Light Speed: Fixed... or Relative? Exploring Einstein's Relativity

ImaFungi

Arbitrageur

ImaFungi
Why is the fundamental nature of gravity field so much harder to grasp and detect then the quark fields

Do you think a 1 with 39 zeroes after it may help explain why gravity is harder to detect on small scales?

Strong Nuclear Force

the strong interaction is the "strongest" of the four fundamental forces; its strength is around 100 times that of the electromagnetic force, some 1000000 times as great as that of the weak force, and about 1000000000000000000000000000000000000000 times that of gravitation.

Why do any of the fundamental constants (like the gravitational constant) have the values they have? We don't know.

edit on 31-1-2014 by Arbitrageur because: clarification

Well thats interesting considering gravity is such a macro phenomenon, and the strong and weak force as phenomenon only really exist in very relatively confined areas of space. These forces, strong and weak, exist due to virtual particles right? Which really is another way of saying...what? There is some coupling to the fundamental spatial field essence that when certain fundamental particles are in close enough proximity they snap together? All of these situations share the same problem, and common theme, they are characteristics and phenomenon (the fundamental forces that is) that are engrained, if not space itself, into space itself.

What do you mean by "gravity is such a macro phenomenon"?

You introduce a term "virtual particle" then you express surprise about it?

I tell you what - a theory must be published (put into science) when you have enough evidence you understand it.
The question about gravity is - "Do you really understand gravity?"

Arbitrageur
Why do any of the fundamental constants (like the gravitational constant) have the values they have? We don't know.

edit on 31-1-2014 by Arbitrageur because: clarification

we don't? aren't those just multiplier ? the name says it, a constant, like the exchange value for money...
Because we have Kg, m, A, V, J and they not really correlated to each other in any way, they just picked out of blue,
we need some "exchange" value if we calculate real forces witch are very well correlated, G - M - E - ??


Video:
Plank's constant in calculations with J ( Joule = kg m^2 / s^2)

GargIndia

ImaFungi

Arbitrageur

ImaFungi
Why is the fundamental nature of gravity field so much harder to grasp and detect then the quark fields

Do you think a 1 with 39 zeroes after it may help explain why gravity is harder to detect on small scales?

Strong Nuclear Force

the strong interaction is the "strongest" of the four fundamental forces; its strength is around 100 times that of the electromagnetic force, some 1000000 times as great as that of the weak force, and about 1000000000000000000000000000000000000000 times that of gravitation.

Why do any of the fundamental constants (like the gravitational constant) have the values they have? We don't know.

edit on 31-1-2014 by Arbitrageur because: clarification

Well thats interesting considering gravity is such a macro phenomenon, and the strong and weak force as phenomenon only really exist in very relatively confined areas of space. These forces, strong and weak, exist due to virtual particles right? Which really is another way of saying...what? There is some coupling to the fundamental spatial field essence that when certain fundamental particles are in close enough proximity they snap together? All of these situations share the same problem, and common theme, they are characteristics and phenomenon (the fundamental forces that is) that are engrained, if not space itself, into space itself.

What do you mean by "gravity is such a macro phenomenon"?

You introduce a term "virtual particle" then you express surprise about it?

I tell you what - a theory must be published (put into science) when you have enough evidence you understand it.
The question about gravity is - "Do you really understand gravity?"

I guess what I mean by gravity being such a macro phenomenon is we cant microly locate how it exists or what causes it to exist on the macro level. Its mainly experienced macroly, with planets and stars and centers of galaxies and debris that interact with these things.

I am surprised about the term and meaning of virtual particle, I dont think it produces an accurate level of understanding of what is actually going on at those most micro levels and what the actual material of space is at those micro levels. Field theory in general, supposes there is a substance like field (what the heck is this, what????) that exists throughout the universe, and it is attached to itself with no components, we have no examples of something like a field existing, its impossible to even imagine how one would exist, unless I am wrong as viewing a field as one total substance/material and it is really a material composed of particles (like an apple or a blanket is a material that is connected to itself as an object, but composed of components), So is the gravity field truly composed of a very very very large number of 'gravity particles', which are stuck together extremely tightly at every point (how might they be stuck together...probably virtual particles right), is the EM field composed of EM particles, so the EM field is one giant light atom, consisting of uncountable subatomic particles?

Ok virtual particles with strong force for example, this has to do with the 3 quarks staying together to make protons and neutrons right? And its said these stick together so well, and the strong force is nothing but virtual particles being compelled up from the energy fabric of space each time a quark vibrates and the harmonic geometries of the vibrations cause the virtual particles like some kind of wave pool rip tide to stick together very tightly and remain the composite particle that is a proton or neutron. I dont get the virtual particle theory because I dont know what the most fundamental fields are, how they are explained to physically exist, how field lines are depended on heavily to explain theory and practice but then are said to not actually exist.

Do I really understand gravity? On a macro scale I think I understand it. On the micro scale I dont understand it, and think that many physicists think they understand it, but just dont have the technological capabilities to pierce those depths of reality and work with the nature of that fundamental gravity causing field. I dont know how matter is coupled to the gravity field, or how the gravity field is made, what its made out of, if it is one whole of a fabric composed of many parts.

KrzYma

Arbitrageur
Why do any of the fundamental constants (like the gravitational constant) have the values they have? We don't know.

we don't? aren't those just multiplier ?

Yes you can call it a multiplier, for example with the gravitational constant, it's a multiplier that when multiplied by your mass (and other factors, like the mass of the Earth) determines your weight.

But, let's say you weigh 100 pounds. If the gravitational constant was twice as large as it is, you could have the same mass you do, but then you would weigh 200 pounds. So, why is the gravitational constant such that your mass gets multiplied so that you end up weighing 100 pounds instead of 200 pounds? We don't know.

Also you are talking about units but you can make many fundamental constants dimensionless, as described here:

Open Questions in Physics

Q: Why are the strengths of the fundamental forces (electromagnetism, weak and strong forces, and gravity) what they are? For example, why is the fine structure constant, that measures the strength of electromagnetism, about 1/137.036? Where do such dimensionless constants come from? Or is this an unanswerable question?

A: Particle masses and strengths of the fundamental forces constitute most of the 26 fundamental dimensionless constants of nature. Another one is the cosmological constant - assuming it's constant. Others govern the oscillation of neutrinos (see below). So, we can wrap a bunch of open questions into a bundle by asking: Why do these 26 dimensionless constants have the values they do?

Perhaps the answer involves the anthropic principle, but perhaps not. Right now, we have no way of knowing that this question has any answer at all!

When we try to calculate or predict what the cosmological constant should be, our result differs from observation by 120 orders of magnitude. We aren't sure if there are ways to predict or show theoretically why the constants have the values they have. It would be a good accomplishment if we could do that, but as the quote says, we don't even know if that's possible.

reply to post by Arbitrageur


her an explanation


as you see G is Newton meter squared kilogram to the minus two

if we could rethink this constants and change the N, kg, m values, we could get no constant, or say constant=1 !

reply to post by KrzYma


Yes that's exactly right, but even after you normalize the gravitational constant to a value of 1, that still doesn't explain why it's not, on that normalized scale, say 1.5.

If we lived in a universe where it had the higher value we could similarly normalize it so again in that universe the value would be 1.

So then you might wonder, well if it's 1 in both universes, 'isn't it really the same?', and the answer is, no. The normalization process has ignored the differences. Looking at both universes we could still say the value is 50% higher in one universe than the other. The 1=1 argument doesn't work because the normalized scales are different. (it would be like saying 1kph = 1mph, it doesn't).

So, we are still left with no explanation of why our universe's normalized value of 1 for the gravitational constant is 50% higher or lower than another hypothetical universe's gravitational constant where the normalized gravitational constant is also 1, but a different 1 which is 50% higher or lower than ours (or any other arbitrarily different value).

reply to post by Arbitrageur

God did it


*slinks away*

Phage
reply to post by Arbitrageur

 

God did it

*slinks away*

That's a popular view of course but what's more interesting is that some apparently otherwise logical people use what seems to me to be an illogical argument to say that not only did God do it, but the fact that G has the value it has (as well as some other constants) is proof of the existence of God. When you dissect that argument it boils down to a tautology that "if things were different, they would be different", which you can't argue with, but how does that prove "God did it?"; and beyond that the argument seems highly speculative.

Maybe God did do it, but I think the better answer is, we don't really know.

If I meet God when I die, I'll ask him if he did it, but I'm not sure how to report the results back in this thread.

reply to post by Arbitrageur

When you dissect that argument it boils down to a tautology that "if things were different, they would be different", which you can't argue with,

Of course you can argue with it. My dog does it all the time.
It only looks like he's chasing his tail, he's really expressing the logic in terms that he's capable of.

Arbitrageur
reply to post by KrzYma

 

Yes that's exactly right, but even after you normalize the gravitational constant to a value of 1, that still doesn't explain why it's not, on that normalized scale, say 1.5.

If we lived in a universe where it had the higher value we could similarly normalize it so again in that universe the value would be 1.

So then you might wonder, well if it's 1 in both universes, 'isn't it really the same?', and the answer is, no. The normalization process has ignored the differences. Looking at both universes we could still say the value is 50% higher in one universe than the other. The 1=1 argument doesn't work because the normalized scales are different. (it would be like saying 1kph = 1mph, it doesn't).

So, we are still left with no explanation of why our universe's normalized value of 1 for the gravitational constant is 50% higher or lower than another hypothetical universe's gravitational constant where the normalized gravitational constant is also 1, but a different 1 which is 50% higher or lower than ours (or any other arbitrarily different value).

I can't see how normalisation of anything can value any dimensional laws. Those dimensions are still separated by some constant.
what is 1 in universe A is not 1 in universe B but A x dimmesionalConstant
or so...

reply to post by Arbitrageur


The reason it has the value it does must be exactly proportional to the energy density of the gravity field and the nature/quantity/value of mass. I think I understand what you mean though; the gravity constant dictates that all mass falls to earth at the same rate right? Is the gravity constant the same on all planets? It has to do with the energy density of the gravity field. If we took a mass to the furthest point of space away from all galaxies, and placed it there, it would not be compelled to 'fall' right? It may be moved by things like dark energy, or radiation, and also depending on the size of this test mass. But from there if we start in a non displaced gravity field, and then add the smallest, mass, and discretely and quantizedly increased incrementally the mass, the gravity field would react in a predictable manner of displacement/curvature (also minding the density of the mass used), so then once you got to substantially massive masses like the earth and moon, and you want to think about why a test mass falls at certain rates towards these massive masses, its because the normal energy density (of the original example of a mass in empty space away from any gravity wells) is altered, so now it can no longer support the mass of the test mass, and the mass of the test mass is compelled towards the path of least resistance which is towards the most stable patch of energy. This is why I am compelled to think that the motion of the mass through the 3d energy tensor of gravity field has to do with the curvature/displacement. The only way I can see it being the case that a mass significantly massive just sitting in free space relatively motionless to all observers, displaces the gravity field so that an object placed close enough to it will fall towards it surface, is if there is some relationship between the gravity field and the matter, in which the matter actually engulfs and stores the gravity field within itself. That is to say, if the earth is sitting in free space, or moving, all the energy associated with the area of gravity field the size/mass of the earth, is sucked into the earth itself, and this suction of energy is what accounts for the lesser quantities of energy surrounding the mass. Is this what is suggested, if not, what is?

ImaFungi
reply to post by Arbitrageur

 

The reason it has the value it does must be exactly proportional to the energy density of the gravity field and the nature/quantity/value of mass. I think I understand what you mean though; the gravity constant dictates that all mass falls to earth at the same rate right?

You're confusing "big G" with "little g" as explained here:

Gravitational constant

The gravitational constant, approximately 6.67×10−11 N·(m/kg)2 and denoted by letter G, is an empirical physical constant involved in the calculation(s) of gravitational force between two bodies. It usually appears in Sir Isaac Newton's law of universal gravitation, and in Albert Einstein's theory of general relativity. It is also known as the universal gravitational constant, Newton's constant, and colloquially as Big G. It should not be confused with "little g" (g), which is the local gravitational field (equivalent to the free-fall acceleration), especially that at the Earth's surface.

Little g is somewhat constant over the Earth's surface, but if you measure it precisely enough, you find variation and we've mapped this as shown here where red means stronger gravity and blue means weaker gravity, and we can even see a gravity well in the Indian ocean.

Gravity of Earth


So not only does little g vary by planet, it varies on Earth. Big G is thought to not vary, but it's such a weak force and so difficult to measure, we sometimes get slightly different values for it and some people make a big deal out of this and think maybe big G is changing or not constant somehow. I suspect it's probably really constant, but to really resolve this once and for all will require more accurate measurements of big G, which hopefully will be forthcoming in the future.

That is to say, if the earth is sitting in free space, or moving, all the energy associated with the area of gravity field the size/mass of the earth, is sucked into the earth itself, and this suction of energy is what accounts for the lesser quantities of energy surrounding the mass. Is this what is suggested, if not, what is?

The string theorist moduli says gravity is understood, but he hasn't explained it to me, meaning I can do the math and predict Gravititational motions, but I can't really explain precisely WHY gravity is associated with mass and at the precise value that it is.

However, we can say that parts of your statement are not consistent with observation, for example "all the energy associated with the area of gravity field the size/mass of the earth, is sucked into the earth itself" is not a statement which I've seen any observations to support, and I think I can find observations to contradict it, like the blackbody radiation (a form of energy) emitted by the Earth is not sucked into the Earth by gravity, though the Earth's gravity does have a small red-shifting effect on this radiated energy.

I would suggest taking some physics courses and learning the terminology that physicists use, because you obviously have an interest in the topic. Part of the issue here I suspect is that physicists have somewhat precise and well-defined ways of describing their models, and when non-physicists use different terminology which doesn't follow these precise definitions, there can be a lot of confusion and misunderstanding.

KrzYma
I can't see how normalisation of anything can value any dimensional laws. Those dimensions are still separated by some constant.
what is 1 in universe A is not 1 in universe B but A x dimmesionalConstant
or so...

Yes and no. Here is an example.

Natural Units

Out of the many physical constants, the designer of a system of natural unit systems must choose a few of these constants to normalize (set equal to 1). It is not possible to normalize just any set of constants. For example, the mass of a proton and the mass of an electron cannot both be normalized: if the mass of an electron is defined to be 1, then the mass of a proton has to be ≈1836.

So lets call our universe "universe A" where the mass of the proton is 1836 if the mass of the electron is 1.

In hypothetical universe B, the mass of the proton may only be 1500 if the mass of the electron is 1.

So in both universes, the mass of the electron has been normalized to 1.

It would be just as valid to normalize the mass of the protons to 1 in both universes.

When comparing the two universes you must take into account that even if you've normalized the mass of the electron to be 1 in both, the mass of the electron may be different as may the mass of the proton. The ratio between them is definitely different. so at least one or the other must be different and possibly both. I'm not sure if that helps but it can get confusing.

Arbitrageur


However, we can say that parts of your statement are not consistent with observation, for example "all the energy associated with the area of gravity field the size/mass of the earth, is sucked into the earth itself" is not a statement which I've seen any observations to support, and I think I can find observations to contradict it, like the blackbody radiation (a form of energy) emitted by the Earth is not sucked into the Earth by gravity, though the Earth's gravity does have a small red-shifting effect on this radiated energy.

I meant that is the way you describe it, the only way I can imagine your view (I remember once when discussing gravity with you, you claimed that earth standing still will have gravitational affects to a near by body, whether it is moving or standing still) I am claiming the only way I can imagine that possible, is if the energy of the gravity field (stress energy tensor or manifold or what have you) that is supposed to be mostly equal throughout space is not equal surrounding a massive body, this is seen and known as the affects of gravity. The only way a non moving massive body can have gravity affects is if that energy which is suppose to be equal at all distances from the surface outward, if a quantity of that gravity field energy is located in the earth, trapped or absorbed within the spatial region of the earth and its matter. Physicists who explain this laymanly overpass this conundrum by using the 2d model of fabric, but space is not 2d! you can imagine the difficulty in using that understanding in a 3d model of energy tensor gravity field, the earth sitting there, how is there a gradient in energy density which increases in energy 'the square of the distance or what have you'? This is why my intuition tells me (unless like I said the gravity field is sucked into the mass, and part of its structure (perhaps that even has to do with the strong and weak force, once gravity forces a mass together it scrunches up and bundles up and densifies gravity field and that becomes the strong and weak force) that the affect of gravity has to do with the mass of earth moving, then we can imagine the 3d energy field of gravity as a medium which is displaced by a mass, and conforms to its motions up to a distance of intensity, lessening in intensity the further you get away from the center of mass.

ImaFungi
earth sitting there, how is there a gradient in energy density which increases in energy 'the square of the distance or what have you'?

The inverse square law is just simple geometry. The area at radius r becomes 4 times as much at 2r and 9 times as much at 3r (3x3=9). This is pretty easy to visualize in 3D in this illustration:



It's a gradient in the gravitational field. You've been studying this stuff long enough now to start getting the terminology right. There are such things as energy density gradients, but that's not an accurate description of the gravitational field.

Also since gravity travels at something like the speed of light, and the motion of the Earth is small compared to that, more or less radial symmetry of the gravitational field is not such a bad assumption. Now if a body was traveling at relativistic velocities, there is more noticeable distortion of spacetime to an outside observer, and then you might say it's not so symmetrical, but that is probably negligible for most practical calculations if talking about planetary motion in our solar system.

reply to post by Arbitrageur


You are missing my points and then talking down to me which is probably more humorous for you then me, but its still quite funny.

The gravity field is an energy gradient, it must be, unless you suppose its a material made strictly of numeral digits.

Imagine a medium, a mixture between a liquid and a solid, that when you displace it perhaps it does snap back together at the speed of light. Imagine all that exists is this medium, and then imagine we place earth (so you dont bring up your details imagine earth is perfectly spherical) into it, since this field before the mass was occupying it is a totality of energy quantity, when the mass enters the equation, it displaces the amount of energy of the field in turn of its mass. Now wouldnt we imagine that the energy it displaces is 'scrunched up', is more predominant from 0 to 1 mile from the earths surface outward, then it is 9 to 10 miles away from the earths surface and outward? Doesnt that make sense? (keep in mind this is a different view then I was suggesting last night, last night I was thinking the reason for objects falling to earths surface may be because of a cavern/lack of energy between earths surface and the distance away from earth where its gravity halts, but now under this view, it seems as if there is more energy per area in that area that causes objects to fall towards earth, so how can this be explained?)

If the earth was stationary in this scenario, I dont know why a body heading towards earth would be compelled to further travel towards it other then its direct path, if there is more energy per area nearer earth. Once again it would make more sense for the movement of the earth, coupled with this displacement reaction to have some kind of waving affect creating a tide pool of sorts, compelling bodies that travel near to get sucked in.

One other thing I was thinking about last night that troubled me, is the idea of area and density and mass. I dont know how (lets be hypothetical to drive home the point) and object can have the area of half the earth, but the mass of twice it, and there fore stronger gravity (to really drive home the point I would have liked to use the imagery of the area of a marble having twice the mass of the earth, implying a stationary marble would attract the moon towards it). Not using 2d models, I dont know how this can be explained. My natural reaction was potential tricks of relativity, That even if the smaller object has more mass, how would you really know neutrally which object was falling towards what, after all in the marble scenario wouldnt the result also appear as a marble on the surface of the moon?

ImaFungi
You are missing my points and then talking down to me which is probably more humorous for you then me, but its still quite funny.

Teaching is not the same thing as talking down. Don't confuse them. It's not humorous to me at all, but it is a little disappointing to see you use your sometimes genuine curiosity to put so much time and effort into asking all these questions about physics, when you are having difficulty expressing your questions clearly because you don't understand the definitions of some basic terms in physics like the difference between "force" and "energy".

The gravity field is an energy gradient, it must be, unless you suppose its a material made strictly of numeral digits.

Then explain this. Take a billiard ball and place it on the ground next to the leaning tower of Piza. Let's define this as the rest state of the ball and say it has zero potential energy at this point.

Now bring the ball up to the top of the tower and hold it over the edge. Would you say the ball now has more potential energy than it did before? I would.

Why do you think the gravitational field is an energy gradient in this example, when the potential energy of the ball is going up as the gravitational force goes down? (hint: gravity is a force, energy is not)

Arbitrageur

Then explain this. Take a billiard ball and place it on the ground next to the leaning tower of Piza. Let's define this as the rest state of the ball and say it has zero potential energy at this point.

Now bring the ball up to the top of the tower and hold it over the edge. Would you say the ball now has more potential energy than it did before? I would.

Why do you think the gravitational field is an energy gradient in this example, when the potential energy of the ball is going up as the gravitational force goes down? (hint: gravity is a force, energy is not)

Why the further you get from the earth, the less gravitational force? This says something about the physical space and field that exists there, there is no spooky action at distance by invisible non existent physically non real lines of force. Only stuff that exists and is real can interact with stuff that exists and is real. There must be a real existent cause of gravitation.

"In a field model, rather than two particles attracting each other, the particles distort spacetime via their mass, and this distortion is what is perceived and measured as a "force". In such a model one states that matter moves in certain ways in response to the curvature of spacetime,[1] and that there is either no gravitational force,[2] or that gravity is a fictitious force.[3]"

When I use the term energy, I mean it in the sense that; everything that exists is energy, use what ever word or number you want, im just saying, the gravity field is something that exists, thats what is important in what im trying to say. The earth exists in this field of something that exists, this gravity field, and the mass of the earth, displaces the something that is the gravity field, as you are familiar with masses displacing things like water and jello, you know that the something field (water, jello,gravity) that was priorly existing, when a mass is placed in this field, that something much go somewhere, and it is proportional to the mass displacing it. Now either the something field (gravity field) is scrunched up near the surface and beyond proportional to the mass (earth) that is displacing it, to a certain distance where it then evens out with the surrounding gravity field of inter solar system space/interstellar space/intergalactic space. Or the energy density of the field is less at the surface, like what may be the case in a sphere in water spinning fast creating a cavern of lesser energy density.

If the earth was standing still, and we go through with your ball and tower of piza experiment, can you describe how the 3d of surrounding gravity field may appear, can you tell me why when you bring the ball to the top it falls to earth, what about the space causes it to fall, why doesnt it hover? And interestingly enough small enough masses do just hover or float. All the heavy stuff was compelled to a common gravitational center I know, and now everything of sufficient mass is compelled to that common gravitational center. But Im asking how is it that the earth sitting still in the gravity field of space, has an influence of miles away from its surface, to cause masses to fall to its surface, how is the mass of earth interacting with space miles away from it, is what I want to know, in a 3d model?

reply to post by ImaFungi


My premise is simple.

The way science is being run is that we observe (with whatever accuracy our instruments have at that time) and then rush to create a theory. Then at a later point we have better instruments and our measurements no longer agree with the previous one. Then we rush to revise the theory and introduce new variables. This goes on.

The problem here is that theoretical Physics cannot and should not be run that way. The theories must be limited to what can be observed accurately.

This creation and revision of theories is rather getting out of hand.

Engineers work differently. Engineers are worried about building stuff that works. Engineers are not out there to prove a theory. So they make choices of introducing design elements that are not needed as per theory - for example error correction. However such feedback loops create limitations in the device being built.

reply to post by Arbitrageur


Let us discuss the example of GPS satellite a bit more.

The issue is why the atomic clock in the satellite shows a different time than the clock on earth.

The gravity on surface of the earth has slight variations. Agreed, as it is due to differences in crust material. But how much variation would be in the gravity at the orbit of the satellite? Please remember that the orbit itself naturally adjusts for this gravitational difference. So why would that make a difference to the clock?

GargIndia
The way science is being run is that we observe (with whatever accuracy our instruments have at that time) and then rush to create a theory. Then at a later point we have better instruments and our measurements no longer agree with the previous one. Then we rush to revise the theory and introduce new variables. This goes on.

The problem here is that theoretical Physics cannot and should not be run that way. The theories must be limited to what can be observed accurately.

We only have limited confidence in our measurement of the Gravitational constant G. It seems very likely that we will have more accurate measurements in the future. But we still explore space, because it's close enough to use for engineering purposes in designing spacecraft to explore our solar system.

It would be helpful if you could provide a more specific example of exactly what you think is a problem, or maybe a case where a theory was revised in a manner which troubles you.

If you're talking about string theory, a lot of experimental physicists might agree with you that 4 decades without substantial experimental results in that field isn't such great physics, but the string theorist who posts on ATS said he expects to see something experimentally confirmed in the next 5 years. I hope he is right as it would be nice to see some experimental progress, finally.

GargIndia
reply to post by Arbitrageur

 

The gravity on surface of the earth has slight variations. Agreed, as it is due to differences in crust material. But how much variation would be in the gravity at the orbit of the satellite? Please remember that the orbit itself naturally adjusts for this gravitational difference. So why would that make a difference to the clock?

When a satellite flies over a mountain range, the orbit of the satellite doesn't follow the mountain range. The mountain range perturbs the orbit very slightly.

The gravity on surface of the earth was just one example of the source of the corrections, but there are others, shown here:

nptel.iitk.ac.in...

Various forces acting on GPS satellites

Mainly gravitational forces act on satellites which can be categorized into two main groups:
- central gravitational attraction
- non-central gravitational (also called the perturbing forces)

Magnitude of central gravitational forces is three order of magnitudes larger than non-central gravitational and all other combined forces. Hence, the modelled satellite motion can be considered by central gravitational field and all other forces are considered as perturbing or disturbing forces.

Various perturbing forces include (Figure 9.1):
-Non-central gravitational force
-Third body effects (gravitational attraction of sun, moon, and planets)
-Atmospheric drag force
-Solar radiation pressure
-Magnetic forces
-Variable part of earth gravitational field arising from tidal and other deformation of solid earth and ocean.

Effect of some of these factors is significant which can be expressed as time dependent variation from mean motion and can be introduced as corrections. Resultant effect of various dynamic model shortcomings is treated as orbital bias.

Now why does perturbing the orbit change the clock?

We have done lab experiments showing we can raise or lower a very accurate clock in a lab by only 1 meter, and see the clock run at a different rate when we do that. Since the GPS clocks require such high accuracy the resulting perturbations in the orbit altitude do have an effect, but as that source says these are three orders of magnitude smaller than the "central gravitational attraction". So, the small perturbations do not overshadow the ~1000x greater effect of relativity from the "central gravitational attraction", but they do require adjustments for accuracy.