DrRocket
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Posts posted by DrRocket
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Is dark energy the result of a total vacuum beyond our visual horizon? A total vacuum would accelerate expansion and maybe explain dark flow. There is no total vacuum anywhere we can see. What do you think?
Nobody has a clue as to the source of dark energy.
A total vacuum would most certainly not accelerate expansion and it has nothing whatever to do with dark flow.
The energy of the quantum vacuum is predicted to accelerate expansion. The problem is it overpredicts the expansion rate by a factor of
10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
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I've been wondering about the expansion of space and the relation to the pressure of space. After reading about the cosmological constant and other things I had questions that I have been unable to find an answer to. I was wondering if the expansion of space and the pressure of space were related? If they're not then why not? I can't seem to find any information about the measurements of the vacuum pressure over an extended period of time to indicate any change in that pressure. To my way of thinking the pressure should correlate with the rate of expansion.( Assuming the two are related. Which I can't see why they wouldn't be.) I was also thinking that gaining an accepted measure of study on pressure changes would tell us what the universe is doing as whole. Not just in our range of observation. It would make sense that if the pressure was to grow stronger (more negative) then our universe is expanding. If the pressure grew weaker (more positive) then our universe is contracting. If the pressure stays the same (with reasonable fluctuations) then we could assume that our universe as a whole is static, but that with in is just in motion. Now all of this is under the assumption that pressure and expansion are related. The reason I believe they are is because the way a vacuum is created. The less matter you have in a space the more of a vacuum is created. We know that space has a vacuum energy, so it could be assumed that that is because of the amount of matter that is in the space. Possibly created in the original expansion. If it is space that is expanding, then the less matter should be in that space as it grows, therefore should affect the pressure of that space. At least up until an absolute perfect vacuum is achieved. Let me know what you all think about this assertion and if there is any info out there related to this connection.
Pressure is probably a factor in the accelerating expansion of space, but not in the way that you think.
Pressure enters into the Einstein field equations of general relativity that determine the curvature of spacetime which in turn results in what is commonly called "gravity". But pressure results in a postive gravitational force, rather than what is required to cause accelerating expansion -- a repulsive force.
However, the energy of the vacuum, as predicted by quantum field theory, would result in a negative pressure which in trun would provide the required negative presssure which is equivalent to a positive cosmological constant, which is effectively a repulsive force.
Unfortunately current estimates of the cosmological constant, based on the energy of the vacuum according to quantum electrodynamics, overestimate the observed cosmological constant by a factor of about [math] 10^{120}[/math] -- probably the all-time record for a misprediction in all of physics. No one understands this.
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Buckling IS the only reason why rockets have isogrid panels, added rips and the like!
Stiffness against axial bending, longitudinal compression, and others, would be best overcome with plain sheet.
Stiffness is still the driver for in-line rocket design, as I stated.
And I am willing to bet that I have been involved in the design of more in-line rockets than have you. In fact we dumped most aluminum structures in favor of composites for weight and stiffness reasons some years back. Isogrids did not work out very well in the trades either.
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http://www.ams.org/home/page professional information and publications for mathematicians, discounts for members
http://www.claymath.org/ info on mathematics and home of the Millenium Problems -- solve a famous problem and win a million $ (or read and understand the problem statements written by world-class mathematicians)
http://genealogy.math.ndsu.nodak.edu/ follow the academic geneology of mathematicians (I tracked mine back to Isaac Newton -- that gets me a cup of coffee at Starbucks for about $5)
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Here's how this thread began:
It is not contrary to normal science practice to expect people to have a basic knowledge of the conventional standard theory, especially if they want to deviate from it, or go beyond it.
Perhaps this can help those interested in delving into cosmology at some depth.
The pillar of modern cosmology is one of the pillars of modern physics, general relativity.
General relativity (GR) was formulated by Albert Einstein and announced in 1915. It has since received a great deal of attention, the mathematical foundations have been examined, the presentation refined, and a host of confirming experiments performed. General relativity, with its mathematical roots in Riemannian geometry is a formidable subject, and some of its predictions are contrary to everyday experience – i.e. “common sense” can be badly mistaken. That is no surprise as even special relativity, the precursor and “little brother’ of GR is surprising at first encounter.
http://math.ucr.edu/home/baez/gr/gr.html
http://en.wikipedia.org/wiki/Introduction_to_general_relativity
http://en.wikipedia.org/wiki/General_relativity
http://rspa.royalsocietypublishing.org/content/368/1732/5.full.pdf
GR treats the universe over all time as a single entity – spacetime. This can also be done in Newtonian mechanics, so there is nothing really new about spacetime. What distinguishes GR is that spacetime is not just affine 4-space, but in fact is a Lorentzian 4-manifold of undetermined topology, with a curvature tensor that is also unknown but is determined by the distribution of mass/energy via a stress-energy tensor defined by a very complex set of partial differential equations. These equations, the Einstein field equations can only be explicitly solved in a few simple circumstances. Gravity is the result of curvature of spacetime.
In general because of curvature neither space nor time have any global meaning. However, if one makes the assumption that spacetime is homogeneous and isotropic, then spacetime decomposes as a 1-parameter foliation by space-like 3-dimensional hyperplanes of constant curvature. The parameter serves as a surrogate for time and the hyperplanes as a surrogate for space. The hyperplanes inherit a true Riemannian metric from spacetime and expansion of space means that the distance between points increases as the value of the time-like parameter increases.
Astronomical observations support the assumption that the universe is homogeneous and isotropic on the largest scales. Observations also support the expansion of space.
http://scienceworld.wolfram.com/physics/HubbleConstant.html
https://www.cfa.harvard.edu/~huchra/hubble/
http://map.gsfc.nasa.gov/universe/uni_expansion.html
http://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe
http://aether.lbl.gov/www/science/cmb.html
http://aether.lbl.gov/www/science/cmb.html
Based on these assumptions and observations Hawking and Penrose in a series of papers used general relativity to conclude that, as a logical consequence, the universe began in an extremely compact form, and in fact predicted singular behavior (which is generally thought to indicate a limitation of general relativity to predict the first fraction of a second)
http://rspa.royalsocietypublishing.org/content/314/1519/529.full.pdf+html
So, while nobody knows what happened in the first fraction of a second, the big bang hypothesis in terms of subsequent expansion from an extremely compact state is on firm empirical and theoretical grounds.
Inflation is not necessary to the big bang, but does use ideas from quantum field theory to explain why the universe is homogeneous on the large scale, yet exhibits anisotropy on smaller scales. It is not a fully verified, or even rigorously formulated, theory, yet. It is promising. It is supported by what has been seen in surveys of the cosmic background radiation. Attacking inflation as unproven is futile, because it is well-known to be just that. But interpreting “unproven” as fanciful or unlikely is simply a demonstration of ignorance.
http://web.mit.edu/physics/news/physicsatmit/physicsatmit_02_cosmology.pdf
Thus, modern cosmology rests on a solid foundation of empirical data and well-formulated theory. That does not make it immutable. Any physical theory is subject to refinement and extension. But any revision must meet equal standards of rigor.
Anyone who rejects modern cosmology must meet the obligation of providing the basis for an alternative . That means providing a theory of gravity to replace GR, and the empirical data to support it. Further, that data must include ALL valid data, including that which currently provides evidence for the validity of GR itself.
Addendum: useful references for the serious (these are NOT popularizations)
Gravitation -- Misner, Thorne, Wheeler
Gravitation and cosmology : principles and applications of the general theory of relativity -- Weinberg
Cosmology -- Weinberg
General Relativity -- Wald
Principles of Physical Cosmology -- Peebles
The large scale structure of space-time -- Hawking and Ellis
General Relativity and the Einstein Equations -- Choquet-Bruhat
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Defining God
in Religion
You have identified the major problem with the "Does God Exist ?" debates -- there are at least as many unstated concepts of God as there are debaters. I strongly doubt that any consensus on a definition could be reached. Ergo, the debate is pointless.
When you address the question on a personal level you are free to formulate your own definition of God. It is on that definition that the outcome of your personal decision process hinges.
If you define God as some sort of entity that not only can but with some regularity does intercede in natural physical processes, then there is a great deal of objective evidence that no such God exists. In fact, the existence of anything that regularly upsets what we have come to expect as the orderly processes of nature is antithetical to science, which seeks to uncover and explain that natural order in terms of predictive models. Without that order there can be no science.
Science seems to work rather well. So any concept of God or any religious tenets that directly contradict science as buttressed by experimental evidence is clearly indistinguishable from superstition. Superstition is, essentially by definition, wrong.
If you define God as some sort of entity that exists outside of the natural universe and does not regularly disrupt the operation of that universe according to the principles discovered by science, then science and religion are disconnected, and neither has anything to say about the other. In this situation neither science nor logic can be brought to bear on the question of the existence of God. The order of the universe could be mere happenstance or it could be the result of God. The question is logically undecidable.
You are free to reach your own conclusion, or forego a final conclusion. But do not deceive yourself that whatever conclusion you reach is based on rigorous logic, unless you formulate a sufficiently narrow definition of God to be able to apply empirical data. In any case you should recognize that, despite the marvelous progress of science, there is a lot that we don't know. If we knew everything the satisfaction and outright fun of scientific discovery would be lost.