gravity waves vs electromagnetic waves

I found the paper below distinctly interesting.

It doesn't involve any new physics, and it does seem to take into account a lot of recent observations that constrain dark matter distribution.

"The Journal of Cosmology" seems to be a fringe journal - to put it kindly - so better refereeing might have found gotcha's that I missed.

I say that there is no such thing as a graviton, period.

You are talking about "gravitational waves":

"Gravity waves" are something else entirely:

But yes, in general you are correct, though there are some picky details:

Yep.

This is where you go all science-fiction. "Spacetime fabric" doesn't have any formal meaning. Yet...

Yes and no. Pack enough electromagnetic energy into a small enough space and you can measure its gravitational field, but though you pack as much el ectrically neutral mass as you want in as small a space as you want, you wi ll never generate an electromagnetic field.

I fiddled around with trying to find connections and similarities between electromagnetism and gravitation some thirty years ago after reading some of Robert L. Forward's papers. Best I could do was superficial- the differe nces outweigh the similarities.

There are two kinds of quantized electrical charge, positive and negative (there's also two levels of quantization- leptons and quarks!), but there' s only one kind of mass with no apparent quantized unit.

ALL forms of matter and energy generate a gravitational field, but only e lectric charges can generate electrical (and magnetic) fields, only quarks can generate color fields, etc.

Matter can be electrically conductive, insulating, or semiconducting, but for gravitational fields all matter is sort of like a weakly polarizable d ielectric (that's technically wrong but it gives a usable mental image) wit h the exact same permittivity. We can do all sorts of fun stuff with EM bec ause we have conductors, insulators, and magnetically active materials, but all matter is exactly the same gravitationally. Imagine trying to build a radio transceiver out of just pure glass.

Yes, we know how to generate and detect gravitational waves, but you need a lot of matter accelerating very quickly to generate them, and ridiculous ly sensitive detectors to see them because gravity is so ridiculously feebl e.

Uh, no.

Mark L. Fergerson

Or course it does. The main tenet of relativity is that there is no absolute motion. Only acceleration is absolute. So a body moving without acceleration can't give off a gravitational wake or it would violate relativity as there is no absolute frame of reference to define its motion. In other words, there will always be a frame of reference in which it would be considered not moving and gravitational waves could still be detected.

Certainly in a classical sense it would have to be, but in a universe already bathed in dilute black body radiation it isn't alone. As soon as you have something else emitting photons that pass near to the path of the object then you have a means to measure its gravitational influence. It helps to have a precision clock like a pulsar handy.

However, in the actual Einstein-Lemaitre universe with the uniform isotropic radiation of the Big Bang the only moving particle in it will feel a slight deceleration due to Doppler shift and the oncoming traffic effect meaning that there are in its frame of reference slightly more incoming photons from its direction of travel.

The effect of this radiation pressure imbalance would be miniscule unless it was relativistic.

This actually leads to a nice way of probing the intergalactic medium in clusters of galaxies via the Sunaev-Zeldovich effect.

Which has nothing to do with gravitational waves.

I think you missed a lecture in the relativity section. You seem to be describing a universe with an absolute frame of reference where your motion is added/subtracted from the speed of photons.

Good to see that your self confidence is holding up well, at least. ;)

Doppler shifts in the CMB were long expected, and first measured by the COB E satellite in about 1990. It's far from subtle.

Cheers

Phil Hobbs

Grin.. no one would every accuse SED of lacking in hubris.

George H.

OBE satellite in about 1990. It's far from subtle.

Mmmh. The CMB is also one of those things I've always thought of as highly suspicious. I'm not denying its existence, but I doubt the conclusions they draw from it. They present us with highly precise measurements of what is basically noise, tweaked to remove the supposed contributions of all sorts of discrete and diffuse objects in the foreground. They then use that to make sophisticated adjustments to a model of the history of the universe that is itself highly suspect.

We're trying to make out teensy fluctuations in a signal that's tiny and noisy to begin with. There is no way to do any experiment. We can only watch and try to understand. We use the results to refine a model that boldly defies all of physics right from the start: Creation of matter out of nothing, superluminal inflation, expansion of emptiness and a load of other unverifiable weirdness.

It scores pretty high on the list of criteria for recognizing bad science. It's fortunate that no politician has yet come up with a way to tax us for it.

I fully expect that some day, today's cosmologists will be the laughing stock of science. How *could* they come up with something *so* breathtakingly impossible. But I don't expect to live to see the day.

Jeroen Belleman

Superluminal expansion does feel like the luminiferous aether of yore, but that just means we haven't found a better explanation for it. Or really an explanation at all; I don't recall that anyone has a good idea about that one, other than "well, the observations say it went really fast /right here/".

There are current theories about making things apparently go really fast (e.g., Alcubierre drive), and perhaps one could wave their hands about the Universe being younger and hotter back then (like the proverbial girlfriend). Which never made sense to me, in that, it doesn't matter how much velocity it has; if it's /the mass of the Universe/, and it's smaller than its Swartzchild radius, it's not a universe, it's a black hole. But again, the measurements say we're here, now, so take from that what you like.

Tim

Well.. I know nothing about CMB. (I have a colleague who did a lot of the RF design work for WMAP.) But if noise is all the data you have, then you make the best of it. What don't you like about the models? We've had a pretty good idea of what had to go on for a long time now... (I just re-read "the first three minutes", by S. Weinberg.)

OK I'm getting way out of my depth, but I don't think the CMB data has much to do with what happened early on with inflation... but only much later in the evolution of the universe, once everything had cooled enough to become transparent to light.

The numbers agree pretty well with data from other measurements. For me that adds to my confidence.

George H.

I've always wondered how we get around the black hole thing, but then I realized the physics of the universe are not constant, but have varied over time. They talk about the four basic forces uniting as we go back in time, but what about gravity? Mass is about the Higgs field, so what was that doing at time=very small?

As to the aether, I believe we are approaching a similar time to the turn of the previous century where we had a few odd contradictions that were being hand waved away mostly. Maybe before I am gone from this planet someone will figure out the mystery and fold back another layer from the onion.

Pretty pictures that we've all seen before, but not good enough to convince me. I'm not a physicist or cosmologist. I can afford to entertain diverging views without risking my career or livelihood.

It's funny how the word 'impossible' always seems to prompt a reference to the Wright brothers. The comparison between the birth of the universe and of working flying machines is incongruous in the extreme.

If you are happy believing in spontaneous creation of matter and superluminal expansion, that's fine by me. Unless you advance some arguments that merit reflection, you don't matter.

Jeroen Belleman

I'm not sure HEP particle folk ought to be throwing such stones ;-)

I have heard HEP described as a hybrid between stamp collecting and studying horology by smashing clocks together at high speed and watching the bits that fly out.

The parts of the microwave background well away from the galactic plane and away from other galaxy clusters are relatively clean (or so they tell me). The standard cosmological model of the universe holds up pretty well these days and we are in a golden age where almost every wavelength can be studied from radio out to X-rays. It tightly constrains the imaginings of theorists to have such good observations.

Gravity waves are interesting since they can potentially see back past the surface of last photon scattering before the universe became transparent to electromagnetic radiation.

The numerical simulations are the only experiments that are possible and they have become really rather good these days.

Your objection to creation of matter out of nothing is a bit rich seeing as how the Casimir effect is well established. It is quite possible that in some hierachy our universe is a quantum fluctuation.

Our model of how it started out may not yet be weird enough to be entirely correct but it works back to miniscule fractions of a second.

The Higg's boson is in that category too and was a much lower sigma detection than the gravitational wave signal.

Today the proponents of Steady State theory are not laughing stocks of science and Fred Hoyle would probably have got a Nobel Prize for his earlier work on stellar nucleosynthesis had he not been so abrasive.

Stephen Hawking first came to attention when he shot one of Hoyle's cosmology papers down in spectacular fashion at the Royal Society.

I do think that there is scope for a new theory that unifies all quantum mechanics and gravitation but that is the Holy grail for theoretical physicists. My instinct is that string theory is barking up the wrong tree but I could easily be wrong on that.

It is possible that Guth's inflation is a bit too ad hoc for some and that a better theory will explain this in a more natural way, but until a better theoretical model comes along we have to test observational data against the best models that we have and look for errors.

It so happens that the CMB also agrees pretty well with the expected average radiation of arbitrarily distant stars. Olbers'paradox, but with redshift.

Jeroen Belleman

I think you have a problem actually knowing what matter is, much less what does or does not matter.

Has everyone given up on antigravity? Anyway great detection work with the gravity waves. Science sure is pressing ahead.

Hi Jeroen, no disrespect, but are you saying you don't "go" for the big bang model. Steady state or something?

George H.

He cannot handle the single point source thing.

There are super-massive black holes in the centers of most galaxies that have stars hundreds of times bigger than our Sun swirling around them at extraordinary speeds, yet he cannot conceive that everything was all once confined to a single place..

BOOM shaka laka laka