What is Time and Space

Page 94/95 of "The fabric of the Cosmos"Greene is refering to some of Einstein's objections to quantum mechanics. Einstein "scaled up" from microscopic objects to the moon to paint what he considered to be an absurdity. In those pages Greene takes no stance on this issue.The answer of the early QM folks was not that the object (from electrons to galaxies) cease to exist but that the question is not answerable so not something there is any point in asking.I'll update this if I can find one later.

Thanks Nosy. I couldn't find that section for the life of me. Your interpretation is obviously correct. Some of these concepts can sure make your head spin though.I was thinking about this idea that as expansion continues that we keep losing galaxies. I assume that we have no idea how many galaxies have expanded beyond our our event horizon. It seems that as our universe was infinitely small prior to the BB is could be infinitely large beyond our event horizon. (Whatever that means. )

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Sorry, I'm a theorist. The universe is a mathematical solution to Einstein's equation (or some possibly string inspired variant). It's (approximately) a 4d hausdorff manifold with pseudo-Riemannian metric and I can integrate "god-like" between any two events I feel like. I don't need the earth or any physical object. I just choose locally non-accelerating frames.

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Yes, but that can't give you the age of the universe from Earth's perspective.
You can choose any two events and integrate, but it won't mean anything with regards to the age of the universe.
Earth's proper time isn't defined before it's existence, when it was just an ensemble of gas and rock (roughly).
To get the age of the universe from Earth's point of view would require Earth existing at the Big Bang.

I really don't understand your reliance on the Earth. The Galaxy has been here a lot longer than the Earth has... is that good enough? And it's been comoving the whole time. Our motion within the Galaxy is negligible. And before that, the density perturbation which caused the Galaxy to form was there. That takes us back to just after the last inflationary epoch. I'm happy with that. Actually, I'm happy to get back to last-scattering which as I said earlier is 300,000 years later than inflation.

Common misconception... amongst those that have thought hard enough to have got this far If the universe is infinite, it was infinite at the big bang... Surprise! Or at least, it was infinite for any time t>0. At t=0 it's size is ill-defined. Does that help? I don't usualy get this far in conversations to make this point. Thank you.If the universe is finite, so closed (possibly accelerating) then the big bang was a point. In this case, back to the balloon analogy, and the event horizon is a circle around us on the balloon. The circle is getting bigger, but the not as quickly as the space is expanding. So galaxies close to us eventually pass over the circle to "the other side" and we just become more and more isolated on this finite balloon. Okay?

Hmmm, I think you seriously underestimate my explanatory powers Remember that the light gets stretched as it crosses the expanding universe? We see this in the redshift of the observed light. If we look at the spectrum of light from a distant galaxy, we see lots of peaks and troughs in the intensity occuring at different frequencies. The peaks and troughs are emssion lines and absorption lines. We know at what frequency they should occur. As we look at further away galaxies, we see the lines occur at lower and lower frequencies: the light has been red-shifted. If we compare the red-shift between two galaxies whose distance we know, we can see how red-shift changes by distance, and we can determine the expansion of the universe. Different, yes. Totally different, absolutely not. The difference is totally negligible. Remember the balloon blowing up... the galaxies we draw on the balloon are not moving. In reality, they might be, slightly. And our galaxy is rotating so we are moving. And Earth is orbiting the sun, etc, etc. But all of these motions, relative to the expanding universe, are negligible. To make a difference you would have to accelerate to a good fraction of c, and then you would be moving with significant velocity with respect to the Galaxy. You would get a different answer to the age of the universe, but it would also be rather obvious that all of the galaxies around you were moving at high velocity with respect to you.

I like the image of the circle on the balloon. That makes it easy.The infinite thing is obviously more difficult. My perception of the BB goes back to E=MC2, but I don't understand the BB as a point but as infinite energy and zero mass. If that is correct then it makes sense to me that the universe beyond the event horizon is infinite because we started off with infinite energy at t=0. If we started with infinite energy then we can't have a finite universe now.... can we?Infinity is so hard to grasp. To go back to my original post where we have photons constantly rocketing around the universe at the speed of light in zero time over zero distance from its perspective. We see it covering billions of light years but as far as it knows it hasn't gone anywhere. Picturing things like that kinda makes infinity seem somewhat sensible. Thanks for the compliment by the way. It is encouraging.Edited to add. I got thinking about what I said about time 0 not being a point but infinite energy. According to string theory everything is little strings of energy. If that is true it would make sense that at t=0 it wasn't a point. (Wouldn't it?) I'm in way over my head, but as you Brits say, "in for a penny, in for a pound". This message has been edited by GDR, 07-30-2005 02:39 PMThis message has been edited by GDR, 07-30-2005 02:49 PM

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Everybody is entitled to my opinion.

Great explanatory powers. You must be a teacher. I largely understand but I want to read more about it again in Greene's book. It also added to my picture of the expanding balloon with the clocks. You can add time to the visual metaphor by picturing time as being represented by the diameter of the balloon. (I think!) That all makes sense. Learned something else new as well. I didn't know that the Milky Way was rotating. (Now I have to picture my clocks rotating on the balloon.)There is a guy in our church who has a PHD in physics and we just happen to be going to his house for supper tonight. I'm sure I'm going to be able to impress the heck out of him with all this new wisdom.

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I really don't understand your reliance on the Earth.

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I amn't relying on the Earth, just using it as an example that there is no object in the universe which can truely say the big bang happened "x" years ago.
All any object can do is extrapolate its proper time back to the big bang and call the integral of this "the age of the universe".
However the problem is no objects "current proper time" existed even 500,000 years after the big bang.

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The Galaxy has been here a lot longer than the Earth has... is that good enough?

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No, not really.
It was an issue in 70s cosmology and is now considered largely unimportant.

What about the 10^28 hydrogen atoms in my body? Are they good enough? (the 28 is a guess...) Or forget them, what about my electrons? Oh, no, wait... there is only one electron, isn't there I think I can see why...This message has been edited by cavediver, 07-30-2005 06:58 PM

Hmmm, as soon as I see E=Mc^2 I reach for my gun The reason for all the confusion is that we have more than one concept of mass... there is rest-mass of a particle. This is a quantum concept. There is mass in the sense of "mass" that curves space-time. This is a relativistic concept. There is "relativistic mass" of a "moving" object. This is an unhelpful concept. I could spend days talking about the differences and the confusion that reigns to this day.For now, let's stick to relativity: the mass within a volume of space is a measure of how curved that space is within that volume. If we measure the mass of the universe today, that mass was always there, all the way back to the singulatity.Talking about "energy" is just as bad. But, yes, an infinite universe started off with infinite energy and a finite universe started off with finite energy. Absolutely. To help even more, Penrose came up with a method of drawing diagrams, which we call "Penrose Diagrams" no less. Actually, Brandon Carter came up with the idea too, so we should really call them Carter-Penrose Diagrams. We rarely did, unless Brandon was in the room and then I used to as he scared me They enable us to draw infinite spaces in finite drawings. Certainly possible. That was one of the big hopes for string theory, that it would "smear" out the classical singularity. Some of my early work was modelling black holes in string theory, and seeing how the concept of singularity changed.

I've only got a minute so I'll just ask a couple of quick points.I mostly see what you are saying about mass. It is really helpful as all through my reading I was wondering why I couldn't understand just what mass was. In my mind I couldn't get away from thinking of it as matter. Then I'd think of matter and I would think of something I could touch and feel, and then I ran into dark matter and it all went out the window. Back to the point at hand though. Couldn't the mass that has existed from the time of the BB have been in the form of energy at t=0? In your opinion; which is it?Thanks again for your time and patience

Yes, this is a great part of the misconception. Matter usually has mass but mass is not matter. Mass is gravitational charge, the equivalent of electrostatic charge. The difference is that gravity itself carries gravitational charge, where as photons are electrically neutral... and a good job too, because if photons were electrically charged, there would be no such thing as sight! Well, having just said that mass is charge, this now doesn't make a lot of sense. If you want to ask

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was all the matter that we see around us in the form of energy at the BB

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then I would say yes, sort of. The trouble is by talking about the matter fields at the BB we are pushing beyond the boundaries of GR and even simple quantum gravity: we're into full blown TOE.And is the universe open or closed? Well, I would like it to be closed on aesthetic grounds. But I'm not that bothered. And don't forget that the chances that our observed 4d universe is the real "universe" are slim... it is much more likely part of a much larger multiverse/encompassing existence, which may embed our universe or more bizarrely "project" our universe.Don't you just love the way that every one of your questions launches fifty more? That's why I love this subject... Every other science is just so obvious: Chemistry? It's just atoms isn't it. Biology/evolution... it's just chemicals isn't it

Let me see if I have this right. Protons are neutral but they act as agents for the electro-static force by, for example, attracting a negatively charged particle to a positively charged one. Gravitons are capable of exercising either positive gravity or negative gravity on mass, which is gravitationally neutral. I'm experiencing positive gravity right now but when might I encounter negative gravity? This kinda threw me at first as I was wondering where the theory of evolution fit into all of this. I eventually figured out that TOE is "Theory of Everything"...... isn't it? It may be TOE but from what I have read it must makes so much sense that it was all energy. We know that a little bit of energy converts to a great deal of mass. From a human point of view it is certainly easier to picture infinite density of energy as opposed to infinite density of mass. Also it seems to me that the original singularity would be different than a singularity in a black hole. A black hole has an incredible gravitational pull, but presumably at t=0 gravity didn't yet exist. If I have it right, mass is something that affects and is affected by gravity. If that is true then how could mass exist at t=0? Doesn't that just leave energy? I can understand that you as a scientist wanting to see the universe as a closed entity but I have to admit, as a Theist, the idea of it being open is much more appealing. Your conclusions seem to pretty much agree with Greene. It just seems to me that the physical in this universe isn't representative of reality. I mean even if string theory is proven wrong I can't help but believe that the final solution will be something along those lines. From my minimal knowledge of QM I can't see physical matter being anything much more than an illusion. It is like watching my shadow and trying to relate what I see back to me, and for that matter the sun. I couldn't agree more. I'm trying to learn some biology but I find that I'm just gathering knowledge. To be honest I read something like your second last paragraph and I get excited. I don't have formal education past high school. Actually physics was the one subject I enjoyed in high school, (that was back when the world was still flat ), but I didn't really enjoy academics in general. I retired a year and a half ago and I'd go back to school, but I'm not prepared to give up my volunteer work to do it, so I'll content myself with books and this forum. I've certainly been furthering my education in the last couple of days thanks to you.This message has been edited by GDR, 08-01-2005 07:29 AM

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Let me see if I have this right. Protons are neutral but they act as agents for the electro-static force by, for example, attracting a negatively charged particle to a positively charged one. Gravitons are capable of exercising either positive gravity or negative gravity on mass, which is gravitationally neutral. I'm experiencing positive gravity right now but when might I encounter negative gravity?

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Gravity is a little weird compared with the other forces*.
Mass is gravitational charge**, but unlike electromagnetism there is only one charge, no positive and negative and it always attracts.
Gravity is also gravitationally charged, which is what makes it especially weird. Gravity itself feels gravity.
In other words just as gravity can pull two objects together it can also pull gravity together.*Some people believe that gravity is so different from the other forces because it isn't truly a force.
**Technically it isn't only mass that is gravitational charge. Stress, angular momentum and electric charge can also cause gravity.

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Also it seems to me that the original singularity would be different than a singularity in a black hole.

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Definitely.
The Big Bang singularity was "special" where as singularities in black holes are "generic".
This is because any star can collapse into a black hole, but the beginning of the universe was obviously specific or balanced in some way.
(In truth it is to do with a thing called phase space but I won't go into that.)