely a continuous-medium wave or a set of multiple photon objects ;

A. Some normal multiple-particle motion properties.
1. Particle motion is not resisted by a vacuum but is by higher-resistance mediums, and the velocity of motion of particles through a low-resistance medium like a vacuum is significantly affected by particle forces such as gravity.
2. Particles can be accelerated to some velocity as by a force like gravity, and in a low-resistance medium like a vacuum will tend to maintain their velocity. And multiple-particle a stream or beam of emitted particles being some regular stream of single particles, or may be pulsed with each pulse being some set of multiple particles.
3. For both multiple-particle source and multiple-particle detector within a low-resistance medium like a vacuum, their motion relative to each other or to the low-resistance medium changes apparent detected velocities or frequencies for the detector but does not change absolute as-emitted velocities or frequencies in the low-resistance medium.
4. In a low-resistance medium like a vacuum, no medium motion will cause multiple-particles motion in it to suffer any velocity or frequency change.

B. Some normal wave properties, as of sound waves.
1. Sound waves cannot propagate through a vacuum, and in any fixed medium the propagation of sound waves through it is not significantly affected by a particle force such as gravity. And wave motion may involve a single wave of some frequency, or may involve multiple waves of differing frequencies that will make it pulsed.
2. In any fixed medium, sound waves will propagate through it at some specific fixed velocity that is often higher for higher-resistance mediums - so the speed of sound in air is 343 m/s, in water is 1,433 m/s and in denser materials can have higher values.
3. For both sound source and sound detector within the same fixed medium, their motion relative to each other or to the medium changes apparent received sound frequency for the detector but does not change the absolute as-emitted sound frequency in the medium nor the apparent sound velocity for the detector.
4. In a medium moving at some velocity, sound will approximately propagate through it at a velocity that is the sum of its specific fixed velocity for that medium and the medium velocity - without change of absolute as-emitted sound frequency in the medium.

While the above wave properties and particle properties are logically mutually exclusive, many claim that some or all physical things (notably including light) possess some or all of both sets of properties.

James Clerk Maxwell's equations for time-oscillating electric and magnetic forces are wave equations, but this really only supports time-oscillation like timed particle emission being wavelike in having a wavelike maths. It is poor support for any general wave physics theory It is certainly no real support for light being any wave, when nothing can be identified that it could be a wave of. And there seems little basis for claims that 'light is electromagnetic', when light is not affected by any steady electric or magnetic field. Nor is there real evidence for electrical or gravitational forces being based on waves rather than being some as yet undetermined emission signals.

And while most modern physics theory may have no natural place for time, signal theory physics in fundamentally involving response to signals fundamentally involves time as a consequence. What basically distinguishes a response event from a signal event is simply time, with signals being causes and responses being subsequent effects. If an attraction response cannot precede an attraction signal, then the universe is not time reversible and has one-direction time inbuilt. Many other physics theories by default predict a time reversibility that seems contrary to many experiments.

light signal theory graphic

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