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#41 Ron

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Posted 03 June 2012 - 11:33 AM



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.


Actually YES you do assume aelyn, unless you can provide ANY other physical phenomena that has NO center AND NO edges. Whenever you make a claim, it is YOUR RESPONSIBILITY to provide the evidences (not mere opinion) for said assertions.

If I have to start giving you formal warnings for such misrepresentations, then you will be responsible for that as well.



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.



Once again, that is incorrect… Mathematical equations (in the context of our conversation) are merely metaphysical descriptions for the physical phenomena. Height, Width and depth are PHYSICAL phenomena, the “maths” merely describe said phenomena.


Further, it seems, you have forgotten to include premises 2 and 3. But, I’ll let that slide for now.



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.



Once again, you are ASSUMING again aelyn,unless you can provide ANY other physical phenomena that has NO center AND NO edges. Whenever you make a claim, it is YOUR RESPONSIBILITY to provide the evidences (not mere opinion) for said assertions.

If I have to start giving you formal warnings for such misrepresentations, then you will be responsible for that as well.


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.



If you understood how GPS worked (if you do then you are intentionally misguiding?), you’d understand that a GPS triangulates three separate geographical locations to determine the intended location exactly the same as a person with a lensatic compass triangulates three separate geographical locations to determine the intended location. The equations are utilized representing PHYSICAL phenomena. You don’t need general relativity at all for either.

As an aside, I use to teach triangulation equations to determine microwave satellite antenna propagation for the Department of Defense. I have SOME experience in this arena.

#42 Ron

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Posted 03 June 2012 - 11:39 AM



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?



Quite simply aelyn, provide JUST ONE example of an item of physical phenomena that is infinite! If you can do that you might have a leg to stand on… Otherwise you are proceeding only on mere opinion, and have absolutely NO argument…







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.





No aelyn, YOU are confusing reality with hypothesis. In reality "evidence" and "proof" are synonymous. What you are doing is known as the fallacious “Conversion by Definition” which is a type equivocation (see forum rules).

#43 Stripe

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Posted 03 June 2012 - 12:04 PM

How do we know it cannot be infinite?

Simple. If matter extended infinitely in every direction, then in every direction a star would be visible. If it were infinite the night sky would be bright white.

But how does it affect light ? What does gravity make light do, to what degree ?

How? Nobody knows. Was that an attempt at an argument?

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 ?

You do not need to use the time dilation and contraction model to calculate GPS positions any more than you need to use multiplication to find the product of two numbers.

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.

No, it's not evidence since it was the observations that controlled the production of the model. The assumptions made in the development of the model need evidence. That your model matches reality is simply asserting your assumptions as evidence.

What am I incorrect about ?

That we must assume general relativity in order to calculate GPS locations.

That's weird given when Einstein developed his model there were no direct observations of gravity affecting light.

So? That what GR remains. And there were the observations of Mercury's orbit.

And how about the direct observation that velocity and gravity affect time ?

There are no such observations without the assumption of GR being carefully hidden. The direct observations are that gravity and velocity affect clocks. A subtle, but profound, difference.

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.

It's completely counter-intuitive and relies upon the assertion of intangible concepts as physical realities. Time and space are not physical things.

No model "becomes reality"

Of course. Stop agreeing with me. You're freaking me out. :)

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.

Because it was built to do so.

And how you propose to do "much of the same calculations" without using the same equations?

I don't.

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

Great! :D

#44 aelyn

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Posted 03 June 2012 - 12:23 PM

If I have to start giving you formal warnings for such misrepresentations, then you will be responsible for that as well.

No more misrepresentation from me then.

As for this :

If you understood how GPS worked (if you do then you are intentionally misguiding?), you’d understand that a GPS triangulates three separate geographical locations to determine the intended location exactly the same as a person with a lensatic compass triangulates three separate geographical locations to determine the intended location. The equations are utilized representing PHYSICAL phenomena. You don’t need general relativity at all for either.


The main issue is the clocks the GPS satellites use to send time signals. At least according to these guys :
http://www.astronomy.../Unit5/gps.html
Or these :
tycho.usno.navy.mil/ptti/1996/Vol%2028_16.pdf
The PDF is mostly about integrating additional relativistic effects for users in space who need more precision than users on the ground, but it does include this bit about the users on the ground : (page 5)

Since GPS receivers work in the time and not in the frequency fomain, they handle the velocity, gravity, and acceleration shifts differently than described above. First, each GPS space vehicle (SV) clock is offset from its nominal rate by about -4.45x10^-10 (=-38 microseconds per day) to allow for the relativistic offsets between the differences between the SV and the ground. Of this -38 microseconds per day, about -45 are due to the gravitational potential difference between the SV at its mean distance and the earth's surface, and +7 to the mean SV speed, which is about 3.87 km/sec. To this mean correction, each receiver must add a term due to the eccentricity of the GPS orbit. It can be shown that this effect produces a variation in the SV clock, as seen from the earth, of
deltaT = -2*(R.V)/c^2
where R is the vector of position of the SV from the ECI, and V the velocity vector. This is the equation given in ICD-GPS-200. It is appropriate for users on or near the earth's surface, but not users in space, who should apply the frequency correction equations given above, or their integrals to transform to the time domain.



#45 Stripe

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Posted 03 June 2012 - 12:31 PM

The main issue is the clocks the GPS satellites use to send time signals.

Right. Those clocks are affected by gravity.

#46 aelyn

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Posted 03 June 2012 - 01:32 PM

Simple. If matter extended infinitely in every direction, then in every direction a star would be visible. If it were infinite the night sky would be bright white.

Except that we already know that we don't see every star that exists. The fact we can see more stars when we use stronger telescopes shows this. The dark patches between stars might be dark all the way through, or they might contain stars that are too faint to see. We can't tell in advance without looking.
There is also the issue of the finite speed of light that would result in a finite observable Universe regardless of the size of the actual Universe, but I have no idea what you think about the speed of light.

How? Nobody knows. Was that an attempt at an argument?

It was a question. You said you would use the assumption that gravity affects light to produce a mathematical model for GPS; I thought that meant you had a quantitative model of how gravity affects light. I guess not.

You do not need to use the time dilation and contraction model to calculate GPS positions any more than you need to use multiplication to find the product of two numbers.

I don't get this analogy. "Multiplication" and "product" are the same thing. Maybe you meant to say you can find the product of two numbers via different algorithms (knowing the answer by heart, long multiplication, the grid method, drawing dots on a piece of paper and counting them), but those all come down to multiplication in one way or another. If they didn't the result you'd get wouldn't be the product.

No, it's not evidence since it was the observations that controlled the production of the model.The assumptions made in the development of the model need evidence. That your model matches reality is simply asserting your assumptions as evidence.

So? That what GR remains. And there were the observations of Mercury's orbit.

GPS did not exist when Einstein elaborated his theories so their observations did not go into the production of the model. And no, the observations of Mercury's orbit aren't the same thing as the behavior of atomic clocks in orbit around the Earth. Independent observations are independent, and here in particular we're looking at different phenomena and vastly different precision levels.

Anyway, I'm not sure how you think science works. Emitting hypotheses, using them to make predictions and then conducting experiments to see whether the predictions are borne out is pretty standard operating procedure. It's what was done with general relativity. Are you saying that a model matching observations and having its predictions confirmed by experiment time and time again has no bearing on the model's validity ?

There are no such observations without the assumption of GR being carefully hidden. The direct observations are that gravity and velocity affect clocks. A subtle, but profound, difference.

Gravity and velocity affect clocks. I guess I shouldn't ask whether you have a mechanism or a quantitative formulation for this phenomenon either. It's true; you can always dismiss the result of any experiment as being caused by some unspecified process that isn't the theory being tested. It's not how science works but we're just laypeople here so I guess it doesn't matter.

#47 Ron

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Posted 03 June 2012 - 02:49 PM



If I have to start giving you formal warnings for such misrepresentations, then you will be responsible for that as well.


No more misrepresentation from me then.



I suppose we’ll see what we see, but I hope you’re serious

As for this :


If you understood how GPS worked (if you do then you are intentionally misguiding?), you’d understand that a GPS triangulates three separate geographical locations to determine the intended location exactly the same as a person with a lensatic compass triangulates three separate geographical locations to determine the intended location. The equations are utilized representing PHYSICAL phenomena. You don’t need general relativity at all for either.



The main issue is the clocks the GPS satellites use to send time signals. At least according to these guys :
http://www.astronomy.../Unit5/gps.html
Or these :
tycho.usno.navy.mil/ptti/1996/Vol%2028_16.pdf
The PDF is mostly about integrating additional relativistic effects for users in space who need more precision than users on the ground, but it does include this bit about the users on the ground : (page 5)

Since GPS receivers work in the time and not in the frequency fomain, they handle the velocity, gravity, and acceleration shifts differently than described above. First, each GPS space vehicle (SV) clock is offset from its nominal rate by about -4.45x10^-10 (=-38 microseconds per day) to allow for the relativistic offsets between the differences between the SV and the ground. Of this -38 microseconds per day, about -45 are due to the gravitational potential difference between the SV at its mean distance and the earth's surface, and +7 to the mean SV speed, which is about 3.87 km/sec. To this mean correction, each receiver must add a term due to the eccentricity of the GPS orbit. It can be shown that this effect produces a variation in the SV clock, as seen from the earth, of
deltaT = -2*(R.V)/c^2
where R is the vector of position of the SV from the ECI, and V the velocity vector. This is the equation given in ICD-GPS-200. It is appropriate for users on or near the earth's surface, but not users in space, who should apply the frequency correction equations given above, or their integrals to transform to the time domain.




The problem you’re running into here is not how the GPS itself works (in order to triangulate the three separate geographical locations to determine the intended location), but rather how the satellites stabilize themselves in order to make the readings (i.e. triangulates three separate geographical locations to determine the intended location) and the latency issues that stem from high orbits. If you want to discuss geosynchronous orbit (or geostationary etc...) and the stabilization equations needed to take photographs from space, then your assertions would be more analogous.

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#48 Stripe

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Posted 03 June 2012 - 04:04 PM

It was a question. You said you would use the assumption that gravity affects light to produce a mathematical model for GPS; I thought that meant you had a quantitative model of how gravity affects light. I guess not.

We already know the quantities.

I don't get this analogy. "Multiplication" and "product" are the same thing.

One is a verb, one is a noun. You don't have to find the noun by doing that verb just as you don't have to run to get to the tree.

GPS did not exist when Einstein elaborated his theories so their observations did not go into the production of the model. And no, the observations of Mercury's orbit aren't the same thing as the behavior of atomic clocks in orbit around the Earth. Independent observations are independent, and here in particular we're looking at different phenomena and vastly different precision levels.

You're going to have to stop talking about precision like you're saying something relevant.

Mercury's orbit needs to be calculated with the effects of the sun's gravity on the light from the planet taken into account. GPS coordinates need to be* calculated with the effect of Earth's gravity on the clocks in orbit taken into account. They are, indeed, exactly the same thing!

Anyway, I'm not sure how you think science works. Emitting hypotheses, using them to make predictions and then conducting experiments to see whether the predictions are borne out is pretty standard operating procedure. It's what was done with general relativity. Are you saying that a model matching observations and having its predictions confirmed by experiment time and time again has no bearing on the model's validity ?

Building a model that accounts for observations and then finding that model matches observations is not evidence for the model being representative of reality. It's just that you've built a model that might be useful.

Gravity and velocity affect clocks. I guess I shouldn't ask whether you have a mechanism or a quantitative formulation for this phenomenon either.

Nobody knows how gravity works. We can all access the observations and see how great the effect is.

It's true; you can always dismiss the result of any experiment as being caused by some unspecified process that isn't the theory being tested.

Who is dismissing any results?

It's not how science works but we're just laypeople here so I guess it doesn't matter.

Speak for yourself!

* "Need to be" for very accurate results.

#49 aelyn

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Posted 04 June 2012 - 02:22 AM

The problem you’re running into here is not how the GPS itself works (in order to triangulate the three separate geographical locations to determine the intended location), but rather how the satellites stabilize themselves in order to make the readings (i.e. triangulates three separate geographical locations to determine the intended location) and the latency issues that stem from high orbits. If you want to discuss geosynchronous orbit (or geostationary etc...) and the stabilization equations needed to take photographs from space, then your assertions would be more analogous.

I provided a link to a PDF from the US Navy about the relativistic corrections they need to make for GPS, it wasn't about stabilizing the satellites themselves.

Here's a paragraph from the other link I gave, since you aren't addressing it :

The current GPS configuration consists of a network of 24 satellites in high orbits around the Earth. Each satellite in the GPS constellation orbits at an altitude of about 20,000 km from the ground, and has an orbital speed of about 14,000 km/hour (the orbital period is roughly 12 hours - contrary to popular belief, GPS satellites are not in geosynchronous or geostationary orbits). The satellite orbits are distributed so that at least 4 satellites are always visible from any point on the Earth at any given instant (with up to 12 visible at one time). Each satellite carries with it an atomic clock that "ticks" with an accuracy of 1 nanosecond (1 billionth of a second). A GPS receiver in an airplane determines its current position and heading by comparing the time signals it receives from a number of the GPS satellites (usually 6 to 12) and triangulating on the known positions of each satellite. The precision is phenomenal: even a simple hand-held GPS receiver can determine your absolute position on the surface of the Earth to within 5 to 10 meters in only a few seconds (with differential techiques that compare two nearby receivers, precisions of order centimeters or millimeters in relative position are often obtained in under an hour or so). A GPS receiver in a car can give accurate readings of position, speed, and heading in real-time!
To achieve this level of precision, the clock ticks from the GPS satellites must be known to an accuracy of 20-30 nanoseconds. However, because the satellites are constantly moving relative to observers on the Earth, effects predicted by the Special and General theories of Relativity must be taken into account to achieve the desired 20-30 nanosecond accuracy.


But since I now seem to have gone two posts doing nothing but quoting more knowledgeable sources than I I'll leave it there. Anyone interested can take it up with said sources.

We already know the quantities.

But we don't. We have a series of observations of clocks and light acting differently in certain gravitational situations. Without a general idea of how gravity affects light or clocks we can't extrapolate from those observations to new situations. Every satellite being sent to an orbit that hasn't been thoroughly observed before is being sent into the unknown. Not to mention sending probes to new places in the Solar System. Considering NASA has crashed probes before for mixing up metric and imperial units, and that even with the current theories of gravity we get surprises when we go too far out of our sphere of experience (such as the Pioneer anomaly), we'd be looking at orders of magnitude more expensive trial and error than we already have. Unless you're talking about using the equations of general relativity while denying they have any real-world basis I guess.

One is a verb, one is a noun. You don't have to find the noun by doing that verb just as you don't have to run to get to the tree.

"Multiplication" is a noun, actually. You might be confusing it with the verb "to multiply". And your run/tree analogy doesn't work because running and trees aren't related the way multiplying and products are; I still think you're confusing the operation of multiplication with the algorithm used to do the operation.

Mercury's orbit needs to be calculated with the effects of the sun's gravity on the light from the planet taken into account. GPS coordinates need to be* calculated with the effect of Earth's gravity on the clocks in orbit taken into account. They are, indeed, exactly the same thing!

So gravity's effect on light and gravity's effect on clocks are the same basic phenomenon ? How would we know that ? Clocks and light are different things.

Building a model that accounts for observations and then finding that model matches observations is not evidence for the model being representative of reality. It's just that you've built a model that might be useful.

So you completely disagree with the "hypothesis -> prediction -> experiment" method of empirical science ?

Would you say that the phenomenon of apples falling onto the ground is the same thing as the phenomenon of planets going around the Sun ?
People before Newton thought those were self-evidently different phenomena. The very concept that the planets might be going around the Sun because they're attracted to it was novel (although Newton wasn't the first to think of it). Newton suggested that falling bodies and celestial mechanics were both caused by the same universal force of "gravity", but really all he had were equations, that he made to fit observations in the first place (it could just as easily have been inverse cube), and later experiments and observations matched the model but that doesn't mean the equations represented reality. In fact we know his theory of gravity was wrong, because while it predicted the vast majority of observations and experiments devised to test it there were still a few anomalies. And we don't really need Newton's theory of universal gravity in the first place, since we have all those observations of how satellites behave in space and how apples fall and how planets go around the Sun, regardless of the force or forces involved.

Anyway, I don't think this conversation can go much further and it's already drifted from the original topic I'll leave you with the last word.

#50 Stripe

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Posted 04 June 2012 - 08:43 AM

But we don't. We have a series of observations of clocks and light acting differently in certain gravitational situations.

Yeah .. those are quantities.

Without a general idea of how gravity affects light or clocks we can't extrapolate from those observations to new situations.

So build a model.

Unless you're talking about using the equations of general relativity while denying they have any real-world basis I guess.

I have no problem with using GR equations. They give usable results.

So gravity's effect on light and gravity's effect on clocks are the same basic phenomenon ? How would we know that ? Clocks and light are different things.

How would we know that? We'd test it.

So you completely disagree with the "hypothesis -> prediction -> experiment" method of empirical science ?

No.

but really all he had were equations, that he made to fit observations in the first place (it could just as easily have been inverse cube)

Yip. And if there were a better explanation than mass is attracted to other mass, I'd be resisting Newton's explanation as well.

In fact we know his theory of gravity was wrong, because while it predicted the vast majority of observations and experiments devised to test it there were still a few anomalies.

Not necessarily. If light has mass and is affected by gravity then a simple extension of Newton's laws will supplant GR.

And we don't really need Newton's theory of universal gravity in the first place, since we have all those observations of how satellites behave in space and how apples fall and how planets go around the Sun, regardless of the force or forces involved.

Just as there is no need to hold GR dear. Another model might well be better.

Anyway, I don't think this conversation can go much further and it's already drifted from the original topic I'll leave you with the last word.

OK, bye.




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