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#1 CygnuS

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Posted 09 October 2013 - 01:43 PM

What evidence do we have that dark matter and dark energy exist? There's certainly a lot of evidence but how do we know that scientists haven't just manipulated the facts because the idea that Newtonian physics just doesn't work on large scales is something they just don't want to accept? Scientists are, after all, just human beings, subject to the same emotions as everyone. Isn't "inventing" dark matter and energy easier than the monumental task of starting from scratch with the laws of physics? Unless the next Newton or Einstein is out there nobody is up to that task. Are scientists taking the easy way out because they don't want to admit that they'd have to have a genius amongst them to figure it out and it bothers them that they are not that genius? Or, does the evidence really support dark matter and energy even if pride is not a factor?

#2 Chuck Hards

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Posted 09 October 2013 - 02:07 PM

Dark Matter is a term that encompasses a phenomenon that nobody knows the nature of. There are theories, but none have yet to have been proven. Even testing the theories is still in it's infancy. So I think you are misinterpreting the definition of dark matter & energy.

#3 GregLee1

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Posted 09 October 2013 - 05:07 PM

Isn't "inventing" dark matter and energy easier than the monumental task of starting from scratch with the laws of physics?

Yes. Do you think this is a reason to doubt the existence of dark matter and energy? If so, what principle are you relying on? To be good for you, medicine has to taste bad?

#4 PeterR280

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Posted 09 October 2013 - 05:14 PM

Newtonian physics doesn't work on the cosmic scale. You need General Relativity. Einstein had originally postulated something like dark energy as a constant in his equations but dismissed it.

#5 llanitedave

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Posted 09 October 2013 - 09:05 PM

Scientists are, after all, just human beings, subject to the same emotions as everyone.


Just because scientists are subject to the same emotions as anyone doesn't mean everyone's emotions are the same.

For example, do you personally feel an emotional need to preserve strict Newtonian mechanisms at all costs? If you don't, then why would the entire physics community? And if you do, does that mean all scientists agree with you?

#6 EJN

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Posted 09 October 2013 - 11:42 PM

There's certainly a lot of evidence but how do we know that scientists haven't just manipulated the facts because the idea that Newtonian physics just doesn't work on large scales is something they just don't want to accept?

So apparently you are unaware of MOND (MOdified Newtonian Dynamics)? -
which is an alternative theory to explain the rotation curves of galaxies without
needing dark matter. There is a relativistic version of it known as TeVeS (tensor-
vector-scalar gravity). There is also a modified version of relativity called STVG
(scalar-tensor-vector gravity, which is different from TeVeS). Kinda blows your
conjecture out of the water.

#7 dvb

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Posted 09 October 2013 - 11:58 PM

What evidence do we have that dark matter and dark energy exist? There's certainly a lot of evidence but how do we know that scientists haven't just manipulated the facts because the idea that Newtonian physics just doesn't work on large scales is something they just don't want to accept? Scientists are, after all, just human beings, subject to the same emotions as everyone. Isn't "inventing" dark matter and energy easier than the monumental task of starting from scratch with the laws of physics? Unless the next Newton or Einstein is out there nobody is up to that task. Are scientists taking the easy way out because they don't want to admit that they'd have to have a genius amongst them to figure it out and it bothers them that they are not that genius? Or, does the evidence really support dark matter and energy even if pride is not a factor?


To suggest that scientists are conspiring to invent dark matter and energy is just nuts.

Like anything else in science, dark matter and dark energy are the best explanations for the current data. If that data changes, there may need to be different explanations. That's how science works.

There are certainly other more counter-intuitive concepts in current physics than dark matter and energy - consider, for example, hyper-inflation after the Big Bang at the cosmic level, and quantum entanglement at the atomic end.

I am sure there are any number of physicists who would like to find easier explanations - Einstein hated the counter-intuitive, probability based quantum physics, but he wasn't up to the task of finding an easier alternative. I don't think that means he wasn't a genius.

But, really, did you expect the universe to be easy to figure out?

#8 FarrOut

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Posted 10 October 2013 - 06:08 AM

One of the concepts I try to pass on to my kids is that just because you don't understand something doesn't mean it isn't true.

#9 CygnuS

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Posted 10 October 2013 - 06:16 AM

There's certainly a lot of evidence but how do we know that scientists haven't just manipulated the facts because the idea that Newtonian physics just doesn't work on large scales is something they just don't want to accept?

So apparently you are unaware of MOND (MOdified Newtonian Dynamics)? -
which is an alternative theory to explain the rotation curves of galaxies without
needing dark matter. There is a relativistic version of it known as TeVeS (tensor-
vector-scalar gravity). There is also a modified version of relativity called STVG
(scalar-tensor-vector gravity, which is different from TeVeS). Kinda blows your
conjecture out of the water.

I really liked MOND but I thought it has been rejected. I've never heard of STVG.

#10 Mister T

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Posted 10 October 2013 - 08:24 AM

Dark energy and Dark matter are not "solutions" to the "Problem"

They are place holders

Based on current understanding, they describe two yet unresolved observable phenomena, that have yet to be resolved using existing theories.

Some may balk at the terminology, as it may be biased more towards certain theories than others, but it is just nomenclature at this point.

we could use "invisible ether and invisible phlogiston" and we would be no closer or further from the ultimate understanding of the two phenomena.

#11 GregLee1

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Posted 10 October 2013 - 09:14 AM

Dark energy and Dark matter are not "solutions" to the "Problem"

They are place holders

They are? Can a place holder cause gravitational lensing? Is ordinary matter also a place holder?

#12 PeterR280

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Posted 10 October 2013 - 09:20 AM

All current theories are place holders until newer theories come along.

#13 PeterR280

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Posted 10 October 2013 - 09:35 AM

you do the best you can with what you have. General Relativity is the best theory we have so to make it work for the expansion that's being observed you have to introduce a dark energy. Likewise you have to keep Galaxies together so you have to introdice some invisible matter.

#14 PeterR280

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Posted 10 October 2013 - 10:32 AM

to make these ideas valid, a theory has to be deveolped as to what they are if in fact they exist. It needs an independent validation. It can't just be a plug to current theory. Then you can stand in line for your Nobel prize. I think it's very exciting because who knows what new ideas will come about.

#15 GregLee1

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Posted 10 October 2013 - 11:34 AM

to make these ideas valid, a theory has to be deveolped as to what they are if in fact they exist. It needs an independent validation. It can't just be a plug to current theory.

This notion of independent validation was proposed as the essential difference between an explanatory scientific theory and a mere model in the 1953 book Scientific Explanation, by R. B. Braithwaite. ("It was Braithwaite's poker that Ludwig Wittgenstein reportedly brandished at Karl Popper during their confrontation at a Moral Sciences Club meeting in Braithwaite's rooms in King's. The implement subsequently disappeared.")

#16 dvb

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Posted 10 October 2013 - 12:39 PM

The real test of a theory is that it is capable of empirical tests that could disprove it if it is not true. Successful theories withstand such tests.

#17 Jarad

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Posted 10 October 2013 - 01:58 PM

They are? Can a place holder cause gravitational lensing?


Yes. Dark matter is a place holder for whatever is causing both the gravitational lensing and the abnormal galaxy rotation curves. If the true cause turns out to be some type of particle with very little interaction, then that particle will replace "dark matter", once it is identified. Or if it turns out that a more rigorous application of GR can explain both, then the place holder will just go away completely. But until we identify what dark matter is, it's a placeholder.

Is ordinary matter also a place holder?


No, because we can detect and identify it.

Jarad

#18 GregLee1

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Posted 10 October 2013 - 02:19 PM


Is ordinary matter also a place holder?


No, because we can detect and identify it.

Jarad

Since evidently we can also detect dark matter, then the difference you're proposing must have to do with identification. What happens when you identify something? If "identify" means find independent verification of a thing's existence, then I'm wondering why discovering gravitational lensing by dark matter doesn't count to let it graduate from place holder to real thing. (That's why I mentioned gravitational lensing above.)

#19 PeterR280

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Posted 10 October 2013 - 02:57 PM

Because you don't know what is causing the gravitational field. You can only speculate that there is some sort of matter that is doing it. It could also be that the gravitational theories are incomplete when you get to Galactic dimensions. Until you identify a specific piece or pieces of matter that can be detected in some other way, it is pure conjecture.

#20 Jarad

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Posted 10 October 2013 - 04:43 PM

Right now I think that it is most likely that dark matter is some type of particle that doesn't interact much with normal matter or itself. But there is still some chance that perhaps we are miscalculating the mass causing the lensing effects due to computer simplifications of general relativity. There are a few people (like DeSitter) who believe this to be the case. While I consider that explanation to be less likely, I still cannot rule it out completely. So I consider dark matter to still be a placeholder until we can either detect what those particles are via some other method than just gravitational lensing, or until all the other potential explanations are completely ruled out.

Jarad

#21 PeterR280

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Posted 10 October 2013 - 11:32 PM

There is more evidence than gravitational lensing. Orbital velocities of galaxies require dark matter to keep the galaxy together.

#22 Jarad

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Posted 11 October 2013 - 06:28 AM

Yes, but I find it easier to believe that approximations to GR used to calculate the orbits is causing that issue than the lensing. It seems to me that the lensing is the stronger of the two for there being real particles there causing it.

Like I said, I think that the data supports there being some type of particle with mass out there. I consider "dark matter" a place holder for 2 reasons:
1 - there is some chance that the effect is due to a miscalculation, and no extra mass is needed (unlikely but possible)
2 - we haven't identified the particle. When we do, then we won't call it "dark matter", we'll give it a specific name and characterize it. "Dark matter" just means "something we haven't identified yet goes here".

Jarad

#23 PeterR280

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Posted 11 October 2013 - 08:05 AM

It's interesting that dark matter is so much more than ordinary matter, yet calculations at the planary level don't show any discrepency as far as I know.

#24 Jarad

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Posted 11 October 2013 - 08:16 AM

Assuming it is spread fairly thinly, it would have much less effect on a planetary scale than on a galactic scale, but yes, that's another reason I am not 100% convinced yet. I still think it's the best answer we have to fit the available data, but it's not a slam-dunk.

Jarad

#25 CygnuS

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Posted 11 October 2013 - 04:03 PM

Thanks for all the responses. Ideas come in and out of favor all the time. Dark matter is certainly popular right now and from everything I've heard MOND is basically dead.
Scientists are treating dark matter like it is set in stone and are no longer considering ideas like MOND (although there are a few exceptions). Is this just because they're hopping on the band wagon that is popular at the moment or have they really proven that dark matter is real and it's not possible that mighty humans could be wrong about Newtonian mathematics and/or general relativity? After all, there are no scientific ideas that seem to last. We would be closed minded to think that certain things will always be viewed as the complete truth, be it an Earth centered Universe or what we now accept as truth.






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