Extraordinary claims require extraordinary proof

[Reality Check]

An extraordinary claim would be stating that dark matter and dark energy exist with no evidence.

Two plausible (and ordinary) claims are

• Galactic rotation curves show that there is about 400 times the observed mass in the galaxies. The velocity dispersions of elliptical galaxies show that there is more mass than is seen. Galactic clusters also have "missing" mass.
  The missing mass in these cases is not observed so a good name for it is: Dark Matter.
  The observed structures of the universe are replicated in models of Big Bang cosmology that include cold dark matter.
• The cosmic background radiation shows that the curvature of the universe is very close to flat. The total matter in the universe (including dark matter) supplies 30% of the mass required for a flat universe. So something else has to supply the missing mass. This is not matter and so it must be energy (remember E = mc²). The name chosen: Dark Energy.

 

[sol invictus]

That doesn't make any sense. Which is why I ignored it.

It makes sense to every other poster in this thread. You might try to understand it, because it's a question that (until you answer it, if you can) renders your point moot.

We have observed a set of phenomena which we can all agree are extraordinary. It's those observations that constitute the extraordinary evidence which is required.

At that point you have two choices - either deny the observations, or find a claim you consider less extraordinary which can account for them. If you can't do either, then we are done, and DM and DE are the best (and least extraordinary) theories about the world.

 

[robinson]

It makes sense to every other poster in this thread.

No, no it doesn't.

Fallacy, dude. You don't need to come up with a better idea to conclude that a particular idea is bad. Ideas can be and often are objectively bad, without comparison.

Of course is a fallacy. Trying to respond is like feeding a troll. Or smacking a tarbaby. Best to ignore it.

 

[edd]

Of course is a fallacy. Trying to respond is like feeding a troll. Or smacking a tarbaby. Best to ignore it.

Actually, it's not obvious it is. If I said something like
"Crows are black because the only thing they eat is coal"
then you wouldn't need a better explanation of why crows are black to say my idea is bad because my idea wouldn't fit the evidence.

However, the case here is that DM and DE are a bad idea because they seem a priori unlikely. In this case, you do need another idea to compare against to decide which is best, as a priori unlikely ideas are not necessarily bad. They can be good when they're the only explanation you have. In the words of Sherlock Holmes:
"when you have eliminated the impossible, whatever remains, however improbable, must be the truth"
If someone had come up to Sherlock with a more probable explanation he'd simply not thought of I'm sure he'd have jumped on it.

 

[sol invictus]

No, no it doesn't.

Fine. Many others then.

Of course is a fallacy. Trying to respond is like feeding a troll. Or smacking a tarbaby. Best to ignore it.

A tarbaby??

You're on very dangerous ground, but I'll ignore that.

Since you obviously can't answer the question, there is nothing to discuss. It's very simple - here are two models: the universe without DM and DE, and the universe with them. A priori the first is more likely - the second is "extraordinary", quite literally.

Now add the (extraordinary) evidence from modern observational cosmology. The odds that the first model is correct are now essentially zero. The odds of the second are unchanged (or increased, depending on your taste). The first model is now far more "extraordinary" than the second. Since there is no third model available, we accept the second, at least for now.

 

[m_huber]

An extraordinary claim would be stating that dark matter and dark energy exist with no evidence.

Two plausible (and ordinary) claims are

• Galactic rotation curves show that there is about 400 times the observed mass in the galaxies. The velocity dispersions of elliptical galaxies show that there is more mass than is seen. Galactic clusters also have "missing" mass.
  The missing mass in these cases is not observed so a good name for it is: Dark Matter.
  The observed structures of the universe are replicated in models of Big Bang cosmology that include cold dark matter.
• The cosmic background radiation shows that the curvature of the universe is very close to flat. The total matter in the universe (including dark matter) supplies 30% of the mass required for a flat universe. So something else has to supply the missing mass. This is not matter and so it must be energy (remember E = mc²). The name chosen: Dark Energy.

Nicely put.

 

[robinson]

In 1998, astronomers found that distant supernovae were dimmer, and thus farther away, than expected. This suggested the expansion of the universe was accelerating as a result of a mysterious entity dubbed dark energy, which appears to make up 73% of the universe.

But trying to pin down the nature of dark energy has proven extremely difficult. Theories of particle physics suggest that space does have an inherent energy, but this energy is about 10120 times greater than what is actually observed.

This has caused some cosmologists to look for alternative explanations. "I don't have anything against dark energy, but we ought to make all possible efforts to see whether we can avoid this exotic component in the universe," says Sabino Matarrese of the University of Padova in Italy.

So he and colleagues, including Edward Kolb of the Fermi National Accelerator Laboratory in Batavia, Illinois, US, decided to model the universe as having large-scale variations in density.

That contradicts the standard model of cosmology, which assumes that the universe is homogeneous on large scales. In the homogeneous model, known as the Friedmann-Robertson-Walker (FRW) universe, the effect of dark energy is to stretch space, thus increasing the wavelength of photons from the supernovae.


A similar effect was seen when the researchers added large-scale spherical holes to the FRW universe. They allowed the density of matter within each hole to vary with radius and found that in certain cases, photons travelling through under-dense voids had their wavelengths stretched, mimicking dark energy.

The extent of the effect depends on the exact location of the supernovae and how many under-dense regions the photons have to cross before reaching Earth. And Matarrese cautions that the deviations are not enough to explain away all of the observed dark energy. He says their model is still very preliminary: "We are very far away from getting the full solution."

Cosmologist Sean Carroll at Caltech in Pasadena, US, says the Swiss-cheese model is interesting and useful as a test of more mainstream theories. "The overwhelming majority of cosmologists think that the completely smooth approximation is a very good one," Carroll told New Scientist. "But if you want to have confidence that you are on the right track, you better not just make assumptions and cross your fingers, you better test it."

http://space.newscientist.com/article/dn12574-swiss-cheese-universe-challenges-dark-energy.html

 

[MattusMaximus]

That doesn't make any sense. Which is why I ignored it.

Hand-wave!!!

Wow, an argument from incredulity to support his argument from incredulity... I must say the wonders never cease

 

[Reality Check]

robinson: The article states "The overwhelming majority of cosmologists think that the completely smooth approximation is a very good one". It is this smooth approximation that requires the existence of dark energy. This make dark energy an ordinary claim.
Sabino Matarrese does describe dark energy as "exotic" but other people would find the concept of a "Swiss cheese" universe just as exotic.

 

[sol invictus]

http://space.newscientist.com/article/dn12574-swiss-cheese-universe-challenges-dark-energy.html

That idea has been quite thoroughly debunked. Furthermore it wasn't supposed to account for DM - just DE. What they were doing is attempting to construct a third model (see my post above). They failed.

One way to see why it couldn't possibly work is to consider the following: we know that standard cosmology plus a positive cosmological constant matches the observational data if the energy density in the CC is many times greater than the energy in ordinary matter. Kolb et al wanted to argue that the effects of inhomogeneities, once properly taken into account, might change the predictions to the point they could match the data. But that would mean that the contributions of the inhomogeneities need to be larger than the energy density in matter - which means the entire approximation that the universe is smooth is completely wrong. There is no way in the world that such a model would evolve just exactly like it a standard smooth cosmology, but with the addition of one (smooth) parameter. That would be extraordinary.

Now, it's obviously possible that someone might, at some point, succeed in constructing a third model - particularly in the case of DE, where the evidence is weaker. But until that time, DE and DM are the null hypothesis.

 

[Mojo]

That doesn't make any sense. Which is why I ignored it.

If the laws of physics are correct and the observations are correct, then there must be a lot of stuff in the universe that we can’t see.

So if there isn’t a lot of stuff out there that we can’t see, we have three possibilities:

1. The observations are wrong;
2. The laws of physics (which are themselves supported by a large body of observations) are wrong;
3. Both the observations and the laws of physics are wrong.

So, which is the least extraordinary claim: that the laws of physics are wrong, that the observations are wrong, or that there is stuff that we can’t see?

What would Occam do?

 

[AkuManiMani]

Extraordinary claims require extraordinary proof

Last I checked it only required extraordinary evidence

 

[Dorian Gray]

Very convincing. You say it's bad, without any argument for why we should take your opinion seriously, without commenting on the fact that every time we build a bigger accelerator we find new particles (making it rather presumptuous to think we've found them all already, no?), without noting that we didn't think neutrinos were massive until we discovered that a few years ago (and a little heavier and that would be that), without offering a better idea, and without noticing that, with about 4 parameters a theory of DM+DE can explain every single one of the millions of observations we've ever made about the universe... but since you say so, it must be.

You sound like a little kid who's going to take his ball and go home.

Someone has an idea: they're going to take all their money and invest it in lottery tickets. If I'm 99% of the population, I can see that is objectively a bad idea without assistance. However, if I'm you, I can't tell if it's a bad idea until someone comes up with a better idea for me to compare it to.

I guess some people are just more perceptive than others.

 

[Dorian Gray]

If the laws of physics are correct and the observations are correct, then there must be a lot of stuff in the universe that we can’t see.

So if there isn’t a lot of stuff out there that we can’t see, we have three possibilities:

1. The observations are wrong;
2. The laws of physics (which are themselves supported by a large body of observations) are wrong;
3. Both the observations and the laws of physics are wrong.

So, which is the least extraordinary claim: that the laws of physics are wrong, that the observations are wrong, or that there is stuff that we can’t see?

What would Occam do?

Occam would observe that the laws of physics didn't work at the quantum level, requiring the invention of quantum physics. Occam would deduce that it might be the case that the laws of physics don't work at the universal/intergalactic level either, requiring the invention of intergalactic physics. Therefore, he would conclude that the laws of physics must be wrong again, and he'd go off and invent intergalactic physics.

 

[sol invictus]

<nonsense cleaned>

Let me summarize your argument from before:

I don't like it, therefore it's wrong.

I called you on it, and you resort to juvenile insults and a strange and irrelevant analogy.

'Nuff said.

 

[sol invictus]

Therefore, he would conclude that the laws of physics must be wrong again, and he'd go off and invent intergalactic physics.

You mean, like modifying our theories by adding dark matter and dark energy?

 

[AkuManiMani]

I swear this forum is awesome. Its like watching the rhetorical equivalent of street fighting xD

 

[robinson]

Or an episode of South Park.

 

[Klimax]

Or an episode of South Park.

This is more like Star Trek and guess who are the aliens. (And no Sol invictus and others NOT!)
(And,no,I do not think you are vulcan...)

 

[robinson]

Vulcan should be capitalized.