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| Author | Topic: What is Time and Space | |||||||||||||||||||||||||
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GDR Member  Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
cavediver writes:
Honestly. I had noticed that myself and edited it between the time you posted and the time that I read your post. It's HAWKING !!! Hawkins was the lad in Treasure Island Thanks for the reply. I've got to think about it more before I can reply to it. This message has been edited by GDR, 07-29-2005 07:57 AM Everybody is entitled to my opinion. 
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
Percy writes: I don't own Greene's book so I can't look it up, but by "notion of time" are you sure he means the same thing as "perception of time"? The excerpt isn't long enough to tell, but I would have guessed that he means that time has the same nature throughout the universe, and that we can figure out what the perception of time would be from another reference frame that is moving or accelerating relative to our own. Thanks Nosy. That helped. There was a lot to absorb in that book for a neophyte and I hadn't mentally connected the two sections. Percy he is replacing the pennies (that represent the galaxies) on the balloon with identical clocks. As the balloon expands the clocks maintain symmetry so that they maintain a consistent cosmic time. Our personal perception of time varies as we move around from place to place within that cosmic model. One question I have of that model though is this. Instead of a balloon we use the planet Earth. I have phenomenal eyesight that is bent by the gravity of Earth so that I can see right around the planet. From Canada I can look east and see cavediver in the UK but I can also look west over a greater distance and see him from the other side. (As carediver’s back look different from his front I wouldn't even realize that I am looking at the same person.)In fact if I look harder enough in any direction I can see my own back. This message has been edited by GDR, 07-29-2005 07:58 AM Everybody is entitled to my opinion.
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
percy writes: Earth's gravity isn't strong enough to bend light around its circumference. For that you need to be at the event horizon of a black hole. I understand that but I'm trying for a metaphor for the universe and that was the best I could do.  Hypothetically then, if the gravitational pull of the Earth bent my vision so that I could see beyond the horizon, (which I know doesn't happen in reality), and if I had strong enough vision, (which I don't), I could see my back. I've probably gotten off the OP with this line of thought however.
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
carediver writes: But it still says Hawkings!! No "s" Well, I was trying to make the point in that sentence that I'm not the brightest light in the chandelier. I rest my case. This message has been edited by GDR, 07-29-2005 11:18 AM Everybody is entitled to my opinion.
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
carediver writes: Don't think of the galaxies moving. Nothing is really moving. It is simply the space between the galaxies that is expanding. Now over a far enough seperation, the expansion of space will be quicker than the light crossing that space. Think of an ant crawling on the balloon while the balloon is inflated... First off, thanks for taking the time to advance my education. I was writing out what I didn't understand when the penny dropped. As I now understand it, the photons from the galaxy are still moving at the speed of light (relative to us) towards us, but the ballon has grown to such a size that the points on the far side of the ballon are expanding away from us at a rate greater than the speed of light. However, if the expansion of the universe is not the same as relative motion, then why isn't the distance affected when the expansion on the balloon is less than the speed of light? Why don’t we subtract the rate of expansion from the speed of the light coming from closer galaxies? It also raises another question. If we can no longer observe or measure the furthest galaxies do they cease to exist?
GDR writes: As we say that the world is about 16 billion years old how would we know that there aren't already galaxies that are beyond 16 billion light years away that are moving away from us at a rate that exceeds light speed?cavediver writes: There are Or at least there had better be! This is all a bit backwards, because we never used to deal with stuff like this except for in de-Sitter space (another story). When the expansion was slowing down, more galaxies were appearing as time went on, as we'd allowed more time for their light to reach us. We said our past particle horizon was growing. But if the universe is accelerating, it all changes, and we get a future event horizon. Oh well... But aren't we basing our estimate of the age of the universe on the distance of the furthest galaxies. If there are galaxies that we can no longer observe couldn't it mean that the universe is a lot older than we think? This message has been edited by GDR, 07-29-2005 04:08 PM Everybody is entitled to my opinion.
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
carediver writes: Because it doesn't make any sense to do that. Think of a photon entering the solar system from Andromeda. If you measure it's speed from Pluto to us, it will be pretty much c. It has just taken longer because it has travelled through expanding space. It hasn't slowed down "locally". However, as the space has expanded, its wavelength must have increased with that expansion, which we observe as the redshift. Are you saying then that from the perspective of Earth, expansion is causing the photon from another galaxy to have to travel a greater distance to get here, (until it reaches our galaxy), than if there were no expansion. (After it hits our galaxy there is no further expansion and the speed is c.) This would mean then that the actual time elapsed, (from our perspective of time) is greater than if there were no expansion? If this is the case then doesn't it once again throw off our calculations of the size and age of the universe? edited to add This is rather esoteric science but somewhere in the Greene book, (darned if I can find it) he refers back to the old axiom "if a tree falls in the forest and there is no one there to hear it does it make a sound". He related it to the moon and said something to the affect that if there was no one observing or measuring the moon it might not exist. This is what crossed my mind when we lose the ability to measure or observe whole galaxies because of expansion. Do they cease to exist? At this point there is no answer, but it seems to me that if that is considered as a possiblity it could certainly give a whole new slant to what is happening to our universe. Like I said, a little knowledge is a dangerous thing. This message has been edited by GDR, 07-29-2005 06:36 PM This message has been edited by GDR, 07-29-2005 06:38 PM
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
Good morning caregiver from my version of spacetime which of course is good afternoon in your universe.
I have just re-read this entire thread. It has been extremely helpful and thank you very much. One question about the expansion and its acceleration. I don't think there is a point in asking how we measure the expansion because I don't imagine there is any hope in me understanding the answer, but does science have confidence in the calculations used to ascertain both the expansion and the acceleration? Another question then. I'm wondering how the motion of bodies through 3 dimensional space affects the perception of time. The planets orbit at different rates of speed around the sun. As we actually have a point in space to use as a reference, (the sun), we can say that they are moving at a different velocity than us. Would an observer on Neptune have a totally different estimate of the age of the universe as us? Another way of asking would be; if I were to relocate to Neptune and live there for a year would my watch still read the same as if I hadn't moved? Everybody is entitled to my opinion.
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
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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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
cavediver writes: 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? 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 PM This message has been edited by GDR, 07-30-2005 02:49 PM Everybody is entitled to my opinion.
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
cavediver writes: 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. 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!)
cavediver writes: 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.
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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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
cavediver writes: 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. 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?
cavediver writes: 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. In your opinion; which is it? Thanks again for your time and patience
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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
cavediver writes: 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! 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?
cavediver writes: was all the matter that we see around us in the form of energy at the BB --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. 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?
cavediver writes: 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. 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.
cavediver writes: 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 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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GDR Member Posts: 6202 From: Sidney, BC, Canada Joined: Member Rating: 2.1 |
Son Goku writes: In other words just as gravity can pull two objects together it can also pull gravity together. I'm having trouble with this concept. Are you saying that all gravitons attract all gravitons? If this is the correct is it true then that the gravitational field not only holds stars, planets etc in place but also hold itself in some sort of cosmic balance? Everybody is entitled to my opinion.
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