Do we really need a new theory? GR explains it all pretty nicely. The Mathematicians – Hawking, Penrose, others – have figured out some nifty implications of GR that Einstein might not have thought of, but, really, they’re still working with his basic ideas.
This thread seems to echo the Einstein/Mach debate. One of them believed that space was a “metric” with intrinsic distances and extents, while the other insisted that it was only the existence of matter within that space that allowed one to talk about distance. (I can never remember which was which!)
As I understand it, the Big Bang is a theory on top of general relativity and quantum mechanics in the sense that it’s not predicted by either one. There’s nothing inconsistent in the Big Bang with general relativity and quantum mechanics (well, from the moment of the Big Bang on, at least), but general relativity and quantum mechanics don’t predict the Big Bang. In the short period after general relativity and quantum mechanics became accepted and before the Big Bang became accepted, physicists didn’t say that, given those theories, it must be a necessary consequence that the universe started some billions of years ago with an expansion (or an explosion or however you want to characterize the Big Bang). Acceptance of the Big Bang began with the observations of Hubble et al. about the fact that galaxies of increasing distance from us moved with increasing speed.
The same thing is true of cosmic inflation, dark matter, and dark energy. Each of them is consistent with general relativity and quantum mechanics, but each is a new theory on top of those theories. Furthermore, general relativity and quantum mechanics by themselves don’t predict the Standard Model of particle physics. The Standard Model is consistent with them, but it’s not predicted by them. General relativity and quantum mechanics by themselves are not all of physics.
For all the reasons, it’s at least possible to imagine that someday there will be a more all-encompassing theory which integrates more of these theories into a single one. Physics is not a completely integrated body of knowledge at the moment. There are various questions about how such a theory should work and various ways in which the theories don’t even seem to be quite consistent at the moment:
This may be the hardest piece to grasp. There is nothing outside the universe. Not a nothing into which the universe is expanding into. Nothing at all. By definition, the universe is all there is. So when scientists say that the universe is expanding, they mean that everything just got larger - not that it moved into something yet unoccupied.
The good old expanding balloon surface works here as an analogy. The balloon is all surface. There is nothing inside it or outside it. Expand the balloon and the spots on the surface grow farther apart. What has it expanded into? Nothing really. There’s just more balloon.
A massless particle still has energy, and you can equate energy with mass. A “piece of space” doesn’t have that energy.
But I think it’s even more fundamental than that. There are things in the universe moving away from us at faster than c when you take the expansion of space into account. So it isn’t just space moving faster than c because space is taking everything along with it.
The key is that c is the top speed of things moving through space. There is no speed limit for the movement of space itself because space isn’t moving through itself. Space expands, and it seems to be able to do so at virtually any rate it wants to.
I disagree whole-heartedly with the idea that the plenum doesn’t have energy. A piece of space most certainly does have energy. This is a well established fact in quantum mechanics.
And again, you (and others), keep talking about “the expansion of space” as if space itself is a thing that can expand. Which is fine and certainly true, but it does NOT answer the question of WHY two points in space can move faster than the speed of light relative to one another, but other massless stuff cannot. Saying that space is “expanding” instead of “moving” is playing semantics. Two points in space that are expanding ARE moving relative to one another with a measurable velocity (as long as there is observable matter that the space is carrying). And somehow, space (which has an energy, and no mass) is allowed to move faster or slower than c. And what is the explanation for this?
I believe c is a limitation on matter and the proliferation of energy and information itself in a more or less direct manner. This wouldn’t mean there aren’t ways around it; indeed the universe itself has already demonstrated so.
Can humans take advantage of these loopholes regarding getting around the limitations of c? If so, not for a very, very long time. But hey, time is relative.
The more I read up and inquire about the nature of the cosmos, GR, QM, M-Theory, etc., the more convinced I am of higher dimensions in space and time.
Even a model as low as 4 spacial dimensions and 2 temporal dimensions 2 (4+2 / 6 dimensional spacetime) on the same macro scale as the 3+1 dimensional “plenum” we see directly, seem able to more elegantly describe some interesting and still unresolved issues involved in singularities and such.
Eintein’s Nobel Prize was in quantum mechanics. I doubt he’d have called it “bunk”. However, for a long time he thought there must be a deterministic explanation beneath the statistical statements of quantum mechanics: “God does not throw dice.”
As it turns out (and sorry but I can’t recall the cite), not only does God throw dice, but he does it from where we can’t see his hands.
I am aware of vacuum energy, which is why I said “doesn’t have that energy” (though perhaps I am making a distinction that isn’t relevant).
In any event, I don’t see that the difference between “expanding” and “moving” is only semantics. It’s the difference between “moving through space” and “moving space.” It’s the difference between ants crawling and the balloon expanding. Space does not move through space, and c apparently does not apply. Particles (massless or otherwise) do move through space and c does apply.
But ultimately I understand much of this is a metaphorical or conceptual way, rather than having a deep understanding of the mathematics. I’m sure someone else can explain it better.
As a balloon expands, you can most certainly measure the speed of two points on the balloon relative to one another. Assuming the balloon is invisible and immeasurable, you could still measure the velocity of two ants sitting on the expanding balloon and conclude that two points on the balloon are moving away from each other at a given velocity.
So if you’re going to argue that space is a thing, and that it has energy, and that it expands (like a balloon), this is no different than anything else in the universe that has energy and moves.
No one here is claiming that space-time is energy or matter. Just that an ‘empty’ point in space has energy. Space-time itself has energy, and in fact, it’s where a good 70% of the energy of the universe resides.
So if you’re going to argue that space-time is a medium, then it’s a thing, and it’s a thing with energy. Now, explain to me why a thing with energy can travel relative to another thing with energy at speeds greater to, less than, or equal to c? What special property does this medium have that photons, or neutrinos, or regular old matter does not? What sets space-time apart?
The only answer, other than “I don’t know,” that one might deduce is that spacetime isn’t bound to c the way matter and energy are, moving of their own accord within it.
Returning back to my boats on a lake analogy, if the area of a lake is continually expanding, and carrying Boat A and Boat B apart from each other in a relative way that seems to violate c, then either something more fundamental is going on, that existing theories will be corrected for, or new theories might clarify or supplant.
Part of the problem may be semantics. When space expands the matter inside doesn’t travel; distances get longer. That seems to me a very different thing. Space never at any time travels. It is all there is at every moment. It can’t go anywhere because that would imply a place outside space. It was all there is before the Big Bang, a moment later when it was the size of pea, and now when it’s many billions of light years across. But it has never moved, or traveled, or done anything that is analogous.
Space is one of the final frontiers, being that, most of the things thrown out there are theories. Whether you believe it or not is your choice. Who knows everything we know about the universe is been told to us, so if you believe everything you see and read then all these things are right, not knowing whats really out there is what makes space so amazing.
I can’t think of the adjective for how this statement–and I do understand it in the descriptive style presented here–blows my mind.
By the reasoning presented–“technically”–everything I see can be assessed by “being here now,” right? But that “here now” is already occupied by “me,” the spacetime point where “I see,” as stated above.
I am trying to fathom this. Unhappily, I feel like I have just rediscovered the Cartesian solution.
“Better not to think too much of it all” means “faith.”
Ok now we’re getting somewhere. So indulge me for a moment.
Imagine two universes, each with two particles, one at point A and one at point B.
In one universe, the two particles are moving apart from one another at a given velocity, such that they begin each at point A and point B in space, and move further and further from these points as time goes on. Space itself is static in this universe.
In the other universe, spacetime itself is expanding and the particles are always at point A and point B in space, but relative to one another, are moving with the same measurable velocity as in universe 1.
How are these two universes experimentally different? What is the meaningful distinction between them, other than just semantics/philosophy?
