The Story of the Universe: : Tutorial :

I like to visualize the possible expansion of the universe as spherical lump of raw raisin bread dough floating weightless in space. If we add some heat and begin to bake the spherical raisin bread, the dough will expand, but the raisins will not. The raisins represent galaxies. An observer on one raisin deep in the dough would perceive the raisins around him to be uniformly moving away in all directions. But some raisins would be sitting on the surface. An observer on one of those raisins would have a very different perspective. That observer would only see raisins in half of the night sky. That observer would know which way was up and conversely which way was down toward the middle of the dough, or the origin of the big bang. In 4 dimensional spacetime we say that no observer should be able to point to the original starting point in space, but I just showed how, in 3 dimensional space, there could be some observers with a better view than others. So, a paradox.

The raisin bread analogy happens in 3 dimensional space. In 4 dimensional spacetime the galaxies are still moving away from each other, whether you say that is because of spacetime expanding or not. The distance between galaxies is increasing either way.

I realize spacetime is 4 dimensional. But that does not cancel out the fact that the universe is still 3 dimensional. I can look around in 3 dimensions. In my 3 dimensional example, the shape of the universe is a sphere, since, according to the big bang theory, the universe expanded in all directions from a very small point. The spherical raisin bread has raisins spread throughout the dough, but some raisins are on or near the surface. The universe should be much same, with at least some galaxies on it's surface. An observer on such a galaxy could look around in 3 dimensional space. That observer would see other galaxies in only half the night sky. Is this true or false? If you say it is false, please explain why. Thanks.



---Futilitist

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No, again you ignore the fact that while the analogy is a good one [the same as the blowing up a balloon analogy]the analogy in describing the observed universe, has limitations.eg: For the blowing up a balloon, the inner part of the balloon plays no part and neither does beyond the surface of the balloon. The balloon skin with dots on, plays the part of spacetime to show that while the dots appear to be moving apart, the reality is that the spacetime/balloon is expanding....The same with the raisin loaf....the baking makes the dough/spacetime expand and the raisins/galaxies receding due to that expansion...the surface of the loaf plays no part in the analogy as in reality, spacetime has no center, or edges.

Yes, because the Universe/spacetime/dough is expanding. That is the message of the analogy.

You are carrying the analogy too far. Remember the Singularity you speak of is a Singularity of all spacetime, as opposed to a BH Singularity being imbedded in that spacetime.
All of spacetime expands and the only center anyone, anywhere in the Universe/spacetime can logically infer, is the center of their own observational Universe/spacetime. eg: The Earth is the center of its observable Universe, just as beings on a planet in the Virgo supercluster is the center of their own observable Universe.

 

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You explain why the balloon analogy has limitations, then you say the raisin bread analogy suffers from the same problems. This is a bait and switch. The two analogies are fundamentally different. I used the raisin bread analogy, not the balloon analogy.

We are 3 dimensional. The solar system is 3 dimensional. Our galaxy is 3 dimensional. Galaxies are situated in 3 dimensional space.

So the universe must be 3 dimensional. The raisin bread is also 3 dimensional. Inside the observed universe we see galaxies moving away from us because the space between them is expanding. Inside the raisin bread we see raisins moving away from us because the dough is expanding. The raisin bread has raisins on it's surface. Why doesn't the universe have galaxies on it's surface?



---Futilitist

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The two analogies are both meant to show that the light we see from receding galaxies is due to a cosmological red shift, not a Doppler red shift.....or that it is spacetime [the balloon skin or the dough in your loaf] that is expanding not the raisins or dots on the balloon.

Plus time makes 4.
"The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality".
 Hermann Minkowski, 1907

Because as I told you, the Universe has no edges or centers to speak of. That's why the surface you speak of is not a part of the raisin loaf analogy and what I mean by all analogies having limitations.

http://www.popscicoll.org/big-bang/the-expansion-of-the-universe.html

A useful analogy is a loaf of raisin bread rising as it bakes. Like space, the dough expands as it rises. Like galaxies, the raisins grow further and further apart as the dough expands, and the distance they move apart is proportional to their initial separation.

It is important to note the limits of this analogy. Unlike a loaf of bread, the universe has no edge, so there is no sense in which it is expanding into some bigger external space. As far as we can observe, the universe is all there is and at every point it is expanding.

 

The Dark Matter Paradox

Any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

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In our solar system, we have the sun in the center, which provides the gravity that causes the planets to orbit about it. The orbital speed decreases as a function of the distance from the sun, so that by the time you get to the outer planets, they are moving a lot slower than the ones in the center. This makes logical sense and is, in fact, what we observe.

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In galaxies, stars orbit the dense center of the galactic mass. Since they are obeying the same law of gravity as planets orbiting a star, they should be expected to behave like planets do, and we should see slower orbits in stars far from the center of the galaxies. Yet that is not what we see at all. The stars far from the center of distant galaxies are, in fact, moving much faster than expected!

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This mystery has been explained by positing the presence of invisible dark matter, which provides the extra mass necessary to make the outer stars orbit at a speed basically equal to the stars that orbit much closer to the center. That makes logical sense and, if true, matches what we observe.

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Knowledge sequence
1) We work out the physics of gravity and use it to predict the motion of planets orbiting the sun to a very high degree of accuracy.
2) We look at distant galaxies and notice that our law of gravity does not accurately predict the motion of stars orbiting galaxies.
3) We postulate the existence of a large amount of hidden mass, in the form of dark matter, to get our law of gravity to produce a result that matches our observations.

This seems logical, but it actually produces a quite a paradox.

We are still using the basic law of gravity to accurately describe the orbital motion of planets around our sun. But we have to use a different law of gravity (gravity + dark matter) to explain the orbits of stars around distant galaxies. If the laws of physics are the same everywhere, why doesn't the presence of dark matter influence the orbits of the planets around our own sun?



---Futilitist

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You could say the same thing about Newtonian gravity and General Relativity.

That doesn't mean there's a paradox.

 

You could say a lot of things. That doesn't mean you have answered my question.

We are still using the basic law of gravity to accurately describe the orbital motion of planets around our sun. But we have to use a different law of gravity (gravity + dark matter) to explain the orbits of stars around distant galaxies. If the laws of physics are the same everywhere, why doesn't the presence of dark matter influence the orbits of the planets around our own sun?



---Futilitist

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Who says dark matter would be evenly distributed?

 

Who says it doesn't?

I don't need to use General Relativity to describe how an apple falls from a tree.

 

What is the other alternative explanation, MOND, but that also has certain conservations issues around it.

You have given the details of the observation, and Physics is required to explain this observation, It is quite likely in this case that the observation itself is bad unintentionally, for whatever reasons. (Quite likely when so much distances and so many motions are involved). But if this is not disputed then explanation is required....and thats where DM came into picture. The Paradox as stated by you is well there, with no resolution.

The problem with mainstream followers is that if anyone questions, then they ask give us the alternative, thats funny, holes can be poked in a theory / hypo without offering an alternative. with so much support from frontline guys, with so much funding, the apple cart is not going to get disturbed so soon..

See this Marcy guy, it took more than a decade to dethrone him, despite direct proof, because he was getting funds. An evil man can remain for more than a decade even after his devilish nature was known, just because he was getting fame and fund, then why not a bad theory, if that theory is getting funds in the name of Physics...But how long ?

I like one of the posters comments, he said I am writing, and waiting for the day this prevalent nonsense falls, then my theories will get prominence. Well he cannot do any better.


DM/DE is anothet BS in line with BH....but they are accepted as of now.

 

How do you explain the observed phenomena, then?

 

Did you understand that futilists created this Paradox ? It is always desirable and prudent to get a hold of the subject before jumpting into argument. And stop these funny one liners, contribute, learn something from Paddoboy.

 

You mean, Futilitist, was trolling.

 

No. Not trolling. You are, though.

I was just thinking about dark matter and I came up with this paradox myself. But it turns out to be a real paradox! You are all obviously just as unaware of this paradox as I was. Otherwise you would say something substantive about it.

I just found out that my dark matter paradox was real when I Googled: "Is dark matter everywhere?" because of your question about the distribution dark matter.

I found this:

http://www.technologyreview.com/vie...-why-astronomers-say-it-is-missing-in-action/

The Incredible Dark Matter Mystery: Why Astronomers Say it is Missing in Action

Astrophysicists believe that our galaxy must be filled with more dark matter than ordinary matter. Now astronomers say they can find no evidence of dark matter’s gravitational influence on the planets. What gives?

Astronomers have a problem. Whenever they study the large scale structure of the universe, it soon becomes clear that the amount of visible matter cannot possibly generate enough gravity to hold together the structures they can see. Things like galaxy clusters and even galaxies themselves ought to fly apart given the amount of ordinary matter they contain.

Something else must be holding these things together. So astronomers have dreamt up the idea of dark matter—mysterious, invisible and non-interacting stuff that fills the universe, generating the gravity necessary to hold everything together.

This isn’t a small problem requiring a tiny amount of extra mass. The problem is huge. According to the latest picture of the large-scale structure of the Universe from the Planck space mission, ordinary visible matter makes up just 5 per cent of the total mass/energy of the Universe whereas dark matter makes up 27 per cent (the rest is the even more mysterious dark energy).

To make the numbers work, astrophysicists tell us that our galaxy ought to be at least 80 per cent dark matter.

That means our Solar System ought to be swimming in the stuff. Indeed, physicists have calculated that particles of dark matter ought to slam into each human on the planet at a rate of 100,000 times a year, as we saw last year.

But that raises an important question. If we’re ploughing through a thick sea of dark matter as astrophysicists suggest, why don’t we see evidence of it?

Most dark matter detectors work by looking for evidence of the collisions that dark matter must make with ordinary matter. A few of these experiments say they have found tentative evidence of these collisions.

But there is another way to look for dark matter—by its gravitational effects on the Solar System itself. If the Sun is surrounded by a thick soup of dark matter, we ought to be able to see its gravitational influence on the orbits of the planets, moons and asteroids.

Today, Nikolay Pitjev at St. Petersburg State University and Elena Pitjeva at the Institute of Applied Astronomy in St Petersburg, both in Russia, have used the most detailed set of measurements of planetary orbits ever made to study this question. Their conclusion is that the gravitational effect of dark matter on the solar system is negligible.

Pitjev and Pitjeva have compiled an impressive data set consisting of some 677,000 measurements of planetary positions taken since 1910. These include optical measurements from observatories on Earth, ranging measurements from various spacecraft such as Cassini at Saturn and the Mars and Venus Express missions plus various Russian radar measurements of planetary positions taken between 1961 and 1995.

This data has become increasingly accurate in recent years. For example, the data from Cassini gives its distance at Saturn to within a metre or so.

Astrophysicists have used these measurements to model the behaviour of the solar system, taking into account the perturbations caused by the major planets, the Moon, the 301 largest asteroids, the other asteroids modelled as a uniform ring, the 21 largest trans-Neptunian objects and so on.

Having taken all this into account, Pitjev and Pitjeva looked for anomalous gravitational effects that might be the result of dark matter. “If dark matter is present in the Solar system, then it should lead to some additional gravitational influence on all bodies,” they say.

The puzzling news is that Pitjev and Pitjeva find no evidence of this stuff in their analysis. If it is there, its effect must be smaller than the errors in the data.

Indeed, to satisfy this limit, they calculate that the amount of dark matter within the orbit of Saturn must be tiny. “The dark matter mass in the sphere within Saturn’s orbit should be less than 1.7 10^−10M⊙,” they say. That’s about the mass of a large asteroid.

So astronomers are left scratching their heads. On the one hand, they say dark matter must hold our galaxy together with a vice-like gravitational grip. On the other, its gravitational effect on the Solar System is negligible. Something has to give.

This problem of the contradictory effects of dark matter on different scales is fast turning into the most fascinating and urgent problem in physics and astronomy.

Researchers are currently spending big bucks to design, build and run giant experiments looking for dark matter in our vicinity. And yet the evidence already gathered from other sources, such as this analysis by Pitjev and Pitjeva, suggest that this investment may produce a very poor return.

That won’t stop them looking and nor should it. But the dark matter problem is likely to generate significant controversy in the coming months and years.

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So this is a real paradox. Got any real answers?




---Futilitist

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MOND [Modified Newtonian Dynamics] is only apparently applicable to certain galaxies without the need to be tweaked.
DM is still a far better viable observable explanation.

You can tell yourself that for as long as you like......You still have nothing other than cheap unsupported talk.
Mainstream physics/cosmology remains mainstream because it is seen as the most logical reasonable explanation for our observations.
The chances of any alternative crank like the god or rajesh or anyone else for that matter, coming to a science forum such as this [which is open to all] and rewriting 21st century cosmology is zero.
It won't happen, but it makes these "would be's if they could be's"feel rather good within themselves.

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While the Black Neutron Star did not even see daylight.

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And if any changes do occur, it certainly won't be as a result of anything published in a science forum such as this.

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Thats good one and a good critical thinking !

I was of the opinion that you were referring to this known paradox, and Daecon was unaware of it.

 

Thanks. We are both right that Daecon was unaware of it.

No. The chances are near zero.

Then why doesn't dark matter affect the motions of the planets around our sun?



---Futilitist

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No this was your answer:

CONCLUSIONS
We investigated and estimated the possible gravitational influence of dark matter in the Solar system on the motion of planets based on the EPM2011 planetary ephemerides using about 677 thousand positional observations of planets and spacecraft, most of which belong to present-day ranging. Our results show that the mass of the dark matter, if present, and its density ρ dm are much lower than the present day errors in these parameters. We found
that the density ρ dm is less than1.1·10−20, 1.4·10−20, and1.4·10−19g cm−3 at the orbital distances of Saturn, Mars, and the Earth, respectively. Taking into account our constraining estimates, we considered the case of a possible concentration of dark matter to the Solar system center. The dark matter mass in the sphere within Saturn’s orbit should be less than 1.7·10−10M ⊙ even if its possible concentration is taken into account.


To which I really don't care. It is already quite well established that there is much more than meets the eye. But it is nice precision.

 

Not logic; just politics pad ; just politics of mainstream physics/cosmology .

 

What a charming baby !! My blessings...

See, Paddoboy, Incompetent fellows generally tend to follow some one for survival..Lets take in broader sense..

- In politics you would find 'side kicks' of a very powerful guy, their survival is dependent on this guy's success.

- In reall life you will find dicks, supporting a bully.

- In science there will be guys who will wholeheartedly support a theory however absurd it may be, becaus they lack that ability to think etc..


Such people have no business to be there in scientific discussions itself, but then they are.

So, you fall in Cat3..