gravity waves vs electromagnetic waves

There is nothing special about the event horizon from the perspective of an observer falling into a black hole apart from the fact that having crossed it like the hotel California you can never leave.

(This assumes you visit a supermassive BH so that you don't get spagghettified on the way in). Objects will appear blue shifted to you and there will be light path distortions of the distant stars.

ISTR there is a raytracing project somewhere that does virtual tours of black holes and their environs. Back in the old days I recall someone (I think Patrick Moore) had a perspex analogue BH simulation cut and polished for him by early numerical machine tools.

You could hold it at arms length and see the effects.

Until recently it looked like it was essentially flat but now it looks like it is accelerating away with increasing time which means that the universe will go on expanding forever getting ever less dense.

Moreover it works at photon rates so low that only one photon is in the apparatus at a time. If the photon has a selection of paths it explores all of them but the wavefunction collapses to the shortest isochrone.

(which apart from the diffraction is equivalent to geometric optics)

Other way around I think! The outside can't see the inside.

It's coming back to me now: The relevant keywords were 'quantum eraser'.

I don't like the image of single photons following multiple paths, but we've gone through that several times in the past and I have nothing new to add. Read "Anti-photon", by W. Lamb.

Jeroen Belleman

You are confusing the final state of the interior of a black hole - which ends with a singularity at the centre after finite real time. However, that finite time to reach the singularity can be made arbitrarily long inside a sufficiently big black hole.

It was originally this conundrum that led Einstein to add a constant of integration to permit steady state solutions to the Einstein-Lemaitre universes. The stable solutions without adding dark energy have to involve dynamic expansion (or contraction). No steady state possible.

If we are inside a black hole then eventually there will be a big crunch when the present universe expansion runs out of steam. However, at the moment it is looking like there is a small acceleration which will tip the balance in favour of forever expanding.

Your reasoning is fallacious.

No. We don't know that at all. The very earliest times of the universe are incredibly difficult to understand since the laws of physics start to break down at ultra high energies that we have no way of probing experimentally. We can only estimate what it was like.

It is the space itself that is expanding taking the objects in it along for the ride. Think bread dough (space) with raisins (galaxies) in as it expands during the proving stage when the yeast gets to work.

"Dark Energy" is the name now given to the constant of integration that Einstein put in his equation to match the then prevalent Steady State model of the universe. TBH I don't much like dark energy - but there is experimental evidence for it in the most distant supernova records. That is that the universe isn't slowing down like you might expect but it expanded ever more rapidly.

How old are you?

Relativity was a coherent fusion of ideas that were part formed by others into a clear physic principle of enormous simplicity namely:

The laws of physics are the same for all observers in an intertial frame.

It doesn't matter whether you like it or not - nature is the final arbiter in these things and it behaves as if the particle has followed both paths available to it. ISTR the closest thing to a cat that has been diffracted through two slits so far is a C60 buckyball.

The latter also provide physical realisations of some of the particle in a box models that we were forced to solve in basic QM classes. The cage of the molecule being the sides of the box and a rare gas molecule deliberately trapped in it during formation.

BTW here is one of the raytracing BH view simulations (not the full video one I was looking for but still of general interest).

Hi piglet... lots of words in there that can have different meanings to a cosmologist. Inflating could be confused (or do you mean) with the very early "inflation" right at the beginning of the big bang. Multiverse sorta relates to a quantum mechanical viewpoint. And let's not go there.

But to try and answer what I think is your question.... inflating = expanding multiverse = universe

So I didn't say the universe was being fed from a black hole... only that a closed universe kinda looks like a black hole in that nothing (including light) can escape from either.

Space is expanding because of the big bang. If the universe is closed, then the best analogy (for me) is to remove one spacial dimension and think of the universe as the surface of a sphere. We live on the sphere and if we shine a light in one direction.. then given enough time.... it will in theory travel around the surface and come back.

The expansion of space is like the radius of the sphere getting bigger.

George H.

Yes, of course, experiment is the final arbiter. There is still room to quibble over theoretical models though. The model works, there is no doubt about that. Shut up and calculate. The right answers come pouring out. However, it requires objects with weird properties which to me signals that there's something wrong. I suppose one gets used to weirdness, eventually. It should be possible to do better.

Jeroen Belleman

You are suggesting that we know nothing about the physics inside a black hole?

Ho there, stop right there. The big bang is the hypothesis concocted to explain why the universe appears to be expanding, not the other way around! It is just the picture you'd get by rewinding the current observations by ~14Gyr. But that's what you meant, right?

Jeroen Belleman

Care to explain that? Mentioning someone else's work without relating it to the point in question is not at all useful.

That is completely wrong. The way George is using the term simply means the matter in the universe is enough to cause the expansion to reverse. That doesn't mean nothing can escape from this expansion reversal, light will. A black hole has such a strong gravity field that nothing can expand at all including light. Everything collapses to a singularity since gravity overcomes all other known forces.

Irrelevant since this is still not a black hole.

Analogs are only useful when they are useful.

OK sure... I guess from my perspective the big bang theory is the only game in town cosmology-wise.

George H.

No, if the universe is closed light doesn't escape... There's no place to go!

George H.

Our sense of what is "weird" is based only on our everyday experience of the physical behaviour of macroscale objects. Our brains evolved to think in this realn. But there is no reason why this should apply "all the way down". And in fact it does not help at all to say that billiard balls behave as they do because they are made of atoms that behave like little billiard balls. Especially when they don't, really.

In one of his lectures Feynmann said that while it is always possible that new "explanations" will be thought of, it has been proven that any such will be at least as weird as QM.

He has miss stated it. We can compute what happens all the way in to the notional singularity at the centre (which will inevitably form in a finite proper time determined by the initial conditions).

Where it gets hairy is when the singularity becomes comparable with the Planck length or thereabouts and at that point the laws of physics as we know them are shot to pieces and the new string M theories make no useful predictions as yet. This may change but don't hold your breath.

Moving inside a black hole event horizon you don't actually notice anything special until you try to leave provided that the mass of the black hole is sufficiently large that you are not spagettified first.

Light still enters the BH from the surroundings but like you it can never leave and will spiral in to the centre in a finite proper time.

Why? The theory now might be imperfect and will always be an engineering approximation to reality constrained by the experiments.

Our common sense is the first thing you have to learn to let go of and trust the mathematics if you want to truly understand relativity. We live in a slow macroscopic world where quantum effects and relativistic corrections are absolutely negligible in all of our common experience.

Your proton accelerators would not work at all if relativity were wrong and the C60 bucky balls wouldn't diffract if quantum mechanics was wrong. However, they do and we have to live with those facts.

Any new theory that supplants both will look extremely weird to our present world view and be very controversial at first. In a couple of centuries it will probably be taught at undergraduate level.

It must necessarily contain both relativity and quantum mechanics as weak field limiting cases as well as working when both are dominant.

We are just about due a paradigm shift but I am not that optimistic about string or M theory. Clifford algebras have their fans too.

Some of this weirdness appears contrived. There is no need at all to introduce objects that travel many paths simultaneously, no need to pretend that unobserved objects have multiple states simultaneously, no need to be mystical about entanglement, no need to postulate instantaneous action at arbitrary distances. All these things have simpler, more intuitive explanations and macroscopic analogs with the same physical laws.

Some of these weird ideas come about because we insist on attributing particle-like properties to waves. Others because we project the statistical results of experiments onto single events. And so on.

Add to that an army of popularizers who have no idea what they are talking about, but who love to awe and mystify their audience and the professional physicists who are unable to talk about anything 'quantum' without throwing bras and kets about like so much confetti, without regard for the poor ignorant layman.

Ah well, enough ranting.

Jeroen Belleman

Hmm so are electrons and neutrons waves? And if not, how do you explain two slit diffraction with electrons or neutrons... or C60?

George H.

Why do you have to be so confrontational? I have provided a reference.

In my first edition of AC it is: p473 10.14 Do the constants of nature change with time?

The actual paper is P.A.M Dirac, 1938 "A New Basis for Cosmology", Proc. Roy. Soc, A 165,199 (1938)

That paper isn't showing up at all for me on ADS but an earlier one in Nature (behind a paywall) a much later free one which discusses the ~10^39 coincidences of various dimensionless ratios does.

I don't believe it is anything more than a coincidence but it was proposed by someone with enormous street credibility and taken seriously for a while (and still included in some teaching texts).

Sorry but you really don't know what you are talking about.

It takes time for gravity to act and provided that the universe is expanding there is no problem at all until the expansion stops and is then followed by a compression phase back to the big crunch.

The system isn't stable it has to either expand forever or expand and then contract - there is no nice steady state equilibrium available.

That was the problem when the Einstein-Lemaitre equation was formulated and solved. It didn't agree with Steady State cosmology and Fred Hoyle coined the derisory phrase "Big Bang" for the new unwelcome contender.

It looks like we are destined to expand forever and accelerating too based on the latest supernova results.

wow, my google-fu is working.

Dirac is under-appreciated outside the physics community. George H.