I’d like to buy you a beer, or 12, sometime.
Yeah I knew that but didn’t notice until I came back to this thread. 9.8 meters per second per second (and 9.81 is getting kind of unnecessarily specific due to the fact that the acceleration due to gravity varies significantly depending on elevation / where you are on Earth).
The assumption is that gravity is caused by the movement of subatomic particles and their interaction with other subatomic particles. But this is mainly based on the fact that the other fundamental forces of nature are caused this way.
These hypothetical particles are called gravitons. But nobody has been able to observe a graviton.
The weird thing (to me anyway) is that gravity works across such long ranges. If it’s being caused by particles and these particles interact with essentially everything, you’d expect them to find something to interact with right in their immediate neighbourhood. You’d expect that gravity like the nuclear forces would operate only at distances smaller than an atom. But in reality, gravity is the longest ranged of all the forces and can effect things across huge distances. So presumably gravitons must be crossing these distances.
There are particles like neutrinos which can travel across great distances like this. But neutrinos pretty much ignore everything along the way. Neutrinos hardly interact with anything.
Here is a visualization of gravity warping space-time that I found much more satisfying than the old rubber sheet. I couldn’t tell you how space-time gets warped in the first place, though.
I don’t think this removes the “falls into a depression”-problem, but in a universe where every damn thing is moving I’m not certain. My counter example is an object moving radially and perhaps preferably starting with zero velocity relatively to the gravitational “disturbance” it’s influenced by. It will have an acceleration towards that depression that I can’t see can be explained as the shortest line between two points.
I may be wrong, but I have a vague recollection that the explanation has to do with the fact that both objects have “depressions”, even if the effect of a tennis ball one is negligible on an Earth sized object, and that the interaction between these is important.
And that video perfectly explains how I was wrong. Excellent!
Light (photons) also travels across long ranges. It is really not correct to think of gravitons as being independent particles being “thrown” by one body and “caught” by another. Gravitons are an idealization of the way gravitational energy is mediated across long distances. Because we don’t have a working quantum theory of gravity we can’t really say why it differs in strength and range of effect from the other forces but a simplified answer is that it has a very small “cross section” of interaction with matter. That is, most gravitons will pass right through a “solid” body without being intercepted.
It is unlikely anyone will ever observe an individual graviton, but there are a handful of programs like VIRGO and LIGO which are trying to detect groups of coherent photons (e.g. gravitational waves) being emitted by supernova or other large gravitationally resonating structures.
Space-time is warped by the presence of mass and energy. Why does mass and energy warp (distort) space-time? Because that’s how space-time responds to the presence. Yes, the answer is unsatisfying, which is why many physicists are trying to figure out a more fundamental mechanism underlying this whole space-time business, but that’s the state of the union with regard to gravitation.
Stranger
After Stranger On A Train’s sweeping and penetrating posts, I hesitate to attempt any miniscule contribution of mine own. Still, “faint heart ne’er won fair lady.”
I note that when I stumble, or otherwise lose my balance, I may fall. It is not a certainty, but still, the possibility is there. That is a fact. It looks as though a certain degree of disequilibrium needs be present for gravity to fully exert its powers. I fancy that this may have some bearing on the issue at hand.
It has approximately zero bearing on the issue. At the surface of the Earth your body is pulled down by the force of gravity G = mg (Force of gravity in Newtons = mass in kilograms * the local gravitational acceleration ~aprox. 9.8 m/s^2). This force doesn’t change if you stumble, only its effects do.
Yeah, I find the bent/pinched grid analogy better all round - I guess it’s harder to set up than the rubber sheet, and yes, it still doesnt explain why (but then, what ever does), but I prefer it as an analogy, because it is more abstracted from the phenomenon it’s trying to illustrate.
The universe couldn’t exist without it. It may be inexplicable how it works, but it’s not just a by-product of the universe, gravity was necessary for it to come into existence at all.
Excellent post, Stranger.
I’ve a passing familiarity with Penrose, and while a lot of his ideas do come across fantastically batshit in a fun way, is there something particular you find uncompelling with his out-on-a-limb hypotheses?
After all, in the light of the surprising weirdness that is Relativity and (especially) QM, it’s hard for a layman to know exactly what might be barking up the wrong, weird tree.
ETA: I’m not trying to single out your opinions; only curious in matters of an expert’s opinion on another work (despite its more ‘IMHO’ nature rather than ‘GQ’.)
You know what else perturbed Newton? Perturbation.
As a totally random aside: Now I think about it, “perturbation” would be a [del]great[/del] half-decent term for something an ex-girlfriend used to particularly enjoy…
A few nitpicks, Stranger on a Train:
Topology isn’t actually all that important in GR. Most GR work is done in a trivial topology, or at most a topology that’s trivial aside from point defects, and momentum and energy don’t have any direct effect on the topology at all. What’s important is the geometry, specifically as encapsulated in the metric: How far apart various points are.
We can actually do GR in the case where mass-energy is quantized: This is called “semiclassical gravity”, and is the milieu in which Hawking radiation, for instance, is studied. It’s hard, of course, but it’s doable. You’re right, though, that there is currently no real ability to deal with quantization of the spacetime itself.
Actually, black holes are the simplest things you can study in GR, so long as they’re decent-sized. With just about any other source of gravity, quantum mechanics can sneak in (for instance, in the forces preventing your object from collapsing), but since black holes don’t have any component parts, you don’t have to worry about this with them.
There is something to this observation. Although gravity maintains its hold on us with the unwavering attention of a seasoned schoolteacher (and the gravitational field is ever-present everywhere in the observable universe whether we can sense it locally or not), we generally don’t notice the effects until we have a change of state of forces and constraints. Interestingly, this also cannot be distinguished from forces which result from acceleration resulting from imposed forces, e.g. inertial forces such as thrust and rotation, except for effects that may result from a particular transformation of the observer’s coordinate frame, i.e. the Coriolis effect. Another way of looking at this is that all bodies in contact are in dynamic equilibrium (i.e. are accelerating at the same rate) until some external force or constraint arrests one of them, after which the acceleration due to gravity is present.
This concept is so blatantly obvious in everyday experience that it took one of the greatest geniuses of natural philosophy–the guy who essentially created classical physics in the form that we know it today–to recognize it, which is sort of like living your entire life in a small home and accidentally pulling on the protrusion on the funny-colored wall panel one day only to discover a whole 'mother, bizarrely different world outside.
Let’s be clear; Roger Penrose is absolutely brilliant, one of the top minds in mathematical physics in the world and likely in history, up there with Archimedes, Euclid, Ptolemy, Wenyuan, Diophantus, Newton, Leibniz, Stevin, Napier, Pascal, Euclid, Reimann, Cauchy, Poincaré, Hilbert, von Neumann, Kolmogorov, Shannon, and Turing. His ideas are ground-breaking, revolutionary, and seem to come from nowhere but almost fully formed at conception. His achievements in mathematics cross individual disciplines, and I would never, ever play against him competitively in backgammon or chess.
But he is significantly stuck on the idea that quantum mechanics and consciousness are inextricably intertwined phenomena and that cognition cannot be reduced to algorithms and basic blocks of instructions which combined to give the sophistication we see and experience in sentient beings. It may be that he has some genius insight that I am simply too dim to grasp at even superficial level, but there is absolutely no observational evidence that this is true and in fact the best work on the biophysics behind cognition that we have to date (which is still not very complete owing to the complex interactions of such systems on anything but a trivial level) is that it can be demonstrated up to our ability to measure and observe by purely electrochemical interactions. The core of his arguments (and similar arguments, including that of David Bohm) is that because both quantum mechanics and cognition are such inherently complex, highly interrelated phenomena that there must be some causal linkage between them, which is sort of like arguing that trees and river systems must have the same root cause because their appearance and method of growth–from a compact, root source, to a branching, diminishing structure–appears similar.
There may turn out to be some common link between the two, but I don’t believe that Penrose’s arguments substantiate it or offer enough information to formulate a falsifiable hypothesis. However, like Bohm (who I regard as one of the most insightful physicists to work in quantum mechanics and who is likely to be reveals as being closer that anyone else to understanding what is actually going on at the fundamental plenum of the quantum-scale world) it is impossible to ignore the genius of Penrose and the nonpareil insights he has brought to various areas of quantum mechanics and cosmology, as well as the art of Penrose tiling.
Stranger
The problem I have with the spacetime stretching analogies is they remind me too much of aether.
In the real universe, what exactly is mass traveling through that is being distorted? When you get down to the lowest levels of reality, you have a bunch of particles with lots of nothing in between them. All of reality consists of what happens when one particle collides into another and the effects of this collision.
I’ve never even begun to understand how gravitons (i.e. discrete particles) and the bending of spacetime (a continuous phenomenon) relate to each other.
Is there an answer that even an internist can understand?
I read the Emperor’s New Mind when I was about 14, so the exact details are bit hazy to me, but Penrose’s views on quantum mechanics and consciousness aren’t IMO batshit: from what I remember the offer a prima facie quite an attractive way of explaining some of the mysteries of consciousness through the lens of QM. Unfortunately the big problem is they don’t seem to stand up very well to close scrutiny: in trying to explain consciousness with QM, the very important issue of the known/knowable physics and physical chemistry of the brain weren’t properly investigated.
The point I’d make though is that Penrose’s views in this area are an interpretation of consciousness through quantum mechanics and not really an interpretation of quantum mechanics through consciousness like the views held by some important early figures like Wigner (though not David Bohm: Bohm’s interpretation of QM does is a realist hidden variables theory, which is still quite popular among experts of QM)
There is an interpretation of QM which Penrose is well known to hold to and it is often called Penrose’s interpretation. In this interpretation (arguably it’s a bit more than an interpretation as it changes the mathematical nature of the wave equation and so can make testably different predictions to standard QM), gravity is responsible for the collapse of the wavefunction.
Way to kibosh the advancement of science, dude. If Einstein had just got used to the fact that Newtonian physics did not actually explain gravity (as most physicists in the generations following Newton - though not Newton’s own generation - did) we would not even have General Relativity.
But that’s the rub. General relativity can tell you a lot about the effects around a “decent-sized” and the sort of geometric distortion in the space-time continuum that could cause them, but it says essentially nothing about what goes on inside of the singularity, or indeed, even if a singularity actually exists. It also can be made to give results that are non-sensible, i.e. that violate causality as we know it, although this may be more of a problem in the assumption of a strictly casual universe rather than with general relativity. Ultimately, I think we pretty much know that general relativity is just a better approximation to reality rather than a fundamental description of it, and there is some deeper layer where the abstraction of macroscopic observations are explicitly carried out by some more fundamental set of mechanics that can be tied into the rest of quantum mechanics. Or there is something deeper yet underlying both.
It needs to be clearly understood that the “particles” are not actually little bits of stuff, and in fact they are probably nothing more than a mathematical abstraction of some disturbance in a fundamental plenum which just serves to make the math easier. The supposed “wave/particle duality” (sometimes erroneously referred to as a paradox) isn’t any kind of duality at all except in our minds and crude mathematics which can’t cope with a phenomenon that simultaneously behaves in a wave-like fashion and is also discrete like a particle. This argues not that there is some kind of fundamental fuckup with reality not being righteous but rather that our description of it is woefully inadequate. In other words, reality is the holistic, spectral truth; our best description of it is a shallow, six-color palette representation on pulp. Everything is fields (at least, from a QED/QCD/GUT standpoint) and [THREAD=“299054”]what you think is solid matter is just an illusion of the interaction of those fields[/THREAD]. And all of it may be fundamentally interconnected in ways that are as totally absurd as a Roadrunner cartoon, and yet as completely rational as a game of chess.
I’m sorry that it isn’t more sensible or intuitive, but that’s what you get for using a brain designed to differentiate edible fruits from poisonous berries to attempt to comprehend the basic laws of the universe. We don’t need a more sensible reality; we just need better brains.
Stranger