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Author | Topic: Big Bang Origin? | |||||||||||||||||||||||||||
Darkmatic Inactive Member |
I seem to remember someone here saying that the farther away a galaxy is from us , the mre red shift that galaxy has and thus it is acclelerating . The energy density is driving force , and supposedly it is dark energy which causes this acceleration .
I did some reading up and another explanation for this percieved acceleration of farther away galaxies is that as we look at distant galaxies we are looking back in time , and thus going by the original expansion theory they would have been going faster then that they are now , thus the percieved acceleration of expansion . If this model is correct , then all matter will eventually slow to a halt and initiate the compression and after that and many eons of tense waiting and fretting over the end of the universe you will get the big crunch , and supposedly it all starts again and you get your gravitational singularity. But the dark energy and accelerating expansion is the latest model going off the latest evidence .
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nwr Member Posts: 6412 From: Geneva, Illinois Joined: Member Rating: 4.5 |
I seem to remember someone here saying that the farther away a galaxy is from us , the mre red shift that galaxy has and thus it is acclelerating .
No, that would not show acceleration. It is perhaps evidence that there was acceleration at the early inflation a long time ago. But it does not demonstrate that there is any current acceleration.
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Omnivorous Member Posts: 3991 From: Adirondackia Joined: Member Rating: 6.9 |
Hello, Darkmatic.
Darkmatic writes: But the dark energy and accelerating expansion is the latest model going off the latest evidence. That is my understanding as well. From Einstein's Dark Energy Accelerates The Universe:
The Supernova Legacy Survey (SNLS) aims to discover and examine 700 distant supernovae to map out the history of the expansion of the universe. The survey confirms earlier discoveries that the expansion of the universe proceeded more slowly in the past and is speeding up today, apparently driven by some unknown form of energy. Since scientists don't know much about this mysterious new form of energy, they call it "dark energy."
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cavediver Member (Idle past 3673 days) Posts: 4129 From: UK Joined: |
the farther away a galaxy is from us , the mre red shift that galaxy has correct
and thus it is acclelerating No, redshift only reveals velocity of recession, it does not reveal acceleration/deceleration.
I did some reading up and another explanation for this percieved acceleration of farther away galaxies is that as we look at distant galaxies we are looking back in time , and thus going by the original expansion theory they would have been going faster then that they are now In a conventional big bang scenario this is true but the observed acceleration contradicts this.
thus the percieved acceleration of expansion No, this conclusion is not compatable with the evidence. The acceleration appears real.
If this model is correct , then all matter will eventually slow to a halt and initiate the compression and after that and many eons of tense waiting and fretting over the end of the universe you will get the big crunch Not necessarily. Slow down occurs in all three original big bang scenarios: closed, flat and open. Only the closed re-collapses.
But the dark energy and accelerating expansion is the latest model going off the latest evidence. Correct. Just to add, Dark Energy is the name given to the driving agent of the acceleration. The mystery is not why is there dark energy, but why is there so little dark energy. We have long predicted its existence, though some of the predicted values have been a little out (~10^100 times out in some cases !!!)
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Jon Inactive Member |
Well, this is how I've come to understand it:
In 8th grade, our science teacher showed us a map of the stars. He then overlaid that map with a map of the stars at a later date. Continuing this, a "spiral-like" image began to take shape. This showed us at most that the Universe is moving in an outwardly direction. I would assume the speed could be measured by simply measuring the change in a period of time, and then measuring the change in another period of equal time. If, for the same period of time, the later measurement showed a greater change, then we could take it to mean that the Universe is not only moving outward, but doing so at an increasing rate of speed. Now, onto what I think of the Big Bang. Really, I dislike it. It doesn't really offer up much of an explanation for why the bang occured. I can accept the outward motion of the Universe, but I cannot accept the Bing Bang, the occurance of which we have little proof. Suppose you were to say that if I saw a car moving north, I could believe it to have come from the south. In that manner, if I see the Universe moving out, I should believe it to have come from the centre? I think not! We can say the car came from the south, but not that it came from, for example, Texas. We can see that the Universe came from a central location, but not that it was all created there, nor that it was as compact as a scientist would like us to believe. I think of the Big Bang about what I think of Creationism: it STINKS! Trék
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1.61803 Member (Idle past 1533 days) Posts: 2928 From: Lone Star State USA Joined: |
The orgin of the BB is "a mystery wrapped in a enigma contained in a riddle." The events that occurred at t=something before Plankes time, are forever obscured from human knowlege. As time and space and the cosmos have they're begining once this event took place. One can use scientific methodology to tease out the details. But anything prior is speculation. It was Carl Sagen that said. " The Cosmos is all there ever was, and all there ever will be." Speculating before that is fun and interesting but just as silly as say "here be dragons." IMO. I doubt we ever stop asking the questions.
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1.61803 Member (Idle past 1533 days) Posts: 2928 From: Lone Star State USA Joined: |
Hello, Trekuhrid.
Trekuhid writes: Heh, wont you be dissapointed if you ever find out there is no why. That is it in a nut shell. It doesn't really offer up much of an explanation for why the bang occured.Reason de entre' a reason for being.
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Jon Inactive Member |
I hope we are talking about the same type of "why." By "why" I do not mean the "reason for", but rather the "cause of."
From what I can observe in the world around me, I can see that all things happen in a cause-effect sort of manner. It is my thinking that if the Universe had a beginning, it must have had just such a beginning, i.e., cause-effect. However, then we must find the cause, and if the cause is found, then we must consider that the cause is actually part of the Universe itself, and that the cause (the Universe at that time) only added to its size by creating the effect. In this case, we must find the cause for the cause, which now becomes our new effect. This endless "tantrum" could go on forever! However, if the Universe were to have always existed, then it shouldn't be moving from a centre. Because if we do rewind the tape, the Universe can become only so compact in that small space. From this, we can conclude that the Universe (at least as we see it) had a beginning. Or, we can conclude that the Universe existed in that state for an infinate period of time, and only recently did it "bang" outward. Once again, we see that there ought be a cause to this "bang." Which leads us to searching for yet another cause, leading us back to the "tantrum." So, there must have been a beginning, and there must have been a cause. The Big Bang focuses on the cause of this beginning, and the explosion for which we have no proof, is really no more a valid argument than an intelligent creator for whom we have no proof. Science is supposed to base its conclusion on evidence, yet, it has come to the conclusion of the Big Bang, with little to none for its support. Trék
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cavediver Member (Idle past 3673 days) Posts: 4129 From: UK Joined: |
Hi Trékuhrid
In 8th grade, our science teacher showed us a map of the stars... ...This showed us at most that the Universe is moving in an outwardly direction. Motion of the stars is not related to the expansion of the universe. The stars move within the Galaxy, both orbiting the centre and having their own proper motions. Even nearby galaxies do not reveal the expansion. Our big sister galaxy, Andromeda, is actually on a collison course with us! You have to look much further afield at the distant galaxies to see the overall expansion.
would assume the speed could be measured by simply measuring the change in a period of time We can't do this because our errors in measuring the distance are many times greater than the actual distance a galaxy will move in a human lifetime. We measure the redshift in the galaxys' spectra. This reveals their recessional velocity and in turn we can determine their distance. This is cross-checked with other distance measuring methodologies for closer galaxies.
Now, onto what I think of the Big Bang. Really, I dislike it. It doesn't really offer up much of an explanation for why the bang occured. This is a common viewpoint but based upon a very large misconception. The expansion of the universe is not what tells us there was a big bang. The mathematics of General Relativity tells us that the universe "began" in a Big Bang, and so we should see that the universe is expanding. We look, and it is, so the expansion is observational evidence for the Big Bang. So the explanation for the Big Bang is very simple: General Relativity tells us that it happened. The Big Bang has exactly the same explanation as why things "fall" towards the Earth, why the Moon orbits the Earth, etc. It is all part of the same theory of gravitation. Check out my other posts in this forum for more details on what the Big Bang is actually all about.
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Jon Inactive Member |
Well, I just took a look at the other threads here, and I can say that I don't understand any of them.
What is general relativity? What does it have to do with the Big Bang? I somewhat understand your globe analogy, and the horn and what not, but I don't understand why scientists think that it is that way. Clearly it must have something to do with that relativity that you're talking about. Trék
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cavediver Member (Idle past 3673 days) Posts: 4129 From: UK Joined: |
What is general relativity? What does it have to do with the Big Bang? Very big questions for New Year's Eve! GR is Einstein's masterpiece. Initially he developed Special Relativity, which is the theory that explains the interconnections between space and time, and how that affects what we call motion. Here the ideas of 4 dimensional space-time, the constancy of the speed of light, time dilation, length contraction, etc are all introduced. It enfoced the role of (4d) geometry in physics. To say that SR revolutionised the way we think about space and time is the understatement of the year. SR was published in 1905, and Einstein spent the next 10 years developing GR, which was the incorporation of our concept of gravity into SR. He was sparked by the thought that if you were trapped in a lift, it was impossible for you to determine whether the lift was sat motionless on the ground or was accelerating through empty space at 1g. Both gave exactly the same sensation inside the lift. Acceleration had already been reduced to a geometrical concept in SR, so he reasoned that gravity was not some mysterious Newtonian force, but another geometrical concept within 4d space-time. Gravity became gravitation, the curvature of the 4d space-time that had remained uncurved or flat in SR. His final equation (the Einstein Equation) G=8(pi)T takes a mass distribution and spits out the shape of space-time around that mass, which determines all associated gravity and motion. If you stick in a spherical mass, you get something called the Swcharzschild solution - this gives the space-time around the earth or the Sun (approximating them as spherical and non-rotating - we can correct for these but it gets messy). This space-time gives all of the predictions of Newtonian gravity plus it explains the anomalies that Newtonian gravity could not explain. If the mass is sufficiently dense (restricted to a small enough sphere) then this same solution predicts what we now call a black hole (so a black hole, like the big bang, is a result of the mathematics... not just some fancy physics idea!). Now, if we put in an infinte uniform mass distribution (like dust scattered through empty space) we get a different solution. The idea is that this distribution mimics the universe on the largest scale. This solution describes space-time as a finite hyper-sphere that starts with zero size (and hence infinite density), expands to maximum, and then contracts back to zero size. When Einstein saw this he was most perturbed. In the early 1900s, the universe was considered fixed and static. Einstein introduced a fudge factor to stop this expansion and contraction, and made this universe balance at a fixed size. He was later to call this his greatest mistake, because it wasn't long before Hubble discovered that the Universe was actually expanding! And thus the big bang theory was born, the big bang itself simply being this initial infinte density point, but the theory governing the entire universe, past and future. Notice there is no concept of explosion in space or any other such popular nonsense. The universe simply expands from zero size. Why should we believe this? Can we trust GR? This assumption of a uniform distribution of matter doesn't look very much like our universe! Well, GR is remarkably well tested. It predicts many strange and bizarre phenomena, many of which have been observed and shown to agree perfectly with the predictions of GR. We have also examined literally hundreds of other possible theories of gravity and none come close to GR (other than a few which are so similar to GR, they still predict a big bang). The uniform assumption was always a worry, but we do notice that the larger the scale we look at matter in the universe, the more uniform it appears. The final proof of this was the observation of the cosmic microwave background, which is more than uniform enough to convince us. What about evidence for the big bang? Well, I have work to do, so go check out the Wikipedia entry and you will see all of the evidence laid out. I hope this helps a little. This message has been edited by cavediver, 12-31-2005 04:37 AM This message has been edited by cavediver, 12-31-2005 04:40 AM
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Jon Inactive Member |
This helps somewhat, but it still seems as though an assumption is being made that the Universe was once a tiny dense little ball.
Are these little "dust particles" pushing on space-time in all directions so as to cause it to expand? Because that is about what I get from what you say... I'm no scientist, but I will have a look at that Wikipedia thing, as soon as I get back from my own New Year's celebtrating. Thanks,Trék
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cavediver Member (Idle past 3673 days) Posts: 4129 From: UK Joined: |
it still seems as though an assumption is being made that the Universe was once a tiny dense little ball. No, it most certainly is not an assumption. It is a prediction of General Relativity. That everything appears to be flying apart from each other is evidence for this prediction.
Are these little "dust particles" pushing on space-time in all directions so as to cause it to expand? No, they are causing the slow down and eventual re-collapse (in the original closed Big Bang model). The initial outward expansion is effectively a negative energy phenomenon to balance the positive energy of the matter (the "dust"). This is what we mean when we say the universe has zero energy.
Thanks You are most welcome. Keep asking. This stuff is not intuitive and has little in common with everyday experience. It is difficult enough for scientists that don't happen to work in this particular field.
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Jon Inactive Member |
From Wikipedia: Big Bang.
quote: This seems to be what I was saying about how the existence of the Big Bang was thought to have happened based on the fact that the Universe is expanding. They say that it was "extrapolated into the past" to "show that the Universe has expanded from a primeval state..." I have to say, I am rather confused now. Trék
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1.61803 Member (Idle past 1533 days) Posts: 2928 From: Lone Star State USA Joined: |
Hi Cavediver,
I do appreciate your post and insights. When you say : "eventual recollapse" ie: as in the original closed universe scenario. Is this a fairly recent view? I was under the impression that the universe had enough mass to expand indefinately.That the 'big crunch' was not in our future.
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