why does dark energy need to exist?

[chesh]

The red shift of distant galaxies is found by comparing <b>spectral lines</b>. These are lines which are either emission, or more commonly absorption lines in the spectrum. They were first noted when a high resolution spectrum was done on sunlight. <br /> <br />Each ELEMENT has absorption and emission lines relative to the electron levels in that element's structure. They are almost unique and give a spectral fingerprint to each element.<br /><br />So when they look for distant galaxies they do a spectral analysis which shows the lines. The brightest lines are usually the ones used, and reflect the commonest elements, such as H. When they see THOSE lines shifted from where they should be as seen on earth, then that measures the spectral shift, either when moving away from the earth, to the red, or towards the earth, to the blue.<br /><br />It's the Red Shift OF the Spectral Lines. Or abbreviated, the Red shift.<br /><br />The problems are that when there is a large red shift, it's not always clear how to identify those being shifted as they can be shifted into the IR and they have to look closely. The other problem is that the more distant the spectra are, the more fuzzy the spectral lines get, so one measures it with less precision, than from earth to the sun.<br /><br />Dark matter & dark energy are NOT guesses. They are hypotheses, which might be the solution to the excess mass found around galaxies. <br /><br />No one knows what that is due to. It's probably some form of neutrino, as that is the easiest and simplest hypothesis, altho some have objected stating that all neutrinos are moving very fast. The Laws of physics do NOT require that neutrinos be fast moving.<br /><br />Facts are only very fast moving neutrinos have been detected, because those are the easiet to detect. This does not logically necessitate that all neutrinos must be fast moving. That's the crazy non sequitur in this business.<br /><br />After 14 billions years, it's likely that many of them have slow

 

[SpeedFreek]

Regarding your reply to John about expansion and FTL speeds of receding galaxies.<br /><br />This is proper physics - from HERE <br /><br /><i> According to the Hubble Law, two galaxies which are a distant D apart are moving away from each other at a speed HD where H is Hubble's constant. In that case two galaxies which are a distance greater than c/H apart are moving away from each other faster than the speed of light. This is quite correct. The distance between two objects can be increasing faster than light because of the expansion of the universe. However, it is meaningless to say that the universe is expanding faster than light because the rate of the expansion is measured by Hubble's constant alone which does not even have the units of speed.<br /><br />As was mentioned above, in special relativity it is possible for two objects to be moving apart by speeds up to twice the speed of light as measured by an observer in a third frame of reference. In general relativity even this limit can be surpassed but it will not then be possible to observe both objects at the same time. Again, this is not real faster than light travel. It will not help anyone to travel across the galaxy faster than light. All that is happening is that the distance between two objects is increasing faster when taken in some cosmological reference frame. </i><br />____________________________________<br /><br />Remember, with cosmic expansion it is the metric describing distance that changes over time. Over a given time, any unit will expand by the same proportion as any other unit. If 1 unit expands to become (what used to be) 2, then in the same time, the universe doubles in size.<br /><br />So in the time it takes 1 meter to expand to become what used to be 2 meters, 1 light year becomes what used to be 2 light years, 1 billion light years becomes what used to be 2 billion light years and so <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[SpeedFreek]

More on the expansion of space and how we see galaxies that recede at the speed of light or faster - from here. <br /><br />Misunderstandings about the relation between redshift and velocity abound. The redshift caused by the expansion is often confused with the more familiar redshift generated by the Doppler effect. The normal Doppler effect causes sound waves to get longer if the source of the sound is moving away--for example, a receding ambulance siren. The same principle also applies to light waves, which get longer if the source of the light is moving through space away from us. <br /><br />This is similar, but not identical, to what happens to the light from distant galaxies. The cosmological redshift is not a normal Doppler shift. Astronomers frequently refer to it as such, and in doing so they have done their students a serious disservice. The Doppler redshift and the cosmological redshift are governed by two distinct formulas. The first comes from special relativity, which does not take into account the expansion of space, and the second comes from general relativity, which does. The two formulas are nearly the same for nearby galaxies but diverge for distant galaxies.<br /><br />According to the usual Doppler formula, objects whose velocity through space approaches light speed have redshifts that approach infinity. Their wavelengths become too long to observe. If that were true for galaxies, the most distant visible objects in the sky would be receding at velocities just shy of the speed of light. But the cosmological redshift formula leads to a different conclusion. In the current standard model of cosmology, galaxies with a redshift of about 1.5--that is, whose light has a wavelength 150 percent longer than the laboratory reference value--are receding at the speed of light. Astronomers have observed about 1, <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[chesh]

It's not proper physics. There is NO way in physics that large masses could be observable going at supraluminal speeds.<br /><br />Tell us, how would one detect it? Physics is silent in this case, just as it is about what goes on inside event horizons of black holes.<br /><br />Show us the physical principles which would create FTL masses? There are none. None have ever been observed, nor does physics even address this.<br /><br />Jsut because some HYPOTHESIZE something, namely FLT spatial expansion, is quite a bit different from the actual observed & confirmed substantiation of such claims.<br /><br />There is no such substantiation there. Thus, such beleifs are mere hypotheses, which to my knowledge are unable to be tested, simply because no one can with ANY physics describe what such masses would be detected as.<br /><br />Thus, the point is moot. I simply don't believe it, any more than I believe in ESP. It's plausible, even logically tenable, but it's not real. Neither have EVER been observed!!<br /><br />Those who do not ground their scientific statements with real, testable observations have clearly left the realms of solid science and that's an observed fact.<br /><br />FTL masses from expansion of the universe is an hypothesis. NOT a fact. and one fact is often worth a thousand unconfirmed guesses.

 

[why06]

WRONG. It is not a hypothesis. It is a theory<br /><br />There has been real data collcted to back up the claims of dark matter. Secondly FTL expansion would be "technically" impossible to detect as the light particles (photons) would not be able to cross the vast expanse of space-time that is growing faster than their speed through a vacuum. <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>

 

[chesh]

"Maybe I should stop using the word guesses, when describing what are indeed hypotheses, but that's all hypotheses really are, educated guesses using all the available data and current theory to make logical deductions about the nature of a given problem. Of course they aren't simply random guesses, plucked out of the blue, and I never implied them as such."<br /><br />Your post brings up an important point. What ARE scientific hypotheses. What are their characteristics nd how can they be recognized and distinguished from run of the mill guesses?<br /><br />And that's the issue here. A scientific hypothesis must be testable. Anyone can say, God made it do that, or X makes it do that. But a scientific hypothesis has the form "that combustion occurs due to chemical reaction of oxygen combining with a substance and producing quite a lot of heat." Every part can be tested, carefully and measured.<br /><br />Or, the Pacific Ocean is 15.8 kms. southeast from my computer keyboard. <br /><br />Either can be tested. The hypothesis that expansion of the universe can be supraluminal cannot. It raises huge impossibilities in physics. Thus, it's very dubious.<br /><br />How do physicists test it? Show us. and because it cannot be tested, it's not scientific. That is my position. & it's very likely a good one to stand upon.<br />

 

[R1]

I do think the universe is expanding, are you thinking it might not even be expanding? <div class="Discussion_UserSignature"> </div>

 

[SpeedFreek]

So, are you denying that cosmology is a science then? Because these are not <b> my </b> theories or hypotheses, I am just explaining the current cosmological view to you here. I'm not making this up as I go along, you know!<br /><br />It is what the physicists test in their particle accelerators (i.e general and special relativity), combined with our observations of the universe around us that allows cosmologists to form <b> theories </b> about the nature of the universe. So far, relativity has held up to any test we care to give it. Read up on what <b> science </b> currently tells us about the nature of the universe - I am only relaying <i> that </i> to you.<br /><br />Are you denying that the Big Bang theory, Cosmic expansion theory and the theories of Special and General Relativity are actually theories? Then it is <b> you </b> who needs to understand the way <i> theoretical </i> science works. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[R1]

chesh what is your model of the universe? If theres linear expansion with an iota of acceleration,<br />the distant galaxies should recede at superluminal rates.<br /><br /><br /><br /><br /><br /><br />A lot of space is being created in the large calm intergalactic regions, and this has a cumulative effect on<br />any two superdistant points in the universe. <br /><br />Any 2 superdistant objects should now be receding FTL from each other.<br /><br /><br /><br />consider distant galaxies a through v below:<br /><br />a---b---c---d---e---f---g---h---i---j---k---l---m---n---o---p---q---r---s---t---u---v<br /><br /><br /><br /><br />now consider one unit of space created between them after one time interval:<br /><br />a----b----c----d----e----f----g----h----i----j----k----l----m----n----o----p----q----r----s----t----u----v<br /> <br /><br /><br />although only one unit of space is created intergalactically, <font color="yellow">only one time interval was needed for<br />galaxy v to move 20 units away from a!</font><br /><br /><br /> <br /> <div class="Discussion_UserSignature"> </div>

 

[R1]

this a to v is a small distance that fits in my computer monitor, <br />but when the distance from a to v measures more than <br />10,000,000,000 light years,<br />the speed of recession (between a and v) is superluminal<br /> <div class="Discussion_UserSignature"> </div>

 

[why06]

Exactly! Great explanation. <br />your explaining the workings of the universe with your Abc's. LOL. -not really, but you get my point<br /><br />(LOL=slightly amusing) <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>