This makes me thinkQuote:
Originally Posted by mal4mac
What is the edge of earth and does infinity equal space?
I think infinity and space are not the same.
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This makes me thinkQuote:
Originally Posted by mal4mac
What is the edge of earth and does infinity equal space?
I think infinity and space are not the same.
What do you recommend that I read?Quote:
Originally Posted by mal4mac
I see space or space-time as a coordinate system with a metric defined on it to measure distance between objects. So it is just a model, not the reality. If the model doesn't work to explain gravitation, for example, one changes it to claim that the model is now "curved". It makes the observations of the orbit of Mercury work better, but it is still a model. An infinite coordinate system does avoid the need to find an edge to the universe.
In looking for some validation for this, the Wikipedia article on the metric expansion of space somewhat helps: http://en.wikipedia.org/wiki/Metric_expansion_of_space The first paragraph makes sense to me although I don't think I understand what this "intrinsic expansion" of space really means. The rising bread image somewhat helps.
The metric expansion of space is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion — that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space as, for example, an explosion of matter. The universe is not expanding "into" anything.
But later it talks about an infinite space to avoid the idea of an edge for which there is as yet no evidence:
At present, observations are consistent with the universe being infinite in extent and simply connected, though we are limited in distinguishing between simple and more complicated proposals by cosmological horizons. The universe could be infinite in extent or it could be finite; but the evidence that leads to the inflationary model of the early universe also implies that the "total universe" is much larger than the observable universe, and so any edges or exotic geometries or topologies would not be directly observable as light has not reached scales on which such aspects of the universe, if they exist, are still allowed. For all intents and purposes, it is safe to assume that the universe is infinite in spatial extent, without edge or strange connectedness.
Ricard's "Happiness" or Maupassant's short stories:)Quote:
Originally Posted by YesNo
But if it must be cosmology then Hawking's "A Briefer History of Time" is pretty good, and Greene's "The Fabric of Reality" - but anybody in the local library who's an actual professor of cosmology might be just as good. So browse - just avoid obvious kooks and hard books (Penrose springs to mind... his "The Road to Reality" was harder than my MSc course work!)
Have you read, "The Grand Design" by Stephen Hawking, he takes this model approach and runs with it - I agree with you and Hawking about this approach - but it does take some of the glory away. "Space is Curved" sounds a lot grander than "my model of space is curved". In fact my acceptance of this position has led me to explore subjectivity & consciousness far more than cosmology these days hence Ricard and Maupassant...)Quote:
Originally Posted by YesNo
I refuse to look at Wikipedia articles, so please don't quote them, it upsets my digestions. It's just a bunch of graduate students showing off, and to h*ll with the general public - or even fellow physicists (!) I tried simplifying a few articles so that my gran could read them and they got upset. You'd be far better off reading professors who are writing for the general public.Quote:
Originally Posted by YesNo
The metric expansion of space is the increase of the distance between *any and all* parts of the universe with time. The old balloon metaphor is the best to start with - think of space as the two dimnensional surface of an expanding ballion, and ink dots on the ballon as galaxies. You blow up the ballon and space expands "intrinsically". The ink spots move further apart - just as the galaxies are observed to move apart.
But, remember, space is now thought to be flat and infinite in extent so instead of the ballon think of an infinite flat rubbery sheet like the surface of the ballon - and think of it still expanding like the balloon surface. Ink spots go apart in exactly the same way!
Now think back to the big bang - the infinite sheet was created in the first moment, and matter/energy distributed uniformly across the sheet. Matter collapsed into galaxies and 'cause the universe is only 14.7 billion years old we can only see some galaxies - not the whole inrfinite collection of them on the sheet. Check out:
http://www.atlasoftheuniverse.com/bigbang.html
I'll see if I can find the Grand Design. I think I've seen it in the library.Quote:
Originally Posted by mal4mac
For special relativity where one has the physical reality of the speed of light being constant, that forces the spacetime model to be what it is. For general relativity, we have replaced an unlikely explanation of gravity being a force instantaneously transmitted to what looks to me like rigging the spacetime coordinate system to get the right results. It doesn't explain why spacetime is curved around matter.
I don't often get the question I'm most interested in answered by the Wikipedia articles either, but they are shorter than a book and usually lead to something else.Quote:
Originally Posted by mal4mac
If there were an infinite number of potential stars created during the Big Bang, it is a good thing space is expanding faster than the speed of light so we can only see a finite number of them since the photons of an infinite number of stars bombarding earth would mean the night sky would be bright.Quote:
Originally Posted by mal4mac
Interesting site that you referenced.
YesNo the issue with the bigbang is that it is too random not as in why and how but as in the time it happened.
It is very easy to imagine what happened but not so easy to imagine why it happened the time it happened.
Time is still a puzzle issue here.
Physics doesn't give ultimate explanations - GR experts just accept that spacetime curves around matter, they do not reason why. Stringy types might come up with an explanation using stringy things, but you are still left with "Why stringy things?"Quote:
Originally Posted by YesNo
.. yes to more unreadable pages. It's far better browsing in the library and looking up stuff in the index of likely looking books.Quote:
Originally Posted by YesNo
If there were an infinite number of potential stars created during the Big Bang, it is a good thing space is expanding faster than the speed of light so we can only see a finite number of them since the photons of an infinite number of stars bombarding earth would mean the night sky would be bright.
Interesting site that you referenced.[/QUOTE]
I don't think that's all there is to it.Quote:
Originally Posted by mal4mac
The universe has been in existence for only 13.7 billion years, so we wouldn't see the light from the infinite number of galaxies that are more than 13.7 billion light years from us, even if space wasn't expanding. Interestingly, the universe would get brighter as more and more light started reach us! But...
Following your argument, the edge of the visible universe *is* expanding at greater than the speed of light, so we will never see the light from those distant galaxies.
Worse, because the expansion of the universe is accelerating, most galaxies will eventually cross a cosmological event horizon where any light they emit past that point will never be able to reach us.
So there will be an infinite number of galaxies but we will not be able to see any (except for the local group... and until the heat death...)
If the speed of light is a hard limit, how can space be expanding faster, not to mention accelerating?
If there is a sound barrier then there must be a speed barrier and so this does not make sense.
The speed of light limit is a limit on information transfer. Also, special relativity is strictly a false theory. It applies only to local, idealized flat regions of spacetime. It does not apply to the universe as a whole, where general relativity takes over. But the information transfer limit of SR holds in GR.Quote:
Originally Posted by Calidore
The universe can and has expanded much faster than light speed because this expansion does not enable faster than light signaling. In the same way, quantum entanglement takes place across arbitrarily vast distances, even across the whole universe instantaneously, but since this phenomenon cannot be exploited to send information, the speed of light limit on information transfer holds.
I agree. I don't know of any explanation that makes sense to me that the big bang should have happened 13.7 billion years ago and not, say 12.5 billion years ago.Quote:
Originally Posted by cacian
I suppose the way around this is to model that big bangs are happening all the time and we just happen to be on one that started 13.7 billion years ago. Conveniently for such random models, we can't see these other universes so these models are not falsifiable. That would make them more of a belief system rather than a scientific model.
Indeed and the other time how could we be exact with our timing and numbering because time I am thinking back then was either non existand or simply pointless. What I mean 13.7 measures up exact but then there was no such thing as exact. Our seconds were presumably nothing compare to how fast it was then.
A bigbang is as a result of a very fast wind up . Is see it as winding a clock but faster then it is set up that is the only time a proper explosion happens as a result of faster elements going even faster their atmospheric elements.
That nothingness before that must have been much faster in comparison to our timescale in fact it would have burst our timescale to have been a bigbang.
I finished Hawking and Mlodinow's The Grand Design. I have read Deepak Chopra and Leonard Mlodinow's War of the Worldviews in the past which was also entertaining.Quote:
Originally Posted by mal4mac
Regarding infinity, they do mention the need to avoid unbounded results in a model, although I suspect they accept an actual infinite quantity of objects in the universe. Unlike an unbounded result for a sum, one can easily skip over an infinite quantity, but I think it poses other questions such as which infinity one is talking about, the infinity that counts the set of natural numbers, or the larger one that counts the set of real numbers, or the even larger one of the set of all functions on a real domain or perhaps an even larger infinity? That is one of the reasons why one should avoid an infinite quantity of anything in a scientific model.
On the last page is their praise for M-theory that seems to suggest that the universe could be finite in their view:
M-theory is the most general supersymmetric theory of gravity. For these reasons M-theory is the only candidate for a complete theory of the universe. If it is finite--and this has yet to be proved--it will be a model of a universe that creates itself. We must be part of this universe, because there is no other consistent model.
Although I think supergravity would make an expansion of space more substantial than an arbitrary expansion of a coordinate system, the way they put this sounds like too much authority talking and not enough evidence to me. For what it's worth, this is what Wikipedia says about M-theory: http://en.wikipedia.org/wiki/M-theory
M-theory (and string theory) has been criticized for lacking predictive power or being untestable. Further work continues to find mathematical constructs that join various surrounding theories. However, the tangible success of M-theory can be questioned, given its current incompleteness and limited predictive power.
If one were pure energy traveling at the speed of light with respect to any massive, aka inertial, frame of reference, would there be any time or space? I suspect there wouldn't, but I don't know what a physicist would say about that.Quote:
Originally Posted by cacian
A meteor in the vacuum of space makes no sound? If it crashes into a planet, would the resultant impact produce ... a crater?Quote:
If a tree falls in the woods and no one is around to hear it, does it make a sound?
Cartoons are 2D they understand time too!Quote:
I thought time was considered a fourth dimension. Is there a school of thought that has it caused by three-dimensional physical motion
© 1993-2003 ENCARTA Microsoft Corporation. All rights reserved.
Time, conscious experience of duration, the period during which an action or event occurs. Time is also a dimension representing a succession of such actions or events. Time is one of the fundamental quantities of the physical world, similar to length and mass in this respect. The concept that time is a fourth dimension—on a par with the three dimensions of space: length, width, and depth—is one of the foundations of modern physics.
The word relativity derives from the fact that the appearance of the world depends on the observer’s state of motion and is relative to the observer ... Time is distorted in regions of large masses, such as stars and black holes. The general theory of relativity predicts that a massive rotating body will drag space and time around with it as it moves. This effect is called frame dragging.
Immanuel Kant, have proposed that newborn babies may experience the passage of time ... Henri Bergson thought of time as something entirely derived from experience. In Time and Free Will (1889; translated 1910), he proposed that time is a matter of subjective experience, [and that] an infant would not experience time directly but rather would have to learn ,,, how to experience it.
Scientists disagree on whether it is a closed curve (such as a sphere) or an open curve (such as a cylinder or a bowl with sides of infinite height). The theory of relativity leads to the possibility that the universe is expanding; this is the most likely theoretical explanation of the experimentally observed fact that the spectral lines of all distant nebulae are shifted to the red; on the other hand the expanding-universe theory also supplies other possible explanations. The latter theory makes it reasonable to assume that the past history of the universe is finite, but it also leads to alternative possibilities.
Contributed By: Clifford A. Pickover Ph.D; IBM Reasearch Staff Member; Author of Time: A Traveler's Guide and and Strange Brains and Genius
Contributed By: Lawrence A. Bornstein Dept. of Physics NYU; Author of A Contemporary View of Elementary Physics and Calculus for the Physical Sciences.