Ask Ethan #18: Why aren't we a black hole?

Thanks, Ethan, your answer to my question made my day :) (also in the sense that we do have all the right being here, in this almost perfectly balanced Universe.) Now all we need is to figure out the Why :)

I can't help being skeptical when I see such tiny changes in a constant making huge differences to future outcomes. Analogy: the vector sum of my thus far travels around the globe currently places me at my keyboard. Had I made a directional bias error of only 1 part in a billion I would now be in my garden and unable to reach my keyboard. This is mathematically correct, however, the absurdity of my extreme navigational accuracy is caused by oversimplification of the analysis of reality. I refer to such absurdities as: analysis using inappropriate domains.

Calculus is such a powerful and commonly used tool it's so easy to forget that using it for things that are not yet fully understood often leads to bizarre results, such as universal constants requiring a precision of 1 part in 10^24, which is far more absurd than my extreme navigational accuracy :-)

Ethan, how does dark energy fit into this? You said that the expansion rate of the universe is slowing, but I thought dark energy is actually causing it to increase.

But in case if Higgs boson and all those crazy particle theories develope and maybe string theories get more developed then many these current universe theories likely get canceled within next 100 years just like pre Hubble period our Galaxy was only known universe then Mr.Hubble saw some strange second galaxy out there.

Alex,

The rate of expansion slows down and asymptotes to a particular value with dark energy, but the apparent recession speed of any distant galaxy relative to our own will speed up.

There is a fuller explanation in an older post of mine here: http://scienceblogs.com/startswithabang/2011/12/15/goodbye-galaxies/. Hope this helps!

Aside from "God did it" and "emergence" and similar black-boxes, how'bout this (y'all feel free to tear this to shreds if it's crap):

Preceding our Big Bang was a series of other "attempted Big Bangs" that started with higher densities and quickly re-collapsed and then "bounced" again. Each "bounce" exhibited slightly lower density, and slightly longer lifespan before it collapsed. (I'll risk a foot-in-mouth maneuver by wondering if this could have been the result of some additional quantity of mass converting to energy in each "bounce".)

At some point the universe starts doing "bounces" that lead to long-term progressions of events that produce stars and suchlike, but these are also within the range of values that lead to a re-collapses after increasingly long periods of time.

Finally we end up with a "bounce" that does not collapse, and just happens to produce an expanding universe. And that happens to be the universe in which we find ourselves, making observations and testing hypotheses. It's fine-tuned for our existence by way of successive iterations up to the present one in which we exist.

What I may have understood, there are also other parameters that are essential for our existence so why the first eternally expanding universe should have all those fixed, too? In this bounce scenario, there could have been a dark and lonely eternally expanding Universe which would have stopped the bouncing but nobody able to notice that (and no more iterations).

I like the idea of infinite multiverse, with parallel stuff which we are part of in our just-perfect Universe. It would just be nice if we found out the mechanism (or an good enough approximate theory) how after the initial moment all parameters and laws got fixed.

then something like this might be interesting for you

http://arxiv.org/abs/1206.2382

of course, it still doesn't answer the question where did the first scalar field come from

I was introduced to an interesting idea recently, the selective evolution of universes. This theory (conjecture might be a better term), assumes that black holes spawn new universes with parameters similar to, but not exactly the same as the parent universel. There is strong selection pressure towards universe parameters which maximize the number of block holes each universe creates.....

If the space contaning the matter of the big bang had a very strong expansion force to override the force of gravity from a black hole from forming, how did the matter get condensed so much in the first place?

It seems that the metric expansion of space force was present during and probably before the big bang, so how did matter pool up so closely?

@Omega

Yes, that's one of Smolin's arguments as a possible evolution of parameters. As opposed to Anthropic principle.

But even Lee Smolin doesn't say that his model is correct, more just to show that it's better to look at it and try to figure it out instead of silly antropic argument

Best I know there are no data points, zero, nada for anything before the quark-gluon soup. The big bang monobloc is just math fun and sometimes we get amazed when it gets verified and sometimes, well, puzzled. I think it is going to be a bit tricky for any data to come through the soup. And my error here is?

I am a little interested because we think we might have made some soup. If so, we might eventually get some sort of experimental evidence about that missing 100k years.

I think G's explanation is a good one. Plausible anyway.

Pete @2: There are, indeed, cosmologists who worry about the fine tuning problem (as it's called in the business). As I understand it, one of the predictions of inflationary cosmologies is that the density parameter Ω is driven toward the critical value of 1, whereas just about any other scenario allows any Ω differing from 1 to drift ever farther from 1. But as this is not my field, I don't pretend to understand just how that works.

"of course, it still doesn’t answer the question where did the first scalar field come from"

Well, a virtual particle will create a scalar field around it. It will create time around it. It will create space around it.

It won't last long.

What if another virtual pair turned up in that small space before the first pair stopped? Would that experience the net-zero of mass-energy and gravitational potential and therefore "bud" a universe, by allowing the system to become real, creating a permanent space/time?

This is just a "Lets think how it could have happened", rather than any treatise of the maths as to whether this works on the science known. It ONLY serves a purpose of saying "This is not *impossible*, by default". It's no less unlikely, and at least has the possibility of no infinite regression, as "God Did It".

"What if another virtual pair turned up in that small space before the first pair stopped?"

this is an interesting scenario... will have to ponder this a bit. The only thing that might be on the "no" side which I can think off at this instant is: something like that ought to happen in our own universe. If you can have 2 virtual pairs a the same place and time, and they bud a universe, how come it didn't already happen in our own?

Back when the Universe was about a picosecond old, that rate was closer to 10^46 km/s/Mpc! To put that in perspective, an expansion rate that large, today, would cause every atom on Earth to expand away from every other atom on Earth so quickly that they’d be more than a light-year distant from the next-nearest atom after just a single second!

Oh, there is a much more interesting perspective than that. If I've converted correctly, that early expansion rate means that any two particles were expanding away from each other faster than the speed of light when they were 9.2E-20 meters apart (I think that's 0.09 attometers; smaller than a single width of a subatomic particle).
Since we think interactions travel at the speed of light, what this means is that there was no possible interaction between any two particles - gravitational, electromagnetic, weak or strong. Which means no black holes, because there was simply no way one particle could gravitationally pull on any other.
It also means no entropy increase; during such an expansion, the universe's deltaS reaches the eyebrow-raising value of 0. Take that, second law of thermodynamics!! Though you can describe this early expanding universe in a way that doesn't seem to break the LOTs by saying that, during the expansion, every single particle in the universe was essentially it's own closed system (each of which was obeying the LOTs).

"If you can have 2 virtual pairs a the same place and time, and they bud a universe, how come it didn’t already happen in our own?"

The probability of it happening in any one planck volume is so monumentally tiny that a google years may have to pass even with the massive number of planck volumes in a sphere 30 billion light years across for it to happen.

But it doesn't matter to creation of the universe, as soon as it did happen, no matter how many times it tried (remember: no time passes because the time only exists whilst there is a virtual pair, and that doesn't exist long enough for "time" to be noticed), it started from then.

With strange aeons may universes arise!

But this is still entirely just a "Well, this shows that it isn't a priori impossible, so to claim it is impossible, you'd have to check that this scenario IS impossible".

Even more than abiogenesis, which had to have happened only the once to start evolution, therefore any rare event could answer it, this "unigenesis" has technically infinite opportunity to occur, since there's nothing that says that the number of attempts has any meaning in a timeless nothing.

Ethan: this is pretty much the standard explanation, but IMHO it doesn't satisfy. The thing is this: gravity alters the motion of light through space, and the motion of matter too. But it doesn't make space contract. Space doesn't fall inwards in a gravitational field. The waterfall analogy is not correct, the sky isn't falling in. So the universe was never ever going to contract, and never ever will. On top of that, if you read Einstein's 1920 Leyden Address you can see him referring to a gravitational field as inhomogeneous space. In inhomogeneous space, the energy density is not uniform. But in the early universe where the energy density was very high, it was very uniform. So there was no gravitational field. That IMHO is why the early universe did not collapse. And here we are.

John,

The Friedmann-Lemaitre-Robertson-Walker solution to GR had not been discovered in 1920; it was worked out by the four names above independently in the 1920s and 1930s, and as you can see from the Friedmann equations, they do make space expand and/or contract.

But there certainly was a gravitational field; your understanding is missing a number of important points. If you want to bone up on those issues, there are a number of excellent introductory cosmology books I can recommend at the graduate level, including Cosmological Physics by John Peacock, Principles of Physical Cosmology by Jim Peebles as well as Dodelson's (relatively) new book, Modern Cosmology.

"Space doesn’t fall inwards in a gravitational field."

If this method of thinking about it is giving you problems, consider this way instead:

Light travels on a path that reduces the time spent taken to get to the destination.

And from that, all curvature of space can be defined not as space bending but the slowing of time by the presence of matter.

Space is still flat near a mass, but if a path is moved to pass nearer the mass, then it discovers that the time taken is reduced even though the integrated path distance has increased slightly.

"In inhomogeneous space, the energy density is not uniform."

Which since mass equals energy includes the masses. Which then means that gravitational fields are not flat and "space falls in" to stretch near the concentrations of matter.

"But in the early universe where the energy density was very high, it was very uniform."

It was still not perfectly uniform, therefore it was inhomogeneous.

@ Wow

if I did my research correctly, only bosons don't obey Pauli exclusion. So in principle you could i.e. collide 2 laser beams and wait to see what happens when 2 photons share the same space.

But then later on, I found this: "particles are described by a wavefunction that may be localised in space to some extent but never localised down to a single point. Heisenberg Uncertainty Principle prevents a particle from being localised down to a point, unless that is you're prepared to allow the momentum to become infinitely uncertain in which case the whole thing turns into a black hole!"

I don't know if the above quoted is correct, but maybe plank size somehow prevents even bosons to occupy "exactly" the same space (if space is quantized like cells i.e. maybe one cell can only accommodate one particle).

I admit that particle physics with it's blurred lines between real and virtual and all the things between is beyond my understanding, but it's an interesting idea.

@Wow #22/23: curved space isn’t gravitational time dilation, the time taken is increased when light passes near the sun, space is not falling into the sun, and the early universe was very homogeneous.

@Ethan #21: thanks for getting back to me. But I must insist that there are issues with the standard explanation. For example the shape of the universe article on wiki is fair. But see this: "One aspect of local geometry to emerge from General Relativity and the FLRW model is that the density parameter, Omega (Ω), is related to the curvature of space". Rewind the universe a billion years and send up a WMAP, and you would find that space is flat. Rewind the universe another billion years and send up another WMAP, and you would again find that space is flat. You could repeat that all the way back. Textbooks naturally avoid such issues, they have to teach current consensus. But this isn't always right. If it was, science wouldn't advance. That said, I respect the fact that you have to try to do that too. I'll maybe start my own blog to explore issues in more detail.

The concensus is that what we thought as "gravity" is actually a bending of space. And that does come from relativity. Gravity doesn't make light bend. Energy/matter bends spacetime thus affecting the motion of everything, including light. It's not the bending that's an illusion, it's gravity (attraction) that is an illusion.

the flatness does deal with matter/energy, but now or back 10 billion years, the matter/energy content was exactly the same as now. and there would a global history sphere around our universe exactly as now. So the topology of our bubble would be the same.

Would it be curved or not was decided much earlier in Universe's hystory than when gravity took over

Disclaimers apply:
- no theory of quantum gravity
- identity of dark matter & dark energy particles or mechanism (i.e. hypothetically 96% of universe) not determined
- Baryon asymmetry unexplained
- supersymmetry, extra dimensions, or multiverse may apply

Diverse professional theories abound e.g. recent arXiv titles:
- Quantum Fluctuations in Cosmology and How They Lead to a Multiverse
-Multiversality
-An Emergent Universe with Dark Sector Fields in a Chiral Cosmological Model
-From Black Holes to Cosmology : The Universe in the Computer
-Towards String Theory models of DeSitter Space and early Universe Cosmology
-Creating the Universe Without a Singularity and the Cosmological Constant Problem
-Conspiratorial cosmology - the case against the Universe
-Quantum gravity, space-time structure, and cosmology
-On a principle of cosmological uncertainty

Our scientific understanding of cosmology (while quite mathematically precise) has major gaps(e.g. 96% of universe missing/unexplained). In this sense, cosmology is much like the sciences of consciousness and abiogenesis. i.e. in their scientific infancy.

While I secretly agree with Smolin's evolutionary approach let me also say that his (and also all the rest) of cosmological hypothses are all just that... hypotheses. Many have already reached the level of religion, like the dark matter one - and this is dangerous. Everybody should think somehow out of the box. Who can say for sure that space-time is uniform? I am much more inclined to MOND, but well, it's just me.
BTW, Ethan, I miss your blogs...

@OKThen #28: I think it's unfair to liken cosmology to consciousness or abiogenesis. Yes there are issues in the standard model of cosmology, but cosmology is an evidential and scientific field. Re your list, sure there's no theory of quantum gravity, but there is general relativity. Dark energy might not exist as particles, just as gravitational field energy doesn't exist as particles, and energy has a mass equivalence so dark matter might not exist as particles. Baryon asymmetry is matched by lepton asymmetry and we don't puzzle about l-glucose. Supersymmetry isn't cosmology, we don't really need it, and there's no evidence for it just as there's no evidence of extra dimensions or a multiverse. But there will always be wild unsupported hypotheses from people clamouring for attention. All these things don't mean we throw away the evidence for an expanding universe or turn away from winding it back to a big bang. We just seek better understanding, and remain alert for any gaps in our understanding.

"Many have already reached the level of religion"

Please explain how they have done so.

Is there prayer meeting?

Are there priesthoods?

Funny hats?

Or was that just bullshit hyperbole?

"@Wow #22/23: curved space isn’t gravitational time dilation"

Indeed not, John.

You can tell this is so BECAUSE THEY USE DIFFERENT WORDS.

Have you ever considered that light waves are not light particles? Because BOTH ARE ACCURATE MODELS OF LIGHT. Yet you, apparently, would prefer to ignore that just so you can make a frigging argument, you ignorant troll.

So, yes, curved space is not gravitational time dilation.

HAVE A FUCKING BIKKIT.

So lets get to the rest of your asinine post.

"the time taken is increased when light passes near the sun"

Wrong.

From OUR point of view, it takes longer because we're not moving with it.

From light's point of view, it takes less time.

Do the bloody maths you moron and from this date on DO NOT ***EVER*** pretend to know how the hell to think accurately.

YOU DO NOT.

"and the early universe was very homogeneous."

NO IT WAS NOT.

WRONG AGAIN.

"Our scientific understanding of cosmology (while quite mathematically precise) has major gaps(e.g. 96% of universe missing/unexplained)"

That's no more a gap in knowledge than 93% of the earth's inhabitable volume being unexplored is a gap in our knowledge of geography, OKThen.

"The concensus is that what we thought as “gravity” is actually a bending of space."

It's a model, SL.

Like the model of a photon being a discrete particle.

And there are other models that explain it just as well from a different frame of reference: photons being waves.

And there are alternative versions of explaining spacetime metric geometry, other than "bent space".

They're equivalent explanations from a different frame of reference.

@ Wow

"It’s a model, SL."

Of course. I was commenting on John's post where he said that space doesn't really contract. I said that, in relativity, yes it does contract and bend and do all kinds of things. Attraction is an illusion while bending isn't... in relativity. We see lensing and other things.. thus light behaves as if it were traveling through curved space. What spacetime "really" does out there.. I don't know. Every theory is different.

"Of course. I was commenting on John’s post where he said that space doesn’t really contract."

OK.

I believe John's "problem" is he doesn't want to like any model of reality held by science.

He doesn't like space contracting, he doesn't like time dilating, he doesn't like any idea except his own.

@wow:
Is there prayer meeting? Sure, only nowadays they are called conferences.

Are there priesthoods? Of course, and could it be that you are one of them..?

Funny hats? How about funny minds?

I must say that I haven't seen the BS word on this site for months, and then probably used by you.

BTW, your discussion style reminds me of an old acquaintence of mine... Lubos?
:)

@Wow

"He doesn’t like space contracting, he doesn’t like time dilating, he doesn’t like any idea except his own."

I think he views gravity as a regular force (i.e. EM). His sentence: "gravity alters the motion of light through space, and the motion of matter too. But it doesn’t make space contract. " He acknowledges the math of GR, but I don't think his comfortable with interpretation of it.

To me, gravity doesn't exist. IMO, energy bends space, and in turn that bended spaces "tells" energy/matter how to move. They are interlinked. In John's view... space is always perfectly flat, and in turn there is this "gravity 2.0" which attracts (like newton's force) but also somehow exibits other propetries to light and matter, without it affecting space.

To me this contradicts a bit all the tensor terms, but am no expert.

"He acknowledges the math of GR, but I don’t think his comfortable with interpretation of it. "

I think he wishes to be uncomfortable with it, hence will be uncomfortable with ANY interpretation of it.

re Wow #33
"That’s no more a gap in knowledge than 93% of the earth’s inhabitable volume being unexplored is a gap in our knowledge of geography, OKThen."

Well it's a bit different. It is more like, we have a system for measuring the mass of bowling balls and people (I for example have a mass of 78 kg) and application Newton's law of gravity determines (via observations and experiment) the mass of the Earth as 5.972E24 kg. But when we go around and add up all of the chemical elements that make up planet Earth we find that 96% of the mass of the Earth is missing.

This is not a issue of missing geography. It is an issue of missing matter/energy or missing forces, or laws of nature, or extra dimensions or... something else that we do not understand or anticipate.

I remain unconvinced of the truth value of Ethan's excellent narrative of our visible universe (which I acknowledge as the current best narrative of our visible universe). Too many pieces of understanding are missing. Our current best theories and understanding are not the only guide to understanding our visible universe; speculative hypotheses abound (and I mean professional speculative hypotheses discussed in arXiv papers) that suggest clues that can be tested.

The overpowering mantra that we got a spot-on understanding of the visible universe with 20th century astronomy needs to be challenged; and as my list of arXiv papers (there are many more) suggests; that that mantra is being challenged by the best minds in physics.

As Frank Wilczek asks in his Jul 2013 paper Multiversality, "Are we human scientists comparably blinkered?"

As Alan H. Guth says in his Dec 2013 paper QUANTUM FLUCTUATIONS IN COSMOLOGY AND HOW THEY LEAD TO A MULTIVERSE, " I think it is time to take the multiverse idea seriously, as a real possibility."

Or as Antonio Enea Romano and Pisin chen say in their Jul 2012 paper Apparent versus true value of the cosmological constant, "Even in the presence of a cosmological constant we cannot exclude nevertheless the presence of a small local inhomogeneity which could affect the apparent value of the cosmological constant. Neglecting the presence of the inhomogeneity can in fact introduce a systematic misinterpretation of cosmological data, leading to the distinction between an apparent and the true value of the cosmological constant."

The point is that physicists and astrophysicists remain professionally unconvinced by the standard cosmological model narrative. Thus my disclaimer so as not to blinker laymen.

@Sinisa #38: my view on gravity comes from original Einstein material. See for example Einstein talking about field theory in 1929. Note the bit in Expanding the theory where he's talking about electromagnetic and gravitational fields, and says this:

"It can, however, scarcely be imagined that empty space has conditions or states of two essentially different kinds, and it is natural to suspect that this only appears to be so because the structure of the physical continuum is not completely described by the Riemannian metric".

A gravitational field is a "state of space". You will be more familiar with it being described as curved spacetime, but note that Einstein used the word space. Also note that a gravitational field isn't a place where space is falling inwards. Einstein never ever said that. Instead he said it's a place where space is inhomogeneous. Not curved. Inhomogeneous. Have a read of Einstein's 1920 Leyden Address for that. When you plot this inhomogeneity you see a curvature in your "Riemannian metric", but it isn't actually space that's curved. See this Baez article where Baez says this: "Note: not the curvature of space, but of spacetime. The distinction is crucial".

"Well it’s a bit different. It is more like..."

Well, I say it's not more like that and more like we haven't surveyed more than a few percent of the earth's habitable locations.

So now where does that get us?

"But when we go around and add up all of the chemical elements that make up planet Earth we find that 96% of the mass of the Earth is missing. "

No, we don't.

We have the mass of the earth and no way of weighing the elements independently of the earth to then tot up.

We may be missing a class of matter. Dark Matter.

This "missing" (20% mass) is no different than never having spotted Helium that makes up several percent of the mass of the universe (because you don't find it on earth, only in the sun and we couldn't detect it for most of human history) means that having all the other 108 elements means we have no chemistry.

And if, for example, MOND could be found to solve the dark energy, then it would be explaining that missing 70%-ish stuff you're talking of with an amendment to the newtonian equation for gravitational force with a factor somewhere around the one-in-a-quadrillion change.

So the vast majority of your "missing 93%" is (if MOND were an answer) a rounding error in on one equation with a change in the 18th decimal place of a constant term.

” I think it is time to take the multiverse idea seriously, as a real possibility.”

Already being done.

However, it's as well noted as room-temperature superconductor research is in mainstream perception: not at all, despite being done.

Wow #43
Clearly you misunderstand my fable (paragraph 2 & 3 in comment #40).

Very well, carry on.

And in #28, I simply tried to explicitly add a few disclaimers which you and others sometimes point out are implicit.

Oh look at this, here is another possible description of our universe by JiJi Fan, Andrey Katz, Lisa Randall, Matthew Reece, Mar 2013, A Dark-Disk Universe, "We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally-supported disk, much as baryons do. We call this proposed new dark matter component Double-Disk Dark Matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas." Very nice research, understandable and testable.

"So now where does that get us?"
In my opinion, disclaimers, margins or errors, levels of confidence, range of professional opinions are best made explicit especially when discussing the Universe with laymen.

Opinions about "the Universe" may vary; please consult with several professional physicists.

@ John
"Note the bit in Expanding the theory where he’s talking about electromagnetic and gravitational fields"
-yes but he says this concerning the Unified Field Theory which he hadn't be able to do. Nor anyone after him. So the part "It can, however, scarcely be imagined..." can in fact be true, however difficult to imagine.

But disregarding that part... in the previous section (same Einstein document you linked - just this time he talks only of relativity and NOT about Unified Theory).. he clearly states:

" In the general theory of relativity, this hypothesis regarding the Euclidean character of our space-time continuum had to be abandoned and the latter given the structure of a so-called Riemannian space."

and further

" If one had used, instead of ruled millimeter paper, a piece which had been stretched or deformed the same determination could still be carried out: but in this case the lines passed would no longer be horizontals or verticals or even straight lines. "

So those are his words.

From the second document you linked:

" When spacetime is curved, the result of parallel transport from one point to another depends on the path taken! In fact, this is the very definition of what it means for spacetime to be curved. Thus it is ambiguous to ask whether two particles have the same velocity vector unless they are at the same point of spacetime.

It is hard to imagine the curvature of 4-dimensional spacetime, but it is easy to see it in a 2-dimensional surface, like a sphere."

and further

"Similarly, in general relativity gravity is not really a `force', but just a manifestation of the curvature of spacetime. Note: not the curvature of space, but of spacetime."

This sounds almost EXACTLY the same as what I have written before. You seem to have quoted the wrong passage as it gives no more weight to your argument, in fact it proves it wrong. But I do agree that there is a big difference between space and spacetime.. yes.. both are affected.. space and time. Just not how you would want it.

And no.. space isn't falling anywhere... do not understand why are you so obsessed with that. Nor is contraction equal to falling. We live in 3+1d space. And everything that happens to spacetime happens there.

"And no.. space isn’t falling anywhere… do not understand why are you so obsessed with that"

The standard lies-to-adults explanation is weighted balls on a rubber sheet. Anyone who takes an interest in science and reads up (or does higher education in science) knows how this doesn't mean it is LITERALLY dropping through an "extra dimension". However, John doesn't know much science other than what appears on "Tomorrows World" et al, despite his professions of competency.

Also, for S&G's, the rubber sheet would apparently give different trajectories to objects than spacetime curvature:

https://medium.com/the-physics-arxiv-blog/b8566ba5a110

"Clearly you misunderstand my fable (paragraph 2 & 3 in comment #40). "

Clearly you didn't understand it any where near as well as I did, OKThen.

The oceans are one single item. Not having explored it, though, means we are "missing" 90+% of the inhabitable places on earth.

This is EXACTLY THE SAME as your claims that "missing" DE/DM is "missing" 97% of the universe.

If Dark Matter is one extra fundamental particle, then we're missing 1 out of the (12?) fundamental particles. If MOND can explain Dark Energy, then that is a modification of one part in 10^18, possibly.

So, missing ONE term of negligible effect on galactic scales in an equation that gets us probes hitting targets 100m across a million miles away and ONE fundamental particle out of a dozen being "missing 97%" is EXACTLY like missing the ocean deeps is "missing 93%".

This is not to say that they are not important bits missing, but calling it 93% missing is entirely unwarranted.

“So now where does that get us?”
In my opinion, disclaimers, margins or errors, levels of confidence, range of professional opinions are best made explicit especially when discussing the Universe with laymen.

And none of that is evident in your claims about "what is the missing matter of the universe more like".

@Wow

" the rubber sheet would apparently give different trajectories to objects than spacetime curvature"

I would be surprised if it did give the same results. It's great for a VISUAL tool, and that's all. I am even more surprised by the arxiv guys, in that they were amazed that it didn't give the same behaviour as actual spacetime.

Orbits aside, for VISUAL tool about bending of light etc.. I find being underwater a much better analogy then 2d visuals. Observing what happens when water of different properties (cold/hot, fresh/salt..) behaves underwater (in terms of optics) to me is much better when thinking how spacetime bends and curves. Sadly, you have to be a diver to see it :)

"Sadly, you have to be a diver to see it "

Well, you can watch an Attenborough series too!

sorry typo..

" Observing what happens when water of different properties (cold/hot, fresh/salt..) behaves underwater"

should be: Observing what happens TO LIGHT when water of different properties ... meet underwater

Sinisa: this space isn't falling is important. The matter in a dense early universe might be "falling" into some central black hole or something, but the space isn't.

I know what you mean about the water. If you were dive-scooting through water that was saltier on the left than on the right, your path would curve left. But the water isn't flowing left. See this abstract for the space equivalent. Space isn't curved where a gravitational field is. Instead it's inhomogeneous. When you plot this inhomogeneity using say light-clock rates in an equatorial slice through & around the Earth, what you then "see" is Riemann curvature like the depiction on wiki. That's your curved spacetime. There's nothing wrong with it provided one avoids confusion between curved spacetime and curved space.

Wow #47
Thank you so much for that clarification and excellent link.
Yes, I recommend that all the readers out here go to that very readable link.

The metaphors help us understand general relativity; because few of us can understand the mathematics. Thus it is especially important for us laymen to understand the limits of the metaphors.

Thanks again Wow!!

No worries, OKThen.

As SL says, the rubber sheet was always a more visual metaphor, rather than a physical representation model (such as light-as-waves model).

"Cosmological observations tell us the standard model explains about 4% of the energy present in the universe. Of the missing 96%.. ", wikipedia

"Telescope to Hunt for Missing 96% of the Universe", Time magazine 2013

"In short: 96% of the universe is missing, 74% being dark energy with dark matter comprising the remaining 22%." Frank Close

"Besides the two well-known inconsistencies of modern cosmological models with the observational data: the problem of missing satellites of normal galaxies and the problem of missing baryons, there arises another one—the issue of missing dark matter." 2012, arXiv:1204.3377

And look at this!
"One of the most outstanding problems of the standard model of cosmology today is the problem of cosmological constant/dark energy. It corresponds to about 73 per cent of the energy content of the universe gone missing. I hereby postulate a modified FRW metric for our universe, which animates a universe spinning rigidly but very slowly with an angular frequency that is equal to the Hubble constant. It is shown by a simple argument that in such a universe there will be an overlooked rotational energy whose average value is identically equal to the matter-energy content of this universe as observed by a coordinate observer... I proposed a spinning universe model, which naturally explains many seemingly mysterious and difficult cosmological issues such as the origin and extreme small value of the cosmological constant/dark energy, its gravitational repulsive force, Hubble’s law, and the so-called cosmic “axis of evil.” " 2012, arXiv:1210.0892
Very nice research. Well done; a good attempt.
Not necessarily correct; but perhaps a grain of truth; the experts (not us laymen) must evaluate. As the village idiot it is easy to fool me.

And how much of the universe is Hydrogen?

So if we had been missing one element of the nearly100 naturally occurring elements, we'd be

a) missing 90% of the mass of the visible universe

b) missing 1% of the elements in chemistry

c) both missing 90% and missing 1%

Answer?

Without hydrogen, we wouldn't be here to miss anything.

@ John

I suggest you re-read once again all the paper and links you posted

@John
No one is saying spacetime moves. As in from point A to point B. It can't, think about it.. if it could, it wouldn't be spacetime, because it would be moving in reference to some other underlying spacetime. You are arguing that spacetime doesn't flow, fall, go to somewhere. But who is arguing that it does???

What it does do, is have different properties at every single point. That's the important thing. It's not static, flat and absolute. And it's not the clocks only.. you "accuse" all here of thinking only of space, yet you commit the same fallacy and focus only on time. It's as real for space deformation (notice the word... deformation... not moving but changing shape) as it is for time dilation. Think on that, because this seems to be the issue for you. Just as time (clocks) are affected, so is space (paths). It's not a mathematical abstract. It's real. We do move differently in presence of energy/matter. And that movement is not caused by attraction as opposite charges attract, and it's not caused by plotting clocks. It's caused because that same energy is bending spacetime and causing path or geodesics or however you want to call them to follow that bend.
Whatever you take as effects for time, same happens for space. Accept it.

On the other hand, I notice you have issues with curved geometry. Why? What, in your opinion, makes Euclidian geometry any more real or fake then Riemman? You think curved differential geometry is some sort of mathematical abstraction to calculate things that really are in Euclidian geometry all along? This is an extreme error. This is a huge bias, and a wrong one, on your part. Sure, you can believe anything you want, but then acknowledge it for personal theory or bias, not as some "conspiracy" or groupthink that somehow distorts what Einstain was really saying.

In most cases I would say that whatever you call something, is of little importance if agree on properties or behavior. But insisting on inhomogeneity leads to misunderstanding, as is in your case of viewing early universe. Strictly speaking, spacetime is always inhomogeneous. Every point has different properties. If you want to get technical, field equations describing my room will be different from your room. Because energy/matter content will never be the same. Even further, my world history is different from yours.

But just sticking to inhomogeneity doesn't give you anything. See your sentence: "Space isn’t curved where a gravitational field is. Instead it’s inhomogeneous." Back up.. what is a gravitational field? You say inhomogeneity.. ok.. So your sentence is: "Space is inhomogeneous where inhomogeneity is". Wow!! There's a revelation!

Instead... Spacetime is curved (space bends, time slows/speeds) where there is a large presence of energy in small space. Input energy, output curvature.

In your scenario is input inhomogeneity, output inhomogenity...??? Gravity isn't a force. Gravity doesn't exists so you can concentrate it somewhere and get inhomogeneity as a side effect on spacetime.

"Without hydrogen, we wouldn’t be here to miss anything."

OK, if that's your definition of "Missing", then we're not missing any dark matter or dark energy, as if it were missing, then we'd have 100% of the constituents of the universe.

p.p.s.
@ John

what you can say is that: In the presence of energy/matter, spacetime becomes "more" inhomogeneous than it's average in a larger region. And that increased inhomogeneity causes trajectories to curve and time to pass differently than in other inhomogeneous regions.

This would be a valid statement. But it's much easier to just say that spacetime curves

Sinisa, I'd put it a little differently. I have read all those papers and links carefully, and in brief, I must reiterate that the distinction between space and spacetime is crucial. The people who argue that “space falls” are those who advocate big-bounce cosmology or who say that one FLRW solution is a collapsing universe. As for my views, I pay close attention to Einstein. Please note this quote from his Leyden Address of 1920 where he’s talking about a gravitational field:

“...This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that ‘empty space’ in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gμν)...”

I don’t have issues with curved geometry, I take pains to read the original material. You should too, and with respect, you will not find Einstein saying “energy is bending spacetime”. Also note this in the wiki FLRW article:

“The FLRW metric starts with the assumption of homogeneity and isotropy of space.

Now look at the Einstein quote above. Einstein said a gravitational field is a place where space is neither homogeneous nor isotropic. So the FLRW metric starts with an assumption that there is no gravitational field.

I didn't define "missing" nor did you in your question.

Thus my answer was only one possible answer (among many) to you ambiguous questions.

So now where does that get us?
In my opinion, disclaimers, margins or errors, levels of confidence, range of professional opinions are best made explicit especially when discussing the Universe with laymen.

Opinions about “the Universe” may vary; please consult with several professional physicists.

"I didn’t define “missing” nor did you in your question."

So if you don't know what missing means, then how can you make the claim:

“Without hydrogen, we wouldn’t be here to miss anything.”

?

National Lampoon said it well:
"You are a fluke of the universe,
you have no right to be here,
and whether you can hear it or not,
the universe is laughing behind you back."
http://www.youtube.com/watch?v=xCGRDnTySCI

The "crucial distinction" between space and space-time is that the latter is a unified view that contains the former. In a curved space-time, it could be that it is the 3 spatial dimensions that are curved while time is flat, the time dimension that is curved while the 3 spatial dimensions that are flat, or any degree of both. And where along that continuum any particular situation falls will vary depending on the observer!

So when John claims that it is space-time that curves, and *not* space, it is contradictory, and he is (once again) displaying a fundamental misunderstanding of basic principles that is masquerading as a deep insight.

"You should too, and with respect, you will not find Einstein saying “energy is bending spacetime”"

Ugh. With all the disrespect I afford anyone who thinks not-knowing and not-understanding is a foundation for profound thought and sufficient to correct those who do know and understand, Einstein doesn't say that because he instead says that the metric of space-time is defined by a function of energy and momentum. Which *is* saying that energy bends space-time, if you actually understand what it means.

Consider for example the paper, Dark matter and alternative recipes for the missing mass, by Crescenzo Tortora, Philippe Jetzer and Nicola R. Napolitano, Feb, 2012, arXiv:1201.6587.

In this paper the phrase "missing mass" applies in a broad sense that covers theoretical alternatives from Λ cold dark matter to MOND to extensions of General Relativity.

But you already know this.
So stop the pedantic semantics.
So stop "missing" the scientific point.

yawn.

CB: see my comment #41 where I referred to a Baez article. The space in the room you're in is not curved. Also see my comment #64 where I gave an Einstein quote. He said space, not spacetime, and he said inhomogeneous, not curved.

@ John

ok.. and how does that inhomogeneity affect the motion and geometry of objects? what happens to meter sticks when they accelerate?

John, an isolated quote where Einstein *doesn't* say something is meaningless, especially when you don't understand what's being talked about.

If you think General Relativity doesn't say that the metric of space-time varies with energy and momentum, then you don't know what GR says. If you think that doesn't mean space-time is curved, which can mean curvature in either space, or time, or both, you don't know what the metric is. If you don't think a metric that varies in 4d position isn't equivalent to saying inhomogeneous, then you don't understand what any of this is about.

But we already knew that. It's just nice to get independent confirmation.

CB #69, #73
Well said.

Sinisa Lazarek
Pseudodiscussion (i.e. with psuedoscientific dogmatist John Duffield) is a waste of time; because like all dogmatists, John Duffield pretends openness; but he is the only one who knows the "Einstein truth".

"I think Einstein worked it out.. He was onto the truth, but people couldn't handle the truth.. If only Einstein has passed on what he knew to Feynman.. No wonder Einstein couldn't find a way.. You won't believe how simple it is.. It is easy when you know how. It is all to do with E = mc^2." John Duffield

BE WARNED: John Duffield can explain "the (Einstein) truth (that) people (e.g. even Feynman) could not handle."

@wow:
Is there prayer meeting? Sure, only nowadays they are called conferences.

So, no, there aren't prayer meetings.

Are there priesthoods? Of course, and could it be that you are one of them..?

No, you're wrong: there aren't.

Funny hats? How about funny minds?

How about what I actually asked for?

I propose a completely different model:

The universe consists already of a giant central black hole attracting our milky way and all other galaxies. The observed red shift can be explained by the 1/r² law of gravitation: galaxies that are nearer than our one to the central black hole have higher speeds towards it than we have. So we see them moving away from us. Galaxies that are further away from the central black hole than our one don't move so fast towards it as we do. So looking at them we see them escaping from us as well. The black hole and our distance to it are so big, that the field gradient is quite low, so we experience no tidal forces. Adjusting Newton's 1/r² law by Einstein's general relativity field equations does make a big difference to this model. The general pattern of galaxy motion relative to each other remains the same.

How can these claims be verified? Here is the principle algorithm. It can be implemented and executed even on a PC:

Take all recorded quasar spectra from the known quasar catalogs. Normalize their spectra to zero red shift. Compare each spectral signature which each other. Try reasonable compensation for differences according to dust or other noise adding effects. If you find two identical or similar ones, check the respective quasar's positions. If their angular positions differ by several degrees, you have some evidence. Because you found the same quasar twice: Once seen in direct (curved) line, and once its light wrapped around by the central black hole's gravitational field.
Twin quasars are already known but turned out to be the result of "small" (means: a massive galaxy in our line of sight to them) gravitational lens effects. In these cases their seeming positions differed by some arc seconds or minutes. A number of twin quasars with significant (several degrees) angular position differences or even at opposite sites of the universe would be a proof for the above model