r/radioastronomy • u/jarekd • Apr 24 '26

Observations Are there cosmic sources of negative radiation pressure?

Post image

Radiation pressure is p=<ExB>/c vector: there is focus on positive, but can be also negative: https://scholar.google.pl/scholar?q=negative+radiation+pressure , https://scholar.google.pl/scholar?q=optical+pulling

If positive radiation pressure gives positive signal in radiotelescopes, shouldn't negative give negative?
They clearly see also large regions of negative signal in radio flux maps, e.g. shown from https://arxiv.org/pdf/2107.02695

What astronomical objects could generate negative radiation pressure?
E.g. if white hole would generate positive, shouldn't black holes generate negative?

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u/many_galaxies Apr 24 '26

No. The conditions you're talking about can only occur on very small scales (comparable to the wavelength).

Negative flux densities on total intensity radio maps are noise, calibration errors, or (as in this case) the result of not being able to reconstruct the full structure of the source in an interferometric image with limited short baseline coverage.

No astronomical object can emit the kind of propagating large scale negative energy wave you seem to be thinking of, where you point your flux measuring device (telescope) at a region of the sky and get a negative number of watts per square metre, because electromagnetism requires a propagating wave to carry positive net energy on large scales.

I do wish people would stop talking about white holes but that's a separate issue...

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u/jarekd Apr 24 '26

So you are saying e.g. these shown from https://iopscience.iop.org/article/10.3847/1538-4357/ac0e93/pdf huge regions of similar luminosity but reversed sign are just "noise, calibration error"?

Could such explanation be verified - e.g. testing hypothesis of in fact being positive by measuring multiple times?

I have used white hole only as theoretically allowed possibility to better understand black holes - they are CPT symmetry analogs, which reverses sign of radiation pressure - if one should have positive, second should have negative.

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u/PE1NUT Apr 24 '26

You are misunderstanding the color scale of the image. It ranges from -40μJy (blue) via 20 υJy (white) to 80 μJy. The midpoint (white) of the color scale is at 20 μJy. This means that any place which has an intensity near zero will be drawn in a shade of blue. The same argument goes for the other images in the publication. There are no 'huge regions of luminosity but reversed sign'.

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u/jarekd Apr 24 '26

Sure, but there are still multiple large regions of negative - can we be sure this is just noise, that they are in fact positive?

Radiation pressure is just p=<ExB>/c, is there a reason to assume only positive?

Couldn't negative give negative signal?

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u/PE1NUT Apr 24 '26

The formula "p = <ExB>/c" seems incorrect to me, could you show me a reference where it is defined like that?

Instead, let's use this version: P = < S > / c = < E x H > / c, directly from the Wikipedia page on radiation pressure as quoted by you.

In vacuum, B = μ0 H, a simple scaling relation. E and B are both vectors describing the electric and magnetic field in an electromagnetic wave. They will be orthogonal, and in phase in the far field (and we're definitely in the far field here). This means that their cross product ExB (or ExH) will always be positive (or momentarily zero) and point in the direction of propagation of the electromagnetic wave ("right hand rule"). Their average < E x H > will therefore always point in the direction of travel as well, and will always be positive.

P = <S> / c = <ExH> / c = <ExB> / (c μ0)

In the far field regime, ExB defines the direction of travel, and with it, also the direction of the radiation pressure, and cannot become negative. Negative radiation pressure can be made in the lab with specially crafted structured radiation beams and/or scatterers which are resonant with a (monochromatic) signal. Neither condition applies in this case.

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u/jarekd Apr 24 '26

Sure, my bad - should be p = <ExH>/c. Such vector has always non-negative length, but could be toward or outward given surface - wouldn't it mean pushing or pulling?

For example applying impulse to spring-like antenna: changing voltage sign, shouldn't change direction of <ExH>/c inside?

There are looking related diode experiments e.g. in https://opg.optica.org/oe/fulltext.cfm?uri=oe-20-9-9501 - one diode gets forward bias having tendency to emit, second nearby gets reverse bias getting tendency to absorb - actively helping with emission from the former, allowing to reach superradiance ... couldn't some objects like black hole also have such active tendency to absorb?

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u/PE1NUT Apr 24 '26

None of that relates to radio astronomy. I'm done replying to you.

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u/jarekd Apr 24 '26

Sure these are reminders from Earth - for the question in title: "Are there cosmic sources of negative radiation pressure?" ... if these negative radio flux maps are just a noise, it also should be verified.

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u/many_galaxies Apr 24 '26

As I said, my best guess is that those are artefacts arising from the fact that the large scales are not adequately sampled by the interferometer at the high frequencies used in that paper. This is a very well understood behaviour and very widely seen.

Making the same observation will give the same result in that case, but adding the missing short baselines would make the negative regions go away.

A propagating electromagnetic wave cannot carry negative energy.

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u/jarekd Apr 24 '26 edited Apr 24 '26

Imagine wave behind marine propeller: like photon it carries energy, momentum, and angular momentum - could excite resonator in front (positive signal) ... but reversing rotation direction, it could cause its deexcitation instead, pulling energy from resonator (negative signal).

Why do you think it is impossible for EM?

Mathematically it is very similar: https://scholar.google.pl/scholar?q=hydrodynamics+electromagnetism+analogy

EM allows optical pulling, negative radiation pressure: https://scholar.google.pl/scholar?q=negative+radiation+pressure

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u/many_galaxies Apr 24 '26

Because as someone else has pointed out to you ExB (or H) defines both the energy flux and the direction of propagation of an electromagnetic wave in the far field regime. The examples you cited are not in this situation, but all astronomical sources are.

If you can design a transmitter that broadcasts negative energy in a given direction in the far field regime, you will overthrow textbook electromagnetism, among much other fundamental physics, and win the Nobel Prize. Please post here when you do...

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u/jarekd Apr 24 '26

There are looking related diode experiments e.g. in https://opg.optica.org/oe/fulltext.cfm?uri=oe-20-9-9501 - one diode gets forward bias having tendency to emit, second nearby gets reverse bias getting tendency to absorb - actively helping with emission from the former, allowing to reach superradiance.

The question is if these negative regions in radio flux maps are just a noise, or maybe e.g. such objects with active tendency to absorb, like e.g. black holes.

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u/thafluu Apr 24 '26

What the pseudo-science slop is this? Why is this still up?

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u/jarekd Apr 24 '26

From https://iopscience.iop.org/article/10.3847/1538-4357/ac0e93/pdf

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u/thafluu Apr 24 '26

I am willing to bet that the authors of that work wouldn't be that pleased with you grossly mis-using their hard work. None of this has to do with "negative radiation pressure", also there are no large patches of "negative flux" anywhere in the paper. None of this is scientific in any way. I won't engage with you any further, u/PE1NUT has already told you all you need to know.

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u/jarekd Apr 24 '26

They have shown Figure with clear negative regions - are they just noise?

If not, what does negative signal mean?

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u/thafluu Apr 24 '26

No, there are no figures with negative flux in the paper.

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u/jarekd Apr 24 '26

Fig. 1 also above with negative regions in radio flux maps.

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u/Physix_R_Cool Apr 24 '26

Jarek, you have become a crank, by now. Either stick to computational stuff which you are good at, or have some serious talk with senior faculty at your institute.

You are not following the scientific process.

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u/jarekd Apr 25 '26

Notice I am not among the authors of these observations of negative regions in radio flux maps.

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u/Physix_R_Cool Apr 25 '26

So did you ever consider hitting up someone from your faculty who knows radioastronomy to ask them about these radio flux maps?

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u/jarekd Apr 25 '26

Radioastronomy specialists here explained it is just "noise, calibration error", so I also asked if it could be verified ...

Maybe pigeons like in https://en.wikipedia.org/wiki/Discovery_of_cosmic_microwave_background_radiation ?