Constructing Theories with Little Information

[wolram]

How can anyone construct a theory with less than 5 % of the information,
i know that you lot are very cleaver, but AE would be a dwarf to any one
that can get a 100% ansewer from 5% information available.

 

[mathman]

What is your point??

 

[selfAdjoint]

What is your point??

I conjecture he means that ordinary matter, which we can expeiment with, is less than 5% of the energy in the universe, the other 95% being dark matter and dark energy, about which (he supposes) we can only theorize.

 

[mathman]

selfadjoint's reply seems plausable, but I would like to hear from wolram.

 

[kmarinas86]

How can anyone construct a theory with less than 5 % of the information,
i know that you lot are very cleaver, but AE would be a dwarf to any one
that can get a 100% ansewer from 5% information available.

You shouldn't. It's like taking someone who just turned 19, measuring their change in height after one year, and mutiplying by 20 to get the height change since birth. It's not a very reliable method. It's also unscientific in the sense that objectivity is proportional to the amount of accurate information used, and a theory that is known be consistent with only 5% of the accurate information is a very dubious proposition. "Precise" information that lacks all accuracy is worthless.

 

[wolram]

selfadjoint's reply seems plausable, but I would like to hear from wolram.

SA, is quite right, AFAIK, no one knows, what dark energy/matter is,
if the higgs exists, if supersymetric particles exist, what the origin of gravity
is, i wonder what AE would think, and if he would modify his theory, i want
to think we know or understand part of the mechanics of the universe, but
it seems to me that in this field maths is more important than reality,
hawkings tells us that black holes evaporate ,with no possibility of observational proof, and so it goes on, maths can model real and imaginary
things, but should imaginary things be included in a theory, i think they can
if the possibility of the existence of them can be verified in a life time.
Space time is the most unintuitive mind sapping theory, we can give it a
few properties but not say what it is or demonstrate it in the lab, yet it is
the foundation of modern theories, i need some thing solid to hold on to
not an arxiv ful lof math that can show all most any thing is possible however improbable.
my rant is over.

 

[rtharbaugh1]

Hi wolram

What if the other 95% is pretty much the same as what we do see? Usually it is assumed that the laws of physics don't change from place to place or from time to time, so why should dark matter be any different from the matter we can see?

My pet theory is a many-worlds variation. I think that the alternate spacetime events are still in contact just before they depart, at very very short time scales. And there are always more alternate spacetimes departing, so the departing spacetime material still affects the gravitational fields.

The ten to one ratio is suggestive. In a Kepler stack of densly packed uniform spheres, twelve spheres surround each one. But in spacetime, there must be three spheres for any event. One is the one we see, one is the "real" past, one is the "real" future, leaving ten that are departing along trajectories that take them away from our time cone. But before they leave, they still have an effect.

Anyway, hope all is well for you in merry old England.

Richard

 

[wolram]

Hi Richard, It is cold and wet in my part of the country, a little snow last night.

In my simlistic minded way of thinking either, dark matter is ordinary matter
that has just not shown itself to us, ( i bet a pound to a penny that the
universe is teeming with stuff) or that some ideas are just wrong.

 

[Son Goku]

what the origin of gravity

The Stress-Energy properties of matter.

is, i wonder what AE would think, and if he would modify his theory, i want
to think we know or understand part of the mechanics of the universe, but
it seems to me that in this field maths is more important than reality,
hawkings tells us that black holes evaporate ,with no possibility of observational proof, and so it goes on, maths can model real and imaginary
things, but should imaginary things be included in a theory, i think they can
if the possibility of the existence of them can be verified in a life time.
Space time is the most unintuitive mind sapping theory, we can give it a
few properties but not say what it is or demonstrate it in the lab, yet it is
the foundation of modern theories, i need some thing solid to hold on to
not an arxiv ful lof math that can show all most any thing is possible however improbable.
my rant is over.

I think you might have a skewed view of what physics is like on a day to day basis. A lot of physicists work in modelling of fluids, condensed matter physics or experimental particle physics. In fact the majority of physicists are experimentalists.

Theoretical physics might have a few "out there" unverified ideas, but these are just current guesses. Nobody is actually saying that supersymmetry is definitely a property of nature. These are just estimates and ideas of what post-Standard Model physics might be like. So they will be unverified by their sheer "recentness".

However theoretical physics has very successful theories such as Quantum Mechanics, Quantum Electrodynamics, Chromodynamics, General Relativity, ...e.t.c. All of these have been confirmed to incredible accuracy.
Add to this the even greater volume of emergent phenomena that experimental physicists have explained and you'll see that physics has explained a great amount and it isn't just maths.

 

[ZapperZ]

SA, is quite right, AFAIK, no one knows, what dark energy/matter is,
if the higgs exists, if supersymetric particles exist, what the origin of gravity
is, i wonder what AE would think, and if he would modify his theory, i want
to think we know or understand part of the mechanics of the universe, but
it seems to me that in this field maths is more important than reality,
hawkings tells us that black holes evaporate ,with no possibility of observational proof, and so it goes on, maths can model real and imaginary
things, but should imaginary things be included in a theory, i think they can
if the possibility of the existence of them can be verified in a life time.
Space time is the most unintuitive mind sapping theory, we can give it a
few properties but not say what it is or demonstrate it in the lab, yet it is
the foundation of modern theories, i need some thing solid to hold on to
not an arxiv ful lof math that can show all most any thing is possible however improbable.
my rant is over.

OK, now it's time for my rant.

The way you put this is as if we know nothing. You also seem to be forgetting that the way we DEDUCE the existence of dark matter is based on what we ALREADY KNOW. It means that if we know nothing, we would not have made the deduction that there is dark matter in the first place! Think about it.

We can construct a theory because we know it works. We just don't know to what extent the theory works. That's why scientists continue to be employed. There are still mysteries of the world we live in. However, just because there are still things we don't know doesn't mean that there are nothing that we already know! We know how your semiconductor works regardless whether we know about the Higgs boson or not (and you'd be surprised to know that the physics of the Higgs mechanism has its origin in the same field of physics as the study of semiconductors).

I've seen these types of claims so many times on here that it is finally getting to me - quotes of people like Feynman and others that we don't understand such-and-such, as if those things can be used as arguments to justify that we know nothing about anything. If I have my ways, people who make claims such as this should be smacked on the back of their heads with a bat and made to read a text on solid state physics so that they finally get it through their heads that their cell phones and computers and iPods etc. would not work if we know nothing.

Zz.

 

[arildno]

Hmm..isn't it just because your predictions WOULDN'T add up unless you postulate the existence of "dark matter", that you say that dark matter exists?

Where is the independent evidence of its existence?

 

[kmarinas86]

OK, now it's time for my rant.

The way you put this is as if we know nothing. You also seem to be forgetting that the way we DEDUCE the existence of dark matter is based on what we ALREADY KNOW. It means that if we know nothing, we would not have made the deduction that there is dark matter in the first place! Think about it.

We can construct a theory because we know it works. We just don't know to what extent the theory works. That's why scientists continue to be employed. There are still mysteries of the world we live in. However, just because there are still things we don't know doesn't mean that there are nothing that we already know! We know how your semiconductor works regardless whether we know about the Higgs boson or not (and you'd be surprised to know that the physics of the Higgs mechanism has its origin in the same field of physics as the study of semiconductors).

I've seen these types of claims so many times on here that it is finally getting to me - quotes of people like Feynman and others that we don't understand such-and-such, as if those things can be used as arguments to justify that we know nothing about anything. If I have my ways, people who make claims such as this should be smacked on the back of their heads with a bat and made to read a text on solid state physics so that they finally get it through their heads that their cell phones and computers and iPods etc. would not work if we know nothing.

Zz.

Our understanding (and the tangibility) of electromagnetism and computer electronics is light years ahead of our understanding (and lack of tangibility) of most of the said Dark Matter and all of the said Dark Energy.

We can create antimatter, neutrinos, build electronic components or what have you. But we have not the slightest clue on how to create dark energy. We enough trouble creating gravitons, tachyons, etc.

But that can change, if we discover ways to harness such energy. But Dark Energy may prove to be more elusive than Neutrinos (and much longer for us to find a way to interact with it).

It rough to compare them this way. That it is "implied" does not mean it is observed. It's almost like palm reading or "reading" a symbolic treasure map. You have a theory of what to expect based on the distribution of matter (the map of what you see), and from there, you deduce the existence of what you can't see. And clearly, there emerges more than one theory, due to the indirectness through which all of this is "observed". The observable dark matter (brown drawfs, orphan planets) may be more than we thought however - I don't dispute about that. However, if there is a claim of something we haven't observed directly, we must expect a controversy (one must necessarily follow as a result of the lack of direct experience).

Well, obviously though, GR has passed many predictions (Gravitational Waves, Black Holes, Bending of Starlight, Gravitational Redshift), but GR, being invisible cause with visible effects, it's hard to get everyone to agree that this is the correct theory (100% agreement has never happened in the Modern Era of Physics). That's the nature of doubt and why people have it.

 

[ZapperZ]

Our understanding (and the tangibility) of electromagnetism and computer electronics is light years ahead of our understanding (and lack of tangibility) of most of the said Dark Matter and all of the said Dark Energy.

We can create antimatter, neutrinos, build electronic components or what have you. But we have not the slightest clue on how to create dark energy. We enough trouble creating gravitons, tachyons, etc.

But that can change, if we discover ways to harness such energy. But Dark Energy may prove to be more elusive than Neutrinos (and much longer for us to find a way to interact with it).

It rough to compare them this way. That it is "implied" does not mean it is observed. It's almost like palm reading or "reading" a symbolic treasure map. You have a theory of what to expect based on the distribution of matter (the map of what you see), and from there, you deduce the existence of what you can't see. And clearly, there emerges more than one theory, due to the indirectness through which all of this is "observed". The observable dark matter (brown drawfs, orphan planets) may be more than we thought however - I don't dispute about that. However, if there is a claim of something we haven't observed directly, we must expect a controversy (one must necessarily follow as a result of the lack of direct experience).

Well, obviously though, GR has passed many predictions (Gravitational Waves, Black Holes, Bending of Starlight, Gravitational Redshift), but GR, being invisible cause with visible effects, it's hard to get everyone to agree that this is the correct theory (100% agreement has never happened in the Modern Era of Physics). That's the nature of doubt and why people have it.

I'm not sure what you wrote here have anything to do with what I wrote. I was NOT trying to stress the validity of "dark energy" or "dark matter". If you read my post again, you'll notice that I never adopted that point of view. I work in a reseach-front field of physics. I realize well enough that things like this should not be adopted as a done deal.

What I DID write was the FACT that we would not have known about any "dark" anything if we didn't have an established theory in the first place. Dark energy would not have come into existence if GR didn't exist. Now maybe there's another explanation for this apparent effect (I've posted about this in another thread), but it is plainly IRONIC to question how we could know about it (or our world) when IT came out of our established theory in the first place.

Zz.

 

[kmarinas86]

it is plainly IRONIC to question how we could know about it (or our world) when IT came out of our established theory in the first place.

Oh I see now. I agree with the "ironic" part.

 

[arildno]

I'd like to emphasize that just because some phenomenon must be postulated by some theory in order to get correct predictions does not necessarily make such postulates into ad hoc measures like epicycles.

Rather, one might say that the theory necessitates the existence of this phenomenon, i.e, the theory generates a scientific PREDICTION.

But in that context, I am curious as to what sort of independent evidence do we have that dark matter does, in fact, exist?

 

[selfAdjoint]

But in that context, I am curious as to what sort of independent evidence do we have that dark matter does, in fact, exist?

I don't think there is a clear statement of the different kinds of evidence over at the astrophysics forum. This question came up when the idea the the rotation patterns of the galaxies, traditionally explained via dark matter, were suggested to be due to subtle GR effects. Critics of the idea then asserted that there are lots of other reasons to believe in dark matter, including conjectured sightings. But AFAIK these reasons were never layed out in a surveyable way. Enquiring minds want to know!

 

[arildno]

Am I right in surmising that the "dark matter"-hypothesis is the simplest/most elegant (in some sense of the word) way of explaining the discrepancy of predictions gained from GR (with NO dark matter postulated) and the observational material?

 

[rtharbaugh1]

http://www.nasa.gov/home/hqnews/2006/feb/HQ_M06067_Milky_Way_Map.html

This link from the news sidebar on PF uses xray evidence to conclude that we are undercounting the star population of galaxies by as much as a hundredfold. Dark matter may not be so very dark after all, but maybe should be called Dim matter instead?

R

 

[wolram]

http://www.nasa.gov/home/hqnews/2006/feb/HQ_M06067_Milky_Way_Map.html

This link from the news sidebar on PF uses xray evidence to conclude that we are undercounting the star population of galaxies by as much as a hundredfold. Dark matter may not be so very dark after all, but maybe should be called Dim matter instead?

R

well that makes me feel a little bit better.

 

[mathman]

To wolram. Unfortunately, there is other evidence that seems to be consistent with the amount (5%) of ordinary matter in current models. Specifically, the deuteron to proton ratio, in addition to other nuclei that came from the big bang.

Also visible matter is only a small fraction of the 5% - the rest is stuff like brown dwarfs and cool gas clouds, which don't emit much radiation.

 

[marcus]

Am I right in surmising that the "dark matter"-hypothesis is the simplest/most elegant (in some sense of the word) way of explaining the discrepancy of predictions gained from GR (with NO dark matter postulated) and the observational material?

Hi arildno, it depends very much on the "sense of the word".
If you are at all interested then I would suggest watching Joao Magueijo's Perimeter talk that he just gave. Or reading the paper on which the talk was based. there is an IN SOLAR SYSTEM test in progress.
Magueijo's talk is very up to date and is based on
a MOND paper he just wrote with Bekenstein
https://www.physicsforums.com/showpost.php?p=917936&postcount=452
http://arxiv.org/abs/astro-ph/0602266
MOND habitats within the solar system
(we know Jacob Bekenstein from BH temperature and entropy, he was in at the start with Hawking----BH could stand either for Bekenstein-Hawking or for Black Hole.

The Perimeter Institute streamer site is down for maintenance until Monday. After Monday go here
http://streamer.perimeterinstitute.ca:81/mediasite/viewer/
and click on "seminar series" in the sidebar menu on the left
and they are listed latest first, so Magueijo will be near the top of the list.

He explains there are two alternative hypotheses to explain galaxy rotation curves and other phenomena----MOND and DM.
You could say that MOND is the simplest/most elegant in some sense.

You could also say that DM is the simplest/most elegant in some sense.

He explains where one is stronger or simpler and where the other one is. for galaxy rotation curves MOND does especially well.

But beyond the simplicity and elegance there is the question of how nature is and what model will pass the empirical test. And there is a possible test of MOND versus DM by the LISA PATHFINDER space probe that measures the solar system gravitational field in the region between the Earth and the Lagrange (L1) point.At this point it is not clear to me that DM is going to win. I think instead of prejudge and lean in either direction, it would be better simply to be aware of both.

 

[arildno]

Thank you,marcus!