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Scale Of The Universe?


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#21 Athelas

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Posted 14 February 2012 - 09:44 AM

Mathematicians are idiots. :D


I seriously hope that you are joking.

#22 jason

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Posted 14 February 2012 - 11:22 AM

i didnt take it that way. stripe did. but there some changes on black holes that i need to read about.im a bit rusty on some of the calculus that i learned.

#23 Stripe

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Posted 14 February 2012 - 06:04 PM

You didn't. Come on, the prediction of Black Holes through math is about 90 years old! This got predicted around WWI with math. We have now confirmed objects that actually fullfill these predictions. What's so weird about it?

The functionality of calculus is not dependent upon the existence of black holes. They may very well be real things, but if there are not any then calculus will still work.

It is over-reaching the scope of mathematics to name parameters or results from calculations as real objects. Maths is just a model of reality - not reality itself.

Hence my little dig. :)

#24 Athelas

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Posted 15 February 2012 - 04:25 AM

The functionality of calculus is not dependent upon the existence of black holes. They may very well be real things, but if there are not any then calculus will still work.

It is over-reaching the scope of mathematics to name parameters or results from calculations as real objects. Maths is just a model of reality - not reality itself.

Hence my little dig. :)


Obviously the functionality of calculus is not dependant upon the existance of black holes and vice versa. Schwarzschild's exact solution of Einstein's equation of general relativity led to Black Holes. Hence if calculus is correct, there must be black holes. I hope this makes sense to you somehow. I'm not sure how to explain this any other way (and the expression doesn't make much sense without a bit of background info). Black Holes were very controversial (and continue to be) at the time they were predicted this way so doubt and even fear made people (including scientists) say weird things.

#25 Stripe

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Posted 15 February 2012 - 08:54 AM

... if calculus is correct, there must be black holes....

Had you said, "If this model is correct, there must be black holes", I wouldn't have an issue.

It is not possible for calculus to be wrong. It is possible that the model is wrong. :)

#26 Codex

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Posted 03 May 2012 - 09:12 PM

I've got a question that perhaps someone can explain to someone like me who is no good at physics or astronomy. I heard somewhere that according to the Big Bang theory, the universe doesn't have a center. But wouldn't it have a center if everything was supposed to blow up out of that little dot somewhere. :)

Now, I don't believe in the BBT but I just wanted to understand it a little better.


You misunderstood, the universe certainly has a center, as any volume does. What you heard was that the expansion that we observe does not seem to be centered on a point. From our perspective, the vast majority of heavenly bodies are moving away from us, so it appears that we are the center... but this is also true from any other point in the universe. No matter where you are you would observe everything moving away from you.

Now, this seems counter-intuitive at first thought, but you have to realize that this is exactly what we would observe if all of the space in the universe was expanding equally. The classic example is to explain this is to attach things to a length of rubber band and then stretch that rubber band apart. As you stretch it it expands across it's entire length, so everything attached to it moves away from everything else. If you consider the perspective of any of those things then it would appear that everything else is moving away from that point, so there is no center of expansion.

Another classic example is that of raisins all moving apart from each other in a loaf of raisin bread that is rising in the oven. All of the material throughout the entire loaf of bread expands, the expansion is not centered on any point in the bread, but the bread of course still has a center.

#27 Stripe

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Posted 04 May 2012 - 09:09 AM

You misunderstood, the universe certainly has a center, as any volume does. What you heard was that the expansion that we observe does not seem to be centered on a point. From our perspective, the vast majority of heavenly bodies are moving away from us, so it appears that we are the center... but this is also true from any other point in the universe. No matter where you are you would observe everything moving away from you.

In quantised fashion? Redshifts of stars group into certain ranges dependent upon their distance. This is best explained if the Earth is near the center of the universe and at the center of the expansion (though there are attempts at ad hoc fixes to protect the big bang theory).

Now, this seems counter-intuitive at first thought, but you have to realize that this is exactly what we would observe if all of the space in the universe was expanding equally. The classic example is to explain this is to attach things to a length of rubber band and then stretch that rubber band apart. As you stretch it it expands across it's entire length, so everything attached to it moves away from everything else. If you consider the perspective of any of those things then it would appear that everything else is moving away from that point, so there is no center of expansion.Another classic example is that of raisins all moving apart from each other in a loaf of raisin bread that is rising in the oven. All of the material throughout the entire loaf of bread expands, the expansion is not centered on any point in the bread, but the bread of course still has a center.

These explanations assume the truth of the cosmological theory of homogeneity and isotropy. The simple model of the 3D observation of matter being the only one easily accepts the observations we see.

#28 Codex

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Posted 04 May 2012 - 09:35 AM

In quantised fashion? Redshifts of stars group into certain ranges dependent upon their distance.



Yes you are correct. In fact what we observe is that stars that are farther away from us are receding faster than stars that are nearer to us, on average. This makes perfect sense if you consider either of the two analogies I presented. From any point on the expanding rubber band the outer edges would appear to recede faster than any other point in the middle closer to your perspective, try it, it's true. This is actually great evidence in favor of a center-less expansion, an expansion of all points in space not centered on a given point.

This is best explained if the Earth is near the center of the universe and at the center of the expansion


Actually, it's evidence against that... if there were a center of expansion and if we were close to it we would not expect to observe a correlation between the distance of other heavenly bodies and their rate of recession from us.

These explanations assume the truth of the cosmological theory of homogeneity and isotropy.


Well, I don't think that's true, but even if it were what is your point? I am explaining a position, why wouldn't I assume that position to explain it? How else could I explain it?

Further, the degree of homogeneity and isotropy of the observable universe has been measured extremely accurately by the WMAP satellite based instrument... are you challenging these measurements and if so on what authority?

#29 Codex

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Posted 04 May 2012 - 09:37 AM

accidental double post...

#30 Stripe

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Posted 04 May 2012 - 10:49 AM

Yes you are correct. In fact what we observe is that stars that are farther away from us are receding faster than stars that are nearer to us, on average. This makes perfect sense if you consider either of the two analogies I presented. From any point on the expanding rubber band the outer edges would appear to recede faster than any other point in the middle closer to your perspective, try it, it's true. This is actually great evidence in favor of a center-less expansion, an expansion of all points in space not centered on a given point.

It defies the simple 3D physics we understand. Much easier to not have to imagine extra dimensions to explain what we see.

Actually, it's evidence against that... if there were a center of expansion and if we were close to it we would not expect to observe a correlation between the distance of other heavenly bodies and their rate of recession from us.

Depends on the reason for the quantisation. And it wouldn't take much to explain what we see with the assumption of the simple model.

Well, I don't think that's true, but even if it were what is your point? I am explaining a position, why wouldn't I assume that position to explain it? How else could I explain it?

I've no problem with you making an explanation. But the observations do not belong to your explanation. The observations can be explained by other models in different ways. You may not coopt an explanation as if it were evidence.

Further, the degree of homogeneity and isotropy of the observable universe has been measured extremely accurately by the WMAP satellite based instrument... are you challenging these measurements and if so on what authority?

I don't challenge the measurements made. I just have alternative explanations based on a simple 3D model.

#31 Codex

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Posted 04 May 2012 - 12:05 PM

I've no problem with you making an explanation. But the observations do not belong to your explanation. The observations can be explained by other models in different ways. You may not coopt an explanation as if it were evidence.


According to astrophysicisists, cosmologists, and astronomers those observations do belong to my (their) explanation. You can certainly assert that they fit your explanation as well, and I may or may not choose to attempt to rebutt you, but I don't like being told that I cannot present data that I feel is evidence of my argument.

#32 Stripe

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Posted 05 May 2012 - 05:07 AM

You can't present explanations as if they are evidence. You can present data as evidence for an explanation, but you must be very careful to understand and accept the very different assumptions we start with.

You can say quantised redshifts are explained by you model by whatever means, but you can't use this explanation as evidence for your model or evidence against another unless you can point out the contradictions between the model and the reality.

#33 aelyn

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Posted 03 June 2012 - 02:04 AM

You misunderstood, the universe certainly has a center, as any volume does.

That isn't true. A finite Euclidean volume has a center, but we don't know that the Universe is either of those things. Consider the analogy with surfaces : any flat, finite surface (like a piece of paper) has a center. But an infinite surface wouldn't have a center, and neither does a finite but unbounded curved surface like the surface of the Earth.

I don't know if we can say that Universe doesn't have a center, I don't think we know enough about its overall shape to say this, but we can't say it has a center either.

Actually, it's evidence against that... if there were a center of expansion and if we were close to it we would not expect to observe a correlation between the distance of other heavenly bodies and their rate of recession from us.

That isn't true either. You described the expansion well, and correctly pointed out that any point in the expanding space would see the same thing (everything moving away from them, and moving away faster the further away they were), but that would be as true of the center as it is of any other point.

It defies the simple 3D physics we understand. Much easier to not have to imagine extra dimensions to explain what we see.

The expansion of the Universe doesn't require extra dimensions beyond the 3 space dimensions we have and time, and those are the dimensions we observe every day.
It does require that space be non-Euclidean, but the whole of General Relativity requires this, and that theory's predictions related to the curving of spacetime (such as time moving more slowly the faster one goes) have been verified experimentally to high levels of numerical accuracy.

#34 Stripe

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Posted 03 June 2012 - 02:37 AM

That isn't true. A finite Euclidean volume has a center, but we don't know that the Universe is either of those things. Consider the analogy with surfaces : any flat, finite surface (like a piece of paper) has a center. But an infinite surface wouldn't have a center, and neither does a finite but unbounded curved surface like the surface of the Earth.

The universe is three dimensional. Every three dimensional object has a center (disregarding the different definitions of the word). If you want to assume the universe is fundamentally not as it plainly appears, you're going to have to provide very compelling evidence.

.. we can't say it has a center...

Sure, we can. :)

The expansion of the Universe doesn't require extra dimensions beyond the 3 space dimensions we have and time, and those are the dimensions we observe every day.It does require that space be non-Euclidean, but the whole of General Relativity requires this, and that theory's predictions related to the curving of spacetime (such as time moving more slowly the faster one goes) have been verified experimentally to high levels of numerical accuracy.

Maybe general relativity isn't necessary. :)

#35 aelyn

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Posted 03 June 2012 - 03:00 AM

The universe is three dimensional. Every three dimensional object has a center (disregarding the different definitions of the word). If you want to assume the universe is fundamentally not as it plainly appears, you're going to have to provide very compelling evidence.

It's just maths. A center is defined with respect to bounds, an unbounded space cannot have a center. Every three dimensional object we encounter is bounded; we can see their edges. We do not see any hint of the Universe's edges and have no reason to think it's bounded. Or, AFAIK, that it's not.

Maybe general relativity isn't necessary. :)

It is necessary to the GPS.

#36 Stripe

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Posted 03 June 2012 - 03:29 AM

It's just maths.

It's maths under the assumptions you bring. What I propose is maths based as well.

A center is defined with respect to bounds, an unbounded space cannot have a center. Every three dimensional object we encounter is bounded; we can see their edges. We do not see any hint of the Universe's edges and have no reason to think it's bounded. Or, AFAIK, that it's not.

The universe is the sum total of the matter created. The area that matter stretches to defines the shape of the universe. Finding its center, given knowledge of the distribution of its matter, would be a simple exercise.

It is necessary to the GPS.

No, it's not. A GPS system could be built and work just as effectively with a different mathematical model that compensates for gravity's effect on light.

#37 Ron

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Posted 03 June 2012 - 03:58 AM



The universe is three dimensional. Every three dimensional object has a center (disregarding the different definitions of the word). If you want to assume the universe is fundamentally not as it plainly appears, you're going to have to provide very compelling evidence.


It's just maths. A center is defined with respect to bounds, an unbounded space cannot have a center. Every three dimensional object we encounter is bounded; we can see their edges. We do not see any hint of the Universe's edges and have no reason to think it's bounded. Or, AFAIK, that it's not.


That would be incorrect… It could be described using mathematical terms, BUT since we are discussing a physical phenomenon (the universe), it is illogical to ASSUME that it has no center or edges.

Premises 1 - The universe is PHYSICAL (therefore it is NOT just “maths”)
Premises 2 - The universe had a BEGINNIG (therefore it is NOT just “maths”)
Premises 3 - Because the universe had a beginning it IS three dimensional (therefore it is NOT just “maths”)
Premises 4 - We have absolutely NO evidence of ANYTHING that is physical, three dimensional and had an origin that is unbounded.

Conclusion: YOUR conclusion is nothing more than an assumption, and therefore unfounded (baseless). And it does NOT follow from your premises; therefore it is a non sequitur.




Maybe general relativity isn't necessary.


It is necessary to the GPS.



Not necessary… But if you can empirically prove your assertion, please do so.

#38 aelyn

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Posted 03 June 2012 - 04:50 AM

It's maths under the assumptions you bring. What I propose is maths based as well.The universe is the sum total of the matter created.

Space and time are also part of the Universe, as the word is understood in physics.

The area that matter stretches to defines the shape of the universe. Finding its center, given knowledge of the distribution of its matter, would be a simple exercise.

If that distribution is bounded and finite, yes. But we don't know the distribution of its matter.

No, it's not. A GPS system could be built and work just as effectively with a different mathematical model that compensates for gravity's effect on light.

No, given it's not gravity's effect on light that needs to be compensated for, it's its effect (and the effect of velocity) on time. How would you calculate the effect of gravity on light by the way ?

That would be incorrect… It could be described using mathematical terms, BUT since we are discussing a physical phenomenon (the universe), it is illogical to ASSUME that it has no center or edges.

I assume no such thing. I say we don't know.

Premises 1 - The universe is PHYSICAL (therefore it is NOT just “maths”)

But many of its properties can be described using maths. The very concept of "three dimensional" is a mathematical concept. That happens to apply to an aspect of our Universe.

Premises 4 - We have absolutely NO evidence of ANYTHING that is physical, three dimensional and had an origin that is unbounded.

Indeed. But nor do we have evidence that the Universe isn't such a thing. We do have evidence that the Universe is very unlike the objects it contains in a few ways. For one, it's so much bigger that the largest object in it is a mere speck compared to the whole thing. Also, it isn't euclidean. So we can't just assume that because everything in it is bounded, the Universe itself is bounded too. Nor can we assume the opposite.

Not necessary… But if you can empirically prove your assertion, please do so.

The calculations that allow GPS to determine a location down to a few meters are extremely precise. You won't get a correct value with qualitative concepts like "the effect of gravity on light" or "time moves more slowly in a strong gravitational field". You need to know exactly how slowly time moves in how strong a gravitational field. The equations that allow those calculations are the equations of general relativity.

#39 Stripe

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Posted 03 June 2012 - 06:48 AM

Space and time are also part of the Universe, as the word is understood in physics.

Space and time are not physical entities. Matter is. Space and time are just descriptions of our observations of matter.

If that distribution is bounded and finite, yes. But we don't know the distribution of its matter.

We know it cannot be infinite. That we do not know the distribution and that we know it is not infinite necessitates a center and a boundary.

No, given it's not gravity's effect on light that needs to be compensated for, it's its effect (and the effect of velocity) on time. How would you calculate the effect of gravity on light by the way ?

Gravity affects light is the assumption I would use in order to produce a mathematical model that could be used to deploy a GPS system. And it would work too.

The application of a model is not evidence that the model is representative of reality.

The calculations that allow GPS to determine a location down to a few meters are extremely precise. You won't get a correct value with qualitative concepts like "the effect of gravity on light" or "time moves more slowly in a strong gravitational field". You need to know exactly how slowly time moves in how strong a gravitational field. The equations that allow those calculations are the equations of general relativity.

Uh .. you're completely incorrect.

General relativity is just an overly complicated, and subtly flawed, way of describing the direct observation that gravity affects light. All the same precision can be achieved with much of the same calculations. But the model, regardless of how useful it is, does not automatically become reality.

I assume no such thing. I say we don't know.

the Universe ... isn't euclidean.


:kaffeetrinker:

#40 aelyn

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Posted 03 June 2012 - 08:47 AM

Space and time are not physical entities. Matter is. Space and time are just descriptions of our observations of matter.

Just out of curiosity, what do you think of energy ? And would you say space and time don't exist independently of matter ?

We know it cannot be infinite. That we do not know the distribution and that we know it is not infinite necessitates a center and a boundary.

How do we know it cannot be infinite ?

Gravity affects light is the assumption I would use in order to produce a mathematical model that could be used to deploy a GPS system. And it would work too.

But how does it affect light ? What does gravity make light do, to what degree ? And if you did produce such a mathematical model, how would you use it to deploy a GPS when what the satellites need to correct for is the dilation and contraction of time under the effect of gravity and velocity ?

The application of a model is not evidence that the model is representative of reality.

You might be confusing "evidence" with "proof". It isn't proof in the mathematical sense, which is why science doesn't deal with that kind of proof, but it is a piece of evidence. Applying models to reality and seeing if they match is what empirical experimentation is all about.

Uh .. you're completely incorrect.

What am I incorrect about ? That GPS involves calculations to determine something's location ? That they're very precise ? That calculations require quantitative, not qualitative concepts ? That the GPS accounts for the effects of gravity and velocity on time ? That it uses the equations of general relativity to do so ?

General relativity is just an overly complicated, and subtly flawed, way of describing the direct observation that gravity affects light.

That's weird given when Einstein developed his model there were no direct observations of gravity affecting light. And how about the direct observation that velocity and gravity affect time ? And there's nothing "overly complicated" about general relativity - quite the opposite, explaining such disparate observations with a single concept and an elegant equation is as simple as theories go. It's Kepler's heliocentric ellipses to Ptolemy's geocentric epicycles.

All the same precision can be achieved with much of the same calculations. But the model, regardless of how useful it is, does not automatically become reality.

No model "becomes reality", and general relativity in particular is almost certainly wrong given it's incompatible with quantum mechanics. But when a model matches reality as closely as general relativity does there's usually a reason. And how you propose to do "much of the same calculations" without using the same equations?

:kaffeetrinker:

Just because the Universe isn't Euclidean doesn't mean it has no center. Non-Euclidean spaces can be finite and bounded too.




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