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richyj8

Galaxy rotation velocity question

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I think based on what has been said here that the galaxies are spinning apart, no dark matter is involved, and that the reason galaxies haven't degraded apart yet is that they aren't billions or even millions of years old, and haven't had the time needed. 

That might be an interesting idea but now it just gives you the problem of explaining why every galaxy we see, we see at an age of less than whatever time it would take to disrupt that galaxy. If the galaxies would disrupt in say 100 million years, a reasonable time scale for that to happen as that's the same order as the rotation period of stars around the galaxy then presumably all the local galaxies are less than 100 million years old, all the galaxies at 1 bn light years are 1 - 1.1 bn years old, all the galaxies at 2bn ly are 2 - 2.1 billion years old and so on which would be a vastly improbable coincidence. Not only that but you also have to explain why all the stars in a galaxy which are not only billions of years old but which have a range of ages of billions of years have all come together at just the same time.

Far simpler to postulate additional matter which stabilises the galactic rotations.

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You assume billions of years, you weren't there. I assume it was created 5800 years ago..I wasn't there. You assume DM, I assume no DM, so far I'm vindicated...

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There is a huge difference between "assuming" something and proving something else by the scientific method. I think your trolling would be better suited to a creationist forum where you will be welcomed with open arms.

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No need for the ad hominem...just because I don't accept DM doesn't mean I'm a troll...remember, DM has never been seen, observed, detected....

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, DM has never been seen, observed, detected....

Dark matter has been detected, the fact that galaxies rotate at a speed which is inconsistent with their observed mass is a detection of dark matter. What it is is a different question which has not been answered because it has not been observed through any mechanism other than its gravitational effects but that is still an observation.

Edited by jnb
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Thursday, November 6, 2014....Inside Science News Service...To Date, Particle Super Collider Detects No Evidence Of Dark Matter; September 21, 2014....The Daily Beast...Still No Dark Matter From Space Station Experiment Experiment

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Which highlight that we have not found what dark matter is while cheerfully ignoring all the astronomical evidence for dark matter. If you can selectively ignore evidence then you can have any result you want regardless if its improbability and there is no point discussing it with someone who can just shove their fingers in their ears when it suits them.

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...remember, DM has never been seen, observed, detected....

hmm sounds like something else!

I have to say some peoples ability to totally ignore evidence put in front of them at will to suit themselves just never ceases to amaze me. 

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Before Einstein, we didn't have a clue what Gravity was, but we knew it existed ..if a person chose not to believe in it, then one would assume that there'd be no problem jumping off a cliff. As there are very few people around who believe that, one can assume that all the ones who did, actually jumped off cliffs and didn't add to the gene pool ;-). Likewise, we know that there is something with lots of mass surrounding the galaxies, and we might as well call it dark matter....what we call it is irrelevant, as is the fact that we don't know what it is. It's not a question of believing or not believing.

It is there.

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You assume billions of years, you weren't there. I assume it was created 5800 years ago..I wasn't there. You assume DM, I assume no DM, so far I'm vindicated...

You assume there is a country called China, I know the whole thing is an elaborate hoax. After all, you've never been there. You assume China, I assume no China - so far I'm vindicated...

Not much of an argument is it?

It's possible to infer the existence of many things without seeing them. For example, I'm pretty sure my great-great-great-grandparents existed, despite never meeting them. 

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We have not directly detected dark matter, but we have good evidence that it exists. Not 100%, but in science we never really get to 100%.

The neutrino was proposed in theory in 1930, it was 1954 before one was detected directly, and that was with something you could make in the lab pretty easily. Even now they are very hard to detect.

Dark Matter may not even be detectable directly, it may have a very very tiny cross section - or indeed none at all. The universe doesn't have to play by a set of rules meaning we can detect everything directly. 

The fact is we have about 5 or 6 lines of independent evidence that all point to something very much like a missing particle. A missing particle fits with all the data. Are there other possible explanations? Yes of course, but much like the Ptolemeic system, you have to add several layers of complexity in to get them to work out. Missing mass sort of just works pretty much, tinkering with gravity less well, other systems struggle even harder.

It just makes the most sense with the data we have.

We have very good data on a lot of stars in the milky way, we will have even better data soon with Gaia. If the stars were flying apart, and exiting the galaxy, we'd pretty much know by now.

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