gravity waves vs electromagnetic waves

That encapsulates you.

Unless you believe in an entropy type "ending" of everything.

I like the ending in "Lexx" myself. Gobble, gobble!

But not as well as it does for a surface of last scattering of photons at the point where the universe becomes mostly neutral hydrogen and helium and so transparent to electromagnetic radiation.

Once you accept that distant galaxies are receding from us and you can measure their distances from standard candle supernovas you are forced to conclude that at some time in the past the universe was very compact.

That isn't true though. The most distant objects have the Lyman alpha line shifted through the visible and into the infrared.

There is plenty of evidence that distant quasars really are distant from the absorbtion line patter known as the Lyman alpha forest see:

But there are active galaxies like Seyferts and quasars where there is strong line emission from hydrogen which does allow spectroscopy. eg.

Even for a galaxy where you cannot resolve stars there may still be a net emission or absorbtion of some of the more common lines. The main reason they use spectral index as a proxy is because it works.

It would be a waste of telescope time to survey every last one spectroscopically unless there was reason to believe it might yield some interesting data. And for the most distant objects you don't have the signal to noise to do any spectroscopy but you can do spectroscopy on the brightest objects out to a respectable redshift these days.

Theoretical predictions of what observers should be looking for at these great distances have been made by the likes of Martin Rees.

But the standard model of cosmology doesn't do that.

Hmm, OK Origin questions are almost all impossible to answer. But I think what we can do is look at how it evolves after the origin. (Big bang and inflation.) And that seems to work. We've got a similar situation with the origin of life. It's very hard to know how it got started here. But once it's started evolution does a decent job at explaining how it changes... evolves.

George H.

Various people have looked for that, but AFAICT the cosmological principle is holding up well. People have introduced a time-varying G several times, but it's always been shown to be unnecessary. One important metric of a good theory is the number of free parameters you need for it to match observations--the fewer the better.

The forces become comparable in strength at very high temperatures and densities i.e. very high energy per particle and many collisions per recombination time. Those conditions only existed in the very very very early universe. There's no evidence I'm aware of that (for instance) G is changing with time.

A more familiar example of this sort of effect is a laser. It behaves very differently for pumping rates just above and just below threshold. The physics is no different, just the results.

So we hope. This stuff is just so far from the ~1 eV energy scale that human concerns exist at--it's primarily an aesthetic activity.

Cheers

Phil Hobbs

Hi,

Anytime the overall combined field of gravitational curvature and electromagnetic polarization don't match the expected velocities of free masses within the fields, then there will be electromagnetic waves and/or gravitational waves emitted from the mass. Essentially to swim upriver takes energy, and going with the flow conserves energy.

Just by sitting in a chair you are emitting gravitational waves since the gravitational curvature created by the earth's gravity, "insists" that any mass has to be falling towards the center of earth, otherwise the stationary mass (ie me) sitting on a chair will be losing weight emitting gravity waves. However luckily this is greatly offset by reduced metabolism sitting.

cheers, Jamie

you pack as much electrically neutral mass as you want in as small a space as you want, you will never generate an electromagnetic field.

after reading some of Robert L. Forward's papers. Best I could do was superficial- the differences outweigh the similarities.

quarks!), but there's only one kind of mass with no apparent quantized unit.

only quarks can generate color fields, etc.

polarizable dielectric (that's technically wrong but it gives a usable mental image) with the exact same permittivity. We can do all sorts of fun stuff with EM because 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.

ridiculously sensitive detectors to see them because gravity is so ridiculously feeble.

Hi,

A couple things I was wondering about with gravitational waves, are if all accelerating mass emits gravitational waves, how is this possible for a mass composed of atomic matter. Where does the energy for the gravitational waves come from in the case of very very very very small gravitational waves like sitting on a chair in earth's gravitational field. For high intensity gravitational waves, ie orbiting black holes, I guess the forces involved are so high that the matter basically ceases to exist (or since it is black holes is in an undefined state) so there is no intermediate step required to convert it to gravitational waves unlike quantized matter, ie a single stable proton in a gravitational field.

Also it is possible that it is a statistical emission of gravity waves associated with the matter changing quantum states? ie this could explain the possible modulation of nuclear decay rates with earth-sun distance (unlikely).

So basically how does a mass emit gravitational waves in normal circumstances where the mass is accelerating but otherwise stable.

cheers, Jamie

I'm not talking about G generally changing with time. I'm talking about the effect of G on the early universe. Obviously we aren't inside a black hole. Equally obvious is that since nothing escapes from a black hole the universe was never inside a black hole. So the only way to explain the early times when the large matter of the universe was in a small space is to assume there was something different about the way matter interacted through G.

One thing that has always confused me is the distinction between material objects flying away from each other and "space-time" itself expanding. I'm not even sure what the latter would mean. But I'm pretty sure that the acceleration of the expansion of the universe means there is something very fundamental that we are not grasping.

BTW, in a recent show I watched they pointed out that at the time of Einstein's early papers it was not completely accepted that atoms existed and so the photoelectric effect by quanta was not widely accepted. I guess I never gave much thought to the timing of some of these ideas. Looking forward I wonder what will be the trigger to reveal the next big idea.

I'm getting in to things I don't know very well... but I think that if the universe is closed. (enough energy density to have it collapse and end in the big crunch..) Then I think that means we are living inside a black hole... nothing escapes the universe. (Of course I'd be happy to have Martin tell me I'm full of horse hockey.)

Yeah it's pretty hard to make a model of this in your head. But it's easy if you get rid of one spacial dimension. Then with two dimensions a closed universe would be like the surface of a sphere, (that changes radius with time.) and an open universe would be an infinite 2-d sheet.

George H.

Faulty reasoning. Axiom: If A then B. If B then A does not follow. Also, you don't really know about the boundaries of the universe. Supposedly distant things will become unobservable to us and so you could argue they "leave" our universe.

I'm not sure you are using closed and open in a way I understand. I thought closed implied the universe would ultimately collapse back on itself as there was sufficient matter to slow the expansion and reverse it. An open universe simply meant there was insufficient matter to cause a reversal of the expansion of the universe. In fact, the expansion of the universe is accelerating which would be a "super-open" universe like an exploding balloon?

Why does any of this map to a plane or sphere?

My question was about the distinction of matter moving away from a more dense state vs. the spacial framework itself expanding which would seem to have no meaning since space has no yard stick other than the matter in it.

How can you be so sure our universe is not actually a black hole? What's the difference between a black hole and a closed universe? (Apart from us possibly being inside it?)

Agreed. I don't grasp what that means either. Surely it's just the way it's being popularized, dumbed down to the point of becoming gibberish.

For a long time, I was puzzled by forces dropping of faster than 1/r^2, that is, until I actually got to see a formula, and it went something like exp(-t/t0)/r^2. Oh, I see, *that* makes sense: The thing that transmits the force decays, gets caught, or is otherwise rendered ineffective. That sort of thing is "too complicated" for laymen.

There are plenty of things like that. Quantum effects, interference, FTL tunnelling and entanglement are other examples. I'm convinced there is nothing so mysterious going on, but it's made to look that way. Awe and wonder, but no enlightenment for common folk.

Heisenberg's cat is not both dead and alive: You do the experiment with lots of cats and you'll have both dead and live cats, that's the way it works.

I have nothing to add there. We've gone over this several times in the recent past.

Jeroen Belleman

If that doesn't make you uncomfortable, try some fiction that plays with the concepts: _Pushing _Ice_, by Alastair Reynolds, is a recent one. _Last_and_First_Men_, by Olaf Stapledon, is a classic.

Yeah OK... black holes exist in the universe.

Open is open, space is then infinite... it doesn't really matter if it's accelerating faster... OK, thinking about an open (infinite) universe makes my brain hurt.

Well those are also 2-D surfaces.

I think it also has a curvature... the curvature is so close to flat at the moment that we can't tell the difference.

But like I said I'm way over my head....

George H.

Because of the definition of a black hole, gravity so large it has an event horizon from which even light can not escape. Should we assume the laws of physics are different inside vs outside a black hole?

When I asked someone about that it was pointed out that there is no frame of reference other than the materials in the universe, so if they are "expanding" then the universe is expanding. I think that is a rather arm waving definition and pointless.

I don't think so. There are experiments that show two paths being taken prior to the act of "viewing" the result which determines which path was taken. I don't recall the experiment but it was one of those photon things. BTW, it was Schrodinger's cat. Heisenberg was a dog man.

How would you tell?

Because things have escaped from the universe in the past? What things?

Why exactly? Initial conditions are initial conditions. Do you have some *a priori* knowledge of what they had to be? I sure don't.

GR has a consistent picture of that.

Why so?

Einstein got the Nobel Prize for the photoelectric effect, not relativity.

There are lots of ideas rattling round.

Cheers

Phil Hobbs

Do you know anything about the inside of a black hole? What is it like? Where is the matter? Compare that to the known universe.

Because we are now not in a black hole and if we didn't escape from a black hole, we must have never been in one.

I have no idea what you are talking about. The entire universe inside a very, very small space would imply a black hole according to the laws of physics we know. The early universe was not a black hole. So clearly there is something different about the laws of physics at that time that allowed the universe to expand beyond the dimensions of a universal black hole.

Care to explain? I'm not clear on how that applies to my point.

Right now we are postulating a mysterious "black energy" which we know nothing. There is no other reason to believe in "black energy". Sounds very ad hoc and mostly likely not "real". I anticipate something analogous to relativity to fundamentally change our image of the universe.

Non sequitur. I have read that even when he got the Nobel, the theory was not widely accepted or even understood. Remember the ideas of atomic and subatomic particles were *very* new. Heck, when I was in college, there were plenty of professors who admitted they didn't have much understanding of relativity.

Most or all of them have no value beyond the dominant theories that we have used for some time now. I'm looking for the new one that actually works better and is a totally new approach... analogous to relativity

I have no clear idea what an event horizon might look like 'from below', if that even means anything.

IIRC, the density of the universe, matter, energy and all, seems to be very close to what's needed to make it collapse back on itself in a very far future. In other words, it would have an event horizon. Then again, none of this is solid science yet. Again, all we can do is observe and model, trying to fit the pieces of the puzzle together until the picture starts making some sense.

You're talking about those experiments where the path taken is determined and the interference pattern vanishes, and then the path information is 'destroyed' and the interference re-appears? The term escapes me, for the moment, but I've read about such experiments.

Ah yes, Schroedinger, of course. The experiment should work with dogs too. ;-)

Jeroen Belleman

So if the universe is being fed by a black hole then is that the reason our spacetime is inflating - from all the time and matter being sucked in from elsewhere in the multiverse??

piglet

No. The universe might look like a black hole from "outside" if there were an "outside" but since the whole point about a black hole is that anything inside it doesn't have access to anything outside, this a pointless observation.

Also in the early universe there was more symmetry in the laws of physics and the distinction between the various forces were less clear.

People as famous as Dirac have explored that conjecture but it doesn't lead to anything particularly interesting. If gets a mention in Harwitt's Astrophysical Concepts.

That is basically right. If we were in a gravitationally bound universe that was destined for a big crunch then we are inside a black hole.

Note that you could hide a uniform spherical shell of material sufficient to close the universe at some enormous distance and by Gauss's theorem we would never be able to detect it's influence.

However, such configurations require a lot of artificial boundary condition lash ups.

Dots on a balloon is as good an analogy in 2D of an expanding universe in 3D as it gets. The balloon surface has no edges and as you blow it up the surface area increase and the dots move apart from each other.

The ability to visualise things in 4D (and even higher dimensions is the mark of a really good cosmologist or mathematician).