gravity waves vs electromagnetic waves

We all tend to turn into caricatures of ourselves as we age, but we have so me control of the process. As a collection of older guys with well-develope d egos, SED displays a wide range of cautionary tales of that sort.

Collins apparently would rather believe he already knows everything than le arn anything.

AFAIR whenever he's shown his errors he clams up and attacks from a differe nt angle. He's a good FPGA guy, by all accounts.

Cheers

Phil Hobbs

I think it was pooh that said, "the arrow of time points in the direction of getting older".

George H. Hey, I think that if you are in a big enough black hole... but not too big, you can point a laser off and have it come back to you... (it might have to decay/drift a bit towards the center.)

ng

some control of the process. As a collection of older guys with well-develo ped egos, SED displays a wide range of cautionary tales of that sort.

You know, I sometimes get the feeling that's it's harder for smarter guys to admit mistakes. (They make fewer of them, and get less practice, perhaps.)

George H.

learn anything.

rent angle. He's a good FPGA guy, by all accounts.

Trying to compete with krw for the position of the group participant who makes the most asinine assertion?

does suggest that you'd need a lot of further education to realise how asinine your unqualified assertion actually is.

Time flies like an arrow.

Fruit flies like a banana.

He's saying it's waves. Are you saying it's particles?

More specifically, you get QM, and thus* reality, from classical waves (namely, matter or probability waves). The reason we observe "events" is because of statistics.

Even more specifically, the waves are in configuration or probability space: what's observed is a dice-roll based on those waves, not the waves directly (after all, the waves are complex-valued and cannot be measured directly, not that we have anything but more matter to measure them with, in the first place).

And discrete "events", energy levels/bands, etc., arise because continuous (wave) systems are not limited to real-valued parameters, but can always create indices taking integer values. These happen to be eigenvalues (and the waves characteristic thereof being eigenfunctions) of the system. Which may seem unfamiliar to the electrical engineer, but there are systems which exhibit that kind of behavior, such as transmission lines, certain feedback systems (e.g., hysteresis), etc.

Regarding neutrons or C60, remember that it's an elegantly approximative method. As long as the internal energy or number-of-accessible-states is small, the Wad-O-Particles looks itself like one whole, jiggling wave-particle. Neutrons are made of quarks and pions (mostly); C60 is made of atoms (made of electrons and nuclei, the nuclei of which are made of protons and neutrons).

So it's not turtles, but probability waves, all the way down. So far as we know.

It's the exact same way that an ensemble of waves/photons can form an image (e.g. optics), or beam (e.g., optics, radio), as long as all the infinite waves superpositioned together are coherent. In the composite particle, all the constituents are moving coherently. It's not same because the particles interact (fermions versus bosons), but in low energy states, with spin pairing, fermions can behave like bosons, for limited circumstances where such remains valid. (Obviously, C60's** tend not to simply tunnel through each other. But when very cold, so their deBroglie wavelength is much larger than their molecular size, they will indeed behave precisely this way.)

(**I'm assuming C60, of suitable isotopic composition, is spin-0 or something like that. If not, there will be other interactions, at least until those molecules pair up, at extremely low temperatures. He4 might be a better example, but superfluidity isn't terribly well understood either. It's certainly suggestive that He3 (nonzero nuclear spin) isn't superfluid until mK temperatures.)

Tim

"Escaping the universe" is a pointless concept. By definition nothing escapes the universe. "Closed" is defined in terms of the observable matter in the universe. If there is insufficient energy in the expansion for the matter not continue to expand indefinitely, that has nothing to do with space itself which can still be infinite. It also says nothing about light continuing to travel indefinitely. There would be no event horizon and no place where the gravity field is so strong it prevents light from continuing. A black hole has an event horizon which nothing including light can not escape from. The universe has no boundaries at all.

This is a discussion of things that none of us understand well. I admit I am not willing to read research papers on the topic but I am happy to read what you guys write... as long as it is clear. I'm not trying to be argumentative, I'm trying to explain how I perceive the topic.

Martin talked about Dirac exploring "that conjecture" in response to something I said and I don't know what "that conjecture" related to. So I asked him "to explain that". I literally don't know what Martin was referring to in my post at that point.

How does that turn into "confrontational" or "he already knows everything"? That is a rhetorical question, not looking for a literal answer. Or maybe I am... not sure. It's late.

Earlier it was said that the universe might be a black hole. I tried to point out the inside of a black hole has particular properties that can't allow the existence of a universe as we know it.

Without assuming anything about a final state, the interior of a black hole has a huge gravitational field. Are you suggesting the black hole could be so large the extreme gravitational field would not be noticed because the gradient is so small?

Even if that were true, how could such a black hole be created where the matter is moving toward the event horizon and not toward the center?

Care to explain how? Saying something is wrong is not explaining it.

You don't directly respond to my points, you seem to talk around them. If the universe was a black hole in the beginning, how could it be what it is now without escaping the black hole? Are you suggesting we are still in the black hole, a really large one?

What sort of gravitational field would be observed inside a really ginormous black hole? Wouldn't we be seeing the backs of our heads or something?

I don't see how you can assert that in a meaningful way. Why would "space" drag anything along with it and what does it mean for "space" to expand. Balloon analogies are not explanations unless we go back to the Aether carrying EM waves and impacting matter where it would be a reasonable analogy.

Rather than "experimental evidence" for dark energy, there are observations that we can try to explain by creating a mysterious "dark energy". Until we have some reason to believe it really exists it is an analog to the Aether.

Too damn old. I was in college in the 70's. I recall asking about relativity and professors attempted to explain it but mostly admitted they didn't understand it well either. Since then I have found many references that explain it much better. University of Maryland. Maybe the undergraduate classes were not taught by the top dogs. I recall seeing pictures in the library of some professors who discovered various subatomic particles I had never even heard of at that point. I would be interested in going back some day to see if I can find those pictures again.

I think the way to view this is to realize that QM is a pretty good description of physics. The physics we knew before QM was just the way it simplifies when considering the "big" picture view of QM. We consider that to be "normal" just because that is what we perceive on a personal level every day. It is just a special case of QM, but likely everyone here realizes that. It means we shouldn't expect any other theories to be any less weird or more normal.

You never actually said what those properties were. Nothing spectacular happens as you "turn up" the density of matter in a region. At some point you have made a black hole, because the escape velocity exceeds c. But that is not obvious from the inside.

Yes! It is not an extreme field at all! It is a large (negative)

When I was at uni ~30 years ago ISTR you could plug in the radius of the observable universe and calculate the mass density needed for it to be a black hole. It was something like 10 times the observed density, in other words too close to call given the uncertainties involved and dark matter etc.

By the Big Bang in the Einstein-Lemaitre solution. It is all in the initial conditions.

As an analogy weightlessness in parabolic flight begins from the moment that the plane starts to fly in a parabola on the way up to the apex so long as you are in free fall you remain weightless.

Because the interior of a black hole is only nasty when the singularity has formed and you are close to it. Provided that the gravitational gradient is low you are safe enough inside a spherical black hole. Doomed ultimately but the time to your demise depends on the mass of the black hole. It only hurts when you get too close to the singularity.

If everything is still flying apart (which is what we observe today) then even if the universe was closed and destined to collapse back in on itself we wouldn't have to contend with the singularity forming until at least another age of the universe has elapsed. We would be in big trouble when expansion stopped for other reasons.

Put another way you can make a black hole out of anything of any density if you make it big enough. At a handwaving level open or closed of our observable universe is determined by the size of the region out to where the recessional velocity of the universe exceeds the speed of light (matter beyond that cannot influence us). It turns out there is additional acceleration too but that is a relatively new result.

Yes. At least in principle we cannot tell whether we are or are not. The fact that we believe that the universe will expand forever (and accelerate) suggests not, but if the universe was slowing down and we were destined to collapse in again then this phase would still look identical to how it does now. Things only turn ugly when the universe stops expanding and Olber's paradox together with blue shifts fry whatever is left.

If the black hole was universe sized then nothing unusual would be observed. The question of periodic boundary conditions on a closed universe does imply in principle that it you could see far enough in one direction you might see the back of your head. But the sheer size and opacity of the early universe prevent that.

You are determined not to understand. The fabric of space time is in some sense what is changing (stretching) as the universe expands.

That is what the mathematics says expressed in words.

The parameter we call "Dark Energy" was invented by Einstein to fix a "fault" in his original equations for the universe. A fudge factor constant of integration to permit stable Steady State universes.

I don't much like Dark Energy myself as it dates from an era after I was active in the field and I would much prefer to believe that there was something odd about the brightness of early supernova but I am assured that is not an option. So we infer that the universe is accelerating as it is expanding. IOW Einstein's constant is non-zero.

That's a bit worrying in a physics department unless it specialised in solid state. Relativity was done and dusted by the mid 1950's so the generation of lecturers in the 1970's should have been very familiar with it. My first supervisor at university was a guy called Ed Shire whose epitaph in the Times was "a device to destroy the flying bomb" (he invented the proximity fuse) and he was certainly up to speed on relativity despite his advanced age. We were his last batch of 1977.

He was experimenting with microprocessors for controlling experiments in his final years. He had loads of stories of working in rotating frames of reference sat in huts with a radar horn in front of him.

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If our universe were closed, it would still be 13.5 billion light years acr oss.

You might be seeing a photon that originated where you are some 13.5 billio n years ago, but your head wouldn't have been there then. Our universe it e xpanding and photos that old have been red-shifted down to much lower frequ encies.

The cosmic background radiation has been around since the 380,000 years aft er the big bang, and originally represented the black body radiation from g as at 3000K. It has been red-shifted down until it looks as if were being e

"Frame dragging" is a known relativistic effect, but my feeling is that the "space itself is expanding" explanation is nonsense. Much easier to say th at matter started flying apart at the instant of the big bang, and has been doing it ever since.

Bits of matter that were close together immediately after the big bang at f ly away from one another more slowly than bits that were further apart, and the statistical fluctuations in density in that primordial matter allowed close neighbours to clump into galaxies, while more remote bits kept on mov ing apart.

ds

Not exactly. The early supernova data that seems to show that the expansion of the universe is accelerating was extremely handy when it showed up.

It allowed us to correct the age of the universe to 13.8 billion years from the pre-acceleration figure of 9.3 billion years (which was handy because there is a 13.2-billion year old star).

The "dark energy" required to do the job provided the necessary extra mass- energy to get the weight of the universe right, which was no less convenien t. The guys who had collected the early supernova observations got their No bel prizes very promptly.

I've just come back from a New Scientist public lecture

Professor Tamara Davis spelled it all out very coherently.

Grin, well since we see two slit interference, we can't call them classical particles.

Well two slit diffraction, (or just diffraction off of crystals) is a low energy process and I don't think all the internal degrees of freedom make any real difference to the outcome.

But QM is real and fun! entanglement and CPT (coherent population trapping) are just bizarre.... I've only got a nebulous grasp of the theory.

George H.

U of Maryland is where Weber was... so someone there knew about gravity.

George H. Relativity was done and dusted by the mid 1950's so the

Why is that not obvious?

I still say it would not be possible to have a universe expanding at an

If we are in a black hole where the force of gravity is stronger than even the nuclear forces, what force could possibly be causing the expansion of the universe?

So pick initial conditions that give you the result you want and don't worry with how possible that would be inside a black hole?

So a G field so strong it will prevent light from escaping won't be noticeable until it gets much stronger? BTW, when does the singularity form?

I still have a problem with those initial conditions.

If we were in a black hole, we would be able to observe the effect on light try to escape, no?

I'm determined? The "fabric" of space time is a teaching construct that has no real manifestation. Why do you talk about that? Where is the fabric in the math? Is this a knit or a tweed?

Now you are talking about a term in an equation. The equation is not the universe. My point is that we don't have experimental evidence to say dark energy exists in the same way as other energy.

That is why I say we will see something new when someone gets a new insight to the problem.

Heck, I had one professor who when confronted with the question, "why?" as applied to a fundamental issue like charge had no idea how to even approach the question.

This is a great discussion, thanks to everyone. May I ask a question re black holes. On Earth, to escape gravity you need to achieve escape velocity. But that applies only to inertial objects. In other words, if you were to throw a ball, it would have to achieve escape velocity when it left your h and in order to escape.

BUT... if the ball had a small engine, it could rise at any small velocity and still escape as long as it had sufficent fuel to continue under power. With enough fuel, it could rise as slow as 1 mile per hour and still event ually escape.

So when we say nothing can escape a BH, does this apply only to inertial ob jects? In our imaginary space ship (with an engine) , if we crossed 1 foot into the the event horizon, why could we not use fuel to turn around and c ross back outside the event horizon?

thanks Mark

The "small engine" need only have a thrust that is greater than its gravitational attraction to the body it's trying to escape.

Seems like your question becomes: how much thrust would your object have to be able to generate, when even photons are trapped?