DaveC426913
Valued Senior Member
Nostradamus at work!
We are beginning to see the cheese under TG's cracker:
http://www.sciforums.com/threads/de...tivity-by-the-god.156616/page-11#post-3388019
Cosmological concept change
- Thread starter timojin
- Start date
We are beginning to see the cheese under TG's cracker:
http://www.sciforums.com/threads/de...tivity-by-the-god.156616/page-11#post-3388019
Schmelzer
Valued Senior Member
The common sense problem with the expansion picture is that there would be arbitrary large relative speeds. Once these large relative speeds are not artefacts of shrinking rulers, the theory has unlimited speeds. To limit it now would, however it is done, destroy translational symmetry. No beautiful solution available.
Note that this is only a problem of the particular interpretation, picture, or how you name it. For GR itself this is not a problem at all.
Sheeple are of course ready to reject common sense if the herd rejects it. The speed limit plays no role in GR except locally. To distinguish mass from spacetime is nonsense from point of GR.
In fact, the coordinates used by all mainstream scientists - the FLRW ansatz - corresponds to the shrinking rulers picture. And this picture clearly has advantages, namely a higher symmetry.
Nonsense. These bound regions are what allows to define a ruler. And these rulers are shrinking.
And you are completely wrong, because above pictures are equivalent physically because of the equivalence principle. Ok, you have, as a layman, no understanding of the equivalence principle. But it appears that whenever you start to argue about the content you get it completely wrong. Here simply rejecting the basic principle of GR.
Why not, once you are an exemplar of this species which does not even pretend to have an own opinion, different from the herd? Fine if sheeple feel happy in the good company of the herd. But, be careful:
That's OK, I'm obviously in good company, not withstanding your usual fabricated definition and cop outs.
Brian: You are all individual.
Herd: We are all individual.
Paddoboy: I'm not!
Herd: Shhhh!!!
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Sheeple are of course ready to reject common sense if the herd rejects it. The speed limit plays no role in GR except locally. To distinguish mass from spacetime is nonsense from point of GR.
↑
In fact, the coordinates used by all mainstream scientists - the FLRW ansatz - corresponds to the shrinking rulers picture. And this picture clearly has advantages, namely a higher symmetry.
Nonsense. These bound regions are what allows to define a ruler. And these rulers are shrinking.
Obfuscate all you like: You have already agreed that the shrinking ruler concept is simply an alternative perspective, and as I already said, it does not really stand up to scrutiny.
↑
And you are completely wrong, because above pictures are equivalent physically because of the equivalence principle. Ok, you have, as a layman, no understanding of the equivalence principle. But it appears that whenever you start to argue about the content you get it completely wrong. Here simply rejecting the basic principle of GR.
The Universe/spacetime expands over large scales: Over smaller denser regions, gravity overcomes the expansion rate.
Shrinking rulers are limited in explaining that.
↑
Why not, once you are an exemplar of this species which does not even pretend to have an own opinion, different from the herd? Fine if sheeple feel happy in the good company of the herd. But, be careful:
Whatever my Maverick friend!
Again in essence, all the shrinking ruler thingy is, is an "alternative perspective"of looking at things rather than any "alternative model"
Much as on occasions we still use the "flat Earth" aspect, and we know how "real" and limited that is.
Perhaps you herd sheep for a living.
Would explain that silly obfuscating statement.Perhaps you need to invalidate the scenario I've given to show the limitations of the shrinking ruler, rather than your sheep herding.
Whatever my Maverick friend...I would guess you are still smarting over your ether hypothetical debacle and how it has vanished into oblivion as I predicted.
Like I said, and like you agreed, the shrinking ruler concept is just an alternative perspective and certainly not an alternative model...much the same way we may still use the archaic and essentially wrong "Flat Earth" model.
Shrinking rulers are seen in a similar vane.
Apologies for the stuff ups...computer is crashing and freezing on me.
Schmelzer
Valued Senior Member
Wow, you have given a scenario? Not seen.
Anyway, I will try to explain. Have you ever seen an FLRW metric? It is $ds^2 = d\tau^2 - a^2(\tau) (dx^2+dy^2+dz^2). What are the trajectories of galaxies which are locally in rest relative to the CMB radiation frame? They are defined by $x,y,z$ being constants. Instead, what is variable is $a(\tau)$, which defines local rulers.
LOL, paddoboy sells Flat Earth as an "alternative perspective".
But, ok, you show at least some progress, naming it "essentially wrong". Contrary to your attempts in the past to name outdated wrong theories (like Newtonian mechanics) true.
Unfortunately, there is an important difference between the shrinking rulers interpretation of GR and Flat Earth, namely that there is actually no better mainstream theory than GR, and the shrinking rulers is a valid interpretation of the FLRW solutions of GR. And, btw, the most natural one, because it agrees with the standard choice of coordinates for these solutions, coordinates preferable because of their symmetries.
Answer the question and how your shrinking ruller nonsense accounts for it.
I'm saying that it is still used in certain disciplines, as you well know.
Again your honesty needs to be questioned.....
I said that Newtonian gives correct answers within its zones of applicability, the same as "Flat Earth" gives correct answers within its zones of applicability.
in answer to your own fabricated nonsense, made of course with your ether in mind, saying that they are both wrong.
Sorry, you may be a "professional" but I see just the usual.
Please answer my scenario with regards to the shrinking rules with regards to large scale expansion and local regions decoupling from that expansion through gravity.
And no, it is not the natural one, as you say, and if that were true, that natural interpretation, would be the popular perspective used.
And besides the scenario already mentioned, the evidence so far shows acceleration which shrinking rulers again, would find difficult to explain, and the fact that previously the expansion was slowing down.
Again, despite your opinion, as professional as you think that may be, all It is, is just mainstream expressed in a slightly clunkier and confusing interpretative framework, that does not answer all the expanding version does.
Shrinking rulers requires way too many arbitrary constructs, and does not match the observations. Plus of course while we are reasonably able to hypothesise DE to explain the accelerating expansion [despite not knowing its true nature although Einstein's CC is a reasonable assertion] what can we hypothesise to make rulers shrink?
A magical spaghetti monster?...Plus of course while we are reasonably able to hypothesise DE to explain the accelerating expansion [despite not knowing its true nature although Einstein's CC is a reasonable assertion] what can we hypothesise to make rulers shrink?
There is just nothing reasonable about DE. It is as good or as bad as your spaghetti monster.
It's your spaghetti monster my friend, and yes, according to the evidence DE is a logical conclusion, although at this stage we are ignorant as to its nature: Probably the CC of Einstein fame though.
danshawen
Valued Senior Member
DE breaks the conservation of energy law, just like perpetual motion machines. A reactionless thrust applied to something, however distant or massive, is still a reactionless thrust. Forces come in PAIRS. What, pray tell, is being pushed against to produce this acceleration? Which of the four or at most five kinds of known forces is responsible? If you can't answer, then all you have is an observation, right? NO hypothesis. NO experiment designed or performed to test a hypothesis. In other words, NOT science. DE does not even attain the level of a superstition as it currently stands. Special relativity says no velocities greater than c, and this agrees with all prior observations, and has been tested to near absolute certainty. Extraordinary claims to the contrary would require extraordinary evidence.
There's a word for such ideas, and it isn't 'science'. No, not that one. It's observational astronomy only until someone figures out exactly what any remaining valid observations of DE really exist and/or mean.
And I believe I already have, in another thread. Conservation of angular momentum isn't limited to the scale of galaxies and below. You would see such rotation as Doppler shifts too. It's already there on the CMBR if you know what you are looking for. One hot and one cold spot per hemisphere is evidence enough to conclude that there is toroidal rotation on the largest observable scale. Cut a cross section in a rotating (about the axis passing through the donut hole) torus, and you will observe exactly one hot and one cold spot. Unless someone still believes in a flat Earth that is the center of the universe, that is.
There's a word for such ideas, and it isn't 'science'. No, not that one. It's observational astronomy only until someone figures out exactly what any remaining valid observations of DE really exist and/or mean.
And I believe I already have, in another thread. Conservation of angular momentum isn't limited to the scale of galaxies and below. You would see such rotation as Doppler shifts too. It's already there on the CMBR if you know what you are looking for. One hot and one cold spot per hemisphere is evidence enough to conclude that there is toroidal rotation on the largest observable scale. Cut a cross section in a rotating (about the axis passing through the donut hole) torus, and you will observe exactly one hot and one cold spot. Unless someone still believes in a flat Earth that is the center of the universe, that is.
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Sean Carroll:
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
extract:
"But many people have just this reaction. It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity. (With caveats to be explained below.)
The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.
It’s not that all hell has broken loose; it’s just that we’re considering a more general context than was necessary under Newtonian rules. There is still a single important equation, which is indeed often called “energy-momentum conservation.” It looks like this:
The details aren’t important, but the meaning of this equation is straightforward enough: energy and momentum evolve in a precisely specified way in response to the behavior of spacetime around them. If that spacetime is standing completely still, the total energy is constant; if it’s evolving, the energy changes in a completely unambiguous way.
In the case of dark energy, that evolution is pretty simple: the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space (comoving along with galaxies and other particles) grows as the universe expands. So the total energy, density times volume, goes up.
This bothers some people, but it’s nothing newfangled that has been pushed in our face by the idea of dark energy. It’s just as true for “radiation” — particles like photons that move at or near the speed of light. The thing about photons is that they redshift, losing energy as space expands. If we keep track of a certain fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy decreases. A decrease in energy is just as much a “violation of energy conservation” as an increase in energy, but it doesn’t seem to bother people as much. At the end of the day it doesn’t matter how bothersome it is, of course — it’s a crystal-clear prediction of general relativity.
And one that has been experimentally verified! The success of Big Bang Nucleosynthesis depends on the fact that we understand how fast the universe was expanding in the first three minutes, which in turn depends on how fast the energy density is changing. And that energy density is almost all radiation, so the fact that energy is not conserved in an expanding universe is absolutely central to getting the predictions of primordial nucleosynthesis correct. (Some of us have even explored the very tight constraints on other possibilities.)
Having said all that, it would be irresponsible of me not to mention that plenty of experts in cosmology or GR would not put it in these terms. We all agree on the science; there are just divergent views on what words to attach to the science. In particular, a lot of folks would want to say “energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.” Which seems pretty sensible at face value.
There’s nothing incorrect about that way of thinking about it; it’s a choice that one can make or not, as long as you’re clear on what your definitions are. I personally think it’s better to forget about the so-called “energy of the gravitational field” and just admit that energy is not conserved, for two reasons.
First, unlike with ordinary matter fields, there is no such thing as the density of gravitational energy. The thing you would like to define as the energy associated with the curvature of spacetime is not uniquely defined at every point in space. So the best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece. (You can sometimes talk approximately about the energy of different pieces, by imagining that they are isolated from the rest of the universe.) Even if you can define such a quantity, it’s much less useful than the notion of energy we have for matter fields.
The second reason is that the entire point of this exercise is to explain what’s going on in GR to people who aren’t familiar with the mathematical details of the theory. All of the experts agree on what’s happening; this is an issue of translation, not of physics. And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down. Whereas if you say “in general relativity spacetime can give energy to matter, or absorb it from matter, so that the total energy simply isn’t conserved,” they might be surprised but I think most people do actually gain some understanding thereby.
Energy isn’t conserved; it changes because spacetime does. See, that wasn’t so hard, was it?
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https://blogs.scientificamerican.co...-haven-t-decided-dark-energy-is-nonexistent/#
No, Astronomers Haven't Decided Dark Energy Is Nonexistent
You might have read otherwise in some headlines lately, but don't be misled
This week, a number of media outlets have put out headlines like "The universe is expanding at an accelerating rate, or is it?” and “The Universe Is Expanding But Not At An Accelerating Rate New Research Debunks Nobel Prize Theory.” This excitement is due to a paper just published in Nature’s Scientific Reportscalled "Marginal evidence for cosmic acceleration from Type Ia supernovae,” by Nielsen, Guffanti and Sarkar.
Once you read the article, however, it’s safe to say there is no need to revise our present understanding of the universe. All the paper does is slightlyreduce our certainty in what we know—and then only by discarding most of the cosmological data on which our understanding is based. It also ignores important details in the data it does consider. And even if you leave aside these issues, the headlines are wrong anyway. The study concluded that we’re now only 99.7 percent sure that the universe is accelerating, which is hardly the same as “it’s not accelerating.”
The initial discovery that the universe is expanding at an accelerating rate was made by two teams of astronomers in 1998 using Type Ia Supernovae as cosmic measuring tools. Supernovae—exploding stars—are some of the most powerful blasts in the entire cosmos, roughly equivalent to a billion-billion-billion atomic bombs exploding at once. Type Ia’s are a special kind of supernova in that, unlike other supernovae, they all explode with just about the same luminosity every time likely due to a critical mass limit. This similarity means that the differences in their observed brightness are almost entirely based on how far away they are. This makes them ideal for measuring cosmic distances. Furthermore, these objects are relatively common, and they are so bright that we can see them billions of light years away. This shows us how the universe appeared billions of years ago, which we can compare to how it looks today.
These supernovae are often called “standard candles” for their consistency, but they’re more accurately “standardizable candles,” because in practice, their precision and accuracy can be improved still further by accounting for small differences in their explosions by observing how long the explosion takes to unfold and how the color of the supernovae are reddened by dust between them and us. Finding a way to do these corrections robustly was what led to the discovery of the accelerating universe. .
The recent paper that has generated headlines used a catalog of Type Ia supernovae collected by the community (including us) which has been analyzed numerous times before. But the authors used a different method of implementing the corrections—and we believe this undercuts the accuracy of their results. They assume that the mean properties of supernovae from each of the samples used to measure the expansion history are the same, even though they have been shown to be different and past analyses have accounted for these differences. However, even ignoring these differences, the authors still find that there is roughly a 99.7 percent chance that the universe is accelerating—very different from what the headlines suggest.
THE COSMIC MICROWAVE BACKGROUND RADIATION, EMITTED A FEW HUNDRED THOUSAND YEARS AFTER THE BIG BANG, PROVIDES AN INDEPENDENT LINE OF EVIDENCE FOR THE ACCELERATING UNIVERSE. CREDIT: NASA/WMAP SCIENCE TEAM VIA WIKIMEDIA COMMONS
Furthermore, the overwhelming confidence astronomers have that the universe is expanding faster now than it was billions of years ago is based on much more than just supernova measurements. These include tiny fluctuations in the pattern of relic heat after the Big Bang (i.e., the cosmic microwave background) and the modern day imprint of those fluctuations in the distribution of galaxies around us (called baryon acoustic oscillations). The present study also ignores the presence of a substantial amount of matter in the Universe, confirmed numerous times and ways since the 1970’s, further reducing the study confidence. These other data show the universe to be accelerating independently from supernovae. If we combine the other observations with the supernova data, we go from 99.99 percent sure to 99.99999 percent sure. That’s pretty sure!
We now know that dark energy, which is what we believe causes the expansion of the universe to accelerate, makes up 70 percent of the universe, with matter constituting the rest. The nature of dark energy is still one of the largest mysteries of all of astrophysics. But there has been no active debate about whether dark energy exists and none about whether the universe is accelerating since this picture was cemented a decade ago.
There are now many new large surveys, both on the ground and in space, whose top priority over the next two decades is to figure out exactly what this dark energy could be. For now, we have to continue to improve our measurements and question our assumptions. While this recent paper does not disprove any theories, it is still good for everyone to pause for a second and remember how big the questions are that we are asking, how we reached the conclusions we have to date and how seriously we need to test each building block of our understanding.
No, Astronomers Haven't Decided Dark Energy Is Nonexistent
You might have read otherwise in some headlines lately, but don't be misled
This week, a number of media outlets have put out headlines like "The universe is expanding at an accelerating rate, or is it?” and “The Universe Is Expanding But Not At An Accelerating Rate New Research Debunks Nobel Prize Theory.” This excitement is due to a paper just published in Nature’s Scientific Reportscalled "Marginal evidence for cosmic acceleration from Type Ia supernovae,” by Nielsen, Guffanti and Sarkar.
Once you read the article, however, it’s safe to say there is no need to revise our present understanding of the universe. All the paper does is slightlyreduce our certainty in what we know—and then only by discarding most of the cosmological data on which our understanding is based. It also ignores important details in the data it does consider. And even if you leave aside these issues, the headlines are wrong anyway. The study concluded that we’re now only 99.7 percent sure that the universe is accelerating, which is hardly the same as “it’s not accelerating.”
The initial discovery that the universe is expanding at an accelerating rate was made by two teams of astronomers in 1998 using Type Ia Supernovae as cosmic measuring tools. Supernovae—exploding stars—are some of the most powerful blasts in the entire cosmos, roughly equivalent to a billion-billion-billion atomic bombs exploding at once. Type Ia’s are a special kind of supernova in that, unlike other supernovae, they all explode with just about the same luminosity every time likely due to a critical mass limit. This similarity means that the differences in their observed brightness are almost entirely based on how far away they are. This makes them ideal for measuring cosmic distances. Furthermore, these objects are relatively common, and they are so bright that we can see them billions of light years away. This shows us how the universe appeared billions of years ago, which we can compare to how it looks today.
These supernovae are often called “standard candles” for their consistency, but they’re more accurately “standardizable candles,” because in practice, their precision and accuracy can be improved still further by accounting for small differences in their explosions by observing how long the explosion takes to unfold and how the color of the supernovae are reddened by dust between them and us. Finding a way to do these corrections robustly was what led to the discovery of the accelerating universe. .
The recent paper that has generated headlines used a catalog of Type Ia supernovae collected by the community (including us) which has been analyzed numerous times before. But the authors used a different method of implementing the corrections—and we believe this undercuts the accuracy of their results. They assume that the mean properties of supernovae from each of the samples used to measure the expansion history are the same, even though they have been shown to be different and past analyses have accounted for these differences. However, even ignoring these differences, the authors still find that there is roughly a 99.7 percent chance that the universe is accelerating—very different from what the headlines suggest.
THE COSMIC MICROWAVE BACKGROUND RADIATION, EMITTED A FEW HUNDRED THOUSAND YEARS AFTER THE BIG BANG, PROVIDES AN INDEPENDENT LINE OF EVIDENCE FOR THE ACCELERATING UNIVERSE. CREDIT: NASA/WMAP SCIENCE TEAM VIA WIKIMEDIA COMMONS
Furthermore, the overwhelming confidence astronomers have that the universe is expanding faster now than it was billions of years ago is based on much more than just supernova measurements. These include tiny fluctuations in the pattern of relic heat after the Big Bang (i.e., the cosmic microwave background) and the modern day imprint of those fluctuations in the distribution of galaxies around us (called baryon acoustic oscillations). The present study also ignores the presence of a substantial amount of matter in the Universe, confirmed numerous times and ways since the 1970’s, further reducing the study confidence. These other data show the universe to be accelerating independently from supernovae. If we combine the other observations with the supernova data, we go from 99.99 percent sure to 99.99999 percent sure. That’s pretty sure!
We now know that dark energy, which is what we believe causes the expansion of the universe to accelerate, makes up 70 percent of the universe, with matter constituting the rest. The nature of dark energy is still one of the largest mysteries of all of astrophysics. But there has been no active debate about whether dark energy exists and none about whether the universe is accelerating since this picture was cemented a decade ago.
There are now many new large surveys, both on the ground and in space, whose top priority over the next two decades is to figure out exactly what this dark energy could be. For now, we have to continue to improve our measurements and question our assumptions. While this recent paper does not disprove any theories, it is still good for everyone to pause for a second and remember how big the questions are that we are asking, how we reached the conclusions we have to date and how seriously we need to test each building block of our understanding.
http://www.forbes.com/sites/startsw...s-the-universe-not-accelerating/#6186951367ca
n 1998, the two leading independent collaborations working to measure distant supernovae in the Universe reported the same bizarre findings: they seemed to indicate that the Universe was accelerating. The only way to explain how distant these lights appeared was if the fabric of space was expanding at a rate that wasn’t decreasing like we’d expect, and if the most distant galaxies were receding faster and faster, despite the pull of gravity. Over the next 13 years, the evidence grew stronger and stronger for this picture, and in 2011 three pioneers in the field were awarded the Nobel Prize. And then, just last week, a new study came out alleging that the supernova evidence for this picture was marginal at best. The study concludes that perhaps the Universe hasn’t been accelerating, after all.
But is that fair and correct? Certainly the news reports are claiming it is, but what does the science say? Let’s start with what the supernova data is, and what it’s told us so far.
more at link
n 1998, the two leading independent collaborations working to measure distant supernovae in the Universe reported the same bizarre findings: they seemed to indicate that the Universe was accelerating. The only way to explain how distant these lights appeared was if the fabric of space was expanding at a rate that wasn’t decreasing like we’d expect, and if the most distant galaxies were receding faster and faster, despite the pull of gravity. Over the next 13 years, the evidence grew stronger and stronger for this picture, and in 2011 three pioneers in the field were awarded the Nobel Prize. And then, just last week, a new study came out alleging that the supernova evidence for this picture was marginal at best. The study concludes that perhaps the Universe hasn’t been accelerating, after all.
But is that fair and correct? Certainly the news reports are claiming it is, but what does the science say? Let’s start with what the supernova data is, and what it’s told us so far.
more at link
from the previous link
extract:
Measuring back in time and distance (to the left of “today”) can inform how the Universe will evolve and accelerate/decelerate far into the future. Image credit: Saul Perlmutter of Berkeley, via http://newscenter.lbl.gov/2009/10/27/evolving-dark-energy/.
Oftentimes, it takes fresh eyes to approach a problem differently from how everyone else is approaching it. In their Scientific Reportspaper out just a few days ago, scientists Nielsen, Guffanti and Sarkar — all of whom don’t specialize in supernova studies – did exactly that. Here’s what their results indicate.
The figure representing the confidence in accelerated expansion and in the measurement of dark energy (y-axis) and matter (x-axis) from supernovae alone. Image credit: Nielsen, Guffanti and Sarkar, 2016, from the preprint at https://arxiv.org/pdf/1506.01354v3.pdf.
Even if all of the supernova data were thrown out and ignored, we have more than enough evidence at present to be extremely confident that the Universe is accelerating, and made of about 2/3 dark energy.
The supernova data from the sample used in Nielsen, Guffati and Sarkar cannot distinguish at 5-sigma between an empty Universe (green) and the standard, accelerating Universe (purple), but other sources of information matter as well. Image credit: Ned Wright, based on the latest data from Betoule et al. (2014), via http://www.astro.ucla.edu/~wright/sne_cosmology.html.
extract:
Measuring back in time and distance (to the left of “today”) can inform how the Universe will evolve and accelerate/decelerate far into the future. Image credit: Saul Perlmutter of Berkeley, via http://newscenter.lbl.gov/2009/10/27/evolving-dark-energy/.
Oftentimes, it takes fresh eyes to approach a problem differently from how everyone else is approaching it. In their Scientific Reportspaper out just a few days ago, scientists Nielsen, Guffanti and Sarkar — all of whom don’t specialize in supernova studies – did exactly that. Here’s what their results indicate.
The figure representing the confidence in accelerated expansion and in the measurement of dark energy (y-axis) and matter (x-axis) from supernovae alone. Image credit: Nielsen, Guffanti and Sarkar, 2016, from the preprint at https://arxiv.org/pdf/1506.01354v3.pdf.
Even if all of the supernova data were thrown out and ignored, we have more than enough evidence at present to be extremely confident that the Universe is accelerating, and made of about 2/3 dark energy.
The supernova data from the sample used in Nielsen, Guffati and Sarkar cannot distinguish at 5-sigma between an empty Universe (green) and the standard, accelerating Universe (purple), but other sources of information matter as well. Image credit: Ned Wright, based on the latest data from Betoule et al. (2014), via http://www.astro.ucla.edu/~wright/sne_cosmology.html.
danshawen
Valued Senior Member
Sean Carroll:
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
extract:
"But many people have just this reaction. It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity. (With caveats to be explained below.)
The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.
It’s not that all hell has broken loose; it’s just that we’re considering a more general context than was necessary under Newtonian rules. There is still a single important equation, which is indeed often called “energy-momentum conservation.” It looks like this:
The details aren’t important, but the meaning of this equation is straightforward enough: energy and momentum evolve in a precisely specified way in response to the behavior of spacetime around them. If that spacetime is standing completely still, the total energy is constant; if it’s evolving, the energy changes in a completely unambiguous way.
In the case of dark energy, that evolution is pretty simple: the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space (comoving along with galaxies and other particles) grows as the universe expands. So the total energy, density times volume, goes up.
This bothers some people, but it’s nothing newfangled that has been pushed in our face by the idea of dark energy. It’s just as true for “radiation” — particles like photons that move at or near the speed of light. The thing about photons is that they redshift, losing energy as space expands. If we keep track of a certain fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy decreases. A decrease in energy is just as much a “violation of energy conservation” as an increase in energy, but it doesn’t seem to bother people as much. At the end of the day it doesn’t matter how bothersome it is, of course — it’s a crystal-clear prediction of general relativity.
And one that has been experimentally verified! The success of Big Bang Nucleosynthesis depends on the fact that we understand how fast the universe was expanding in the first three minutes, which in turn depends on how fast the energy density is changing. And that energy density is almost all radiation, so the fact that energy is not conserved in an expanding universe is absolutely central to getting the predictions of primordial nucleosynthesis correct. (Some of us have even explored the very tight constraints on other possibilities.)
Having said all that, it would be irresponsible of me not to mention that plenty of experts in cosmology or GR would not put it in these terms. We all agree on the science; there are just divergent views on what words to attach to the science. In particular, a lot of folks would want to say “energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.” Which seems pretty sensible at face value.
There’s nothing incorrect about that way of thinking about it; it’s a choice that one can make or not, as long as you’re clear on what your definitions are. I personally think it’s better to forget about the so-called “energy of the gravitational field” and just admit that energy is not conserved, for two reasons.
First, unlike with ordinary matter fields, there is no such thing as the density of gravitational energy. The thing you would like to define as the energy associated with the curvature of spacetime is not uniquely defined at every point in space. So the best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece. (You can sometimes talk approximately about the energy of different pieces, by imagining that they are isolated from the rest of the universe.) Even if you can define such a quantity, it’s much less useful than the notion of energy we have for matter fields.
The second reason is that the entire point of this exercise is to explain what’s going on in GR to people who aren’t familiar with the mathematical details of the theory. All of the experts agree on what’s happening; this is an issue of translation, not of physics. And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down. Whereas if you say “in general relativity spacetime can give energy to matter, or absorb it from matter, so that the total energy simply isn’t conserved,” they might be surprised but I think most people do actually gain some understanding thereby.
Energy isn’t conserved; it changes because spacetime does. See, that wasn’t so hard, was it?
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Carroll has a good eye for a significant equation, but the passage you quoted turned me off when I realized he was recycling and peddling the defunct "tired photon" theory.
I spent about a year keeping up with the goings on in his "Preposterous Universe" before deciding that it was too preposterous. Carroll digresses into philosophy a little too often to my taste, and his debates with YECs like William Craig Lane just leave both sides wondering which one really knows what he is talking about. I'm on Carroll's side of course, but resorting to philosophical arguments is usually less than convincing either way,
Sure, many against the accepted conclusions of physics and cosmology were based on poor reasoning and philosophical arguments address the quality of reasoning. Why should we use good tools to address the appropriate problem?
http://phys.org/news/2016-10-expansion-universe.html
Relax, the expansion of the universe is still accelerating
October 28, 2016 by Tamara Davis, The Conversation
extract:
So why does this new paper claim that the detection of acceleration is "marginal?"
Well, it is marginal if you only use a single data set. After all, most big discoveries are initially marginal. If they were more obvious, they would have been discovered sooner.
The evidence, so far
The supernova data alone could, at only a slight stretch, be consistent with a universe that neither accelerates nor decelerates. This has been known since the original discovery, and is not under dispute.
But if you also add one more piece of information - for example, that matter exists - then there's nothing marginal about it. New physics is clearly required.
In fact, if the universe didn't accelerate or decelerate at all, which is an old proposal revisited in this new paper, new physics would still be required.
These days the important point is that if you take all of the supernova data and throw it in the bin, we still have ample evidence that the universe's expansion accelerates.
For example, in Australia we did a project called WiggleZ, which over five years made a survey of the positions of almost a quarter of a million galaxies.
The pattern of galaxies isn't actually random, so we used this pattern to effectively lay grid paper over the universe and measure how its size changes with time.
Using this data alone shows the expanding universe is accelerating, and it is independent of any supernova information. The Nobel Prize was awarded only after this and many other observational techniques confirmed the supernova findings.
So the evidence for some interesting new physics is now overwhelming.
I could go on, but everything we know so far supports the model in which the universe accelerates. For more detail see this review I wrote about the evidence for dark energy.
Read more at: http://phys.org/news/2016-10-expansion-universe.html#jCp
Relax, the expansion of the universe is still accelerating
October 28, 2016 by Tamara Davis, The Conversation
extract:
So why does this new paper claim that the detection of acceleration is "marginal?"
Well, it is marginal if you only use a single data set. After all, most big discoveries are initially marginal. If they were more obvious, they would have been discovered sooner.
The evidence, so far
The supernova data alone could, at only a slight stretch, be consistent with a universe that neither accelerates nor decelerates. This has been known since the original discovery, and is not under dispute.
But if you also add one more piece of information - for example, that matter exists - then there's nothing marginal about it. New physics is clearly required.
In fact, if the universe didn't accelerate or decelerate at all, which is an old proposal revisited in this new paper, new physics would still be required.
These days the important point is that if you take all of the supernova data and throw it in the bin, we still have ample evidence that the universe's expansion accelerates.
For example, in Australia we did a project called WiggleZ, which over five years made a survey of the positions of almost a quarter of a million galaxies.
The pattern of galaxies isn't actually random, so we used this pattern to effectively lay grid paper over the universe and measure how its size changes with time.
Using this data alone shows the expanding universe is accelerating, and it is independent of any supernova information. The Nobel Prize was awarded only after this and many other observational techniques confirmed the supernova findings.
So the evidence for some interesting new physics is now overwhelming.
I could go on, but everything we know so far supports the model in which the universe accelerates. For more detail see this review I wrote about the evidence for dark energy.
Read more at: http://phys.org/news/2016-10-expansion-universe.html#jCp
When did you evidently do a 180 and embrace Carroll's position? Yesterday, last week, when? Given you have been a long time numerous cut & paste supporter of the opposing camp's zero-energy universe notion. Championed by the likes of Lawrence Krauss "A Universe from Nothing" 'fame'.Sean Carroll:
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
extract:
"But many people have just this reaction. It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920’s: energy is not conserved in general relativity. (With caveats to be explained below.)
The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.
It’s not that all hell has broken loose; it’s just that we’re considering a more general context than was necessary under Newtonian rules. There is still a single important equation, which is indeed often called “energy-momentum conservation.” It looks like this:
The details aren’t important, but the meaning of this equation is straightforward enough: energy and momentum evolve in a precisely specified way in response to the behavior of spacetime around them. If that spacetime is standing completely still, the total energy is constant; if it’s evolving, the energy changes in a completely unambiguous way.
In the case of dark energy, that evolution is pretty simple: the density of vacuum energy in empty space is absolute constant, even as the volume of a region of space (comoving along with galaxies and other particles) grows as the universe expands. So the total energy, density times volume, goes up.
This bothers some people, but it’s nothing newfangled that has been pushed in our face by the idea of dark energy. It’s just as true for “radiation” — particles like photons that move at or near the speed of light. The thing about photons is that they redshift, losing energy as space expands. If we keep track of a certain fixed number of photons, the number stays constant while the energy per photon decreases, so the total energy decreases. A decrease in energy is just as much a “violation of energy conservation” as an increase in energy, but it doesn’t seem to bother people as much. At the end of the day it doesn’t matter how bothersome it is, of course — it’s a crystal-clear prediction of general relativity.
And one that has been experimentally verified! The success of Big Bang Nucleosynthesis depends on the fact that we understand how fast the universe was expanding in the first three minutes, which in turn depends on how fast the energy density is changing. And that energy density is almost all radiation, so the fact that energy is not conserved in an expanding universe is absolutely central to getting the predictions of primordial nucleosynthesis correct. (Some of us have even explored the very tight constraints on other possibilities.)
Having said all that, it would be irresponsible of me not to mention that plenty of experts in cosmology or GR would not put it in these terms. We all agree on the science; there are just divergent views on what words to attach to the science. In particular, a lot of folks would want to say “energy is conserved in general relativity, it’s just that you have to include the energy of the gravitational field along with the energy of matter and radiation and so on.” Which seems pretty sensible at face value.
There’s nothing incorrect about that way of thinking about it; it’s a choice that one can make or not, as long as you’re clear on what your definitions are. I personally think it’s better to forget about the so-called “energy of the gravitational field” and just admit that energy is not conserved, for two reasons.
First, unlike with ordinary matter fields, there is no such thing as the density of gravitational energy. The thing you would like to define as the energy associated with the curvature of spacetime is not uniquely defined at every point in space. So the best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece. (You can sometimes talk approximately about the energy of different pieces, by imagining that they are isolated from the rest of the universe.) Even if you can define such a quantity, it’s much less useful than the notion of energy we have for matter fields.
The second reason is that the entire point of this exercise is to explain what’s going on in GR to people who aren’t familiar with the mathematical details of the theory. All of the experts agree on what’s happening; this is an issue of translation, not of physics. And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down. Whereas if you say “in general relativity spacetime can give energy to matter, or absorb it from matter, so that the total energy simply isn’t conserved,” they might be surprised but I think most people do actually gain some understanding thereby.
Energy isn’t conserved; it changes because spacetime does. See, that wasn’t so hard, was it?
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You are confused q-reeus. I have quoted and linked to many articles from Professor Carroll, particularly his view/s on time and space. So, no, no sudden embrace at all.
My cut n pastes of reputable material is from many reliable, sources, and will certainly continue when and if I see fit to raise them. Thank you for your approval.