why does dark energy need to exist?

[yevaud]

Next to the concept of "Dark Energy" - <br /><br />I am truly not certain why people are so up in arms about this.<br /><br />Given all factors that we know with respect to universal expansion, <i>something</i> appears to be accelerating events, not allowing Omega to go flat and expansion to slow down and stop.<br /><br />This is why this idea was floated. It was designed to fit what we do know about the increase, and that is simply all. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[emperor_of_localgroup]

Kudos to R. Dolan.<br />Finally someone got the courage to attack the ever neglected subject of 'empty space' or 'vacuum'. This is a start.<br /><br />This doesn't mean I agree with all he said in his paper (I'm upto page 20 of 55 pages) but this sure is a new way to look at the world. We have been building mathematical theories ignoring the origin or effects of 'empty space' for too long, we couldn't see the forest for the trees. <br /><br />Though Dolan's idea of spacetime 'points' and regeneration of points are not very clear to me yet, but it sure is more feasible than a single point big bang burst. The paper also make us rethink about the concept of time. His third postulate can also lead to higher dimensions of string theory.<br /><br />I'll be watching for works by others in this line of thinking. <div class="Discussion_UserSignature"> <font size="2" color="#ff0000"><strong>Earth is Boring</strong></font> </div>

 

[alokmohan]

Red shifts are two types,gravitational and Doppler.Which one you mean?

 

[why06]

Dark energy and Matter are considered "dark" not merely for the fact that they can not be seen, but that there is no stated candidate for dark matter or energy yet. It seems scientists are still deciding. Question: can dark matter planets exists? Or are darkmatter only attracted to regular matter?<br /><br /><br /><br />I won't discuss this here, but I believe tachyons can explain the effect of both. Nonetheless theres my question. Pay no attention to the "tachyon" part. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[yevaud]

<i>Dark energy and Matter are considered "dark" not merely for the fact that they can not be seen, but that the can not be observered.</i><br /><br />Since these are virtually the same, I'll take them as one question.<br /><br />Cue Vera Rubin.<br /><br />Vera Rubin was one of a handful of female Astrophysics PhD's decades ago. While employed at the Department of Terrestrial Magnetism (the Carnegie Institution of Washington), she noted that the rotational velocities of observed galaxies didn't match predictions (based on known science). Something had to be affecting it.<br /><br />This is where "Dark Matter" comes from. Something we can't directly observe is gravitationally affecting the rotational rates of all galaxies. It's "Dark" as we cannot observe it, only it's effects.<br /><br />Dark Matter is hypothesized to be any one of several candidates. Here is a good explanation. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[why06]

That is what we call a typo.... <img src="/images/icons/wink.gif" /> ill fix that.. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[vandivx]

<blockquote><font class="small">In reply to:</font><hr /><p>Correct me if I'm wrong, but if we assume that space-time is limited to 3 physical dimensions and one time component, then "dark matter" and "dark energy" are likely components that have to be identified and quantified.<br /><br />However, seeing that we can't quantify gravity in 4 dimensional space-time or explain the observational results of universal expansion based on "known" masses and forces, doesn't that imply that there are forces acting on the Universe "outside" our 4 dimensional space-time model?<p><hr /></p></p></blockquote><br />gravitation qua mathematical theory of GRelativity is multidimensional (more than 3 or 4 dimensions) affair simply because it is essentially calaculation of curved surfaces (space curvatures), it is a calculation of surface topology and as such it require the use of tensors to be at all feasible<br /><br />in principle one could do the calculation of curved space with normal numbers (not numbers grouped in tensor) but that would be forbiding in complexity and probably not practicable at all, however just because one uses tensor mathematics in multidimensional mathematical (read abstract) space doesn't mean that the real space out there is more than 3d plus Td<br /><br />the complicated multidimensional tensor math of GR is simply the outcome one gets when one calculates curved surface topology (2d) within 3d space and it says nothing about dimensions in real space, that is in reality<br /><br />all this talk about extra dimensions of reality I see as failure to distinguish between mathematical calculations and reality out there, mathematics uses abstract methods but we shouldn't start thinking that those methods express one to one correspondence to reality, else we would do the same mistake like the ancient thinkers who might have equated numbers with natural elements (like that 3 is fire or that cube is earth and triangle space etc) TBS we don't do that anymore in these primitive ways nowad <div class="Discussion_UserSignature"> </div>

 

[vandivx]

<blockquote><font class="small">In reply to:</font><hr /><p>you're not being specific about any issues you have with that article, you're very generalized,<br />It's difficult for me to learn anything meaningful from what you say unless you're more specific <p><hr /></p></p></blockquote><br />well, I skimmed the whole article reading a bit here and bit there and I also went to look at the man's other paper on consciousness to round out my picture of him (since consciousness, concept formation and all that relates to it interests me and I think I know a bit about that) and I decided that the paper in question here is not worth wading into it, that is arguing with it how it is wrong simply because the guy doesn't supply any arguments (well structured and built up reasoning theory in sufficient detail) that you could really argue against, all that one would be doing would be fighting claims that are not supported (and if the guy would talk back it would turn into claim against claim and it would be stalemate or else mud slinging match as the case may be)<br /><br />so, from this second post at least, you could 'learn' that there are theories and theories, that some can be argued with and some that can't and that it is not wise to argue with those that don't supply good (carefully built and structured theories) argument to beging with<br /><br />that paper disposes of (includes in its theory) some outside theory in one or two paragraphs and it does it by using some woodo like words associated with them and then it goes onto next theory... <br /><br />there is that story for little kids (in the country I grew up in) that talks about how two animal friends, cat and dog wanted to treat themselves to something good and decided to bake a cake and then they argued what to put into it and ended up with agreement of each of them putting in ingredients that he likes best... and the result was a mishmash cake that gave both the cat and dog big belly ache, I remembered that story when reading that gu <div class="Discussion_UserSignature"> </div>

 

[why06]

Why cant we "quantify" gravity in 4 dimensional space-time? <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[R1]

thanks to everyone.<br /><br />why06 good question, <br />I don't know. But I personally do fear that even the current gravity equations might not be 100% correct yet, <br />especially on the extremes,<br /><br /><br /> space apparently is being 'produced' at an accelerating rate in faraway<br />places away from gravity (where 'dark energy' plays its role), <br /><br />and space seems to get real slow and sticky<br />near gravity, and even go down the drain where singularities (or string balls, whatever) play their role.<br /><br /><br /><br />I agree with emperor_of_localgroup, that's why I'm trying to learn more about empty space, <br />and time too I believe has been neglected quite a lot.<br /><br /><br /><br />vanDivX, yes I'm starting to see that there are theories and theories too.<br /><br />I just hope to learn a lot more about empty space (and overfilled space, the holes)<br />I get too busy from time to time, but I'm trying my best <br /><br /><br /><br />Yevaud, I need to read over your article some more, but when the rotational speed of the outer parts<br />or galxies truned out to be faster, are other options completely disproven and disallowed?<br />I can't think of them all, but for 1: that our understanding of gravity at long distances is flawless?<br />2: that neutrinos and black holes don't account for enough matter? 3: that the flow of time closer to<br />the massive galctic centers might be slowed enough or have even the slightest role?<br />4: or better yet does science have the time descrepancy formulae precisely solved?<br /> <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

Scientists give so many option.Dark energy is compulsory but.

 

[R1]

if this energy is accelerating expansion, shouldn't we be able to observe the most accelerated expansion closer<br />to us around the Milky Way where the neighboring galaxies' light is the most recent and is a record of most recent events (and most recent speeds of expansion)?<br /><br />If acceleration over the past 8 years has been constant, the fastest expansion should be occuring now (and<br />therefore observed in the most recent galaxy lights, ie our closest neighbors)<br /><br />and if the universe has been accelerating for billions of years shouldnt the speed be way too high by now?<br />even an ion propulsion engine could have a spaceprobe flying at record speeds if it has been accelerating <br />continuously for the past 8 billion years!<br /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

Hello John1R,<br />Re:<br />"if this energy is accelerating expansion, shouldn't we be able to observe the most accelerated expansion closer <br />to us around the Milky Way where the neighboring galaxies' light is the most recent and is a record of most recent events (and most recent speeds of expansion)? "<br /><br />This has been my problem with Dark Energy all along. If the discrepancies in redshift do not show acceleration is occuring in the nearer galaxy clusters, then we can not say if there is a speeding up of expansion, or if there was a time in the past that the universe was expanding way faster and is now slowing down. All that the data really says is that the universe has expanded more than theory would expect.<br /><br />Here is where accuracy of the measurements have failed us. According to others here at SDC (and I have no reason to doubt what I've been told), the minute amount of redshift one would have to measure for the nearer objects to determine an acceleration is just too tiny for us to measure at this time.<br /><br />We have only taken the red shift, and brightness studies in a very narrow stretch of time (recently). In fact, you could say that our observations only relate to a near single point in time compared to the vastness of time that the discrepancy is observed.<br /><br /><br />Either the curve shows acceleration (curving one way ), or it could show slowing down (curving the other). Which ever is the case you can not plot any kind of curve without extra data points on the time line.<img src="/images/icons/wink.gif" /><br /><br /> I guess I am in the camp that is a little skeptical of Dark Matter, but should it prove that the universe is accelerating it is as good a name for the cause as any. The real issue is to sort out what we can actually state from the data we have and figure out what to do next from there. Anything else we theorize without more knowledge on the subject is interesting, and we do not lack for theories at this point. <div class="Discussion_UserSignature"> </div>

 

[R1]

yes, I know, Ianke.<br /><br />Now the inflation expansion, or accelerated expansion, <br /><br />by that I'm talking about billions and billions of years ago, I would have no problem understanding that.<br />If starlight that was emitted far away almost 10 billion yrs ago is highly redshifted, I have not problem<br />understanding that back then the universe was expanding rapidly.<br /><br />But anything else, we really should get more accurate measurements of light that was emitted just in<br />the past few million years, to see if the acceleration has been continuing since a long time ago.<br />And unfortunately it seems to me that young light that was emitted less than 2 or 3 million years ago<br />does not appear to convince me the acceleration has been increasing for the last 10 billion years.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

You hit the nail squarely there John1R. That has been my point since the "Is the redshift discrepancy the same at all distances" thread. I've been following your discussion and we seem to be stating the same need for more and improved data. <div class="Discussion_UserSignature"> </div>

 

[why06]

Okay I was just asking because Dragon04 gave this as a reason for something... I just thought that if those terms are gonna be used we should know what we're talking about...Or at least tell me? <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[R1]

why06,which terms?<br />abount quantifying gravity? <br /><br />Dragon4, personally I do think a lot of other stuff goes on in other dimensions.<br />But it doesn't mean that 3 and 4 dimension science is bad.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[why06]

anyway about the expansion.... Doensn't the red-shift show up in closer galaxies than the ones billions of light yeats away? <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[SpeedFreek]

Hi John1R and Ianke!<br /><br />About redshift and how astronomers (or astrophysicists or comsomologists) came to the conclusion that the expansion is accelerating.<br /><br />Redshift (and blue shift) are characterized by the relative difference between the observed and emitted wavelengths of the light from an object. The key here is the <i> emitted </i> wavelength as we can only ever assume this figure, based on our observations and assumptions. In astronomy, redshift is defined by the quality known as <i> z, </i> where z = (observed wavelength - emitted wavelength) / emitted wavelength.<br /><br />If z < 0 then the object is moving towards us, and if z /> 0 then the object is moving away from us. At redshift figures below z = 0.1 (i.e the stars in our galaxy) observed redshifts are almost always related to the line of sight velocities associated with the objects being observed. We cannot calculate any expansion from this as the amount of expansion would stretch the light by such a small amount (even if the expansion was accelerated and thus at its highest factor) that it is almost negligable.<br /><br />In contrast, the luminous point-like cores of quasars were the first "high-redshift" (z /> 0.1) objects discovered before the improvement of telescopes allowed for the discovery of other high-redshift galaxies. Currently, the highest measured quasar redshift is z = 6.4, with the highest confirmed galaxy redshift being z = 7.0 while as-yet unconfirmed reports from a gravitational lens observed in a distant galaxy cluster may indicate a galaxy with a redshift of z = 10. The cosmic background radiation on the other hand has a redshift of z = 1089!<br /><br />Hubble suggested (and other methods using other assumptions have seemed to confirm) that there seems to be a linear relationship between redshift and distance. The bigger the redshift, the further away it is. This seems to hold true in most cases. There aren't many things closer to us moving away faster than things <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[search]

The main point of the article:<br /><br />"The roles of the inflaton and dark energy are played by spacetime itself"

 

[R1]

why06 no, I the highest redshift shows up in (older) more distant objects, in older light, in fact the oldest light<br />dating to the cmbr has the highest shift<br /><br /><br />holy cow! z=1089, speedfreek!<br />that's the highest value of redshift I've ever heard of. Though, of course, this speed of recession record <br />(this photograph) is about 13 billion years old. That's interesting about the quasars let me think about it.<br /><br />I know you tried to explain an accelerating universe, but after<br />I thought about it if the expansion had been accelerating for the past 8 billion years, for example, then <br />the current (today's) local speed of recessions should <br />we should be getting readings of redshift z />3 or z>5 here locally, in the more younger light near the<br />Milky Way<br /><br />because an acceleration over the past 8 billion years is what you can think of it as the ion propulsion engine<br />effect: by having just a minimal amount of acceleration over a few years, you can end up with incredible speeds<br />so if it's been accelerating for an incredible amount of time, we're just not seeing high redshifts in all recent light<br />photos.<br /><br /><br />Search, yes that's a good point, and science hasn't elaborated much on why it's 'not' anything else except <br />mysterious energy. So now there's probably hundreds of questions and I can't even think of them all<br />if spacetime is naturally self-expanding, self-straightening, (self tendency to flatten ove time), that's right, science wouldn't need to baffle itself further <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

Don't forget that cosmological redshift is cumulative, in that the lights wavelength is being stretched all the time it is passing through expanding space. <br /><br />So we wouldn't see higher values for z for closer objects <i> relative</i> to distant objects, only a difference in the ratios. With the cumulative nature of cosmological redshift, if space is expanding fastest more recently, the light from distant objects will have that extra redshift in it too.<br /><br />For example, if a quasar 1 billion light years away had a redshift of, say, z = 1, and a quasar 2 billion light years away had a redshift of, say z = 1.8, then we could say the expansion had accelerated.<br /><br />But if the quasar 1 billion ly away had a redshift of z=1 and the quasar 2 billion ly away had a redshift of 2.2, then the expansion would be slowing. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[R1]

that's right, thanks, I need to visualize the cumulative effects a lot more, the<br />receeding distances, redshift lengthening , and expansion is all contributing cumulatively <br />the more distant something is from us.<br /><br />Yet the expansion acceleration must still be small and relatively microscopic, otherwise it would be locally<br />large and quite obvious.<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[ianke]

Hello speedfreek,<br /><br />Re:" And the closer the quasar the more the difference between expected redshift and measured redshift. This is why we think the expansion may be accelerating."<br /><br />This is the observed data needed to say that acceleration occurs. Do you have a link that shows this anomaly? If this turns out to be true, after all the smoke clears, then the jury would be deliberating and acceleration wins. At least I see (from the last 2 of your posts) the logic in why the accelerated expansion idea makes sense.<br /><br />Thanks again<br />Ianke<br /> <div class="Discussion_UserSignature"> </div>

 

[chesh]

"Redshift (and blue shift) are characterized by the relative difference between the observed and emitted wavelengths of the light from an object. The key here is the emitted wavelength as we can only ever assume this figure, based on our observations and assumptions. In astronomy, redshift is defined by the quality known as z, where z = (observed wavelength - emitted wavelength) / emitted wavelength."<br /><br />There is something very important missing in this paragraph. How does any astronomer know, including Hubble, how much red shifted the light was? What's the standard? There seems to be a key element missing here.<br /><br />There are NO essential assumptions being listed as your post missed the key element in measuring redshift. Thus the post is mistaken on this point.<br /><br />Further, with greater & greater distances, the light fuzzes up and blurs. It's assumed due to interceding dust, gas and such, but not proven to be so. With the existence of dark matter, the whole or part of the redshift might well be found to be a good deal more complicated than once thought.<br /><br />Masses(dark matter) which are at least 6 times greater than visible mass in the universe might have a serious effect upon light moving past such enormous gravity collections, such as dark matter. The fact that normal light is NOT diffused or lensed by such 'dark matter' means very clearly that dark matter is NOT concentrated, it's diffuse, and it doesn't interact very much with light.<br /><br />But the long range gravitational effects would still be there & thus alone could shift light into the red wavelengths, more or less. This means the red shifts might well need to be adjusted.<br /><br />& due to varying concentrations of dark matter, would give some differences in red shifts, as well. These issues are not addressed. Nor is there any necessity that a universe expand linearly, as almost all of the universe is not linear at all. It could pulse, speed up, slow down, or any other o