why does dark energy need to exist?

[SpeedFreek]

Heheh, that's the tricky part. The data we have so far is limited, and as with most graphs the dots appear <i> close </i> to a constant expansion line, but all distributed around that line rather than on it - but with more tending towards an acceleration curve than not. Add in the margin of error which could be up to z = 0.5 depending on how the measurements are made, and you can see why we haven't been able to confirm it yet.<br /><br />The <i> trend </i> of the data is towards the acceration side, but it is by no means overwhelming evidence.<br /><br />I can't give you a link for this, my quote in your post is just describing the theorised mechanics based on this trend. I describe it all in this way by using my memory of reading lots of different things in lots of different places about expansion over the years, and this is the picture I have built up about it. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[SpeedFreek]

Yes, as I said, <i> The key here is the emitted wavelength as we can only ever assume this figure, based on our observations and assumptions. </i><br /><br />Astronomers have to <i> guess </i> what the emitted wavelength is. I do not have the knowledge of the subject to suggest what assumptions are used in their guess, so I chose not to address them directly, but just to point out that assumptions are being made.<br /><br />Please go ahead and make things clearer! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[chesh]

Guess again. The answer is really quite elementary and most miss it.

 

[chesh]

Guess again. The answer is really quite elementary and most miss it.<br /><br />"I do not have the knowledge of the subject to suggest what assumptions are used in their guess, so I chose not to address them directly, but just to point out that assumptions are being made."<br /><br />It's logically & necessarily true, that if a person does not know what assumptions are being made, that person does NOT know for sure that assumptions ARE being made, because he cannot name one, and thus prove the case.<br /><br />Maybe tomorrow......

 

[ianke]

Hello chesh,<br /><br />I withdrew my post because it was a big understanding on my part. I was thinking Dark energy not Dark Matter.<br />Sorry if I cut someone off. OOPS!<br /><br />Ianke <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

Well, for one, astonomers assume that all quasars are similar enough to be able to use them as "cosmic candles", a kind of benchmark star, on which to base other measurements.<br /><br />An assumption is also made that similar redshift equals similar distance in this context, which it may not. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[why06]

So wait Im a little lost.... we are discussing red shift discrepencies right?.... Well heres my question. Is the universe really accelerating so much that it can be attributed to a foriegn substance. Im unclear on how dark energy will accelerate galaxies and such.<br /> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[R1]

chesh, what's the answer?<br />------------------------------------------------------------------<br /><br />why06, It's probably not accelerating very much at all, <br /><br />--------------------------------------------------------------------<br /><br /> we just think that distant things were receding quickly, but it's really just an optical illusion<br />pertaining to the cumulative effect of light passing through 'so much' space that could be 'slowly' accelerating.<br /><br />It makes me wonder, what kind of antenna or instrument would we need to detect electromagnetic wave clues<br />from deep beyond the cmbr area, since this wave would more than likely have a redshift value exceeding<br />z=2000 the wavelengths that could very well be 100 to 1000 miles long or even longer and dimmer than<br />the cmbr too<br /><br />---------------------------------------------------------------------<br /><br /><br /><br /> <div class="Discussion_UserSignature"> </div>

 

[why06]

Hence the first question:<br /><br />"why does dark energy need to exist?"<br /><br /><br />maybe in bold...<br /><b> "Why does dark energy need to exist?"</b> <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>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<p><hr /></p></p></blockquote><br />you totally misunderstand what the term 'dark energy' means<br /><br />it is nothing more than a sort of a placeholder name for some unknown phenomenon - energy of something, like gremlins or whatever pushing the universe appart or the discovery that space naturally self-expands (your current favourite) and until we can satisfactorily explain the fact of observation that is puzzling us we will talk about dark energy and look for what is doing the pushing but all along nobody thinks there is physically some energy out there called dark energy<br /><br />science doesn't insist on some 'mysterious energy', as I said, it is just a name given to the phenomenon and if scientists still talk about dark energy these days, that's because they either aren't sold on your natural space self-expansion or else they are ignorant of that solution, its only problem of telling them and convincing them about it, once they come to agree with you or anybody else on something, all that talk about dark energy that irritates you so much will be a thing of the past<br /><br />you ask "Why does dark energy need to exist?" but that's not how the question stands as you should see in the light of what I said here, nobody is insisting on existence of anything, not on existence of dark matter or dark energy per se, those are names like in the old days you had written on maps in unexplored areas 'hic sunt leones' and nobody was asking why the map makers insisted on lions being there LOL and you do just that, that was also only placeholder name to mark areas that we didn't know yet what's to <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

<i> we just think that distant things were receding quickly, but it's really just an optical illusion <br />pertaining to the cumulative effect of light passing through 'so much' space that could be 'slowly' accelerating. </i><br /><br />Just so we are clear about this, the huge relative velocities we attribute to the most distant objects is due to the nature of the metric expansion. They aren't moving fast compared to their local neighbourhood, but they <i> are </i> (or were!) moving very fast relative to us. That is not an illusion. If the space between them and us has expanded so much that they seem to be receding faster than light relatively to us, then they <b> are! </b> Because it is the metric defining distance that is changing rather than objects moving in space, this expansion (and the resultant movement apart of objects) is not restricted by the speed of light upper bound that results from special relativity.<br /><br />Assuming there is expansion, even with a expansion rate that had never changed, the furthest objects would still be receding from us at huge speeds, as any given unit expands at the same rate (if 1 unit expands to become 2 units, any given distance doubles in size, including the actual diameter of the universe!) The difficulty we are having is establishing if the expansion rate has changed or not.<br /><br />As far as I know, measuring the redshift of quasars and comparing it to their brightness is the only evidence of acceleration we have so far.<br /><br />Hmmm.. I'm wondering if it was the <i> brightness </i> that chesh was alluding to? (The thing he said most people miss - I wonder if he will come back?). I have trouble thinking of all the aspects of these subjects at the same time, and tend to forget details like this until they come up!<br /><br />And for chesh: All I meant by assumptions in my earlier post was to point out that we don't <i> know </i> any of this, most cosmology is based on certain assumptions, like redshift=distance, speed of l <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[why06]

You know it is possible that something else could be causing the red-shift. Maybe the light is losing energy through some unknown feild. Perhaps light loses energy while traveling long distances. I think this doesn't work, but I forgot why. Acceleration seems like one of many reasons for red-shift.<br /> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[SpeedFreek]

Yes, I agree. And the same is true of a lot of cosmology. All it boils down to is <i> our best guess, </i> based upon what we observe and how we interpret those observations.<br /><br />I don't know if you saw one of my early posts here, where I stated something along the lines that I may not actually <b> believe </b> anything I write, I just try to <i> understand </i> what a concept means, and if it seems plausible I try to find ways to convey those concepts to others who seek to understand the concept. If I find it implausible I try to convey my reasons for thinking that, and if I don't understand it yet I ask more questions!<br /><br />We could be wrong about a lot of things! <img src="/images/icons/smile.gif" /><br /><br />As to my posts on redshift and expansion in this thread, I saw people asking questions that I could answer using my understanding of current theories. Maybe I need to have a signature that says "Note: All the above could turn out to be wrong, but this is what we currently assume" But I thought that was taken as read.<br /><br />All I really do is try to convey the logic behind all these principles, in the hopes that others will either see the logic themselves, or find other answers. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[why06]

Lol. Yes Im feeling the new signature. It suits you well.... <img src="/images/icons/laugh.gif" /><br />It nice to see people who approach thing logically and aren't gunhow about one thing or another. The middle is the best place to be. Especially since it turns out that the best answer is usually a happy median.... <img src="/images/icons/wink.gif" /><br /> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[R1]

speedfreek, I understand <br />anyone could be mistaken, but that's how the forums help everyone, by discussing<br />different ideas, by learning, asking and explaining our knowledge and guesses<br /><br />but anyway, that's right, with standard expansion, the more distant galaxies<br />could be recedeing FTL!<br /><br />now then, since we would observe this by their luminal behavior here on earth,<br />what if we need to be searching for thousand mile long wavelengths?<br /><br /><br /><br /><br />vanDivX thanks for your clarification <br /><br /><br /><br />why06, as far as just losing energy just from simply traveling long distances, that's<br />right, that wouldn't work, I think that's what 'tired light' refers to, and light<br />just doesn't seem to get tired of long distances, or of old age either.<br /> <div class="Discussion_UserSignature"> </div>

 

[R1]

well no, since my previous post I'm learning on a parallel thread the tired light phenomena may be<br />getting revisited, just trying to keep up to date<br /> <div class="Discussion_UserSignature"> </div>

 

[vandivx]

<font color="yellow"><br />You know it is possible that something else could be causing the red-shift. Maybe the light is losing energy through some unknown feild. Perhaps light loses energy while traveling long distances. I think this doesn't work, but I forgot why.</font><br />problem with 'tired light' hypothesis is not that it wouldn't work, it would work just dandy, problem with it is that nobody can supply believable theory that would show us how the light gets tired<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[chesh]

But if the galaxies are receding FTL, then we cannot then tell how large the universe is. and how could we verify that FTL expansion? <br /><br />It simply makes no sense at all. If it's FTL, then anything moving that speed could not be detected. How does one observe mass travelling FTL in a vacuum? Physics simply forbids that. Therefore FTL means that the hypothesis is intrinsically not testable. Untestable scientific hypotheses are as forbidden as lit candles in a gunpowder factory.

 

[chesh]

"...the same is true of a lot of cosmology. All it boils down to is our best guess, based upon what we observe and how we interpret those observations."<br /> <br />It's not a guess. I'd guess you don't know how astrophysics operates. There are the rules of the sciences to be obeyed. No one can postulate ANY kind of cosmology based upon an absence or violation of known scientific laws.<br /><br />It's not a guess. It's based upon careful observations and testing of hypotheses. Science is just not guessing. It's testing those hypotheses, NOT making your best guess as a final answer. That's not science at all.<br /><br />Also whether a conclusion or statement is "plausible" is also not science. The statement must be SHOWN to be real & exising. It must be carefully tested by experiments and shown to describe how events behave.<br /> <br />Plausibility is simply not scientific. Testing statements' plausibility with an eye to find out which describes events, THAT is science.<br /><br />This is not day to day life decisions. This is a scientific forum. The rules of the sciences apply here, careful logic, critical thinking, careful substantiation of statements, and stating whether or not a statement is a guess, a fact, or whatever.<br /><br />Failure to understand those points will make posts incomprehensible as too many so often are.<br />

 

[ianke]

Hello chesh,<br /><br />I have been reading your posts on this thread, and am wondering what your theories are about the cosmic expansion. Just what, exactly, does your "careful logic, critical thinking, and careful substantiation" tell you of the subject here on this post? You seem to have a lot to say about what isn't correct. Perhaps you would inform us on your theories of what is going on. Please enlighten all of us as to what you know. <br /><br />1.Are you saying the red shift does not show distance or speed? I do not wish to answer for you but you seem to have said as much with your Dark Matter blurring light thought. (Is that a theory, or fact, or just your thoughts on the matter)<br /><br />2. (If no to #1 ) Do you ascribe to dark energy, and on what basis?<br /><br />3. Do you subscribe to the Big Bang Theory? If not, then what theory do you use to describe the universe?<br /><br />4. What about Einstein's theories(GR, STR)? <br /><br />Regarding statements like:<br /><br />"Guess again. The answer is really quite elementary and most miss it. "<br />or<br />"I'd guess you don't know how astrophysics operates."<br />or<br />"This is not day to day life decisions. This is a scientific forum. The rules of the sciences apply here, careful logic, critical thinking, careful substantiation of statements, and stating whether or not a statement is a guess, a fact, or whatever."<br /><br /><br />These type of statements serve no purpose here. You can dissagree with someone without being condesending. I welcome someone correcting something I have said (as I am sure the others do) if they can be helpful in their critique. At least offer a counter point if you insist on being rude. <br /><br />Perhaps you have something to add, perhahp you do not, but at least be civil.<br /><br /><br />thanks <img src="/images/icons/wink.gif" /><br />Ianke <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

I'm sorry chesh but I think you are totally misunderstanding me. I'm on the side of science. I do not deny the validity of any scientific theories. I understand how astrophysics operates which is <i> how </i> I was able to say what I did.<br /><br /><font color="yellow"> <i> "No one can postulate ANY kind of cosmology based upon an absence or violation of known scientific laws." </i> </font><br /><br />So what are dark matter and dark energy then? They are our <b> best guesses </b> as to what is going on with the motion of stars in galaxies, which seem to <i> violate </i> current scientific understanding of how gravity works at large scales, and the observation of quasars redshift versus brightness, which seems to be due to some <i> absent </i> (i.e. unobserved) source of negative pressure.<br /><br />Of course, I know that plausibility alone is not scientific! That was just my answer to a question that asked "You know it is possible that something else could be causing the red-shift?". It was a question as to whether I think it possible the currently most favoured theory has it wrong about cosmological redshift. Maybe I should have used the word <i> logical </i> instead of plausible, for that is how I decide what is plausible, using logic!<br /><br />I understand this is a scientific forum and I detest psuedo-science, so you won't find me posting pseudo-scientific ideas here and presenting them as science. But what I <i> will </i> do, is try to convey scientific concepts to people seeking to understand them, using simplified models and examples to hopefully help their understanding.<br /><br />Maybe sometimes I simplify too much, but I try not to post falsehoods.<br /><br />So when I say something like "A lot of cosmology boils down to what is our best guess, based on our interpetation of our observations" that is true. We do not <i> know </i> absolutely that the expansion of the universe is accelerating. We use logic to deduce the acceleration from our observations <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[R1]

<br /><font color="yellow">But if the galaxies are receding FTL, then we cannot then tell how large the universe is. </font><br />chesh, we really don't know how large the universe is<br /><br /><font color="yellow">It simply makes no sense at all. If it's FTL, then anything moving that speed could not be detected. How does one observe mass travelling FTL in a vacuum?</font><br />nobody said mass is travelling FTL in a vacuum <br /><br /> <div class="Discussion_UserSignature"> </div>

 

[why06]

I agree with speedfreek.<br />Your rebuttal is warranted, but I believe that you are trying to convey something else than denying that a theory is a guess. I will explain:<br /><br />A theory: is a hypothesis or a combination of multiple hypotheses supported by fact.<br />A hypothesis: Is an <i>educated</i> guess.<br /><br />Hence a theory is:<br />"a [educated guess] supported by many fact and currently complies to the Laws of the universe"- nevertheless though these <i>are</i> guesses; perhaps with much support, but nevertheless they are merely the brainchilds of some designer(s). And as such they should be treated with some such needed and allowed skepticism for else development of the theory is impossible. I doubted you needed someone else to say that, but thats my two cents. <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>

 

[nojocujo]

It is the apparent brightness relative to the Z that has been confused with light losing energy. The loss of photons i.e. not observedhas been construed to mean that the universe is expanding and at higher z the loss increases indicating an acceleration in the expansion.

 

[chesh]

Frist of all, those who state that the expansion of the universe can create supraluminal expansion have violated a basic rule of physics ,which states that nothing can exceed light speed. If it does, then what does it look like?<br /><br />If some belive that the universe at extreme distances is travelling FTL, then tell us, by the laws fo physics, what does that look like? We should not be able to detect it.<br /><br />No one knows. so the point is moot. Nothing can travel FTL at least on a macroscopic level, not in this universe, nor at the edge of it or anywhere else.<br /><br />That's the point, to state that something does is simply nonsense. There is no description of it possible in our physics. So to state that it happens, is not physics. It's fantasy.<br /><br />That's the point.