Is the CMBR Data Truly Singular?

[Nile3]

I was watching through the wormhole and it occurred to me that the probe they sent in space to collect data on the cmbr couldn't do triangulation, meaning we could not test or see if the cmbr actually came from 2 sources of energy. How do we know for sure without testing it if the CMBR didn't come from multiple sources?

 

[Nile3]

"through the wormhole" is a show btw... I didn't look through one literally. :D

 

[russ_watters]

I was watching through the wormhole and it occurred to me that the probe they sent in space to collect data on the cmbr couldn't do triangulation, meaning we could not test or see if the cmbr actually came from 2 sources of energy. How do we know for sure without testing it if the CMBR didn't come from multiple sources?

Not sure what exactly you're talking about, but if the CMB came from multiple point sources, it would look like multiple point sources when we mapped it, instead of like it was coming from from everywhere. Perhaps you could go into some more detail about what you (the show) are trying to say. Triangulation of what? How should a CMB look if it came from two sources of energy?

 

[Nile3]

Not sure what exactly you're talking about, but if the CMB came from multiple point sources, it would look like multiple point sources when we mapped it, instead of like it was coming from from everywhere.

Well this is interesting, I guess I have problems grasping the way cosmologists proved this had to be coming from a big bang rather than something else since there may be a lot of unknown phenomenon yet to be discovered out there.

Let's say hypothetically the universe didn't come from a big bang, instead it is the way it is and has always been(with inflation/deflation) but some unknown process creates the CMB from the edge of the universe or outside(?) since 14 billion years ago, how would you eliminate this possibility with our current empirical data?

:D

 

[russ_watters]

Well this is interesting, I guess I have problems grasping the way cosmologists proved this had to be coming from a big bang rather than something else since there may be a lot of unknown phenomenon yet to be discovered out there.

That's the way theory works - you can't disprove an explanation you haven't thought of, you can only prove an explanation you have. The the data on the CMB fits the theory and no alternative theory exists that fits it as well. That's all that can be asked of a theory.

Let's say hypothetically the universe didn't come from a big bang, instead it is the way it is and has always been(with inflation/deflation) but some unknown process creates the CMB from the edge of the universe or outside(?) since 14 billion years ago, how would you eliminate this possibility with our current empirical data?

Well the universe has neither an edge nor an outside: current theory doesn't allow it and the uniformity of the CMB is a good indicator of it.

Also, I'm not sure how you can have an expanding universe without a Big Bang. If it is expanding, that means it was once a lot smaller...how small?

 

[Nile3]

I was imagining it could grow, shrink and deform itself depending on gravitational pull and dark energy.

Here's a neat little quote I found:
Astrophysicist George F. R. Ellis explains: "People need to be aware that there is a range of models that could explain the observations….For instance, I can construct you a spherically symmetrical universe with Earth at its center, and you cannot disprove it based on observations….You can only exclude it on philosophical grounds. In my view there is absolutely nothing wrong in that. What I want to bring into the open is the fact that we are using philosophical criteria in choosing our models. A lot of cosmology tries to hide that."

I think this and your explanation clarify what I had in mind. Thanks.

 

[russ_watters]

I was imagining it could grow, shrink and deform itself depending on gravitational pull and dark energy.

So you are suggesting these forces could be changing all the time? Based on what?

Here's a neat little quote I found:
Astrophysicist George F. R. Ellis explains: "People need to be aware that there is a range of models that could explain the observations….For instance, I can construct you a spherically symmetrical universe with Earth at its center, and you cannot disprove it based on observations….You can only exclude it on philosophical grounds. In my view there is absolutely nothing wrong in that. What I want to bring into the open is the fact that we are using philosophical criteria in choosing our models. A lot of cosmology tries to hide that."

I think this and your explanation clarify what I had in mind. Thanks.

I have a tough time believing one could actually make such a model explain the evidence, but regardless...

The "philosophical grounds" is Occam's Razor. That model (a fish tank universe) requires adding features and assumptions for which there is no evidence and not even any theoretical mechanism for how it could work. The assumption that we are at the center of the universe is unlikely given what we know of the universe (we're on a planet orbiting a sun, orbiting a galaxy, orbiting the center of a galaxy cluster) and the assumption that there is solid surface bounding it has no evidence to support it. Neither of these assumptions is necessary to explain the CMB and both add very difficult problems to deal with in the model, so why add them? (That's what the quote is saying, btw.)

There are also still people looking for the lumiferous ether in the margins of error in experiments on light. That's also not a very useful pursuit.

 

[Nile3]

There are also still people looking for the lumiferous ether in the margins of error in experiments on light. That's also not a very useful pursuit.

I heard about this before, could you expand on why this is a useless pursuit?

Also, I understand Ockham's razor has to be used continuously in science but is there a point where the lack of accuracy may mislead us in believing wrong or bad pictures of how the universe work?

 

[Chalnoth]

Also, I understand Ockham's razor has to be used continuously in science but is there a point where the lack of accuracy may mislead us in believing wrong or bad pictures of how the universe work?

Occam's Razor can be considered an unavoidable consequence of simple counting. Let's compare the following. Let's imagine I have two competing theories. One fits all the data perfectly with only one parameter. Another fits all the data perfectly with two parameters. So, given this contrived scenario, which of the two theories is more likely?

There are a couple of different directions to look at the problem from, but no matter which way you go, you're led right back to Occam's Razor. Here is how. First, let's take a data-centric view. Let's imagine that the True Universe could be a wide range of things, but happens to just be the way it is now. The second theory, since it contains two parameters instead of just one, would be accurate with a much larger number of potential True Universes. So, if Theory Two is true, then we must ask why it just so happened that the universe aligned itself perfectly so that Theory One also appears to be true. Most Theory Two universes will not look at all like Theory One universes, but ours happened to. The most reasonable explanation for this is that Theory One is actually the correct theory.

The other direction one can consider this from is the theory direction. Imagine that we just consider that even though Theory One fits the data, the truth is a two-parameter theory, but we don't know whether it is Theory Two or some other two-parameter theory. We know that with current evidence, both Theory One and Theory Two are indistinguishable. So, the question is, how many possible two-parameter theories could we produce that would replicate Theory One's results? There would be a tremendous number of them, perhaps an infinite number. We know, given the problem, that one of this tremendous number of two-parameter theories is correct. What is the probability that we just managed to hit upon the right one?

If, by contrast, the truth is a one-parameter theory, the space of one-parameter theories that match Theory One will be dramatically smaller, and so we have a higher probability of being correct. And even if we aren't absolutely right, it is actually more likely that Theory One will be a good approximation to the true behavior than Theory Two, for the same reasons outlined above. Thus while we have a one-parameter theory that correctly explains all of the evidence, any search for a two-parameter theory is useless.

 

[russ_watters]

I heard about this before, could you expand on why this is a useless pursuit?

It is useless because it is pursuing an idea that has no basis in evidence or theory.

Also, I understand Ockham's razor has to be used continuously in science but is there a point where the lack of accuracy may mislead us in believing wrong or bad pictures of how the universe work?

Lack of accuracy? You misunderstand: Occam's razor provides us with the quickest path to the most accuracy in our theories.

 

[Nile3]

Lack of accuracy? You misunderstand: Occam's razor provides us with the quickest path to the most accuracy in our theories.

Lack of accuracy in testing, not in the conclusions.


Thank you Chalnoth, nice explanation. As I finished re-reading it a second time, it dawns on me that the explanation you give is actually saying that string theory and other untestable theories (m-brane) may be possible to throw out entirely. Why is there so much hope in those fields of physics then? Are physicists just getting bored?

 

[Chalnoth]

Thank you Chalnoth, nice explanation. As I finished re-reading it a second time, it dawns on me that the explanation you give is actually saying that string theory and other untestable theories (m-brane) may be possible to throw out entirely. Why is there so much hope in those fields of physics then? Are physicists just getting bored?

Well, no, there are other reasons to think that string theory may be on the right track. First, unification between gravity and the other forces has been long sought-after, while string theory predicts the existence of quantum gravity. That alone is probably the biggest reason to think that maybe, just maybe, there may be something to it.

The second point is that string theory is actually a remarkably simple theory at its core. In particular, it has no free parameters, and it looks like the potential realizations of string theory are actually one and the same. So in this respect, it's actually the simplest theory possible.

The main difficulty, however, comes from working out the dynamics of the theory, which is fantastically difficult. And it makes it even more difficult when one considers that string theory doesn't predict one sort of region of space-time, but many, ours being just one of a vast array of possibilities. However, I would contend that this is actually a point in string theory's favor.

Specifically, if we just look at the standard model of particle physics and General Relativity, there are a large variety of numbers, many of which have to take on very particular values for life to be even remotely possible. There are two possible resolutions to this:
1. The fundamental theory of the universe uniquely predicts that these parameters take on those values, and so obviously life is going to be possible.
2. The fundamental theory predicts a wide variety of possibilities, and so life is guaranteed to happen somewhere at some time.

I strongly favor the second possibility because if a fundamental theory is to predict specific values for the parameters of the standard model, why would they just happen to fall only within the range where life is possible?

In the end, I think string theory falls in the category of, "interesting, needs work."

 

[russ_watters]

Lack of accuracy in testing, not in the conclusions.

I'm not following - what are you referring to?

 

[atyy]

"A CMB of cosmic origin (rather than one generated by starlight processed by iron needles in the intergalactic medium) is expected to have a blackbody spectrum and to be extremely isotropic. COBE FIRAS observations show that the CMB is very well approximated by an isotropic blackbody." http://nedwww.ipac.caltech.edu/level5/March03/Lineweaver/Lineweaver7_3.html

Concerning the cosmological principle (what Ellis was talking about), yes, many standard texts do talk about it being an assumption which may be problematic.

http://books.google.com/books?id=qh...=0CDUQ6AEwBQ#v=snippet&q=observations&f=false "the early universe is not yet directly accessible to our instruments, so we have no direct knowledge that has the high degree of isotropy and homogeneity that the present universe has. Any theory framed in a homogeneous, isotropic model must be treated very cautiously. We do not have the time here to study anisotropic or inhomogeneous models of the early universe, but this is a very active field of reserahc today"

http://books.google.com/books?id=uG...&resnum=7&ved=0CCAQ6AEwBg#v=onepage&q&f=false "Today the cosmological principle still has no direct observational verification, while models not obeying the principle ... are known .... inertia in thinking and of emotional attachment to the, mathematically elegant ... However, natural sciences, ... are said to use the criterion of consistency with observation ... At the very least in order to verify the cosmological principle, alternatives have to be considered ..."

 

[Chronos]

Assumptions are always tested, and data is data. The basic assumptions in cosmology have passed all observational tests to date. If you have a gripe, pick an assumption and apply your observational evidence that disputes it.

 

[Phrak]

I was watching through the wormhole and it occurred to me that the probe they sent in space to collect data on the cmbr couldn't do triangulation, meaning we could not test or see if the cmbr actually came from 2 sources of energy. How do we know for sure without testing it if the CMBR didn't come from multiple sources?

Two big-bangs, or naively, two matter-energy decouplings?? I like it. May your very
strange ideas come to empirical fruition and cause a massive panic attack, and frantic back-peddling among pontificates of shallow dogma.

 

[Chalnoth]

Two big-bangs, or naively, two matter-energy decouplings?? I like it. May your very
strange ideas come to empirical fruition and cause a massive panic attack, and frantic back-peddling among pontificates of shallow dogma.

Evidence-based conclusions are not dogma.

 

[George Jones]

How do we know for sure without testing it if the CMBR didn't come from multiple sources?

The CMBR did come from multiple sources.

 

[Chalnoth]

The CMBR did come from multiple sources.

Heh. I suppose if you want to call every atom in the early plasma a "source", sure :)

 

[Phrak]

Evidence-based conclusions are not dogma.

A false dichotomy.

 

[Chalnoth]

A false dichotomy.

No, it's just pointing out that the definition of dogma as used in George Jones' sentence does not include evidence-based conclusions. From Merriam-Webster: "dogma - a point of view or tenet put forth as authoritative without adequate grounds". This is clearly the sense in which he meant it, and it is just wrong.

 

[Chronos]

I believe George's intent was to say CMBR 'data' came from multiple sources, not the radiation itself.