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Relative
2012-Apr-25, 09:20 AM
If „nothing can exceed speed of light“, this should hold true for the expansion of the (observable) universe itself. The „total current diameter“, therefore, shouldn‘t increase faster either.

Currently the age of the universe is estimated to be 13.75 billion years (4.339x10^17 s). The „current diameter“ to be 1.3x10^26 m. So, after one second, this may become 1.3x10^26 m + 299792458 m at most. Or after one year, 1.3x10^26 m + 9.46x10^15 m.

The „current factor of growth“ in this case would be 2.3046x10^-18 per second, or 7.2727x10^-11 per year.

Let‘s see what this would mean for example for the distance earth–moon in one year. Applying the factor to the value of 384400000 m, we get 2.796 cm per year.

The Lunar Laser Ranging Experiment states that the distance earth–moon is increasing 3.8 cm per year. It is concluded that the moon is „travelling away“ from earth.

Questions:
a. May the above mentioned 2.796 cm may be part of this value?
b. If moon is not „travelling away“ but its distance just subject to expansion of the univers, may the measurement of 3.8 cm give us the „correct“ age of the (observable) universe to be 18.69 billion years?
c. May c be „slowing down“ with time, so lose 2.796 cm per year (or 3.8 cm)?

Strange
2012-Apr-25, 10:51 AM
If „nothing can exceed speed of light“, this should hold true for the expansion of the (observable) universe itself. The „total current diameter“, therefore, shouldn‘t increase faster either.

The (apparent) relative motion between objects caused by the expansion of space is not limited in this way.

Also, the changing distance of the moon has no connection with the expansion of the universe (perhaps someone else can provide more detail on that).

Hornblower
2012-Apr-25, 12:49 PM
The (apparent) relative motion between objects caused by the expansion of space is not limited in this way.Also, the changing distance of the moon has no connection with the expansion of the universe (perhaps someone else can provide more detail on that).

My bold. Let me expand on that a bit, as I think I understand it. That relative speed limit is a local property as measured under conditions in which special relativity can be used as the basis for calculation. Those conditions break down on a cosmic scale because of a fundamental property which still has me scratching my head.

At the local level, strong gravitational binding overpowers the tendency toward universal expansion. I will leave rigorous explanations of it to those who are up to speed in modern physics. I am just too rusty after 40 years away from it.

Cougar
2012-Apr-25, 01:04 PM
The „current factor of growth“ in this case would be 2.3046x10^-18 per second, or 7.2727x10^-11 per year.

Could you explain how you got this? And fill in your units?

Relative
2012-Apr-25, 01:25 PM
Could you explain how you got this? And fill in your units?
The values are the reciprocals of the age of the univers in 1/s or 1/y, respectively, and tell the "relative current aging".
(For example: Instead of saying " I just turned 51" you could say "I've been aging by 2 percent last year", this is equivalent)

ShinAce
2012-Apr-25, 02:54 PM
My bold. Let me expand on that a bit, as I think I understand it. That relative speed limit is a local property as measured under conditions in which special relativity can be used as the basis for calculation. Those conditions break down on a cosmic scale because of a fundamental property which still has me scratching my head.

Allow me to attempt an analogy. Your car goes 65 mph on the highway, no matter where on the highway you are. The highway itself, even though it is built at a snail's pace, can accumulate road at more than 65 mph because we can work on all parts of it. Dark energy is like someone cutting slots into the highway every mile or so, pulling the road sections apart a bit, and then patching the cracks with filler. As you drive by, it looks like I'm adding a few inches to the road every mile or so, but when you consider that the road can be thousands of miles long, I'm actually adding thousand of inches between the start and end of the highway everytime I do this work.

The local property is the fact that the road builders can't add single sections at the speed of light. If they could, that would be the big rip. The cosmic scale allows me to employ as many road builders as I want. No one builder is going faster than light, but overall, progress can.

If you apply the expansion due to dark energy to a galaxy, you'll find that it must be growing very quickly. But the galaxies aren't showing any signs of expansion. The space between them is expanding.

Yet another angle. If the distance to the moon is increasing because of expansion, why isn't the sun getting bigger due to expansion? Gravity holds the sun together just as gravity holds the moon in orbit. They should experience the same force of expansion.

When the force of gravity is large enough(basically within a galaxy and smaller), dark energy cannot overcome gravity and change positions.

Relative
2012-Apr-25, 05:50 PM
Yet another angle. If the distance to the moon is increasing because of expansion, why isn't the sun getting bigger due to expansion? Gravity holds the sun together just as gravity holds the moon in orbit. They should experience the same force of expansion.
Well, as you see from OP the „growing factor“ was very little. Applying this to sun‘s diameter would make a difference of 10.12 cm per year. We aren‘t even able to determine its current diameter precisely in terms of hundreds of kilometers. So we could neither approve nor deny. (Same with the galxies...)

ShinAce
2012-Apr-25, 06:10 PM
The moon's recession from Earth is explained in terms of torque induced from tidal forces. No dark energy involved. The correction factor from dark energy should be extremely small, to the point of being dwarfed by the tides' effects. So my answer to question a) is: yes, but the correction is too small to show up against experimental error. Therefore, it is not included at the cm/year level.

Apply the same idea to Saturn's rings. They stretch 360 degrees around the planet so if space is expanding, the rings stretch out evenly. Maybe Cassini data is enough to get a figure to check consistency. Your theory suggests that the rings be expanding, with the outside radius receding faster than the inside radius. In other words, the rings should expand out in radius and also expand in width.

As for questions b) and c): no and no.

edit:
How do you propose to resolve the fact the moon is tidally locked to the earth? If dark energy was simply making the orbit spiral out, then there should be no reason for the existence of a 'dark side of the moon'. Tidal locking seems to be all too common. There's also a problem with Phobos, a moon of Mars. Why is it falling in instead of spiralling out?

Squink
2012-Apr-25, 07:26 PM
the distance earth–moon in one year. Applying the factor to the value of 384400000 m, we get 2.796 cm per year.Hubble constant (73 km/secMpc) and distance to moon (in megaparsec) will get you about the same value.

Relative
2012-Apr-25, 08:01 PM
The moon's recession from Earth is explained in terms of torque induced from tidal forces.
First of all, I would like to state that I apprecciate your answers, although I cannot follow your argumentation:
1) As far as I know the observed recession of the moon leads to the conclusion of tidal forces being responsable for it, not vice versa. Even more, if you are trying to argue vice versa, just with torque due to tidal forces, this value is still considered to be „abnormously high“.
2) You invoke „dark energy“, when it seems to be applicable and call it „extremely small“ when it comes to the order of the earth-moon-system. Even though we don‘t know what „dark energy“ is, shouldn‘t this underlie the same expansion of the universe? Furthermore, you state that expansion of the universe only takes place inbetween galaxies, but not within the galaxy itself due to gravitational or "dark energy" influence. At least, there must be places within each galaxy, where these forces (may it be centrifugal or due to „dark enrgy“) cancel out, so what about these regions which, therefore, may just underlie expansion of the universe.
3) Sure, the outer Saturn rings in terms of OP should expand „at the same rate“, therefore, in a higher absolute value. Again, this is not measurable with our equipment today. That‘s why I have supposed to look at distances we can a.) handle somehow, like earth-moon and b.) are within the accuracy of our current technology.

Relative
2012-Apr-25, 08:04 PM
Hubble constant (73 km/secMpc) and distance to moon (in megaparsec) will get you about the same value.
Thank you, Squink.

caveman1917
2012-Apr-25, 09:19 PM
Even if we factor in dark energy (not just expansion, accelerating expansion) in the earth-moon system (which strictly speaking we can't) then all that would happen is that we have to change the equilibrium position of the gravitational force, it wouldn't cause the system to expand over time, only change its equilibrium state in the sense that the gravitational force would look a tiny bit weaker. The actual increasing distance to the moon would still be solely due to conservation of angular momentum and tidal effects.

Relative
2012-Apr-25, 09:50 PM
The actual increasing distance to the moon would still be solely due to conservation of angular momentum and tidal effects.
Exactly this is in doubt.
Just an example: http://creation.com/the-moons-recession-and-age

Strange
2012-Apr-25, 11:25 PM
Exactly this is in doubt.
Just an example: http://creation.com/the-moons-recession-and-age

Perhaps you could provide a scientific reference to this "doubt".

Reality Check
2012-Apr-26, 04:25 AM
We do not expect any effect of the expansion of the univese (with or without dark energy!) on the Earth-Moon system because they are gravitaionally bound. So the answers are simpley:
a) no.
b) no.
c) no. This sounds like the debunked c-decay idea from Barry Setterfield.

ShinAce
2012-Apr-26, 04:40 AM
3) Sure, the outer Saturn rings in terms of OP should expand „at the same rate“, therefore, in a higher absolute value. Again, this is not measurable with our equipment today.

How do you know it's not measurable? Some of Jupiter's moons are farther than the moon. We can measure the periods to great precision and see if they are getting longer or shorter. Your theory predicts that they will all spiral away from Jupiter, with the farthest ones doing so the quickest. Have you checked data to see if there's a link? One moon and some back of the envelope math, that's what you're working with. Again, why is Phobos getting closer to Mars?

It's hard to tell if you're asking a question or looking to introduce a new model.

Strage: The only article I can think of is http://arxiv.org/abs/0704.0003 . However, it involves a dark matter fluid model which is not very well defined.

Relative
2012-Apr-26, 04:52 AM
Perhaps you could provide a scientific reference to this "doubt".
I will look for it. I heard about "that moon today is retreating from Earth anomalously rapidly" (so not solely can be explained by tidal effects) in TV documentations so far. The mentioned citation in the last sentence is form this link http://www.talkorigins.org/faqs/moonrec.html

Relative
2012-Apr-26, 05:02 AM
How do you know it's not measurable? Some of Jupiter's moons are farther than the moon. We can measure the periods to great precision and see if they are getting longer or shorter. Your theory predicts that they will all spiral away from Jupiter, with the farthest ones doing so the quickest. Have you checked data to see if there's a link? One moon and some back of the envelope math, that's what you're working with. Again, why is Phobos getting closer to Mars?
To measure it precisely, I'm afraid we have to install a laser experiment between the surface of Jupiter and the moons. Sure, there may be ones like Phobos who are not in an equilibrum orbit. There are always phenomena like that. For example it is also supposed that our neighbour galaxy and ours are going to collide one day. If the space inbetween ALL galaxies is expanding, approaching must exceed this.

Hornblower
2012-Apr-26, 11:42 AM
The moon's recession from Earth is explained in terms of torque induced from tidal forces. No dark energy involved. The correction factor from dark energy should be extremely small, to the point of being dwarfed by the tides' effects. So my answer to question a) is: yes, but the correction is too small to show up against experimental error. Therefore, it is not included at the cm/year level.

Apply the same idea to Saturn's rings. They stretch 360 degrees around the planet so if space is expanding, the rings stretch out evenly. Maybe Cassini data is enough to get a figure to check consistency. Your theory suggests that the rings be expanding, with the outside radius receding faster than the inside radius. In other words, the rings should expand out in radius and also expand in width.

As for questions b) and c): no and no.

edit:
How do you propose to resolve the fact the moon is tidally locked to the earth? If dark energy was simply making the orbit spiral out, then there should be no reason for the existence of a 'dark side of the moon'. Tidal locking seems to be all too common. There's also a problem with Phobos, a moon of Mars. Why is it falling in instead of spiralling out?

My bold. That one is easy. Phobos, in its 8-hour orbit, is overrunning the planet's rotation rather than lagging behind as our Moon is doing. Thus the induced bulge on Mars is giving it a small retrograde tug.

Jeff Root
2012-Apr-26, 01:38 PM
The Moon's recession from the Earth due to pull from the tidal
bulge was predicted many years before there was any way to
measure it.

-- Jeff, in Minneapolis

Cougar
2012-Apr-26, 01:40 PM
a. May the above mentioned 2.796 cm may be part of this value?

One might expect this amount of recession due to universal expansion if there was no gravitational field between the Earth and Moon. Well, there is a significant field there. Such a tiny expected rate of local expansion is overwhelmed in local gravitational settings. The gravity between the Milky Way and Andromeda galaxy (at 2 million lightyears away) obviously exceeds the effect of expansion. Even with galaxies in the Virgo Cluster at 54 million lightyears away, it's difficult to differentiate between the effect of expansion and the galaxies' own relative intrinsic motions. The moon is only 238,855 miles away. Expansion has only been measured between objects at very great distances, between which any gravity becomes negligible.

ShinAce
2012-Apr-26, 02:32 PM
To measure it precisely, I'm afraid we have to install a laser experiment between the surface of Jupiter and the moons. Sure, there may be ones like Phobos who are not in an equilibrum orbit. There are always phenomena like that. For example it is also supposed that our neighbour galaxy and ours are going to collide one day. If the space inbetween ALL galaxies is expanding, approaching must exceed this.

Are you going to sell Jovian laser's to this guy? http://en.wikipedia.org/wiki/Ole_R%C3%B8mer . He managed to measure the speed of light thanks to Jupiter's moons over 300 years ago. What is an equilibrium orbit? I'm afraid this is as far down the road as I can take you. I'm going back to civilization.

cjameshuff
2012-Apr-27, 06:21 PM
To measure it precisely, I'm afraid we have to install a laser experiment between the surface of Jupiter and the moons.

Nonsense. Measuring the orbital period doesn't require anything of the sort.



Sure, there may be ones like Phobos who are not in an equilibrum orbit.

What exactly is an "equilibrium orbit"?



There are always phenomena like that.

Mainstream theory fully describes the orbit of Phobos just as it describes the orbit of Earth's moon. You can't brush it off as an exception.



For example it is also supposed that our neighbour galaxy and ours are going to collide one day. If the space inbetween ALL galaxies is expanding, approaching must exceed this.

Yes? Galaxy velocities are non-zero and the rate of expansion is quite small. Expansion of the universe does not mean nearby galaxies never move toward each other. This is entirely in line with mainstream theory, and not some unexplainable exception.

And no, c is not changing anywhere near fast enough to account for the moon's motion. LIGO uses the constant speed of light to measure the distance between two mirrors spaced 4 km apart to within 10e-18 m. A change in c large enough to change the moon's apparent distance by 3.8 cm would make an apparent change between these mirrors of around 400 nanometers, about 40 billion times that distance. The measured distance would be growing by over 1000 times the smallest measurable change, per second. That...would be noticed.

Cougar
2012-Apr-27, 09:08 PM
If „nothing can exceed speed of light“, this should hold true for the expansion of the (observable) universe itself. The „total current diameter“, therefore, shouldn‘t increase faster either.... Currently... The „current diameter“ to be 1.3x10^26 m. [13.74 billion lightyears]

Actually, you start out with a misconception and then proceed to compound that with additional misconceptions. (http://en.wikipedia.org/wiki/Observable_universe#Misconceptions) As wiki notes:



The comoving distance from Earth to the edge of the observable universe is about 46 billion light years in any direction. The observable universe is thus a sphere with a diameter of about 93 billion light years). ... These figures are distances [I]now (in cosmological time), not distances at the time the light was emitted.


The Universe cannot be modeled like you're looking at a snow globe. (http://www.dreamstime.com/stock-images-stock-images-empty-snow-globe-image17192694)

Relative
2012-Apr-27, 11:13 PM
Nonsense. Measuring the orbital period doesn't require anything of the sort.

I was not talking about the orbital period, but the distance



What exactly is an "equilibrium orbit"?
Sorry for this, I should have used „neither retrograde or prograde“





Mainstream theory fully describes the orbit of Phobos just as it describes the orbit of Earth's moon. You can't brush it off as an exception.

Yes? Galaxy velocities are non-zero and the rate of expansion is quite small. Expansion of the universe does not mean nearby galaxies never move toward each other. This is entirely in line with mainstream theory, and not some unexplainable exception.
I didn‘t „brush it off“. Just the exact opposite. This was meant as an answer to ShinAce, that there are „execptions“, which in this context I have used as an example that if gravitation exceeds the „quite small“ expansion of the universe (I DO agree!), these things (like galaxies approach) occur, absolutely!


And no, c is not changing anywhere near fast enough to account for the moon's motion. LIGO uses the constant speed of light to measure the distance between two mirrors spaced 4 km apart to within 10e-18 m. A change in c large enough to change the moon's apparent distance by 3.8 cm would make an apparent change between these mirrors of around 400 nanometers, about 40 billion times that distance. The measured distance would be growing by over 1000 times the smallest measurable change, per second. That...would be noticed.No, first af all, these mirrors in 4 km distance seem not to be installed to measure waht is going on inbetween them, but taken as a reference for measurings in directions pointing away from them.
Furthermore, the distance change between these two mirrors according to OP (or the Hubble constant, by the way) would be 3 nanometers per year (not per second!, which makes a difference in the order of 3x10^7)

Relative
2012-Apr-27, 11:16 PM
Actually, you start out with a misconception and then proceed to compound that with additional misconceptions. (http://en.wikipedia.org/wiki/Observable_universe#Misconceptions) As wiki notes:



The comoving distance from Earth to the edge of the observable universe is about 46 billion light years in any direction. The observable universe is thus a sphere with a diameter of about 93 billion light years). ... These figures are distances now (in cosmological time), not distances at the time the light was emitted.


The Universe cannot be modeled like you're looking at a snow globe. (http://www.dreamstime.com/stock-images-stock-images-empty-snow-globe-image17192694)
Well, I won't call the reciprocal of the age of the universe (visible or invisible) a misconception

Relative
2012-Apr-27, 11:32 PM
a.) Well, there are a number of moons (like ours) that have been „tidally locked“ to its partner (i.e. sideral and synodic period are synchronized). I just wonder: If we take our earth-moon-system to the scale of Sun-Mercury, we find an (almost) 1:1 situation, if I didn‘t make a mistake in the inverse square gravitational law:
squareroot of (330.000 times earth mass (sun) multiplied by 0,23 times mercury mass (moon)) is 271, and the distance ratio earth–moon to sun-mercury is 378. OK, it is not really 1:1, but but 1:0.7.
Anyway, why hasn‘t Mercury „stopped“ so far.

b.) When the Moon „stopped“ (i.e. sideral and synodic period became equal), the force that was required to slow down its angular momentum, was „needless“ and must have been put into the recession speed, right or wrong?

c.) What about the friction inside the earth mantle, due to the fact that the equilibrum garviational point is located within it and the fact that earth isnot only rotating but wobbling around it. There must be enourmous friction. Is all this converted to heat and nothing to the rotation speed, and the latter only a matter of tidal influence of the moon?

cjameshuff
2012-Apr-27, 11:54 PM
I was not talking about the orbital period, but the distance

The two are inextricably related. Measuring changes in one is equivalent to measuring changes in the other.



Sorry for this, I should have used „neither retrograde or prograde“

That doesn't make sense. The only orbit that is not retrograde or prograde would be a perfect 90 degree polar orbit. Nothing in reality is in such an orbit. Phobos isn't even close, it's in a prograde orbit with an inclination to Mars's equator of slightly over 1 degree.



I didn‘t „brush it off“. Just the exact opposite. This was meant as an answer to ShinAce, that there are „execptions“, which in this context I have used as an example that if gravitation exceeds the „quite small“ expansion of the universe (I DO agree!), these things (like galaxies approach) occur, absolutely!

Oh, you certainly did, responding with "There are always phenomena like that." instead of an explanation for Phobos. You can't just handwave contradicting observations away as "exceptions".



No, first af all, these mirrors in 4 km distance seem not to be installed to measure waht is going on inbetween them, but taken as a reference for measurings in directions pointing away from them.

The interferometers are built to measure changes in the distance between the mirrors in order to detect gravitational waves, which would temporarily produce such differences as they pass through the interferometer. They do so using the speed of light. They would not function if the speed of light varied fast enough to make the moon appear to be moving away at several cm/year.



Furthermore, the distance change between these two mirrors according to OP (or the Hubble constant, by the way) would be 3 nanometers per year (not per second!, which makes a difference in the order of 3x10^7)

Your math is just wrong. 3.8 cm/384400 km*4 km = 400 nm per year. Even using your 2.796 cm figure, it's 290 nm/year, growth by 920 times the minimum measurable difference every second.

cjameshuff
2012-Apr-28, 12:21 AM
a.) Well, there are a number of moons (like ours) that have been „tidally locked“ to its partner (i.e. sideral and synodic period are synchronized). I just wonder: If we take our earth-moon-system to the scale of Sun-Mercury, we find an (almost) 1:1 situation, if I didn‘t make a mistake in the inverse square gravitational law:
squareroot of (330.000 times earth mass (sun) multiplied by 0,23 times mercury mass (moon)) is 271, and the distance ratio earth–moon to sun-mercury is 378. OK, it is not really 1:1, but but 1:0.7.
Anyway, why hasn‘t Mercury „stopped“ so far.

It is currently in a highly elliptical orbit, and the 1:1 locked condition is unstable due to the varying speed along its orbit...the current 3:2 spin-orbit resonance is currently favorable, being very nearly rotationally locked when Mercury is closest to the sun.



b.) When the Moon „stopped“ (i.e. sideral and synodic period became equal), the force that was required to slow down its angular momentum, was „needless“ and must have been put into the recession speed, right or wrong?

Wrong. When the moon stopped rotating with respect to Earth, the torques resulting from its rotation stopped as well. The forces resulted from its rotation within Earth's gravitational field, they didn't have to go anywhere when that rotation stopped.



c.) What about the friction inside the earth mantle, due to the fact that the equilibrum garviational point is located within it and the fact that earth isnot only rotating but wobbling around it. There must be enourmous friction. Is all this converted to heat and nothing to the rotation speed, and the latter only a matter of tidal influence of the moon?

The friction has nothing to do with the "equilibrium gravitational point". If you mean the point where gravitation from both the Earth and the Moon are equal, that's way out near the Earth-Moon L1 point, closer to the moon than the Earth and certainly not inside Earth.

As for the tidal drag within Earth, it slows Earth's rotation with respect to the moon just as the drag within the moon slowed its rotation with respect to the Earth. In the process, it raises the moon's orbit (through gravitation of the tidal bulge raised on Earth by the moon), as Earth rotates faster than the moon orbits. It's a simple transfer of angular momentum.

Relative
2012-Apr-28, 12:47 AM
The two are inextricably related. Measuring changes in one is equivalent to measuring changes in the other.
Well a clockhand, whether it is one cm long or one kilometer has the same orbital speed. To make a statement about the radius in the way I guess what you mean is: we need the correct masses. And here is, where it begins: Neither earth's nor moon's mass are determined within the accuracy needed. Even more, these are estimated due to their angular momentum behavivour, and not vice versa.

Oh, you certainly did, responding with "There are always phenomena like that." instead of an explanation for Phobos. You can't just handwave contradicting observations away as "exceptions".
I never did. If my last answer didn't show this, I'm afraid I will be unable.


The interferometers are built to measure changes in the distance between the mirrors in order to detect gravitational waves, which would temporarily produce such differences as they pass through the interferometer. They do so using the speed of light. They would not function if the speed of light varied fast enough to make the moon appear to be moving away at several cm/year.

Your math is just wrong. 3.8 cm/384400 km*4 km = 400 nm per year. Even using your 2.796 cm figure, it's 290 nm/year, growth by 920 times the minimum measurable difference every second.
At least my math mixing nanosconds was "less wrong" than yours, mixing seconds with years. And I didn't know, we were able to measure within 10^-14 to 10-15 meters within an accuracy of more than one number before the decimal point.

Relative
2012-Apr-28, 12:54 AM
The friction has nothing to do with the "equilibrium gravitational point". If you mean the point where gravitation from both the Earth and the Moon are equal, that's way out near the Earth-Moon L1 point, closer to the moon than the Earth and certainly not inside Earth.
No, I meant the equilibrum rotational point of the system earth-moon which is located inside erath's mantle.

caveman1917
2012-Apr-28, 02:01 AM
No, I meant the equilibrum rotational point of the system earth-moon which is located inside erath's mantle.

The term is the barycenter of the system. And no, the mere fact that the earth orbits the barycenter doesn't induce any stresses, just like the mere fact that the earth orbits the sun doesn't induce them. The stresses are there because of tidal effects, irrespective of where the barycenter is.

cjameshuff
2012-Apr-28, 03:41 AM
Well a clockhand, whether it is one cm long or one kilometer has the same orbital speed. To make a statement about the radius in the way I guess what you mean is: we need the correct masses. And here is, where it begins: Neither earth's nor moon's mass are determined within the accuracy needed. Even more, these are estimated due to their angular momentum behavivour, and not vice versa.

...what?
If the distance is increasing, so is the orbital period. Measuring changes in one is equivalent to measuring changes in the other. You don't even care about the masses...those don't change by any meaningful amount, they're a constant factor.



I never did. If my last answer didn't show this, I'm afraid I will be unable.

Um, it's right there in post #18...

You know, rather than arguing you didn't say what you did, you could just explain the orbit of Phobos. And while you're at it, other oddball terms you've thrown around like "equilibrium orbit".



At least my math mixing nanosconds was "less wrong" than yours, mixing seconds with years. And I didn't know, we were able to measure within 10^-14 to 10-15 meters within an accuracy of more than one number before the decimal point.

My math wasn't wrong, and I didn't mix seconds with years.

As for the measurement precision...well, I stated the precision and instrument in my first post on the subject. I did mistakenly quote the wrong number, though...LIGO can detect a strain of one part in 10^21, which given the 4 km arm length is actually more sensitive than the quantity I gave.



No, I meant the equilibrum rotational point of the system earth-moon which is located inside erath's mantle.

That's the barycentre...it's got nothing to do with any equilibrium point and nothing to do with tidal forces.

Relative
2012-Apr-28, 06:59 AM
The barycenter, yes. Thank you both.
(sometimes I hate missing vocabulary in English)
Or mistaking like "orbital speed". I misunderstood "angular speed", sorry!! for it, cjameshuff.
And the last one:
"There are always phenomena like this" was mistaken as exceptions. (So I used "exceptions", when replying) No, there are a lot of them ("always" rather to be pronounced as in "always and everywhere")

PS. The word "Equilibrum" can mean a barycenter (I guess, it is derivated from it?). I didn't state that this has an influence on the tidal forces between earth-moon. I just wondered whether this is unconsidered in terms of slowing down earth's rotation and the effect is only seen as tidal influence

PPS. I read the Wiki article about LIGO (in my native language :-)) ). Interesting project, but it works (or should work) very differently from what I've understood after you mentioned it, starting with 75 times passing the 4 kilometers, two observatories 3000 km apart and so on. I need more time for it...

Relative
2012-Apr-28, 09:16 PM
So, I have voted myself to this interesting project.
As far as I can figure out they make laser runtime comparisions between the two 4 km long legs. This is the reason for their „incredible“ accuracy in the order of 10^-22 meters.
It is like comparing the ratio of 1/x to x, (which becomes 1/x^2 then), therefore, their „accuracy gets squared“ in comparison to the accuracy of what can be measured by atomic clocks when it comes to absolute values.
The problem is: IF (I want to state this as BIG if), c changes in terms of OP, these people won‘t notice, because it would effect both legs, so the relative diifference would be zero.
So what about each leg itself, will they notice that differnce ?
I guess they put their pants on the same way as you, so using the newest atomic clocks which have a relative accurcy of 10^-16 seconds. What does this mean: The longer a laser experiment is or the greater the distance we will get a more precise absolute value.
For a laser experiment of duration one second, our current atomic clock time measurement will be precise to the order of 3x10^-8 meters. If we use an experiment whichs is 8000 meters (back and forth the leg lenght of LIGO), we get a precision of 7.5x10^-12 meters (note: square of this is 5.6x10^-23m, so the above mentioned LIGO accuracy) per second of duration. The changing value of OP per second and 8000 meters is 1.84x10^-14. So only after about 7 minutes a change in the last digit!! (15 behind the decimal point that this atomic clock shows) should be noticed.
Im just afraid, that those more than 30 parameters of LIGO (as stated on their homepage) have already been „adjusted“ meanwhile...
I hope, I didn‘t make too much „miscalculation“ this thime. On this platform you must watch like a hawk.

But, as always, you are welcomed to show me we're I failed

cjameshuff
2012-Apr-29, 04:43 PM
They might not measure the second-to-second difference if that measurement precision is purely of the difference in strain between arms, but that's not the only example of things that would be influenced by changes in c. A great many pieces of high precision instrumentation depend on it being constant, it is part of what determines the spectral lines emitted and absorbed by atoms, which we can observe across intergalactic distances and time spans of a good part of the age of the universe, and so on.

And you keep avoiding answering this...what about Phobos? What about the tidal locking of every large moon in the solar system, including Triton, which appears to be a recently captured Kuiper belt object? That's not coincidence. Each of those moons is an example of transfer of angular momentum between an object's rotation and its orbit through tidal drag effects, and those effects work on the planet's end too. This is why the moon, which orbits much slower than Earth rotates, is being pulled into a higher orbit, and why Phobos (which orbits faster than Mars rotates) and Triton (which orbits in the opposite direction of the rotation of Neptune) are being dragged down into lower orbits.

Cougar
2012-Apr-30, 01:23 PM
As far as I can figure out they make laser runtime comparisions between the two 4 km long legs. This is the reason for their „incredible“ accuracy in the order of 10^-22 meters.

If I understand it correctly, LIGO doesn't exactly use "runtime comparisons," that is, it does not use atomic clocks to measure the times and compare them. It uses light wave interferometry. When the laser beams are brought back together, any slight shift in the phase of one wavelength compared to the other can be detected, indicating a slight change in distance for one of the legs. After all, LIGO is short for Laser Interferometer Gravitational-Wave Observatory.

Relative
2012-Apr-30, 06:12 PM
They might not measure the second-to-second difference if that measurement precision is purely of the difference in strain between arms, but that's not the only example of things that would be influenced by changes in c. A great many pieces of high precision instrumentation depend on it being constant, it is part of what determines the spectral lines emitted and absorbed by atoms, which we can observe across intergalactic distances and time spans of a good part of the age of the universe, and so on.

And you keep avoiding answering this...what about Phobos? What about the tidal locking of every large moon in the solar system, including Triton, which appears to be a recently captured Kuiper belt object? That's not coincidence. Each of those moons is an example of transfer of angular momentum between an object's rotation and its orbit through tidal drag effects, and those effects work on the planet's end too. This is why the moon, which orbits much slower than Earth rotates, is being pulled into a higher orbit, and why Phobos (which orbits faster than Mars rotates) and Triton (which orbits in the opposite direction of the rotation of Neptune) are being dragged down into lower orbits.

Well yes, I guess the determination of the spectral lines would be effected. A peak, for example at 1000nm, would shift in the order of 7.27x10^-17m per year. Even at cosmic scale (let‘s say 13 billion years) this would mean a difference of only 55 nm, whereas about 7960nm are observed (redshift). So the first could still be „a part“ of the latter.

Same with Phobos and all the moons which are dragged to lower orbits. One question of OP was, if that value could be „a PART of it“. Even if the net amount is negative, it still could contain a positive other value: 3 + 1= 4 vs. -3 + 1 = -2. Looking at this simple example, the spiraling away thing just should be relatively faster than the lowering orbit stuff. Unfortunately, I don't know whether or not this is observed...

cjameshuff
2012-Apr-30, 07:04 PM
Well yes, I guess the determination of the spectral lines would be effected. A peak, for example at 1000nm, would shift in the order of 7.27x10^-17m per year. Even at cosmic scale (let‘s say 13 billion years) this would mean a difference of only 55 nm, whereas about 7960nm are observed (redshift). So the first could still be „a part“ of the latter.

That's not what I mean. Consider the effect of changing the speed of light on the physical processes that cause those spectral lines...the reason the resonances and quantization levels are where they are. The spectral lines would more than just shift a few nm.



Same with Phobos and all the moons which are dragged to lower orbits. One question of OP was, if that value could be „a PART of it“. Even if the net amount is negative, it still could contain a positive other value: 3 + 1= 4 vs. -3 + 1 = -2. Looking at this simple example, the spiraling away thing just should be relatively faster than the lowering orbit stuff. Unfortunately, I don't know whether or not this is observed...

Well, with the numbers you were throwing around, you were considering it to be most if not all of the moon's recession.

Relative
2012-Apr-30, 09:04 PM
That's not what I mean. Consider the effect of changing the speed of light on the physical processes that cause those spectral lines...the reason the resonances and quantization levels are where they are. The spectral lines would more than just shift a few nm.
Like how much so?



Well, with the numbers you were throwing around, you were considering it to be most if not all of the moon's recession.
I would be "satisfied with less than the half" :-)
In this context, and as promised in post #17, the LATEST scientific article (published 20th April 2012) concerning the moon's recession anomaly:
http://www.planetary-science.com/content/pdf/2191-2521-1-1.pdf
Note that the author also considers "several possible explanations", and focusses on speed of light decreases.
At least, I'm not alone :-)

Reality Check
2012-Apr-30, 10:23 PM
http://www.planetary-science.com/content/pdf/2191-2521-1-1.pdf

Actually Louise Riofrio's GM = tc^3 speculation has been around for at least 6 years so it is not that new. The physics that she uses in this speculation is simplistic and wrong based on her Recent GM=tc^3 Paper (http://riofriospacetime.blogspot.com/2006/09/recent-gmtc3-paper.html) (2006!). She states that the "relative" (to what?) radius of the universe (R) is R = ct where c is the speed of light and t is the age of the universe. This ignores General Relativity and so is wrong.

Relative
2012-May-01, 12:33 AM
Actually Louise Riofrio's GM = tc^3 speculation has been around for at least 6 years so it is not that new. The physics that she uses in this speculation is simplistic and wrong based on her Recent GM=tc^3 Paper (http://riofriospacetime.blogspot.com/2006/09/recent-gmtc3-paper.html) (2006!). She states that the "relative" (to what?) radius of the universe (R) is R = ct where c is the speed of light and t is the age of the universe. This ignores General Relativity and so is wrong.Sorry, that I didn‘t answer your post #15. But your last one just confirms my estimation.
In the above mentioned post you statet that „we do not expect any effect of the expansion of the universe on the Earth-Moon system because they are gravitaionally bound“.
Gravitaion is the weakest of all fundamental forces to be in the order of 10^-34 compared to stronge force. BUT: It STILL claims its rights, as you can see when your pencil is dropping.
So, you may call the value of OP negligalbe, but it still would have its influence, even if „gravitational bounding“ of two bodies seem to overpower it. Otherwise, if this influence would totally be gone (so, zero as you conclude) our seek of a „theory of everything“ must be questioned. Expansion of the universe, if it exists, MUST have (even if it is very little) an influence on galaxies or even the earth-moon-system, despite their value of gravitation.

caveman1917
2012-May-01, 01:05 AM
That's not what I mean. Consider the effect of changing the speed of light on the physical processes that cause those spectral lines...the reason the resonances and quantization levels are where they are. The spectral lines would more than just shift a few nm.

I suppose we could let c vary if we let the other constants vary accordingly such that the physical results would be the same. But then it is of course hardly meaningful to say that c varies.

cjameshuff
2012-May-01, 01:29 AM
Sorry, that I didn‘t answer your post #15. But your last one just confirms my estimation.
In the above mentioned post you statet that „we do not expect any effect of the expansion of the universe on the Earth-Moon system because they are gravitaionally bound“.
Gravitaion is the weakest of all fundamental forces to be in the order of 10^-34 compared to stronge force. BUT: It STILL claims its rights, as you can see when your pencil is dropping.
So, you may call the value of OP negligalbe, but it still would have its influence, even if „gravitational bounding“ of two bodies seem to overpower it. Otherwise, if this influence would totally be gone (so, zero as you conclude) our seek of a „theory of everything“ must be questioned. Expansion of the universe, if it exists, MUST have (even if it is very little) an influence on galaxies or even the earth-moon-system, despite their value of gravitation.

For a reasonably circular orbit, the only result would be a slight mis-estimation of the primary body's mass. The presence of expansion means the moon orbits very slightly closer to Earth, where gravity balances the sum of centrifugal force and expansion (which appears as an outward force directly proportional to distance, and is thus constant for circular orbits). It might make a major difference in large, highly eccentric orbits that are barely bound, but the moon is not in such an orbit...and I think the major effect would be precession or a gradual increase in eccentricity, not spiraling outward.

caveman1917
2012-May-01, 01:41 AM
For a reasonably circular orbit, the only result would be a slight mis-estimation of the primary body's mass. The presence of expansion means the moon orbits very slightly closer to Earth, where gravity balances the sum of centrifugal force and expansion (which appears as an outward force directly proportional to distance, and is thus constant for circular orbits). It might make a major difference in large, highly eccentric orbits that are barely bound, but the moon is not in such an orbit...and I think the major effect would be precession or a gradual increase in eccentricity, not spiraling outward.

That's not quite correct. Expansion per se will not have an influence even if we factor it in. The change in equilibrium is from the acceleration of expansion, which would not depend on distance , but more importantly can be negative. If the expansion is decelerating (which it has been doing for a good part of the history of the universe) the result will be an extra inward force. Which is incidentally one of the reasons it really doesn't even make much sense to factor in expansion in non-homogeneous backgrounds (even if we could).

*ETA: erratum: it does depend linearly on the distance

cjameshuff
2012-May-01, 02:06 AM
That's not quite correct. Expansion per se will not have an influence even if we factor it in. The change in equilibrium is from the acceleration of expansion, which would not depend on distance, but more importantly can be negative. If the expansion is decelerating (which it has been doing for a good part of the history of the universe) the result will be an extra inward force. Which is incidentally one of the reasons it really doesn't even make much sense to factor in expansion in non-homogeneous backgrounds (even if we could).

In general, sure. But we're talking about human observations of the moon's orbit. Expansion is currently accelerating, but not at a particularly high rate, and for this purpose and timespan it seems reasonable to consider it to be constant.

caveman1917
2012-May-01, 02:45 AM
In general, sure. But we're talking about human observations of the moon's orbit. Expansion is currently accelerating, but not at a particularly high rate, and for this purpose and timespan it seems reasonable to consider it to be constant.

True, it just seemed to me that Relative is thinking of the effect of the "base" expansion (at least that's how he calculates it) and i'm not sure the distinction has been made clear in the discussion.

caveman1917
2012-May-01, 02:51 AM
Relative, consider the following:

I throw a ball away from me (in empty space). When it has reached a certain distance, i grab it with my hand. From that moment i and the ball form a bound system. Would you consider the ball to keep "pushing away" in my hand? I (hopefully) presume not. Then why would you consider the moon to keep "pushing away" from the earth even when they are a gravitationally bound system?

Think of it this way: why was the ball moving away from me before i grabbed onto it? Because it was doing so a moment before. Once i grabbed onto it, it lost that tendency to move away from me. The reason we see galaxies move away from us is likewise because they were doing so in the past and nothing ever "grabbed onto them", however because the moon is gravitationally bound to the earth it simply does not have that tendency anymore (assuming it ever had that in the first place).

Relative
2012-May-01, 03:03 AM
Relative, consider the following:

I throw a ball away from me (in empty space). When it has reached a certain distance, i grab it with my hand. From that moment i and the ball form a bound system. Would you consider the ball to keep "pushing away" in my hand? I (hopefully) presume not. Then why would you consider the moon to keep "pushing away" from the earth even when they are a gravitationally bound system?

Think of it this way: why was the ball moving away from me before i grabbed onto it? Because it was doing so a moment before. Once i grabbed onto it, it lost that tendency to move away from me. The reason we see galaxies move away from us is likewise because they were doing so in the past and nothing ever "grabbed onto them", however because the moon is gravitationally bound to the earth it simply does not have that tendency anymore (assuming it ever had that in the first place).
Hm, well if you consider that in terms of c "grabing" the ball would make no difference to the fact that you wouldn't have grabed it, what next?

caveman1917
2012-May-01, 03:28 AM
Hm, well if you consider that in terms of c "grabing" the ball would make no difference to the fact that you wouldn't have grabed it, what next?

I'm not sure what you mean by "in terms of c", but what i'm trying to say is to look at it the other way. Rather than say that galaxies recede because space expands, space expands because galaxies recede. I can frame my example of throwing the ball away in terms of an expanding space between me and the ball. But that picture only works in so far as nothing intervenes in the ball moving away from me. There is no universal law saying that the ball must constantly try to move away from me, it just happens to do so because it was doing so in the past. Neither is there some law saying that the moon must try to move away from the earth.

Once something intervenes, me grabbing onto the ball, or likewise the moon being gravitationally bound to the earth, the picture of expanding space simply fails. Grabbing onto it or not makes all the difference. In a sense, expanding space is nothing more than the statement that nothing has intervened in something moving away because it was doing so in the past. Those galaxies we see receding aren't constantly being coerced into receding, no more than the ball needs constant coercion to keep moving away from me, as long as nothing intervenes they just keep doing what they're doing and we find it convenient to frame that behaviour in terms of an expanding space. Expanding space is not a cause, it's a way of picturing a situation. The ultimate cause lies in what made those galaxies start moving away in the first place, not in what happens afterwards.

After that you get into the effects of acceleration of expansion, but that's quite another story. But i think that is not where the main misunderstanding lies.

Relative
2012-May-01, 03:35 AM
I'm not sure what you mean by "in terms of c", but what i'm trying to say is to look at it the other way. Rather than say that galaxies recede because space expands, space expands because galaxies recede. I can frame my example of throwing the ball away in terms of an expanding space between me and the ball. But that picture only works in so far as nothing intervenes in the ball moving away from me. There is no universal law saying that the ball must constantly try to move away from me, it just happens to do so because it was doing so in the past. Neither is there some law saying that the moon must try to move away from the earth.

Once something intervenes, me grabbing onto the ball, or likewise the moon being gravitationally bound to the earth, the picture of expanding space simply fails. Grabbing onto it or not makes all the difference. In a sense, expanding space is nothing more than the statement that nothing has intervened in something moving away because it was doing so in the past. Those galaxies we see receding aren't constantly being coerced into receding, no more than the ball needs constant coercion to keep moving away from me, as long as nothing intervenes they just keep doing what they're doing and we find it convenient to frame that behaviour in terms of an expanding space. Expanding space is not a cause, it's a way of picturing a situation. The ultimate cause lies in what made those galaxies start moving away in the first place, not in what happens afterwards.

After that you get into the effects of acceleration of expansion, but that's quite another story. But i think that is not where the main misunderstanding lies.
OK, I know comparisions flaw. But, since you have used the "grabbing ball metaphor":
What about grabing the ball on your 6th birthday. And, then growing up to an adult, still holding the ball in your hand?

caveman1917
2012-May-01, 03:49 AM
OK, I know comparisions flaw. But, since you have used the "grabbing ball metaphor":
What about grabing the ball on your 6th birthday. And, then growing up to an adult, still holding the ball in your hand?

During none of that time would the ball have had any tendency to move away from me, it just rested in my hand the entire time, which is kind of my point. Any such tendency it may have had before would have been lost the moment i first grabbed onto it. Or to frame it in different terms, even if everything else had been moving away from me during that time (the space around me "expanded"), the ball has during that time not participated in the expansion of space, and has never "tried" to do so. So why would you consider an equally bound system (earth-moon) to behave differently?

Reality Check
2012-May-01, 04:29 AM
Ed Wright is a good resource for cosmology questions:
Why doesn't the Solar System expand if the whole Universe is expanding? (http://www.astro.ucla.edu/~wright/cosmology_faq.html#SS)

This question is best answered in the coordinate system where the galaxies change their positions. The galaxies are receding from us because they started out receding from us, and the force of gravity just causes an acceleration that causes them to slow down, or speed up in the case of an accelerating expansion. Planets are going around the Sun in fixed size orbits because they are bound to the Sun. Everything is just moving under the influence of Newton's laws (with very slight modifications due to relativity). [Illustration (http://www.astro.ucla.edu/~wright/bound.html)] For the technically minded, Cooperstock et al. (http://xxx.lanl.gov/abs/astro-ph/9803097) computes that the influence of the cosmological expansion on the Earth's orbit around the Sun amounts to a growth by only one part in a septillion over the age of the Solar System. This effect is caused by the cosmological background density within the Solar System going down as the Universe expands, which may or may not happen depending on the nature of the dark matter. The mass loss of the Sun due to its luminosity and the Solar wind leads to a much larger [but still tiny] growth of the Earth's orbit which has nothing to do with the expansion of the Universe. Even on the much larger (million light year) scale of clusters of galaxies, the effect of the expansion of the Universe is 10 million times smaller than the gravitational binding of the cluster.

Relative
2012-May-01, 08:19 AM
During none of that time would the ball have had any tendency to move away from me, it just rested in my hand the entire time
It's the arm length, to stay in this picture, that would have grown from childhood to adult, too.

caveman1917
2012-May-01, 02:23 PM
It's the arm length, to stay in this picture, that would have grown from childhood to adult, too.

Then you have the picture wrong because if the arm length grew accordingly with the distance to say some other guy, then that other guy would be staying at the same amount of arm-lengths and you'd see no expansion. If the ruler with which you are measuring the distance to some other galaxy grows along with the distance to that galaxy there would be no discernable expansion. Expansion isn't something a local object does, it's what happens to the distance between two different objects.

Even so, if the arm length grew than the distance between you and the ball only grew because you pushed the ball away (your growing arm exerted an outward force on the ball). That's obviously not the right picture for the earth-moon system, gravity does a lot of things but it doesn't "push" :)

Reality Check
2012-May-03, 08:55 PM
Sorry, that I didn‘t answer your post #15. But your last one just confirms my estimation.

My last post does not mention your estimation at all.
Post #15 states that your estimation is wrong.


Expansion of the universe, if it exists, MUST have (even if it is very little) an influence on galaxies or even the earth-moon-system, despite their value of gravitation.
You are right: It does have a very little influence on galaxies, the earth-moon-system or even the earth-sun system.
That effect on the the earth-sun system is 1 part in a septillion (1,000,000,000,000,000,000,000,000) over 4.6 billion years. So your estimate is really, really wrong because you do not include that the earth and moon are gravitationally bound.
Why doesn't the Solar System expand if the whole Universe is expanding? (http://www.astro.ucla.edu/~wright/cosmology_faq.html#SS)

This question is best answered in the coordinate system where the galaxies change their positions. The galaxies are receding from us because they started out receding from us, and the force of gravity just causes an acceleration that causes them to slow down, or speed up in the case of an accelerating expansion. Planets are going around the Sun in fixed size orbits because they are bound to the Sun. Everything is just moving under the influence of Newton's laws (with very slight modifications due to relativity). [Illustration (http://www.astro.ucla.edu/~wright/bound.html)] For the technically minded, Cooperstock et al. (http://xxx.lanl.gov/abs/astro-ph/9803097) computes that the influence of the cosmological expansion on the Earth's orbit around the Sun amounts to a growth by only one part in a septillion over the age of the Solar System. This effect is caused by the cosmological background density within the Solar System going down as the Universe expands, which may or may not happen depending on the nature of the dark matter. The mass loss of the Sun due to its luminosity and the Solar wind leads to a much larger [but still tiny] growth of the Earth's orbit which has nothing to do with the expansion of the Universe. Even on the much larger (million light year) scale of clusters of galaxies, the effect of the expansion of the Universe is 10 million times smaller than the gravitational binding of the cluster.

Hetman
2012-May-03, 10:34 PM
That effect on the the earth-sun system is 1 part in a septillion (1,000,000,000,000,000,000,000,000) over 4.6 billion years. So your estimate is really, really wrong because you do not include that the earth and moon are gravitationally bound.
Why doesn't the Solar System expand if the whole Universe is expanding? (http://www.astro.ucla.edu/~wright/cosmology_faq.html#SS)

I am afraid that these are arguments like this:
is raining now, because the swallows were flying low before.

We simply observe the redshift of distant galaxies.
Why? Probably because the cosmos is not empty. After all dissipation of energy is a completely natural phenomenon, and perhaps even inevitable according to thermodynamics - entropy increases.

Reality Check
2012-May-03, 11:02 PM
I am afraid that these are arguments like this:
...snipped trivial stuff and a bit of gibberish...
I am afraid that these are arguments actually like this: Gravity exists. We know how it works. Over scales of millions of lightyears the acceleration it causes dominates any acceleration caused by the observed expansion of the universe. The science is explained in Why doesn't the Solar System expand if the whole Universe is expanding? (http://www.astro.ucla.edu/~wright/cosmology_faq.html#SS)

Hetman
2012-May-03, 11:18 PM
Standard non-empty universe and standard thermodynamics is not negotiable - neither here nor in the ATM.

In the given link are factual errors, unfortunately - in particular:
definition of the curvature of space is only one, not two alternatives.

John Mendenhall
2012-May-03, 11:24 PM
Starting with post #21, all the posters that invoke gravitational binding are correct. The expansion of the universe in gravitationally bound systems, and this includes structures as large as galaxy clusters (galaxy -> group -> cluster), is negligible. Myself or others must type this out at least once a week in some part of the forum. Expansion is not a local phenomenon.

Say it to yourself over and over. 'Not local. Not local. Not . . . .'

Regards, John M.

Swift
2012-May-04, 01:49 AM
Originally Posted by Hetman
I am afraid that these are arguments like this:
...snipped trivial stuff and a bit of gibberish...
Deliberately misquoting someone like that is rude. Hetman got an infraction for advocating ATM outside of the ATM forum, you get one for rudeness.

tusenfem
2012-May-04, 04:59 AM
Standard non-empty universe and standard thermodynamics is not negotiable - neither here nor in the ATM.

Not at all, if you actually have a well thought through model that goes against ATM, with the appropriate math and explanations and think you can defend it, then go ahead and open your discussion there.

John Mendenhall
2012-May-04, 06:27 AM
Standard non-empty universe and standard thermodynamics is not negotiable - neither here nor in the ATM.

In the given link are factual errors, unfortunately - in particular:
definition of the curvature of space is only one, not two alternatives.

http://www.astro.ucla.edu/~wright/cosmology_faq.html#FLAT

You did read the above, right?

"In 2004 Prof. Wright was elected as a Fellow of the American Association for the Advancement of Science, in 2007 he was elected as a Fellow of the American Academy of Arts and Sciences, and in 2011 he was elected to the National Academy of Sciences." :eek:

Please, I'd like to here more about the errors in the above author's tutorial.

Thanks, John M.

Hetman
2012-May-04, 11:53 AM
Not at all, if you actually have a well thought through model that goes against ATM, with the appropriate math and explanations and think you can defend it, then go ahead and open your discussion there.

That's right, we can discuss, but only the mechanism of the energy dissipation - propose methods of implementation of the observed phenomena.

By contrast, the fact the dispersion/dissipation is indisputable, and this means that we should calculate the density of matter (physical condition of intergalactic space) directly from the observed redshift, and not some of the Doppler velocity.

The same applies to the law of gravity: the mechanism is subject to discussion, but the very fact of its existence is indisputable.

cjameshuff
2012-May-04, 01:25 PM
By contrast, the fact the dispersion/dissipation is indisputable,

As a cause for redshift? No, it isn't. There is no mechanism for dispersion or "dissipation" by intervening matter to cause a red shift. Thus, no way to use redshift to estimate density of matter.

Cougar
2012-May-04, 01:32 PM
We simply observe the redshift of distant galaxies.
Why? Probably because the cosmos is not empty. After all dissipation of energy is a completely natural phenomenon...

I believe this "redshift alternative" has been previously debunked in this thread. If redshift is caused by "dissipation" of light, how is it we can see objects more than 10 billion lightyears away in perfect focus?

Also, if the mainstream interpretation of redshift is wrong, which I presume implies the universe is not expanding, why do Ia supernovas exhibit time dilation?

Hetman
2012-May-04, 05:46 PM
As a cause for redshift? No, it isn't. There is no mechanism for dispersion or "dissipation" by intervening matter to cause a red shift. Thus, no way to use redshift to estimate density of matter.

It does not matter that such a mechanism is currently unknown.
And this is the norm rather than the exception - we do not know the mechanisms of many other important phenomena, including the gravity, which is perhaps the key here.

Hetman
2012-May-04, 05:52 PM
I believe this "redshift alternative" has been previously debunked in this thread. If redshift is caused by "dissipation" of light, how is it we can see objects more than 10 billion lightyears away in perfect focus?

Also, if the mainstream interpretation of redshift is wrong, which I presume implies the universe is not expanding, why do Ia supernovas exhibit time dilation?

Interpretations are needed only for unrecognized phenomena.
After a full recognition the interpretations automatically disappear - they are no longer needed.

Strange
2012-May-04, 06:10 PM
It does not matter that such a mechanism is currently unknown.

But as we have a known mechanism, why bother inventing an unknown one?

Hetman
2012-May-05, 02:49 PM
But as we have a known mechanism, why bother inventing an unknown one?

The mechanism must take into account the presence of matter, and the idea of stretching of space totally ignores this fact.

Besides stretching the space is not a mechanism, but the math - the transformation of space.
It is known that such transformations have no effect on the physical processes - the principle of relativity.

You might as well suggest an inverse transformation:
contraction of matter - from atoms to the galaxies, rather than stretch the distance between them.

The final result will be identical, despite the evident global stationarity.

cjameshuff
2012-May-05, 03:54 PM
The mechanism must take into account the presence of matter, and the idea of stretching of space totally ignores this fact.

What is there to take into account? The redshift due to the presence of matter is 0.



Besides stretching the space is not a mechanism, but the math - the transformation of space.
It is known that such transformations have no effect on the physical processes - the principle of relativity.

This is just confused and wrong. The principle of relativity applies to systems in uniform relative motion, not to systems undergoing expansion or contraction.

Hetman
2012-May-05, 04:28 PM
What is there to take into account? The redshift due to the presence of matter is 0.

We do not know the cases of lossless transmission of energy through areas filled with matter, because it is impossible under the laws of thermodynamics.


This is just confused and wrong. The principle of relativity applies to systems in uniform relative motion, not to systems undergoing expansion or contraction.

The general principle of relativity does not care about such trifles.
Processes does not depend entirely on methods of formulation: a frame of reference, adopted coordinates, units of measurement, etc.
It is a mathematical principle, a fundamental and obvious.

This variant is probably consistent with all observations - local and global:
galaxies grow continuously, and hence the observed redshift.

cjameshuff
2012-May-05, 04:42 PM
We do not know lossless power transmission through areas filled with matter.

I didn't say it was lossless. There are losses due to scattering and absorption. These don't produce a red shift.

Redshift is a very particular phenomenon, doppler shift due to an object moving away. Spectral lines and such remain intact and have the same relative locations, they are simply shifted toward longer wavelengths. Reddening by preferential scattering of short wavelengths or absorption and re-emission at cooler temperatures does not shift the spectrum and can not be confused for redshift.



The general principle of relativity does not care about such trifles.

They're hardly trifles, but that's otherwise right, it says nothing about them. It is only concerned with the relative motion of the systems, and does not apply to expansion or contraction.



Processes does not depend entirely on methods of formulation: a frame of reference, adopted coordinates, units of measurement, etc.
It is a mathematical principle, a fundamental and obvious.

We're not talking about changing units of measurement, we're talking about expansion of space. Distances between objects not bound to each other are getting larger with time. Your claim is essentially that the physical behavior of a system doesn't depend on density...which is simply wrong, and not what the principle of relativity means.

tusenfem
2012-May-05, 08:09 PM
hetman if you believe that redshift, as it is observed in astrophysics, can be caused by scattering and other interactions with matter, then take itto ATM and present your model there. And don't forgetcto take into account what cjameshuff just told you about spectral lines, and the still focussable distant universe.

Hetman
2012-May-05, 08:14 PM
Redshift is a very particular phenomenon, doppler shift due to an object moving away. Spectral lines and such remain intact and have the same relative locations, they are simply shifted toward longer wavelengths. Reddening by preferential scattering of short wavelengths or absorption and re-emission at cooler temperatures does not shift the spectrum and can not be confused for redshift.

Energy dissipation is inevitable during transmission by any medium.

Assume for simplicity that the medium is in equilibrium, the incoming stream must affect them, the entropy increases, which is already irreversible.


We're not talking about changing units of measurement, we're talking about expansion of space. Distances between objects not bound to each other are getting larger with time. Your claim is essentially that the physical behavior of a system doesn't depend on density...which is simply wrong, and not what the principle of relativity means.

What is the stretching space, and why this would the electromagnetic waves get longer?
These waves are not oscillations of space, this idea presupposes.

Relative
2012-May-05, 10:30 PM
Energy dissipation is inevitable during transmission by any medium.

Assume for simplicity that the medium is in equilibrium, the incoming stream must affect them, the entropy increases, which is already irreversible.

Unfortunately, due to personal reasons, I didn't follow this thread for a couple of days and was surprised how it developed... Althouh somehow away from OP, still interesting.
So, as it was mentioned above, during my studying, I always wondered about "entropy" and that it is supposed to "always increase".
If this is the case, why do we observe every lifeform (plants or animals) to exhibit patterns that are anything but disorganized. Why do systems (gravitational, pressure, electrostatic or whatsoever) seek an equilibrum, if entropy tells us, that everything seeks for a "chaos" rather than being "well-done"? Entropy, therefore, I never could really "accept" as a concept. But, I'm afraid, this may become a more different thread than it already is... Just take this as marginal note

TooMany
2012-May-05, 11:10 PM
Rather than say that galaxies recede because space expands, space expands because galaxies recede. I can frame my example of throwing the ball away in terms of an expanding space between me and the ball. But that picture only works in so far as nothing intervenes in the ball moving away from me. There is no universal law saying that the ball must constantly try to move away from me, it just happens to do so because it was doing so in the past.

The phrase "space is expanding" leads to confusion because it carries with it the implication that particles at rest with respect to each other will move apart. The way caveman describes expansion get's rid of this problem. He seems to be saying that the expansion is "inertial" and that the momentum was imparted at the Big Bang. Once matter is moving apart it continues to move apart except as affected by some other force like gravity. So once you grab the escaping ball, the ball comes to rest relative to you and will remain with you indefinitely, even if you release your grip on the ball.

There is no force causing things to move apart. They were just initially moving apart. Consider this from Ned Wright pages:


Are galaxies really moving away from us or is space just expanding?

This depends on how you measure things, or your choice of coordinates. In one view, the spatial positions of galaxies are changing, and this causes the redshift. In another view, the galaxies are at fixed coordinates, but the distance between fixed points increases with time, and this causes the redshift. General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views.


Consider the 2D balloon analogy. The problem with viewing expansion the second way is that people tend to think that each particle of matter is stuck in a certain spot on the expanding balloon. But they are not stuck, they adhere to the surface without any friction in this analogy. So if two particles of matter on the balloon are static relative to one another and the balloon is large, their separation is not affected by the expansion of the balloon. The surface of the balloon being friction-less cannot carry them apart.

Here's something interesting that just occurred to me. Let's suppose that the expansion of the balloon accelerates (dark energy). Those two particles (at respective rest) will still not begin to move relative to one another. If this analogy is correct for dark energy, then the idea of a "big rip" seems like nonsense.

-----

Probably incorrect: This view of the analogy does not explain how light waves get longer as they travel, except as a Doppler shift.

Van Rijn
2012-May-05, 11:29 PM
So, as it was mentioned above, during my studying, I always wondered about "entropy" and that it is supposed to "always increase". If this is the case, why do we observe every lifeform (plants or animals) to exhibit patterns that are anything but disorganized.


Because they're not a closed system, and entropy can be decreased locally at the expense of increasing total entropy. Life ultimately gets energy from the sun, and the Earth loses energy to deep space, increasing entropy. It won't last forever: The sun will eventually stop fusing hydrogen, and life on Earth won't last that long.

cjameshuff
2012-May-06, 12:03 AM
Because they're not a closed system, and entropy can be decreased locally at the expense of increasing total entropy.

And life is really effective at this. Those forms with advantages in tapping existing energy sources and converting them to low-energy disorganized waste, heat, and copies of themselves will outcompete others, and without competition or attrition will expand exponentially to consume whatever's available. It's gotten to the point where at least one life form has even developed the capability to extract nuclear energy from heavy elements by splitting them into ones with lower energy content, far faster and more completely than would occur on any lifeless world.

Relative
2012-May-07, 04:27 PM
And life is really effective at this. Those forms with advantages in tapping existing energy sources and converting them to low-energy disorganized waste, heat, and copies of themselves will outcompete others, and without competition or attrition will expand exponentially to consume whatever's available. It's gotten to the point where at least one life form has even developed the capability to extract nuclear energy from heavy elements by splitting them into ones with lower energy content, far faster and more completely than would occur on any lifeless world.

Well. I don‘t only mean "locally" (one of your aguments) life forms. If entropy was dominating we shouldn‘t find ANY structure, neither in cosmic scale, we observe the opposite: Galaxies are very large structures, which never could have been developed, if „chaos“ was the main concern.
If the law of conservation of energy is valid, and in contrast entropy is considered to always grow, then we must ask a.) what is its reason and b.) what is its reciprocal and do we find an appropriate counterpart? Do we find something like that?
"The only thing to always grow" for human beings seem to be time. So is "Entropy" related to it?

cjameshuff
2012-May-07, 05:16 PM
Well. I don‘t only mean life forms. If entropy was dominating we shouldn‘t find any structure, neither in cosmic scale.

This is not so. Firstly, the laws of thermodynamics do not forbid local and temporary decreases in entropy, they do not mean that every process must immediately result in higher entropy. Second, galaxy and star formation represents an increase in entropy. An assortment of dense objects with mid-high nuclear masses is a lower energy and higher entropy state than a diffuse, uniform cloud of hydrogen gas. You are assuming increase in entropy means loss of structure, which just isn't true...in fact, it can be seen as fundamentally the opposite, as increasing entropy means the system takes more information to describe.

Jeff Root
2012-May-07, 05:20 PM
If entropy was dominating we shouldn‘t find ANY structure,
Entropy doesn't "dominate". It just is. The fact that
the entropy of any closed system can only increase does
not mean that entropy dominates everything else that
is going on. There are a lot of different interactions
possible in the Universe, and they happen, along with
the inevitable increase in entropy.



... neither in cosmic scale. But we observe the opposite.
Galaxies are very large structures, which never could have
been developed, if „chaos“ was the main concern.
There is no "main concern". That is an idea you invented.
The entropy of any closed system -- presumeably including
the Universe as a whole -- inevitably increases when the
energy in that system is tossed about by interactions.
Nothing prevents orderliness from appearing out of the
mess. Overall the Universe becomes more disordered,
but that is not obvious when the most visible parts are
highly ordered.



If the law of conservation of energy is valid, and in contrast
entropy is considered to always grow, then we must ask
a.) what it is reason
What is the reason entropy always grows?

That is a question which can probably only be answered
through experience. Play with energy and matter and
carefully observe how they interact. If you pay attention
to the relevant interactions, you will see why entropy
must always grow. A verbal description only works for
someone who already understands it.



and b.) what is its reciprocal and do we find an appropriate
counterpart? Do we find something like that?
I don't understand these questions. Interpreting "reciprocal"
very literally, perhaps the term "enthalpy" is what you want.
You can look that up.



"The only thing to always grow" for human beings seem to
be time. So is "Entropy" related to it?
Time is a factor in everything that happens. Everything.
But time isn't the *only* factor in *anything*. So noticing
that time is involved in entropy doesn't tell you anything
about entropy that doesn't apply to every other process.

-- Jeff, in Minneapolis

Relative
2012-May-07, 05:27 PM
Ok. thanks both of you.
So, my last question: Would you consider then, the "overall entropy" in the entire universe not to change, let's say just eventually decreases when whe observe "locally patterns" and, on the other hand, therefore increases somewhere else. So, literally, do you think entropy is a universal unchangeble constant?

Hornblower
2012-May-07, 11:48 PM
Ok. thanks both of you.
So, my last question: Would you consider then, the "overall entropy" in the entire universe not to change, let's say just eventually decreases when whe observe "locally patterns" and, on the other hand, therefore increases somewhere else. So, literally, do you think entropy is a universal unchangeble constant?

No, as I understand it the total entropy can remain constant or increase, but not decrease.

Jeff Root
2012-May-08, 09:08 AM
The entropy of a very small system could decrease just by
chance, but that would be rare, completely unpredictable,
and momentary. The more elements in a system, the less
likely its entropy is to decrease.

-- Jeff, in Minneapolis

cjameshuff
2012-May-08, 02:33 PM
Ok. thanks both of you.
So, my last question: Would you consider then, the "overall entropy" in the entire universe not to change, let's say just eventually decreases when whe observe "locally patterns" and, on the other hand, therefore increases somewhere else. So, literally, do you think entropy is a universal unchangeble constant?

It's not a conserved quantity at all. It can't be destroyed, but is created by any irreversible process. In any closed system, it will tend to increase. It is a statistical quantity, random fluctuations can briefly reverse it, but will not continue to do so. And it is not required to be uniformly distributed, especially in systems not in thermodynamic equilibrium...the universe isn't even close.

DrChinese
2012-May-10, 03:23 PM
If „nothing can exceed speed of light“, this should hold true for the expansion of the (observable) universe itself. ...

As Cougar indicated, this is not an accurate representation of things per our current standard model. Numerous high z objects have been located throughout the universe that are receding from us well in excess of twice the speed of light. Furthermore, those objects have always been receding from us faster than the speed of light.

Here are references if you would like to learn more about this (both from Davis and Lineweaver, the 2nd is a more technical description):

http://space.mit.edu/~kcooksey/teaching/AY5/MisconceptionsabouttheBigBang_ScientificAmerican.p df
http://www.mso.anu.edu.au/~charley/papers/DavisLineweaver04.pdf

DrChinese
2012-May-10, 03:47 PM
Galaxies are very large structures, which never could have been developed, if „chaos“ was the main concern.


This is really a meaningless statement (that is not intended as an insult, and hope you are not easily offended).

The mere existence of structures as we define them does not go against the 2nd law. Similarly, while the 2nd law is manifest, I would not call it "the main concern" in physics.

When one says "entropy increases" in a context such as this, the best way to translate that is to say "the total number of possible states of the system increases". (For example, a system at absolute zero would have only 1 possible state.) Using terms like "order" or "chaos" tends to mislead conversations such as this one in ways that are not useful (since they lead to meaningless statements).

Relative
2012-May-11, 01:53 PM
As Cougar indicated, this is not an accurate representation of things per our current standard model. Numerous high z objects have been located throughout the universe that are receding from us well in excess of twice the speed of light.
Well, as far as I understand: z is the relation of (lamda(obeserved)- lamdba0))/lambda0. For the microvave backgound to be 1089. But not greater than ∞. Otherwise the wavelenght is less than zero and, therefore, not observable. By the way, I haven't heard about a z which supports that conclusion. Actually we are dealing with 8.6 to somewhat 10.3 for z.
Second, to cite one of the mentioned papers, "...the Hubble distance is not fixed, because the Hubble constant, on which it depends, changes with
time. In particular, the constant is proportional to the rate of increase in the distance between two galaxies, divided by
that distance."
That's exactly what it is all about. Let's call the current constant k. The "rate of increase" (this is (1/k)/k) is "divided by" 1/k: So, (1/k^2)/(1/k). That is simply 1/k.

Relative
2012-May-11, 05:22 PM
For example, a system at absolute zero would have only 1 possible state.
Where did you get this from? As far as we know, at absolut zero there are still protons, neutrons end electrons, all of which representing different (energy) states.
And, if we go to "common temperatures", why do 3H and 3He (and some hundred other isotopes in the chart of nuclides) only have one (known) state, inspite of not being observed at absolute zero