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  1. #1 Dark Energy 
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    "Dark Energy" is what scientists are calling the mysterious, unexplained force that is causing the expansion of the universe to accelerate. Without it, the expansion of the universe would slow down until it ultimately began to shrink back toward the center. In this scenario, the universe would end in a "big crunch".

    We literally know nothing about dark energy. What is pulling the universe apart? Any ideas?


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    Quote Originally Posted by Chimoshi View Post
    "Dark Energy" is what scientists are calling the mysterious, unexplained force that is causing the expansion of the universe to accelerate. Without it, the expansion of the universe would slow down until it ultimately began to shrink back toward the center. In this scenario, the universe would end in a "big crunch".

    We literally know nothing about dark energy. What is pulling the universe apart? Any ideas?
    It certainly makes you think. I can't imagine it is due to anything pulling on the galaxies.


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    Forum Radioactive Isotope cosmictraveler's Avatar
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    Could it be that there isn't enough gravity to keep the galaxies closing in on themselves and they keep expanding due to the force of the big bang ?
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    Quote Originally Posted by cosmictraveler View Post
    Could it be that there isn't enough gravity to keep the galaxies closing in on themselves and they keep expanding due to the force of the big bang ?
    That doesn't explain why the expansion of the Universe appears to be increasing in speed, though.
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    Is it possible that dark matter is expanding space due to the heat of stars?

    Could it be that the universe is (almost imperceptibly) 'heating up'?
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    No, the average distance between stars is far too large for any appreciable heating of interstellar space.
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    Quote Originally Posted by citizen James5218 View Post
    Is it possible that dark matter is expanding space due to the heat of stars?

    Could it be that the universe is (almost imperceptibly) 'heating up'?
    On the contrary, the Universe was a lot hotter and denser in the past, it's actually cooling down.
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  9. #8  
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    Quote Originally Posted by Daecon View Post
    Quote Originally Posted by cosmictraveler View Post
    Could it be that there isn't enough gravity to keep the galaxies closing in on themselves and they keep expanding due to the force of the big bang ?
    That doesn't explain why the expansion of the Universe appears to be increasing in speed, though.
    As the galaxies are expanding away from each other there's less resistance to keep them close so they are moving away faster due to less gravity near them.
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    That doesn't work, a force getting weaker cannot cause an increase in velocity just a decrease in deceleration they are not the same..
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  11. #10  
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    Quote Originally Posted by cosmictraveler View Post
    Quote Originally Posted by Daecon View Post
    Quote Originally Posted by cosmictraveler View Post
    Could it be that there isn't enough gravity to keep the galaxies closing in on themselves and they keep expanding due to the force of the big bang ?
    That doesn't explain why the expansion of the Universe appears to be increasing in speed, though.
    As the galaxies are expanding away from each other there's less resistance to keep them close so they are moving away faster due to less gravity near them.
    That would just result in a lessening of the deceleration.

    Without DE, there are two possibilities:
    1. The mutual gravitational attraction strong enough to eventually halt the expansion and cause a collapse.
    2. It is not strong enough to ever halt the expansion. The weakening gravity from the increasing distances never quite is enough to get rid of the last bit of expansion. The rate of expansion still decreases with time, just never to zero.

    What we see instead is an acceleration of the expansion.

    Its the difference between applying the brakes to a coasting car so that it comes to a stop, slowly letting up on the brake as you slow so that you never actually stop (ignoring all other friction), and stepping on the gas.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
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    I perceived the question which may not have been asked directly, but implied; What is driving the accelerating expansion observed ?
    Let there be no doubt it is observed and tested. The observable Universe is expanding at a accelerating rate. The answer is...
    ~ We do not know. ~ Is it being pulled or released ? Why is it speeding up ?
    Dark Energy is the term given to what we do not understand., and to be clear, we do not understand yet.
    A unpopular view is that the observation of accelerating expansion is a mistake. Regardless of that argument we still do NOT know why or even how. That the answer is awaiting we trust.. or will we ever know ?
    At this point I can tell you I trust the expansion observed is real, and still called DARK because we do not know the answers yet. There seems to be ' A force being applied to cause the universe to be increasing it's expansion exponentially...
    ~ Hmm.. ( was that the right word )..
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    I think this phenomenon is likely due to some substantial, unrecognized flaw in our model of the universe. Perhaps gravity doesn't work quite the way we think it does, and the discrepancy only shows up on very large distance scales. Perhaps there is some fifth fundamental force we have so far failed to recognize. Perhaps there is some mechanism that affects photons that have traveled long distances or existed for long periods of time that causes our suppositions about the position and velocity of the objects that emit those photons to be wrong, and the universe isn't expanding at an accelerating rate but merely appears to be doing so. Whatever the flaw is, I look forward to someone figuring it out and expanding our understanding of the universe. Resolving this mystery will probably just raise different but equally interesting questions.
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    I watched a science program some time ago that talked about virtual particle pairs of particle and antiparticle that annihilate each other almost as fast as they appeared. They claimed this interaction of virtual particles makes up the fabric of our spacetime. I don't know, it all sounds pretty far out to me. But if it is true, it makes sense that even a very small increase in virtual particle activity would cause our space to expand in the way that our scientists tell us it is expanding.

    Quantum fluctuation - Wikipedia, the free encyclopedia
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    i think the real question should be, in what direction we gonna take off.
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    Quote Originally Posted by astromark View Post
    I perceived the question which may not have been asked directly, but implied; What is driving the accelerating expansion observed ?
    Let there be no doubt it is observed and tested. The observable Universe is expanding at a accelerating rate. The answer is...
    ~ We do not know. ~ Is it being pulled or released ? Why is it speeding up ?
    Dark Energy is the term given to what we do not understand., and to be clear, we do not understand yet.
    A unpopular view is that the observation of accelerating expansion is a mistake. Regardless of that argument we still do NOT know why or even how. That the answer is awaiting we trust.. or will we ever know ?
    At this point I can tell you I trust the expansion observed is real, and still called DARK because we do not know the answers yet. There seems to be ' A force being applied to cause the universe to be increasing it's expansion exponentially...
    ~ Hmm.. ( was that the right word )..
    Hi all.

    (my bolded) In simple laymans terms, can you please explain briefly how ?
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    Quote Originally Posted by marcbo View Post
    Quote Originally Posted by astromark View Post
    I perceived the question which may not have been asked directly, but implied; What is driving the accelerating expansion observed ?
    Let there be no doubt it is observed and tested. The observable Universe is expanding at a accelerating rate. The answer is...
    ~ We do not know. ~ Is it being pulled or released ? Why is it speeding up ?
    Dark Energy is the term given to what we do not understand., and to be clear, we do not understand yet.
    A unpopular view is that the observation of accelerating expansion is a mistake. Regardless of that argument we still do NOT know why or even how. That the answer is awaiting we trust.. or will we ever know ?
    At this point I can tell you I trust the expansion observed is real, and still called DARK because we do not know the answers yet. There seems to be ' A force being applied to cause the universe to be increasing it's expansion exponentially...
    ~ Hmm.. ( was that the right word )..
    Hi all.

    (my bolded) In simple laymans terms, can you please explain briefly how ?
    Assuming you mean how about the bolded part, the person who said that should be the one to answer you.
    While it may be correct, I have found that many times people have no doubt about things that are later proven untrue.
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    Quote Originally Posted by Mayflow View Post
    Quote Originally Posted by marcbo View Post
    Quote Originally Posted by astromark View Post
    I perceived the question which may not have been asked directly, but implied; What is driving the accelerating expansion observed ?
    Let there be no doubt it is observed and tested. The observable Universe is expanding at a accelerating rate. The answer is...
    ~ We do not know. ~ Is it being pulled or released ? Why is it speeding up ?
    Dark Energy is the term given to what we do not understand., and to be clear, we do not understand yet.
    A unpopular view is that the observation of accelerating expansion is a mistake. Regardless of that argument we still do NOT know why or even how. That the answer is awaiting we trust.. or will we ever know ?
    At this point I can tell you I trust the expansion observed is real, and still called DARK because we do not know the answers yet. There seems to be ' A force being applied to cause the universe to be increasing it's expansion exponentially...
    ~ Hmm.. ( was that the right word )..
    Hi all.

    (my bolded) In simple laymans terms, can you please explain briefly how ?
    Assuming you mean how about the bolded part, the person who said that should be the one to answer you.
    While it may be correct, I have found that many times people have no doubt about things that are later proven untrue.
    Yes, to both sentences.

    Edit, OOPS, Hi Mayflow. Thanks for the comment.
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    ~ So I return to attempt a answer in a way that can be understood.. I am sorry my answer seemed not complete.
    I shall ask for greater minds than mine to swing into this with a wisdom I lac.. Astronomers while observing the distant galaxies noted a receding action was apparent. That the more distant, the greater the velocity. In the study of neutron stars and pulsars it was found a standard brightness because of the size and content of mass were all the same.. and no. No suggestion is made that all are the same.. It's just that when a star of the mass required to become a neutron star has a nova event.. the are of equal brightness.. I ask for other than my explanation may be required.. Much study of distant nova events confirmed this as a rule we can trust. So from this came the 'standard candle' of a rotating neutron star, and a observation of the greater the distance so to the greater the recession velocity.. was made.. This has been confirmed by many such observations.. by astronomers more numerous and wiser than 'me'. and that 'I' will venture to add that as I claim to be driven by the scientific principal.. I will throw this whole idea away if information is presented to convince the science community of such.. and that 'science' being the ONLY rule I will not sway from. I hope not to have added to the confusion.
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  20. #19  
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    I'm going to clarify and expand on Astromark's answer:

    As he noted, Astronomers had determined a relationship between the distance of galaxies and how fast they are receding from us. This was first noted in the early 20th century. The relationship was very close to to being 1 to 1 (if a galaxy was twice as far away, it was receding twice as fast.)

    It was not expected to be exactly 1 to1, because this would represent a constant speed of expansion, and since the mutual gravitational attraction of the universe would work against the expansion, it was expected that it would slow the expansion over time. Since as we look out at further and further galaxies we are seeing them as they were further and further in the past, any change in the rate of expansion would show up as a variance form that exact 1 to 1 relationship.

    For a long time, it was not known if the mass of the universe was enough to stop the expansion completely or not. If it wasn't, the universe's expansion would continue to expand, just at a slower and slower rate.

    We could measure the recession speed quite accurately. What was needed was a accurate way to measure distance. Luckily, such a method was found. It came in the form of IA supernovae. This is a particular type of supernova that is triggered when a white dwarf star orbiting a larger star bleeds material from the larger star. As the material accumulates on the white dwarf it increases it mass. When the mass reaches a certain point, it triggers an explosive fusion reaction in the star causing it to nova. Since the trigger mass is a set point, All type 1A super novae have the same peak brightness. Thus by knowing how bright one appears to us, we can tell how far away it was. In addition, type 1A supernovae occur in all types of galaxies and are bright enough to be detected at intergalactic distances. The type 1A supernova was a standard candle by which distance to distance galaxies could be accurately measured.

    In 1998, at team of researchers used this standard candle to plot distance vs recession speed to determine how the expansion of the universe has changed over time. They hoped to answer the question as to whether the expansion was slowing fast enough to ever come to a stop and then re-collapse. They found the exact opposite of what they expected. The distance vs recession plot did veer away from the straight 1 to 1 relationship, but in the other direction! Instead of slowing down over time, the observations showed that the universe has been speeding up. The observations have been independently confirmed. The observations are not in doubt, "Dark energy" is just the place-holder term for whatever is the cause. (In much the same way we got the terms "X-ray" or "cathode ray tube". With X-rays, the X just stood for "unknown", and before it was determined that the cathode was emitting particles in the form of electrons, we just called them cathode rays, and we still use the term CRT.)
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    Quote Originally Posted by Janus View Post
    I'm going to clarify and expand on Astromark's answer:

    As he noted, Astronomers had determined a relationship between the distance of galaxies and how fast they are receding from us. This was first noted in the early 20th century. The relationship was very close to to being 1 to 1 (if a galaxy was twice as far away, it was receding twice as fast.)

    It was not expected to be exactly 1 to1, because this would represent a constant speed of expansion, and since the mutual gravitational attraction of the universe would work against the expansion, it was expected that it would slow the expansion over time. Since as we look out at further and further galaxies we are seeing them as they were further and further in the past, any change in the rate of expansion would show up as a variance form that exact 1 to 1 relationship.

    For a long time, it was not known if the mass of the universe was enough to stop the expansion completely or not. If it wasn't, the universe's expansion would continue to expand, just at a slower and slower rate.

    We could measure the recession speed quite accurately. What was needed was a accurate way to measure distance. Luckily, such a method was found. It came in the form of IA supernovae. This is a particular type of supernova that is triggered when a white dwarf star orbiting a larger star bleeds material from the larger star. As the material accumulates on the white dwarf it increases it mass. When the mass reaches a certain point, it triggers an explosive fusion reaction in the star causing it to nova. Since the trigger mass is a set point, All type 1A super novae have the same peak brightness. Thus by knowing how bright one appears to us, we can tell how far away it was. In addition, type 1A supernovae occur in all types of galaxies and are bright enough to be detected at intergalactic distances. The type 1A supernova was a standard candle by which distance to distance galaxies could be accurately measured.

    In 1998, at team of researchers used this standard candle to plot distance vs recession speed to determine how the expansion of the universe has changed over time. They hoped to answer the question as to whether the expansion was slowing fast enough to ever come to a stop and then re-collapse. They found the exact opposite of what they expected. The distance vs recession plot did veer away from the straight 1 to 1 relationship, but in the other direction! Instead of slowing down over time, the observations showed that the universe has been speeding up. The observations have been independently confirmed. The observations are not in doubt, "Dark energy" is just the place-holder term for whatever is the cause. (In much the same way we got the terms "X-ray" or "cathode ray tube". With X-rays, the X just stood for "unknown", and before it was determined that the cathode was emitting particles in the form of electrons, we just called them cathode rays, and we still use the term CRT.)
    combined with the fact that the expansion of the universe was slowing down a few billion years ago, leaves room of my idea of a streaming universe.

    could it also be, that the cmbr only determines the line line of what we're able to observe?

    thinking it could take billion of years of observing/or working on technologies to find out, we'll prolly never find out.
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    Dark energy does not give us much to work from. All we see of it is a Universe-wide cosmological-constant-like density and pressure:
    (pressure) = - (mass density) * c2
    The minus sign is a feature, not a bug.

    Dark matter is distinct from it, and it gives some more clues, like being much of the mass of galaxies and galaxy clusters. But even that is not very helpful, though there are several attempts to observe dark matter nongravitationally, both directly and indirectly. None have unambiguously succeeded, however.

    My favorite guess is that it's some Theory of Everything field that has almost no nongravitational coupling with Standard-Model particles. Beyond that, it's likely a scalar (spin-0) field. I've seen some theories where it is dynamical, theories of "quintessence" ("fifth stuff").

    I've seen this dictionary of traditional elements to Universe constituents:

    • Earth: baryonic matter
    • Water: dark matter
    • Air: cosmic-background neutrinos
    • Fire: cosmic-background photons
    • Quintessence / aether: dark energy
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  23. #22  
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    traditional elements
    ...seriously? Please tell me you're joking...
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    It was some whimsy that I once saw.

    Baryonic matter is like earth because it is the most condensed and solid.

    Dark matter is like water because it is fluid and relatively dense.

    Neutrinos are like air because they are collectively fluid and relatively low-density.

    CMB photons are like fire because they are not only collectively fluid and relatively low-density, they are much more reactive than the other fluid components.
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  25. #24  
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    Phew, for a horrible moment I thought we had a alchemist in the forum
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    I came up with a couple theories today that might explain what "dark energy" is.

    Theory 1: If the default state of the cosmos prior to the beginning of the universe was similar to that of a black hole existing not as a singularity, but everywhere, then perhaps the universe is surrounded by a black hole like expanse. The expanse is bigger and has more gravitational pull than the black hole at the center of the universe, so the expansion of the universe accelerates.

    Theory 2: What if dark energy isn't a force at all, but an illusion caused by our perception of time. We've been thinking about it as, "why is the expansion of the universe accelerating", when in reality it could be time that's accelerating while the universe simultaneously expands.

    I apologize if these are dumb ideas. After all, I'm a Biologist, not an Astrophysicist.
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    Here's another interesting wrinkle being tied to Dark matter.

    NASA Science News for July 24, 2014

    A mysterious X-ray signal from the Perseus cluster of galaxies, which researchers say cannot be explained by known physics, could be a key clue to the nature of Dark Matter.

    FULL STORY: Mystery in the Perseus Cluster - NASA Science

    VIDEO: https://www.youtube.com/watch?v=3439YtdQZ1Y
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  28. #27 Dark Energy Theory 
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    Quote Originally Posted by Chimoshi View Post
    "Dark Energy" is what scientists are calling the mysterious, unexplained force that is causing the expansion of the universe to accelerate. Without it, the expansion of the universe would slow down until it ultimately began to shrink back toward the center. In this scenario, the universe would end in a "big crunch". We literally know nothing about dark energy. What is pulling the universe apart? Any ideas?
    Provided that Dark matter is the exact opposite to matter (I'll mention why after), can we not infer, that dark matter is container of matter. since mass attracts other forms of mass, dark matter repels (Which is what is theorized), they are opposites. If mass cannot be created nor destroyed except under special circumstances. Couldn't that mean Dark matter can be created or destroyed except under some circumstances. And that Special circumstance could be when dark matter converts into matter. Hence leading to my point that. I personally think that, this will lead to an balance between the two. Which would lead to the Dark matter expanding to a point where all the mass in the world is surrounded by Dark matter, and cause of matter's physical properties of attraction, attract the dark matter around it to form into a dense compressed ball like theorized in the original Big Bang Theory and cause the same cycle to repeat its self. Some what like happens to waves undergoing Diffraction. The wave goes around the diffracted item and conjoins at the other end. Except the item has attractive properties. so everything is pulled towards to it. Let me know, what you think of it.
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    Word salad...
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    The original energy for the expansion of the universe was supplied by the Big Bang. The expansion was slowed for the first few billion years by the gravity of dark matter, and by ordinary matter as it formed from the 5% component of energy plasma in the original explosion. A principle of the universe is that all matter, information, and energy was supplied at the time of the Big Bang, and nothing further may enter from "outside." (There is no "outside.") Therefore, the extra "dark energy" that has caused the expansion rate of the universe to increase must be supplied from within. To see the source, look at the night sky. As ordinary matter began to congeal into stars and galaxies, it began to be converted into energy, first in thermonuclear reactions, and later in supernova events. The energy spills into the universe, and is added to the residual Big Bang energy. As star formation and evolution proceeds, enough energy is inserted to cause the expansion rate to increase. This process will continue as long as there is enough ordinary matter to form stars. (Since the source of the energy is mainly from stars and supernova, a better term for "dark energy" would be "bright energy.") When the ordinary matter fuel is exhausted, the energy input will cease, and the expansion rate will slow again as the universe approaches its end.
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    I do like that idea, science must have considered it. If light sails can be used in the gravitational confines of our solar system, once gravity is taken out of the equation, IE: inter-galactic interaction, the energy repulsion is all the is left. So light energy makes sense to me.
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    Hi TVMOORE and welcome to the forum

    Quote Originally Posted by TVMOORE View Post
    The original energy for the expansion of the universe was supplied by the Big Bang.
    No problem here yet current scientific consensus appears to suggest that all conserved quantities have zero values (allowing for the current popular notion that the universe may have arose from 'nothing' eg. a quantum event). These ideas hold if the total positive energy of the universe are exactly offest by gravity which has a negative contribution to total energy......anyway, your notion that all the energy was supplied from the Big Bang is a good starting point which means we assume that this total value is conserved through the remaining history of the universe.

    Quote Originally Posted by TVMOORE View Post
    The expansion was slowed for the first few billion years by the gravity of dark matter, and by ordinary matter as it formed from the 5% component of energy plasma in the original explosion.
    Not sure what you mean by the "5% component of energy plasma in the original explosion". Do you have a source for this? ....or do you mean 27% component of the energy plasma. I think the current accounting for the total energy of a 'flat' universe is 4% ordinary matter, 23% dark matter and 73% missing energy (or dark energy).

    Quote Originally Posted by TVMOORE View Post
    A principle of the universe is that all matter, information, and energy was supplied at the time of the Big Bang, and nothing further may enter from "outside." (There is no "outside.") Therefore, the extra "dark energy" that has caused the expansion rate of the universe to increase must be supplied from within.
    A good principle. There is 'nothing' outside this universe is a very holistic way to view things. This therefore means there are no observations that you can make from a perspective 'outside this universe' as no observer holds a priveleged 'gods-eye-view'. All empirical evidence is taken from within this universe which fairly well dictates the boundaries of where science and philosophy meet.


    Quote Originally Posted by TVMOORE View Post
    To see the source, look at the night sky. As ordinary matter began to congeal into stars and galaxies, it began to be converted into energy, first in thermonuclear reactions, and later in supernova events. The energy spills into the universe, and is added to the residual Big Bang energy.
    I am having problems here as energy is neither created or destroyed, just transformed. I am not sure how the total energy contribution of the universe can increase from this example unless you treat energy and matter differently. E=mc^2 would beg to differ with you here. Furthermore, energy is gravitationally 'attractive' in nature whereas 'dark energy' is repulsive in nature leading to an accelerating model of expansion. I am not sure how you thoughts reconcile this property.

    Quote Originally Posted by TVMOORE View Post
    As star formation and evolution proceeds, enough energy is inserted to cause the expansion rate to increase. This process will continue as long as there is enough ordinary matter to form stars. (Since the source of the energy is mainly from stars and supernova, a better term for "dark energy" would be "bright energy.") When the ordinary matter fuel is exhausted, the energy input will cease, and the expansion rate will slow again as the universe approaches its end.
    I still have a few reservations on this but I like your ideas. :-))
    Last edited by Implicate Order; July 31st, 2014 at 01:30 AM. Reason: Basic accounting error *slaps forehead*
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    Seems like a lot of handwaving.

    [1103.5870] Dark Energy mentions several theoretical speculations on what it could be. Several of the models involve some scalar (spin-0) field, much like the Higgs particle and much like the particle likely responsible for cosmic inflation.

    The energy scale of dark energy is at present about 0.003 eV, in particle-physics units. This is about 3*1011 times less than the mass of a proton and not much less than the likely masses of neutrinos.

    This energy scale is MUCH less than what one gets from naive applications of several theories.
    Quantum gravity: 1028 eV
    Grand unified theories: 1025 eV
    Electroweak unification: 1011 eV
    Quantum chromodynamics: 109 eV

    There is also the question of whether the energy density of dark energy varies, and how it varies if it does. I've seen some speculations about "tracking", how it tracks the overall mass-energy density of the Universe.
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    Alot of people are forgetting that even though galaxy clusters are expanding galaxy's are not expanding as much. At the center of every galaxy(or at least theorized to be) is a supermassive black hole. This is so dense that its gravitational field is extremely strong, meaning it can hold galaxy's together. Also, another large example of the existance of dark matter or a subatomic particle of which it is theorized to be, is that when the total weight of the universe was 'measured' it was not as heavy as it should be, so there had to be some mass that existed that is invisible to us. One that does not emit light. But with testing facilities deep underground and a detector aboard the ISS the search is ongoing
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    Quote Originally Posted by spectre View Post
    Alot of people are forgetting that even though galaxy clusters are expanding galaxy's are not expanding as much. At the center of every galaxy(or at least theorized to be) is a supermassive black hole. This is so dense that its gravitational field is extremely strong, meaning it can hold galaxy's together.
    The central black hole of a galaxy is not instrumental in holding the galaxy together. For example, our own galaxies SMBH is estimated at 4.1 million solar masses. There are ~300 billion stars in our galaxy. The SMBH only represents a small fraction of the mass of the galaxy and thus is responsible for an equally small fraction of the galaxy's gravitational pull and thus it ability to hold together against the expansion.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    I recently watched a documentary by Brian Green about black matter and the expanding of the galaxies. He said that black matter is made up of sub-atomic particles (go back to the original string theory and the most basic particle of string energy) and that the energy generated by the movement of these particles are causing enough energy to expand the galaxies in the now considered multiverse. Black matter appears to still be up for discussion. Apparently the energy created by the subatomic particles (I think they were called quorks?? please correct me) has been measured at .000 120 zeros and then a 1 which although quite miniscule is enough force to exert the expansion in our galaxy. If measured in the other galaxies in the multiverse then measurement would vary according to the elements in the universe but would be relevant to the amount of expansion measured. He discussed the theory of parallel universes and other universes of varying degrees of habitability by life forms and the likelihood of lifeforms of which we would have no recognition due to their "alienness" (I made that up. I don't know what to call something that is beyond human comprehension)
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