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What if Gravitational Constant G Isn't?

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drdemjanenko
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Gravitational model
drdemjanenko   8/11/2014 1:05:12 PM
Since gravity has the ability to escape from a black hole, our model must be incomplete.  Relative to a moving mass nearby a rotating black hole, as the rotation rate gets higher and higher (relative to c), a portion of the black hole (a conical region), should disappear (its relative speed appearing higher than c).  Similarly, it has been observed that the gravitational field "bulges" along the plane perpendicular to its axis of rotation.  The effective gravity should be taking the relative speeds of the masses into account.  The equation for gravitational attraction would probably be :

F = G x (1 + (relative velocity between 1 and 2)/ c) x (mass1 × mass2)/r2

with the caveat that the relative velocity can never be bigger than -c and has implied limits of 2 and 0.  The gravitational event horizon is thus for mass which has been moving ever since the Big Bang into our forever non-visible universe and for mass that accumulates onto black holes that spin at nearly c.

 

 

BobSnyder
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Re: Gravitational model
BobSnyder   8/11/2014 10:01:52 PM
"Yet, as most engineers and scientists know, getting consistent, accurate results in any test-and-measurement challenge to better than three or four significant figures is rarely easy. Every added significant figure means ever-more-subtle sources of error must be uncovered, understood, calibrated out, or compensated for in the fixture and equipment."

How many significant figures are currently possible in state-of-the-art scientific research?

Annual global mean sea level rise is currently estimated to be 2.28 mm/yr. The newest and most precise satellites having this ability, Jason-1 and Jason-2, orbit at a mean altitude of 1336 km (1.336 billion mm). Detecting a 1 mm change in sea level would require a measurement uncertainty of less than one part per billion.

Many factors can affect a satellite's position: Mountain ranges have more mass, and therefore more gravity, than prairies. The moon and sun have strong gravitational attraction. The solar wind is variable and turbulent. When the satellites' orbits begin to decay, booster rockets are fired to restore their altitude. All of this has to be modelled and corrected for.

A RADAR altimeter is used to measure sea surface height relative to the satellite. Two RADAR frequencies are used so that the effects of atmospheric moiisture can be accounted for. Higher ocean waves result in earlier arrival of initial RADAR reflections. A correction can be made by looking at all reflected energy, not just the earliest, but this correction depends on assumptions about the shape of sea surface waves.

The satellites complete one orbital cycle every 10 days, and they are separated by 5 days, so the sea surface height is measured only once every 5 days at each location. According to the Nyquist sampling theorem, that means any sea surface waves having a period less than 10 days will undergo temporal aliasing because the sampling rate is too low to capture the true waveform.

NASA goes to great lengths to make the satellite altimetry measurements as precise as possible. For example, the GRACE satellite mission maps the earth's gravity field, and this data can then be used to improve the real-world models used by the Jason missions.

My question is:  Can I really believe the claims of one part per billion accuracy in the global mean sea level data? My gut is saying 'no', but I was wondering if someone with experience in this area could shed any light.

 

 

jackOfManyTrades
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Re: Gravitational model
jackOfManyTrades   8/12/2014 4:24:18 AM
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I think you can believe them for this simple reason: the chances that complete amateurs can find holes in the work of professionals is extremely low. You put together a good argument, but I think the chances of you having thought of something they haven't is very low indeed. You must have a speciality, a day job. What do you think the chances are that they'd spot something you hadn't thought of in one of your projects?

mhrackin
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Re: Gravitational model
mhrackin   8/12/2014 9:40:25 AM
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@jackxxxx: My guess is that you (presumably as an engineer) never read the classisc Hans Christian Andersen story "The  Emperor's New Clothes."  Otherwise you might be a bit skeptical about "expert" opinion. Anytime I hear the phrase " but everybody knows..." in an informal debate I know then and there that the speaker is WRONG!  Consensus is not truth.  If it were, the sun would be in orbit arounbd the earth.

Max The Magnificent
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Re: Gravitational model
Max The Magnificent   8/12/2014 9:53:01 AM
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@mhrackin: If it were, the sun would be in orbit arounbd the earth.

Well, in a way it is ... they are both orbiting each other, but the sun is so much more massive that the effect of the Earth on it is miniscule. This effect is much more pronounced with regard to the Earth and Moon, which orbit about their barycentre (common centre of mass) that lies about 4600 km from the Earth's centre (about three quarters of the Earth's radius).

mhrackin
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Re: Gravitational model
mhrackin   8/12/2014 9:55:51 AM
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That is certainly true; however, my reference was to the pre-Galilean "consensus" which obviously was not based on any understanding of orbital mechanics.

Max The Magnificent
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Re: Gravitational model
Max The Magnificent   8/12/2014 9:59:40 AM
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@mhrackin: ...my reference was to the pre-Galilean "consensus" which obviously was not based on any understanding of orbital mechanics.

I know -- I was just being pedantic -- I haven't had enough coffee yet LOL

BobSnyder
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Re: Gravitational model
BobSnyder   8/12/2014 12:29:22 PM
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"the Earth and Moon, which orbit about their barycentre (common centre of mass)"

Yep. And the moon's gravity causes not only ocean tides, but also the so-called "solid earth tide" which causes the land under your feet to rise and fall tens of centimeters every 12 hours.

http://geography.about.com/od/physicalgeography/a/Land-Tides-Or-Earth-Tides.htm

A high-precision GPS receiver (which I lack) should be able to detect this.

http://phys.org/news/2013-05-tidal-displacement-gps.html

Max The Magnificent
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Re: Gravitational model
Max The Magnificent   8/12/2014 12:32:35 PM
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@Bob: And the moon's gravity causes not only ocean tides, but also the so-called "solid earth tide" which causes the land under your feet to rise and fall tens of centimeters every 12 hours.

Keeping this in mind, it's amazing to me that we don't have more Earthquakes than we do. So if we went ~4 billion years back in time when the Moon had just formed and was much closer to the Earth than it is today, how big would the sea and earth tides have been then?

BobSnyder
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Re: Gravitational model
BobSnyder   8/12/2014 1:07:55 PM
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Land-based lasers are used to measure the altitude of the satellites which use RADAR to measure the sea surface height. But the land-based lasers are themselves experiencing vertical movement due to the solid earth tides caused by lunar and solar grivity. They may also be experiencing long-term horizontal and vertical movement due to tectonic plate movement. I have no doubt that all of these factors, and plenty more, are build into the model that is used to calibrate the system and to correct the raw data. I think NASA is probably the most trusted part of the US government, and rightly so. But NASA also has to constantly worry about funding, so it may be difficult for administrators to admit the limitations of their systems. (e.g. warnings of engineers not taken seriously by administrators prior to Challenger disaster) There may be a temptation for NASA administrators and NASA press correspondents to use "typical" values instead of "worst case" values.

A lot of the literature I have read talks about "precision", but precision is not the same thing as accuracy.

The satellites Jason-1 and Jason-2 are part of the much larger "geodetic infrastructure". The National Research Council issued a report in 2010 entitled "Precise Geodetic Infrastructure - National Requirements for a Shared Resource". I bought a copy online, and it is fascinating reading. But the following statement gave me pause:  "Modern geodesy delivers precision to one part per billion, and precision of one part per trillion can be envisioned in the foreseeable future.".

Presision, maybe, but I can't help wondering about accuracy, which depends upon having a stable reference point. If every part of the earth is moving, then all calibration must be performed with respect to an imaginary reference point, such as the earth's center of mass. After all of the available data is factored into the model, aren't we still left with a lot of assumptions?

jimfordbroadcom
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Re: Gravitational model
jimfordbroadcom   8/15/2014 2:54:41 PM
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@Bob Snyder - NASA the most trusted govt agency?  Not according to Richard Feynman who researched the Challenger disaster.  Didn't he say that NASA was the only govt agency that out-and-out lied to him?  Must have been because they had the most to lose.

RichQ
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Ancient tides
RichQ   8/14/2014 1:56:20 PM
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Max, depending on whose model you want to consider, estimates of ancient tides range from about 3X today's tides to tides of 1000 feet or more. Also, the length of the day seems to have been considerably shorter, on the order of 6 hours when the moon was formed. These are all estimates, of course, that depend on how you model the transfer of angular momentum from the earth to the moon over billions of years. Fossil records seem to show a length to the day of only 21.9 hours about 650 million years ago, and lasers measuring the earth-moon distance using mirrors left behind by Apollo astronauts confirm the creeping increase, so we're pretty sure things were considerably different long ago. But how different is mostly a matter of conjecture and modeling.

I personally favor the idea of 1000 foot tides occurring every few hours. It would go a long way toward explaining why the ocean is as salty as it is.

Here's some reading for you:

http://www.scientificamerican.com/article/earth-rotation-summer-solstice/

http://www.npr.org/blogs/13.7/2012/09/12/160944289/time-moves-with-the-moon

jimfordbroadcom
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Re: Ancient tides
jimfordbroadcom   8/15/2014 2:57:12 PM
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@RichQ - Maybe those giant ancient tides can help to explain why fossils of sea creatures have been found on mountaintops?

RichQ
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Re: Ancient tides
RichQ   8/15/2014 3:01:17 PM
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Could be I suppose. Plate tectonics and the rise of mountains that results does a better job of explaining it though.

jackOfManyTrades
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Re: Gravitational model
jackOfManyTrades   8/12/2014 10:50:14 AM
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In the global warming debate, we have experts saying one thing and complete non-experts saying the opposite. Yes, it is wise to be a bit skeptical about expert opinion. A bit. It is utterly insane to not be at all skeptical about inexpert opinion.

In the case of the Emperor's New Clothes and a geo-centric universe, the "experts" in question were nothing of the sort. In the case of climate science, the experts in question really are, just like they are in every other branch of science. If you dismiss that expertise, you may as well dismiss every other form of scienctific or technical expertise.


I am an expert in VHDL. And in OFDM. Surely you would agree that the chances of John Doe climate scientist finding fault in that expertise is basically zero. You must be expert in something, too. Surely you wouldn't expect John Doe climate scientist to be capable of finding fault in that expertise either?

MeasurementBlues
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Re: Gravitational model
MeasurementBlues   8/13/2014 9:19:05 AM
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The non-experts use religion to counter the experts. Religion is how we explain the unexplainable. Most people don't understand scientific explanations and therefore they don't trust them. But, they trust religious explanations. Fact vs. faith. Faith wins until proven otherwise and then the experts say "We told you so, you didn't believe us, and now it's too late."

In the global warming debate, we have experts saying one thing and complete non-experts saying the opposite. Yes, it is wise to be a bit skeptical about expert opinion. A bit. It is utterly insane to not be at all skeptical about inexpert opinion.

Rodney.Sinclair
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Re: Gravitational model
Rodney.Sinclair   8/13/2014 12:29:02 PM
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This is complete nonsense -- it represents a dogmatic anti-religious attitude more than it does a logical argument.

It is also irrelevant to the discussion(s) at hand.

BobSnyder
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Re: Gravitational model
BobSnyder   8/13/2014 12:43:35 PM
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I think it's quite rational for educated people to be somewhat skeptical of scientific consensus. Most people probably experience Science most frequently in the context of Health and Medicine. Most people like their doctors and trust them, but they also realize that medical professionals, and the medical research community, are fallible. Many of us have changed our daily habits due to medical consensus, only to learn that the consensus had been reversed or revised at a later date.

When I was growing up, people were advised to eat liver and other organ meats because they contained lots of vitamins. We were advised to use stick margarine in place of stick butter. A decade ago, adults over a certain age were advised to take a baby aspirin every day to protect their hearts. All of this advice was based upon medical consensus which was subsequently revised or reversed in light of new or better data.

Medical researchers are not dishonest. They are doing the best they can with data that is frequently incomplete and/or ambiguous. Scientists, and the scientific community, are fallible.

Until recently it was generally accepted that the universe is expanding, but at a steadily decreasing rate, and that eventually the universe would collapse in upon itself. In light of recent evidence, it is now generally accepted that the universe is expanding at a steadily INCREASING rate.

Satellite altimetry is providing new insights into the dynamics of ocean waves and currents as well as vertical movements of land masses. I would be very surprised if our understanding of sea level does not change in significant ways in the coming decades.

jackOfManyTrades
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Re: Gravitational model
jackOfManyTrades   8/15/2014 3:48:23 AM
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Are the different health messages caused by science flapping around or caused by journalists attaching far too much significance to any research with shows a marginal benefit or danger?

cookiejar
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Solar Output
cookiejar   8/11/2014 3:08:34 PM
Another "constant" that is very difficult to measure with precision is the sun's energy output.  Meteorological (weather) services the world round use pyroheliometers, which use a black surface to absorb the sun's energy with a thermopile sensor's output measuring the differential temperature between the black surface and ambient temperature.  The sensor itself is housed in a hemispherical Dewar (vacuum bottle).
As you can guess, there is no end to the uncertanties of this sensor, from the optics of the Dewar and thermal leakage to the changing absorption properties of the "black" body as it is exposed to radiation.

Meteorologists from the world gather each year at the time of the summer solstice on a mountain top, pick a clear day and after a countdown take readings from their "reference" instruments.  These instruments are then used as transfer standards based on the assumption that the sun's output is constant.

While there is a lot of data showing the sun's output variations in the short term, there is no sensor stable enough to read the sun's long term variability.

As we all know, the sun provides the energy feeding our weather.   But the sun's varying output is not a variable in any climate models.  Being unmeasurable, it is assumed to be constant.  Most scientists attribute past climate changes, from ice ages to tropical conditions in the Antarctic to varying solar output.


No doubt, the more we know, the more we realize we don't know.

Bill_Jaffa
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Re: Solar Output
Bill_Jaffa   8/12/2014 10:51:53 AM
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Good point about problem of assessing solar output. It's naive and irresponsible, IMO, to think the Sun's output has been constant over the years--yet that's what most models assume. Further, any historical data on Sun's output that is more than 40-50 years old is useless. So if someone asks about sun's output 100 years ago, the honest answer is "can't really say." And for more-recent output, honest answer is "not really sure." 

Max The Magnificent
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Re: Solar Output
Max The Magnificent   8/12/2014 11:11:35 AM
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@Bill: It's naive and irresponsible, IMO, to think the Sun's output has been constant over the years...

Surely we know it's not been constant. Did you see my book review of Alone in the Universe by John Gribbin. People talk about the Earth inhabiting the "Goldilocks Band" that's warm enough to have liquid (none-ice) water yet cool enough that the water doesn't boil off. As I recall, Gribbin presented lots of evidence for variations in the sun's temperature/outout over time showing the the Goldilocks Band moved in or out over time and that Earth was lucky to have always remained within the extreme end points.

Bill_Jaffa
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Re: Solar Output
Bill_Jaffa   8/12/2014 10:53:14 AM
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Also, our personal human time scale versus the time scale of geologic and solar events are quite different. I read one geologist a few years back saying that the big California Northridge earthquake of 1994 could be considered, if you step back, as mostly an aftershock of the San Francisco quake of 1906. He had a good point there!

Max The Magnificent
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Re: Solar Output
Max The Magnificent   8/12/2014 11:12:58 AM
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@Bill: Also, our personal human time scale versus the time scale of geologic and solar events are quite different.

I don't know -- when you get to my age, the personal and geological time scales start to feel very similar LOL

Max The Magnificent
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Reinventing Gravity
Max The Magnificent   8/12/2014 9:49:43 AM
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Check out my review of Reinventing Gravity by John Moffat

mhrackin
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Re: Reinventing Gravity
mhrackin   8/12/2014 9:58:19 AM
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Unfortunately your link doesn't appear to get to its object.  I get an EETimes error message instead:

 

 

Hello.  We were unable to find the address you requested.  You may search for the content you are seeking using our search form or email technical support with any questions.

mhrackin
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Re: Reinventing Gravity
mhrackin   8/12/2014 10:00:39 AM
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Interestingly, I DID find the review using the EET search engine!  Gotta love those strange IT folks...

Max The Magnificent
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Re: Reinventing Gravity
Max The Magnificent   8/12/2014 10:02:03 AM
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@mhrackin: Unfortunately your link doesn't appear to get to its object.

My bad -- I just fixed the original comment, and here's the link again

Etmax
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Interesting Question
Etmax   8/12/2014 10:16:34 AM
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In some ways an odd question to be asked in this forum, but certainly one worth pondering. The real gem here is the places others talke this. I'm not one to pooh pooh amateurs thoughts and questions, because it's not been uncommon in history for a new viewpoint  to derail accepted thinking. There's also the benefit of cross pollenation where a seemingly unrelated field can offer new insights. Anyhow Bill, many thanks.

Max The Magnificent
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What if G doesn't actually exist per se
Max The Magnificent   8/12/2014 10:39:32 AM
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The title of this column is "What if Gravitational Constant G Isn't?" -- but what if it doesn't actually exist at all.

The whole concept of G comes from Newtonian mechanics, which turned out to be an approximation of Einsteinian general relativity (which itself may or may not be 100% true as per my review of Reinventing Gravity).

As per Einstein, gravity isn't an "attraction" between two masses -- but rather the masses distort the space time continuum around them and these distortions interact to produce the effect of gravity ... having said that, as far as i know, we still don;t have much of a clue as to what gravity actually is -- we waffle on about things like "gravitons" as the gravitational force carrier and people make comparisons to the Higgs Boson and the Higgs Field (which doesn't help me at all).

 

Bill_Jaffa
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Re: What if G doesn't actually exist per se
Bill_Jaffa   8/12/2014 10:42:19 AM
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As Einstein's simple thought-experiment showed, you can't distinguish between gravitational mass and inertial mass. That's always worried me!

Max The Magnificent
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Re: What if G doesn't actually exist per se
Max The Magnificent   8/12/2014 10:44:52 AM
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@Bill_Jaffa: That's always worried me!

Why?

Bill_Jaffa
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Re: What if G doesn't actually exist per se
Bill_Jaffa   8/12/2014 10:47:57 AM
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I'm a "feet on the ground" guy, the idea of not knowing if I sense my weight due to me standing on Earth's surface, versus being in a closed box accelerating through space at 9.8 m/sec2, bothers me!

Max The Magnificent
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Re: What if G doesn't actually exist per se
Max The Magnificent   8/12/2014 10:50:57 AM
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@Bill: ...not knowing if I sense my weight due to me standing on Earth's surface, versus being in a closed box accelerating through space at 9.8 m/sec2, bothers me!

Open the nearest door and look outside -- if you get sucked out by explosive decompression, then you are (or at least, were) in a box accelerating through space -- otherwise, relax and take another bite of your apple :-)

Bill_Jaffa
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Re: What if G doesn't actually exist per se
Bill_Jaffa   8/12/2014 11:03:46 AM
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Sorry, can't do that--Einstein's thought experiment specifically stated a closed box, no view. That way you don't know where you are--on Earth or in space. And think of complementary case of being in an elevator (not one of those cool ones in hotels, where you can look out) and someone cuts the cable: you free fall and feel weightless. So are you falling in a gravitational field, or are you out in space, away from any objects that would give you weight?

Max The Magnificent
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Re: What if G doesn't actually exist per se
Max The Magnificent   8/12/2014 11:06:35 AM
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@Bill: So are you falling in a gravitational field, or are you out in space, away from any objects that would give you weight?

I'll need a beer to quaff while I'm mulling that over...

mhrackin
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To get back to Bill's original questions
mhrackin   8/12/2014 10:41:09 AM
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I had been working for Motorola for about a year when I was transferred to the Product Research labs of the Comm division.  My first assignment was to look at how to improve the small-signal sensitivity of VHF receivers. As I had at that point not only a couple of EE degerees, but also had been building radio receivers since I was about 10 (as a ham radio operator) I thought I knew what to look into.  Improved noise figure, and minimizing losses in the front-end band-pass filter wre the things to look at.  My mentor/supervisor explained to me that may be the theoretical approach, but in the "real world" the problem was the crowded VHF spectrum leads to intermodulation products that masked the desired signal.  Thus the real assignment was to come up with a mixer design that would be used with NO RF amplifier in front of it that had much lower IM distortion than the current state of the art.  This was in 1968, and to this day I remember to ALWAYS consider the REAL WORLD aspects of any engineering problem before trying to solve it!

Max The Magnificent
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Where are you?
Max The Magnificent   8/12/2014 11:18:08 AM
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This article from the Science Magazine website is quite interesting: Fundamental Constant May Depend on Where in the Universe You Are

Rodney.Sinclair
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Exponent of 2.0
Rodney.Sinclair   8/13/2014 9:02:51 AM
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With respect to 'erhaps the "squared" exponent in the denominator of Newton's Law is not exactly 2.0,' this exponent usually occurs because there is conservation in an expanding sphere.  For example, a pulse of light emitted from a point source and spreading uniformly in all directions is effectively spreading on the surface of an expanding sphere.  Since the surface area of this sphere is proportional to r^2.000000..., we have a 1/r^2 law for the intensity of light.

A different exponent would require a different method of propagation.

Bill_Jaffa
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Re: Exponent of 2.0
Bill_Jaffa   8/13/2014 9:06:45 AM
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Hmmmm...that assumes gravity propagates like light--but we really don't understand much about gravity. Still looking for gravity waves, and trying to understand gravity as part of the fabric of space. So I don't know if your assumption about "conservation" nor your analogy to light apply here. Great minda are working on the problem!

Rodney.Sinclair
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Re: Exponent of 2.0
Rodney.Sinclair   8/13/2014 9:09:00 AM
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Nor do we currently have good reason to think that it isn't a conservation-like process.

Rodney.Sinclair
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Precise measurements
Rodney.Sinclair   8/13/2014 9:07:56 AM
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An alternative to measuring sea surface height to extreme precision, which would require knowing the satellite height to extreme precision along with all the other phenomena affected the RF signal propagation, is to measure the sea height relative to fixed objects.

For example, if the local sea height is measured with respect to the nearly simultaneously measured land height, then it could be easier to infer variations in the local sea height.

ScRamjet
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Earth Moon Center of Gravity
ScRamjet   8/19/2014 8:56:27 AM
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Max;  While I knew the moon had to affect Gravity I feel here on earth, I had not realized it was such a large change in the common center of mass.

Perhaps this explains why some days I feel really heavy and others I feel much lighter.

I had always attributed that to lack of rest but perhaps it is a combination.

I do know this and it's probably just all in my head. I always feel more energetic at a full moon.

Which brings to mind, There must be a similar shift of gravity center of the earth and the sun as well. Tthings that make you say, Hmmmmm.....

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