Quote:
Originally Posted by xelasnave
Hi Robert
Firstly thank you for your post I found it very interesting.
I was under the impression that dark matter was a form of matter which in effect we are unaware of its nature, further that it is something exotic and not normal matter.
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Hi Alex,
Well, all we have to go on is the
observations of the velocities of galaxies and stars and other astronomical objects. In fact, mainly, with the spectrograph attached to our telescope, we can find only the 'radial' (in the observer's line-of-sight) velocities of astronomical objects.
Subject to various assumptions, we can convert these radial velocities of objects into approximate (statistically correct)(averaged) knowledge about the orbits and velocities of astronomical objects in three-dimensional space.
The most parsimonious assumption,
without introducing unnecessary and additional hypotheses (= Occam's razor), is simply that the
observed velocities of galaxies and stars , because they do not correspond to the velocities that we would
expect to observe if these objects were just under the influence of the
matter we can observe by means of its emission of electromagnetic radiation (light, X-rays, infrared, radio waves, etc.), are best explained by the combined influence of
gravity that comes from ::
(1) a component of matter which we can easily see from its emission of photons
(2) Another component of matter which is currently
not detectable at any wavelength, with the current state-of-the-art Light Gathering Power and sensitivity and noise-level of our telescopes and detectors.
Quote:
Originally Posted by xelasnave
Your post hints that it may be dust or stars even journals that dont throw light on anything are we to take this to mean that some exotic particle is but one option and somewhat normal matter may be there but we simply can not detect it.
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All we know is that there is a lot of additional gravity there that we cannot account for.........the galaxies and the clusters of galaxies would not be stable, and would fly apart, if all that was holding them together was the gravity from the observable stars and gas and other objects.
But of course, the objects that are producing the necessary additional gravity are not known, as we cannot currently detect them with our telescopes and their attached instruments. As mentioned, Zwicky knew about this in the 1930s, from his observations of the orbits of galaxies within clusters of galaxies, but astronomers were not ready to accept this implication until the early 1970s.
Quote:
Originally Posted by xelasnave
Your comments re dwarf galaxies surprised me as to the amount of dark matter required.
Two to three hundred times more dark matter required I find extraordinary.
but two to three hundred times more in a specific situation makes me think back to my original concern that our sums are wrong.
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Alex, the sums are not wrong, if we assume conventional gravitational theory, and while it seems far-fetched to believe that 299/300 of the mass of a dwarf galaxy is in some unknown form, very simple algebraic calculations of the sort that some of us learn to do in Year 12 Physics Class show that
the gravitational effect of this additional matter is there and likely to be real. Which gets back to my original point that there is no reason to believe any other hypothesis about the origin of the velocities of galaxies and their constituent stars.
The case of dark matter may be compared to the case of the theory of evolution........
the story revealed by science seems extraordinary, and perhaps counter-intuitive, but "these are the truths that we must cling to, in the absence of further observations disproving them or modifying them".
As I mentioned before, science cannot provide absolute certainty, and we can only say that it is more likely than not that something is true. So, for now, we must earnestly speak about dark matter as being something real, as that is where the current observations point.
Quote:
Originally Posted by xelasnave
I suffer from no education in this matter and look to you (and always Steven) for help.
I am not a nutter orcrank in that I really do try to understand and accept mainstream position.
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I absolutely respect your open mind, and your strong desire to learn ever more about what is physically real and what is not physically real, in this grand universe of ours.