The earth is round because of one simple observation.

Quote from: TexasH on October 20, 2015, 05:50:48 PM

Also, TheEngineer isn't a FE'er, and I don't believe he has ever said satellites don't exist.

This, my good sir, is heresy!

Quote from: jroa on October 20, 2015, 05:58:57 PM

Quote from: TexasH on October 20, 2015, 05:50:48 PM

Also, TheEngineer isn't a FE'er, and I don't believe he has ever said satellites don't exist.

This, my good sir, is heresy!

Okay...

It is fairly obvious; I figured it out fairly quickly.

My cell phone has no trouble telling me where I am, even with the GPS turned off.  Please don't tell me that the only way to know where you are is to get radio signals from flying space trashcans. 

You say "GPS does not require satellites."  Oh, really!

I have a feeling he actually works for Garmin (or similar GPS company). 

My cell phone has no trouble telling me where I am, even with the GPS turned off.

Always read what TheEngineer says carefully.  "GPS does not require satellites." is not the same as "GPS does not use satellites."

You can triangulate locations using ground-based towers.

Using cell tower triangulation (3 towers), it is possible to determine a phone location to within an area of “about” ¾ square mile.

Law enforcement does this to locate a cell phone.

Quote from: TexasH on October 20, 2015, 05:50:48 PM

I have a feeling he actually works for Garmin (or similar GPS company). 

Ooh, good guess, but, no.

Quote from: TexasH on October 20, 2015, 05:50:48 PM

Always read what TheEngineer says carefully.  "GPS does not require satellites." is not the same as "GPS does not use satellites."

You don't have to read it carefully to realise it's factually incorrect either way.  Location services in general may not require satellites, however the Global Positioning System does need satellites to work.  A GPS device works by scanning the sky for timestamps transmissions from satellites, works out your distance from each one via the lag, and then uses trilateration to calculate your position.

Take away the satellites and the GPS device does not work.  Therefore "GPS does not require satellites" is not a correct statement.  The GPS system does require satellites - there is literally no other way a GPS device could work.

Quote

You can triangulate locations using ground-based towers.

They do not give you a 3D position, whereas GPS does.    And never to 5 metre accuracy - nowhere near.  This would be impossible from cell towers.  Even in range of 3 towers:

Quote

Using cell tower triangulation (3 towers), it is possible to determine a phone location to within an area of “about” ¾ square mile.

http://wrongfulconvictionsblog.org/2012/06/01/cell-tower-triangulation-how-it-works/

Although I've seen claims of a few hundred metres in very dense areas - still nothing like GPS accuracy.

It also becomes increasingly inaccurate as cell towers become sparser (outside of cities), up to the point where there are no, or an insufficient number of towers to triangulate.  Whereas GPS works, err, globally.

Quote

Law enforcement does this to locate a cell phone.

Actually, that evidence is being treated with increasing scepticism.

I know how GPS works.

  You are missing the point here though.  Imagine the Earth is actually flat and satellites do not exist.

  It would still be possible to develop a global positioning system that works using ground-based towers.

If you want to make an argument about satellites (other than being able to see them), satellite television seems to be a better argument.  If satellite television was using ground-based towers, all the satellite dishes wouldn't have to be pointed to the south (for us here in the northern hemisphere).

Quote from: rabinoz on October 20, 2015, 04:08:59 PM

You say "GPS does not require satellites."  Oh, really!

Yes, really.  No part of the locating process requires the signal originate exoatmospheric.

Quote

  You are missing the point here though.  Imagine the Earth is actually flat and satellites do not exist.

Then the Global Positioning System would not work.  It requires satellites.   Other systems, such as LORAN, have worked with ground based towers - these do not require satellites.  The GPS is a particular system utilising particular technologies, namely satellites.

Quote

  It would still be possible to develop a global positioning system that works using ground-based towers.

Not one that could give you a 3D position you couldn't.  And, strictly speaking, you will need millions of sea based towers as well.

Quote

If you want to make an argument about satellites (other than being able to see them), satellite television seems to be a better argument.  If satellite television was using ground-based towers, all the satellite dishes wouldn't have to be pointed to the south (for us here in the northern hemisphere).

Well, not just the fact they point south, but they are pointing into the sky.  I'm not sure it is better argument anyway - a television works without satellites, whereas a GPS device won't.

Quote from: JimmyTheCrab on October 21, 2015, 07:32:51 AM

Quote

  You are missing the point here though.  Imagine the Earth is actually flat and satellites do not exist.

Then the Global Positioning System would not work.  It requires satellites.   Other systems, such as LORAN, have worked with ground based towers - these do not require satellites.  The GPS is a particular system utilising particular technologies, namely satellites.

You can't just refute the other person's argument this way.

Quote from: TexasH on October 21, 2015, 09:04:23 AM

Quote from: JimmyTheCrab on October 21, 2015, 07:32:51 AM

Quote

  You are missing the point here though.  Imagine the Earth is actually flat and satellites do not exist.

Then the Global Positioning System would not work.  It requires satellites.   Other systems, such as LORAN, have worked with ground based towers - these do not require satellites.  The GPS is a particular system utilising particular technologies, namely satellites.

You can't just refute the other person's argument this way.

I can, and I have.  As you stated before, TheEngineer is keen on "lawyerly" (disingenuous!) arguments and that is what we are having here.  I'm not talking about the generalities of creating a positioning system, but the specifics of the Global Positioning System.

"GPS does not require satellites."

Is incorrect.  Every single GPS device on the planet will calculate its position using time-stamp / almanac information from 3 or more satellites.  If those satellites weren't there, or you blocked the device's line of sight to them, then it couldn't work out a position.  Therefore GPS does require satellites.

Of course, hypothetically, ground based systems that don't require satellites could be built, like LORAN.  However we are not discussing LORAN, we are discussing GPS.

"GPS does not require satellites."

Is incorrect.

Quote from: Dinosaur Neil on October 19, 2015, 10:51:05 AM

Quote from: TexasH on October 18, 2015, 12:17:50 PM

Quote from: Dinosaur Neil on October 18, 2015, 11:57:17 AM

Quote from: TexasH on October 17, 2015, 07:32:28 PM

If you make an accurate statement, he doesn't refute it.

He refuted the statements that gravitational attraction obeys the inverse square law, and that it is capable of imparting motion to a static body. Both of those are accurate.

Newton's model follows the inverse square law.

Gravitation doesn't impart motion on a static body.

The inverse square law of Newton's model does not conflict with anything subsequently amended by the current gravity model. It still applies. It remains an accurate statement.
I genuinely fail to see how motion is NOT imparted to a static body by gravity. I suspect your lack of explanation is a deliberate attempt to get someone to disagree with you and trip up (strange, you're almost like the "Engineer"'s alt in that respect...) Therefore, I would like you to explain what imparts motion to an apple which I'm holding stationary, and then I let go of it. I strongly suspect your answer will rely heavily on semantics rather than physics.

Newton's model is great for most applications.  It doesn't work at relativistic speeds or in strong gravitational environments though, that is why we need Einstein's more complex model.  I use Newton's model all the time, it is a lot simpler to work with and provides an accurate answer for most applications.

Also, don't compare me to TheEngineer, that's a bit insulting.  Sorry for not explaining further, I was running errands, and typed out a quick response on my phone.  Mass curves/distorts space time.  The greater the mass, the greater the curvature/distortion.  The difficulty in seeing this is due to us being used to seeing objects in a non-curved space.  An object in free fall actually follows a straight line, but space time is curved/distorted, so it has the appearance that the object is curving/moving.  The easy way to visualize this is to think of how airline flights fly along great circle routes.  On a flat map, it appears the aircraft is flying a curved route, but if you look at the flight in a curved space (a globe), the flight is straight (neglecting the curvature of Earth, since it can't fly through the Earth).

Anyway, the surface of the Earth is accelerating up to meet the object, however, this isn't the same as a flat Earth accelerating upward as if propelled from underneath as the acceleration varies all over the surface of the Earth.  We can measure this acceleration with accelerometers to confirm that the acceleration varies across the globe.  If the flat Earth model were true, it would have ripped apart a long time ago due to these variations in acceleration at different points. 

Back to your original question, when you are holding an apple, you are accelerating the apple.  A force is required to hold it where it is as the apple wants to follow a geodesic to the center of mass that is causing the gravitational field.  Release the apple and it is no longer subject to the force from your hand and follows the geodesic towards the center of Earth's mass until the Earth has accelerated up to meet it.  Geodesics in a gravitational field can go in all sorts of directions depending on the initial motion of the object.

Now, all of that is harder to visualize and calculate.  If we switch the frame of reference, we get Newton's model, which is much simpler and easier to use.  To summarize, Einstein's model is correct and true (as far as we know at least) and Newton's model is correct for a certain set of circumstances (which includes dropping an apple from your hand).  Newton's model is never true, but it doesn't have to be to correctly answer most questions.  Most engineers understand this and I want to believe TheEngineer does as well.  If two models are both correct for the application, use the simpler model.

Quote from: JimmyTheCrab on October 21, 2015, 10:58:27 AM

"GPS does not require satellites."

Is incorrect.

What part of the locating process requires the signal originate exoatmospheric?

That's all nice and a good read, but you didn't understand the question:
What part of the locating process requires that the signal originate in space?

Quote from: TexasH on October 19, 2015, 02:46:44 PM

Quote from: Dinosaur Neil on October 19, 2015, 10:51:05 AM

Quote from: TexasH on October 18, 2015, 12:17:50 PM

Quote from: Dinosaur Neil on October 18, 2015, 11:57:17 AM

Quote from: TexasH on October 17, 2015, 07:32:28 PM

If you make an accurate statement, he doesn't refute it.

He refuted the statements that gravitational attraction obeys the inverse square law, and that it is capable of imparting motion to a static body. Both of those are accurate.

Newton's model follows the inverse square law.

Gravitation doesn't impart motion on a static body.

The inverse square law of Newton's model does not conflict with anything subsequently amended by the current gravity model. It still applies. It remains an accurate statement.
I genuinely fail to see how motion is NOT imparted to a static body by gravity. I suspect your lack of explanation is a deliberate attempt to get someone to disagree with you and trip up (strange, you're almost like the "Engineer"'s alt in that respect...) Therefore, I would like you to explain what imparts motion to an apple which I'm holding stationary, and then I let go of it. I strongly suspect your answer will rely heavily on semantics rather than physics.

Newton's model is great for most applications.  It doesn't work at relativistic speeds or in strong gravitational environments though, that is why we need Einstein's more complex model.  I use Newton's model all the time, it is a lot simpler to work with and provides an accurate answer for most applications.

Also, don't compare me to TheEngineer, that's a bit insulting.  Sorry for not explaining further, I was running errands, and typed out a quick response on my phone.  Mass curves/distorts space time.  The greater the mass, the greater the curvature/distortion.  The difficulty in seeing this is due to us being used to seeing objects in a non-curved space.  An object in free fall actually follows a straight line, but space time is curved/distorted, so it has the appearance that the object is curving/moving.  The easy way to visualize this is to think of how airline flights fly along great circle routes.  On a flat map, it appears the aircraft is flying a curved route, but if you look at the flight in a curved space (a globe), the flight is straight (neglecting the curvature of Earth, since it can't fly through the Earth).

Anyway, the surface of the Earth is accelerating up to meet the object, however, this isn't the same as a flat Earth accelerating upward as if propelled from underneath as the acceleration varies all over the surface of the Earth.  We can measure this acceleration with accelerometers to confirm that the acceleration varies across the globe.  If the flat Earth model were true, it would have ripped apart a long time ago due to these variations in acceleration at different points. 

Back to your original question, when you are holding an apple, you are accelerating the apple.  A force is required to hold it where it is as the apple wants to follow a geodesic to the center of mass that is causing the gravitational field.  Release the apple and it is no longer subject to the force from your hand and follows the geodesic towards the center of Earth's mass until the Earth has accelerated up to meet it.  Geodesics in a gravitational field can go in all sorts of directions depending on the initial motion of the object.

Now, all of that is harder to visualize and calculate.  If we switch the frame of reference, we get Newton's model, which is much simpler and easier to use.  To summarize, Einstein's model is correct and true (as far as we know at least) and Newton's model is correct for a certain set of circumstances (which includes dropping an apple from your hand).  Newton's model is never true, but it doesn't have to be to correctly answer most questions.  Most engineers understand this and I want to believe TheEngineer does as well.  If two models are both correct for the application, use the simpler model.

You just used the phrase "until the Earth has accelerated up to meet it."
Since strictly speaking there is no difference (according to relativity) between the earth moving to meet the apple, and the apple moving to meet the earth, and you have just stated that motion occurs (two objects change relative positions in spacetime, which is a fairly good definition of motion). You have also stated that this motion is a result of objects following spacetime geodesics (which is what gravity is if it isn't a force).
If there were no geodesics to follow (i.e. gravity was absent) then according to your description, that motion would not occur. The fact that the apple is static due to the force from my hand does not negate that it is static. It is static because two opposing influences are in balance.
Therefore, according to your own description, gravity causes an object to move, and is therefore capable of imparting motion to a static body.
As I suspected, your argument rested entirely on fancy language and making something very simple very complicated and hoping nobody would notice that saying "the earth accelerates to meet the apple" is a reversible statement.
2/10.

I understand how GPS works just fine and I know why almanacs are used. 

That does not address my question:

What part of the locating process requires the signal originate in space?

Could it have been designed to work with terrestrial transmitters? Possibly. But it wasn't.

Quote from: Alpha2Omega on October 22, 2015, 03:50:45 PM

Could it have been designed to work with terrestrial transmitters? Possibly. But it wasn't.

Thank you for agreeing with my statement that GPS does not require satellites.

Quote from: TheEngineer on October 21, 2015, 08:43:40 PM

I understand how GPS works just fine and I know why almanacs are used. 

Really? Then why is the next question necessary?

Quote

That does not address my question:

What part of the locating process requires the signal originate in space?

The SV part (those are the transmitters) is located on Space Vehicles. They don't start transmitting until they reach space. It's how the system is designed.

The current GPS system requires satellites. A GPS system does not.

Please stop dodging the question and simply answer:

What part of the locating process requires that a signal originate exoatmospheric?

• The system is designed to be Global (that's what the 'G' in 'GPS' stands for). Satellites in high orbits have a big footprint - one transmitter covers a very large portion of the Earth at the same time, while using very short wavelengths (about 20 - 30 cm, in the L-band, in the case of GPS), and they operate just as well over the open oceans and hostile territory as anywhere else. Short wavelengths provide numerous advantages. 
  
• Deploying a constellation of satellites is cheaper for worldwide coverage than building and maintaining the equivalent network of surface stations, if it's possible at all.
  
• Altitude information is available when the transmitters are distributed over a wide range of angles, from near the horizon to zenith, you instead of all being near the horizon.
  
• The location of satellites in high orbits are very predictable - this is essential since they are the benchmarks for locations.

I don't think you understand the question:
What part of the locating process requires the signal to originate in space?

Answer:
No part of the locating process requires that the signal originates in space.

All you need is a transmitter that knows where it is and has an accurate clock which can transmit this information, and a receiver that can decode this info and compare with its own regular clock. 

Good Lord, you RE'ers are dense.