Is "scalar wave" a legitimate term?

[EleanorW]

For years, the term "scalar wave" has been swirling around the Internet. Posts typically describe "scalar waves" as capable of doing things that textbook electromagnetic signals cannot do, e.g. penetrate all shielding, opening up the possibility of really serious Earth-penetrating radar.

I asked a physics professor at a major university about 20 years ago what "scalar waves" are, how they are generated, how they propagate, and what effects have been generated by such signal type. He pretty much laughed in my face.

Sources given seem to be Nikola Tesla. I'm not sure that his claims have become widely accepted at this point.

Today, does the average major university physics professor (a) accept that "scalar waves" are a real and demonstrated signal type and (b) will he/she have documenation on the characteristics available?

Thanks,

EleanorW

 

[PeterDonis]

For years, the term "scalar wave" has been swirling around the Internet.

Where? Please give specific references. We can't respond to vague statements that are "swirling around the Internet". We need something specific to look at.

 

[Dale]

The term "scalar wave" is a legitimate term and would include waves of any scalar property. So pressure is a scalar and sound is a pressure wave, thus ordinary sound would be a legitimate scalar wave.

I suspect that whatever internet thing you are talking about is probably not a legitimate concept. Often psuedo-science uses legitimate science terms in ways that are completely nonsensical. So a specific citation of the "swirling" concept would be helpful.

 

[renormalize]

I suspect that whatever internet thing you are talking about is probably not a legitimate concept. Often psuedo-science uses legitimate science terms in ways that are completely nonsensical. So a specific citation of the "swirling" concept would be helpful.

Surprisingly, a google search on "Tesla scalar waves" returns a prominent link to a CIA (!) document that attempts to describe these waves, complete with blacked-out, redacted portions (fodder for conspiracy theorists).
https://www.cia.gov/readingroom/docs/CIA-RDP96-00792R000500240001-6.pdf
The technical content reads like a mathematical curiosity. It invokes a peculiar and unphysical choice of scalar and vector potentials in electrodynamics, intended to yield zero electric and magnetic fields, while still admitting a free scalar field (but sourced by what?).

 

[Vanadium 50]

Disinformation from an intelligence agency? I'm shocked. Shocked!

 

[Drakkith]

Disinformation from an intelligence agency? I'm shocked. Shocked!

We prefer the term "limited-accuracy-information-devoid-of-intelligence". For brevity, this can be referred to as CRAP. That's not an acronym, it's an adjective. Capitalization optional.

We will now return this account to its intended user. Have a wonderful day!

For years, the term "scalar wave" has been swirling around the Internet. Posts typically describe "scalar waves" as capable of doing things that textbook electromagnetic signals cannot do, e.g. penetrate all shielding, opening up the possibility of really serious Earth-penetrating radar.

Great! Radar that penetrates through its own receiving antenna and every target along the way! Further cost and weight savings can be achieved by removing the power source, receiver, transmitter, and all antennas since it will all be redundant for a wave that completely penetrates everything.

Generally, I'd be extremely wary of anything on the internet that purports large advances in science or technology, especially if it doesn't talk about the costs and drawbacks.

 

[sophiecentaur]

So pressure is a scalar and sound is a pressure wave, thus ordinary sound would be a legitimate scalar wave.

Not sure about this. There is a vector involved in the net displacement of the molecules in a sound wave and there's a gradient of pressure which is also a vector. Imo, the term 'scalar wave' is a bit of a stretch for sound.

 

[Drakkith]

Not sure about this. There is a vector involved in the net displacement of the molecules in a sound wave and there's a gradient of pressure which is also a vector. Imo, the term 'scalar wave' is a bit of a stretch for sound.

Kind of like saying the magnitude of an EM wave is a scalar wave?

 

[Dale]

and there's a gradient of pressure which is also a vector

You can take a gradient of any scalar field. The fact that there is a gradient of every scalar doesn’t make every scalar not a scalar.

If pressure is a scalar field then a pressure wave is a scalar wave (not in the CIA conspiracy sense)

 

[mitchell porter]

There is a big underworld of believers in super-technology via "scalar electrodynamics". Ultimately it derives from a very old reformulation of Maxwell's equations that was discussed on PF in 2012.

 

[EleanorW]

You can take a gradient of any scalar field. The fact that there is a gradient of every scalar doesn’t make every scalar not a scalar.

If pressure is a scalar field then a pressure wave is a scalar wave (not in the CIA conspiracy sense)

My thoughts too!

Thanks to all who have replied.

EleanorW

 

[sophiecentaur]

You can take a gradient of any scalar field. The fact that there is a gradient of every scalar doesn’t make every scalar not a scalar.

If pressure is a scalar field then a pressure wave is a scalar wave (not in the CIA conspiracy sense)

Just to be difficult, I could point out that there is no wave if there’s no (vector) pressure gradient.

 

[Dale]

Just to be difficult, I could point out that there is no wave if there’s no (vector) pressure gradient.

Is pressure a scalar or not?

 

[sophiecentaur]

Is pressure a scalar or not?

All waves consist of Energy Flow.

Pressure is a scalar but how does that make a wave a scalar when it propagates in a particular direction (even a standing wave)? In any case, the displacement quantity in a wave is a vector so I think that makes the wave a vector wave.

If you describe an EM wave (along a line, for instance) in terms of Voltage then you have the same thing because Voltage is potential which is a scalar. I think we've been sucked into a void here because, as I often say, classification, on its own, gets you nowhere.

 

[Dale]

Pressure is a scalar

So if pressure is a scalar then a pressure wave is a scalar wave.

how does that make a wave a scalar when it propagates in a particular direction (even a standing wave)?

Why would that make a difference?

Look at the wave equation Wiki. "This article mostly focuses on the scalar wave equation describing waves in scalars by scalar functions u = u (x1, x2, ..., xn; t) of a time variable t (a variable representing time) and one or more spatial variables x1, x2, ..., xn (variables representing a position in a space under discussion), while there are vector wave equations describing waves in vectors such as waves for an electrical field, magnetic field, and magnetic vector potential and elastic waves." (emphasis added)

So a scalar wave is just a solution $u$ to the equation $$\frac{\partial^2 u}{\partial t^2}=c^2 \left( \frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} + \frac{\partial^2 u}{\partial z^2} \right)$$ There is no implication that $$\frac{\partial u}{\partial x} = 0$$ nor that $$\frac{\partial u}{\partial t}=0$$ The only implication of calling a wave a scalar wave is that $u$ is a scalar function.

 

[sophiecentaur]

So if pressure is a scalar then a pressure wave is a scalar wave.

I'm more convinced now but I still have a question: a sound wave consists of moving molecules. Does not that motion involve a vector quantity. So a physical wave will always have some sort of displacement. When you use the term 'pressure wave', is it actually 'a thing', other than a mathematical equation?

 

[Dale]

When you use the term 'pressure wave', is it actually 'a thing', other than a mathematical equation?

Pressure can be measured. I don’t know if that makes it a “thing”, but it is definitely more than a mathematical equation.

a sound wave consists of moving molecules. Does not that motion involve a vector quantity.

Molecules are moving, but pressure is still not a vector. Just because there is something moving doesn’t mean that every quantity you can measure about it must be a vector.

 

[sophiecentaur]

Pressure can be measured. I don’t know if that makes it a “thing”, but it is definitely more than a mathematical equation.

Molecules are moving, but pressure is still not a vector. Just because there is something moving doesn’t mean that every quantity you can measure about it must be a vector.

You can measure pressure but a wave doesn't just consist of pressure. Wouldn't you concede of there is a vector quantity (displacement) involved in a wave then it should / could be described as a vector wave? I already made the point that, with no displacement then there is no 'wave' to propagate.

 

[renormalize]

You can measure pressure but a wave doesn't just consist of pressure. Wouldn't you concede of there is a vector quantity (displacement) involved in a wave then it should / could be described as a vector wave? I already made the point that, with no displacement then there is no 'wave' to propagate.

Your argument presupposes an atomistic view of a fluid, with molecular motion back and forth along the direction of wave propagation. But at the classical level, pressure waves in a continuous fluid consist of periodic regions of compressed and rarefied density, with no displacement or motion of the fluid in any direction. Hence, the waves in a continuous fluid are classically described as "scalar".

 

[sophiecentaur]

Your argument presupposes an atomistic view of a fluid, with molecular motion back and forth along the direction of wave propagation. But at the classical level, pressure waves in a continuous fluid consist of periodic regions of compressed and rarefied density, with no displacement or motion of the fluid in any direction. Hence, the waves in a continuous fluid are classically described as "scalar".

Wow. So there is no displacement. Is that realistic?
So the speed of sound in a fluid is not dependent on the Bulk Modulus? Strikes me as a bit unrealistic and contrary to experience.

 

[Dale]

You can measure pressure but a wave doesn't just consist of pressure.

What else does it consist of? A sound wave is nothing more than variations in pressure (satisfying the scalar wave equation above). Are you calling variations in pressure something more than pressure?

Wouldn't you concede of there is a vector quantity (displacement) involved in a wave then it should / could be described as a vector wave?

I think you are misunderstanding how sound works. In a place where the pressure is dropping the air molecules are moving away. In 3D they are moving away in all 3 directions. So which direction would you assign as the vector direction?

 

[Baluncore]

Wow. So there is no displacement. Is that realistic?

For a liquid yes, for a gas no.

 

[sophiecentaur]

I think you are misunderstanding how sound works. In a place where the pressure is dropping the air molecules are moving away. In 3D they are moving away in all 3 directions. So which direction would you assign as the vector direction?

The motion is in the direction of the pressure gradient. In the tangential plane of the wavefronts there is no pressure gradient so no displacement. You surely understand that.

 

[Dale]

The motion is in the direction of the pressure gradient

The acceleration is in the direction of the pressure gradient. Not necessarily the motion. Even for a plane wave the motion is still “away” where the pressure is dropping. It is not isotropic, but it is also not a vector.

 

[sophiecentaur]

For a liquid yes, for a gas no.

No mean motion? How can the air not move if there is a pressure gradient? What would hold it in place?

 

[sophiecentaur]

The acceleration is in the direction of the pressure gradient. Not necessarily the motion.

Doesn't Newton apply in gases? SUVAT rules. Acceleration for a time has to involve displacement.

 

[Dale]

Acceleration for a time has to involve displacement

But not necessarily in the direction of the pressure gradient. You can speak to someone upwind, for example.

 

[sophiecentaur]

But not necessarily in the direction of the pressure gradient.

Try a free body diagram on an elemental packet of air. What other possible direction than the net force?

 

[Dale]

Try a free body diagram on an elemental packet of air. What other possible direction than the net force?

It depends on the initial velocity. You can have motion in any direction with force in any direction, depending on the initial velocity.

In sound you can and do have molecules that are moving in the opposite direction of the pressure gradient. They are accelerating in the direction of the pressure gradient but not moving that direction.

I know that you know the difference between acceleration and velocity.

 

[Dale]

The particles have a change in mean velocity in the direction of the gradient

A change in mean velocity in the direction of the gradient is not a mean velocity in the direction of the gradient.

 

[sophiecentaur]

It depends on the initial velocity. You can have motion in any direction with force in any direction, depending on the initial velocity.

In sound you can and do have molecules that are moving in the opposite direction of the pressure gradient. They are accelerating in the direction of the pressure gradient but not moving that direction.

I know that you know the difference between acceleration and velocity.

I also know that the CM of a small mass of gas will accelerate in the direction of the pressure gradient. The pressure gradient in the plane of the wave is zero and also the acceleration (that's referred to as a wave front). Which is why I jumped a step. The pressure and displacement are in time quadrature - just like any other longitudinal wave. Molecular motion is a red herring here - just as with electron motion in a metal; just consider bulk movement of an elemental volume.

I don't see why you don't just try the line of masses and springs model as a starter for any longitudinal wave. Google "is sound a longitudinal wave?". How is a longitudinal wave described? You say pressure is in all directions so something must be longitudinal; how about displacement?

 

[PeterDonis]

You say pressure is in all directions so something must be longitudinal; how about displacement?

You're mixing up different levels of description, and making things a lot harder than they need to be in consequence.

As @Dale has said, pressure is a scalar field. Describing a fluid using pressure means we are ignoring the fact that the fluid is made of individual molecules with individual motions. We are averaging all that out and that leaves us with a fluid-level description in terms of scalars like pressure and temperature, and, if the fluid is in bulk motion, a velocity field, which is a vector field.

At that level of modeling, sound waves, as waves of variation in pressure, a scalar, are scalar waves. Whether they are longitudinal or transverse is a separate question and doesn't affect the fact that they are scalar waves. But if you are interested in longitudinal vs. transverse, at this level of modeling, what is longitudinal in sound waves at this level of modeling is the variation in pressure.

If you want to talk about "displacement" in the sense of individual molecules (as opposed to bulk motion of the fluid), then you are at a different level of modeling, in which concepts like "pressure" and "scalar wave" don't even exist. You just have a huge number of molecules and you are (at least claiming to) keep track of the individual motion of each one.

I also know that the CM of a small mass of gas will accelerate in the direction of the pressure gradient.

Sound waves are variations in pressure about an average value. There is no net pressure gradient associated with them; the variations in pressure average out to zero. If you are thinking about individual fluid molecules moving about, again, as above, you are at a different level of modeling for which "pressure" and "pressure gradient" are meaningless.

 

[Dale]

Molecular motion is a red herring here - just as with electron motion in a metal; just consider bulk movement of an elemental volume.

I agree. All of your motion and gradient comments are a red herring, not just the molecular motion stuff.

The only relevant fact is that a scalar wave is defined as a wave of a scalar quantity, pressure is a scalar quantity, therefore a pressure wave is a scalar wave.

Gradients are a red herring. Air motion is a red herring. Scalar wave is a clearly defined term and a pressure wave clearly meets the definition.

 

[sophiecentaur]

So a scalar wave is just a solution $u$ to the equation $$\frac{\partial^2 u}{\partial t^2}=c^2 \left( \frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} + \frac{\partial^2 u}{\partial z^2} \right)$$ There is no implication that $$\frac{\partial u}{\partial x} = 0$$ nor that $$\frac{\partial u}{\partial t}=0$$ The only implication of calling a wave a scalar wave is that $u$ is a scalar function.

I am trying to deal with some Physics here and that (I think) should involve dealing with cause and effect. That wave equation is 'just maths' and ignores what the quantity 'u' is. An animated wave pattern on a TV screen (u = brightness) would be a true scalar wave and the relevant difference here is that a picture of a moving wave transfers no energy. When energy is carried by a wave, there are always two physical quantities involved and how can you ignore displacement?

I take your point about the possibility of describing a sound wave in terms of pressure; it makes practical sense but using displacement is also valid. Gases have a bulk modulus too. The term Longitudinal Wave is accepted for describing a sound wave; you seem not to acknowledge this.

 

[Motore]

The point of this thread was to reaffirm that the term scalar wave is a legitimate term, which it is and a pressure wave was given as an example. So the thread can be closed right? I suggest the mentors split the thread if others want to disccuss other type of waves and what they apply to...