CharlesChandler wrote: When the predictions of a best-fit numeric model confirm the predictions of a totally different model (i.e., GR), I call that coincidence. You'd have to show me where GR predicted the motions of the celestial bodies to nine places past the decimal point, of sufficient accuracy to be worth something in explaining gravitational lensing. But it doesn't.
This is GR. "Post-Newtonian mechanics" is what the simulation is, that's general relativity. The equations don't look the same because this is computational GR derived specifically to deal with the problem in a way that can be computed as simply as possible whist reducing errors. There is no coincidence here. That is GR predicting the orbits of bodies good enough to land spacecraft on Mars.
CharlesChandler
Re: Relativity
Sain84 wrote: This is GR. "Post-Newtonian mechanics" is what the simulation is, that's general relativity. The equations don't look the same because this is computational GR derived specifically to deal with the problem in a way that can be computed as simply as possible whist reducing errors. There is no coincidence here. That is GR predicting the orbits of bodies good enough to land spacecraft on Mars.
My bad — I didn't know that GR was a best-fit numeric model. But there goes all of your assertions about the physical forces at work. Of course the "predictions" of a best-fit model will come true — and to a high degree of accuracy — the model was fitted to that which is being predicted!!! That proves nothing, and it rules out nothing. Good numeric models can "predict" new observations by interpolation, but they tend to extrapolate poorly, and they typically leave the physical forces unidentified. So if all you have is numeric models, you're liable to be surprised every time a new type of data is collected, because your numeric model was fitted to the existing data, but that didn't give it the ability to extrapolate out into new territory. And how often do you hear scientists say that they were surprised at the results that they got when they tried something new? This is where physical models outshine numeric models. Once the causal factors are identified, the full range of behaviors can be derived a priori. For example, using the atomic theory, chemists can now predict the properties of chemicals that have never been observed before. And the economy of accurate extrapolations is the whole reason to engage in theory in the first place. If you just want to do fit curves after the fact, you don't need (or want) theory — you just go with whatever works numerically. If interpolations are all that you need, that's the way to go. Just expect to be surprised if you ever try something new. IMO, we've passed the point of diminishing returns with that strategy. I'm tired of hearing how proud scientists are of the accuracy of their after-the-fact numeric modeling, while being very comfortable with being surprised every time they collect a new type of data. Those are people who just like playing with numbers, and see no need in pursuing the economy of physical modeling. It's good money if you can get it. But in no sense does the accuracy of numeric modeling preclude debates over the actual physical forces behind the observations.
Sain84
Re: Relativity
CharlesChandler wrote: My bad — I didn't know that GR was a best-fit numeric model. But there goes all of your assertions about the physical forces at work. Of course the "predictions" of a best-fit model will come true — and to a high degree of accuracy — the model was fitted to that which is being predicted!!! That proves nothing, and it rules out nothing. Good numeric models can "predict" new observations by interpolation, but they tend to extrapolate poorly, and they typically leave the physical forces unidentified. So if all you have is numeric models, you're liable to be surprised every time a new type of data is collected, because your numeric model was fitted to the existing data, but that didn't give it the ability to extrapolate out into new territory. And how often do you hear scientists say that they were surprised at the results that they got when they tried something new? This is where physical models outshine numeric models. Once the causal factors are identified, the full range of behaviors can be derived a priori. For example, using the atomic theory, chemists can now predict the properties of chemicals that have never been observed before. And the economy of accurate extrapolations is the whole reason to engage in theory in the first place. If you just want to do fit curves after the fact, you don't need (or want) theory — you just go with whatever works numerically. If interpolations are all that you need, that's the way to go. Just expect to be surprised if you ever try something new. IMO, we've passed the point of diminishing returns with that strategy. I'm tired of hearing how proud scientists are of the accuracy of their after-the-fact numeric modeling, while being very comfortable with being surprised every time they collect a new type of data. Those are people who just like playing with numbers, and see no need in pursuing the economy of physical modeling. It's good money if you can get it. But in no sense does the accuracy of numeric modeling preclude debates over the actual physical forces behind the observations.
It's not. You might want to read that document again, the dynamics are not fitted. What was fit was the parameters of the problem, I repeat, not the model. You fit the masses, locations and velocities based on the data. The model is GR, the physics is not being fitted. GR is not a data fitting model. This is just like Mawell's equations with the permittivity and permeability, you need to measure them first, with the solar system you cannot go weigh planets. Maxwell's equations are also a quantitative model like GR, they don't describe what electromagnetism actually is, they describe how it acts, that's what GR does. Atomic theory is another quantitative model which does not describe the physical nature of what's happening. Nobody can tell you with any certainty what the wavefunction is but, as you point out, it does a damn good job of making predictions. For theoretical chemistry it must usually be solved numerically or with approximate solutions.
For the record you seem to be confused about the meaning of numerical, it means it was solved by a simulation and not an exact solution. In complex dynamics such as the solar system or plasma interactions numerical models are one of the best ways to model systems of individual interacting particles. GR can be solved numerically or with some exact solutions.
CharlesChandler
Re: Relativity
You're right — I am confused. So GR is a quantitative model, which describes how stuff acts, but without explaining why or anything like that. Is that correct? And because it describes how stuff acts, without explaining why, there is no need to wonder why — am I on the right track here?
Sain84
Re: Relativity
CharlesChandler wrote: You're right — I am confused. So GR is a quantitative model, which describes how stuff acts, but without explaining why or anything like that. Is that correct? And because it describes how stuff acts, without explaining why, there is no need to wonder why — am I on the right track here?
Correct apart from the last bit. It is the Maxwell's equations of gravity, it described the "how" not the "why".Why is a good question and a lot of people work on that question, the answer isn't known yet. Another good question is why such simple founding principles build such an empirically strong theory. Until the former is answered we probably won't know that either.
Aardwolf
Re: Relativity
Sain84 wrote: That is GR predicting the orbits of bodies good enough to land spacecraft on Mars.
Complete and utter rubbish.
NASA Earth Observatory wrote: At slow speeds and at large scales, however, the differences in time, length, and mass predicted by relativity are small enough that they appear to be constant, and Newton's laws still work. In general, few things are moving at speeds fast enough for us to notice relativity. For large, slow-moving satellites, Newton's laws still define orbits. We can still use them to launch Earth-observing satellites and predict their motion. We can use them to reach the Moon, Mars, and other places.
Relativity has never been incorporated into calculating orbits, satellites trajectories etc. and never will be. It's useless mathematical erotica.
Solar
Re: Relativity
Aardwolf wrote:
Sain84 wrote: That is GR predicting the orbits of bodies good enough to land spacecraft on Mars.
Complete and utter rubbish.
NASA Earth Observatory wrote: At slow speeds and at large scales, however, the differences in time, length, and mass predicted by relativity are small enough that they appear to be constant, and Newton's laws still work. In general, few things are moving at speeds fast enough for us to notice relativity. For large, slow-moving satellites, Newton's laws still define orbits. We can still use them to launch Earth-observing satellites and predict their motion. We can use them to reach the Moon, Mars, and other places.
Relativity has never been incorporated into calculating orbits, satellites trajectories etc. and never will be. It's useless mathematical erotica.
I'm having one of those priceless moments wherein I've read something and wish that I had said it. Thank you Aardwolf
Sain84
Re: Relativity
Aardwolf wrote:
Sain84 wrote: That is GR predicting the orbits of bodies good enough to land spacecraft on Mars.
Complete and utter rubbish.
NASA Earth Observatory wrote: At slow speeds and at large scales, however, the differences in time, length, and mass predicted by relativity are small enough that they appear to be constant, and Newton's laws still work. In general, few things are moving at speeds fast enough for us to notice relativity. For large, slow-moving satellites, Newton's laws still define orbits. We can still use them to launch Earth-observing satellites and predict their motion. We can use them to reach the Moon, Mars, and other places.
Relativity has never been incorporated into calculating orbits, satellites trajectories etc. and never will be. It's useless mathematical erotica.
They are quite correct but they do not say they do not use relativity. At low speeds and large distances from the Sun Newtonian dynamics is fine, there GR reduces to Newtonian dynamics. If you took the time to actually read what I posted you would see plain and simple, the use of relativistic post-Newtonian physics. The JPL ephemerides in particular strive for maximum possible accuracy, hence why relativistic factors are used which only become important in some situations.
Here is the link I posted to the description of the DE405 ephemeris since you missed it:
For DE 421 the positions of the moon and planets were integrated using a n-body parameterized post-Newtonian metric (Will and Nordtvedt, 1972; Will 1981; Moyer 2000). The PPN parameters γ and β have been set to 1, their values in general relativity.
They do indeed use relativity. As you can see it is applied in the real world.
David
Re: Relativity
Relativity has never been incorporated into calculating orbits, satellites trajectories etc. and never will be. It's useless mathematical erotica.
General Relativity has, from its inception, been used to accurately predict the perihelion precession of mercury's orbit; a feat that Newtonian mechanics has never been able to accomplish.
A-wal
Re: Relativity
oz93666 wrote: I've been very keen on Physics all my life, but I still don't feel happy with my grasp of relativity. If I had to explain it to a 10 year old (always a good test of your understanding ) then , well, 'it's about mass and energy being interchangeable. it's about time not being constant, it slows down if you're moving. it's about the speed of light being the fastest you can go. it was quite revolutionary, it didn't make Newton obsolete , it fine tuned his laws for extreme conditions. And that's about it ... lets have a look at Wikipedia they're normally give a very good summary ....
I wrote this ages ago. I don't agree with general relativity, I think it's complete bollocks but I love special relativity and everything I've written here is what the standard description and my way of thinking of it have in common. I hope this helps to clarify a few things.
Relativity Made Simple
If an object is stationary (inertial (not accelerating)) in space and it sees another object coming towards it at half the speed of light then you could just as easily say that it's moving towards the other object at half the speed of light and the other object is stationary. There is no distinction between which one is moving. The only statement you can make is that they moving towards each other at half the speed of light. All the laws of physics remain the same in any inertial frame, meaning all frames are equal and no frame can be said to be unique in any way. Having said that, you could use the cosmic background radiation as a frame of reference for all others, but you could do that with any frame of reference. If you're in a car and you throw a ball into the air then it doesn't go flying backwards because the laws in all non accelerating frames are the same, including the speed of light. You can't measure your speed relative to light because you'll always get the same answer of 186,000 miles per second. So if two objects are heading away from Earth at different relative velocities and you shine a flash light then the light beam will pass both of them at the same speed, meaning all three observers measure time and space differently to keep the speed of light the same for all of them. Velocity is just a measurement of distance over time. There's one spacial dimension involved because you can always draw a straight line between any two objects, and time. Both shorten from the perspective of an accelerating observer to keep the speed of light constant. This is called length contraction and time dilation. They're caused by the fact that energy has to travel different distances from the perspective of two observers in motion relative to each other, and the difference is length contraction and time dilation.
If a ship were flying away from Earth and a signal was sent from Earth to the ship and from the ship to Earth then would both signals take the same amount of time to reach their destination? Yes, but both Earth and the ship would say no. Both observe outgoing signals taking longer than incoming signals because outgoing signals have to catch up to the receding destination. Outgoing signals have to travel further and take longer than incoming ones do to make the same journey, because outgoing signals are measured to when they arrive while incoming signals are measured from when they're released. Signals sent by the other observer would be travelling a shorter distance and wouldn't take as long to reach the destination as a signals sent from themselves to the other observer because outgoing signals are travelling to where an object is going to be and incoming signals are travelling to where an object is and the difference is length contraction and time dilation. Objects are always travelling through space-time at the speed of light from all frames of reference. In your own frame your stationary and moving through time at the speed of light. Objects also see other objects with a different relative velocity moving at the speed of light because they're moving through time slower (time dilation) from each others perspective and their total velocity through space-time will always equal the speed of light.
Imagine two ships moving at different velocities, both with a light beam moving up and down between the ceiling and the roof. It takes one second for the light to travel up or down from mirror to the other. Each would see the light on the other ship move in a zigzag as its relative velocity is added to the lights vertical motion. Light doesn't speed up to make up the difference, so it takes longer than one second for the light to get from one mirror to the other on the others ship from both perspectives. A second for either is a shorter amount of time than a second for the other, so each sees the other moving in slow motion because the light on the other ship has further to go. Now one is stationary relative to a tunnel which the other ship travels though. The ships front end comes out one second after its back end enters, but space is length contracted in the direction that it's travelling in, making anything in the other frame including the tunnel length extended by comparison. Its front end emerges before the back end enters from the perspective of the ship at rest relative to the tunnel. From this frame, the ship is longer than the tunnel.
Everything up until now has been symmetric, so each twin sees the same affects on the other, and in exactly the same way. The twin paradox (not actually a paradox at all) is that the one leaving Earth will be younger than their twin when they return. To start with we'll give both twins a rolling start and finish. The twins pass Earth moving in opposite directions at just over half the speed of light relative to an observer on Earth who sees them moving away from each other at over the speed of light, which is fine as long as no one sees themselves moving above light speed relative to anyone else. Each twin sees themselves moving at just over half light speed relative to Earth (Earth sees them moving at that speed so the same must be true in reverse) and each twin sees the other moving at below light speed because of length contraction and time dilation. But this isn't a real affect because each sees the other one moving in slow motion and length extended (because the space is contracted), which stops anyone from moving faster than light relative to anyone else. When they turn round they have to accelerate in the opposite direction (there's no such thing as deceleration in relativity because it's just acceleration in the opposite of some arbitrary direction). If one is at rest and the other accelerates and comes back then it becomes a real affect and one twin is literally younger than the other one.
A uses one unit of energy to travel up to half the speed of light relative to E. A is now static in its new frame of course. A then uses another unit of energy to again reach half the speed of light relative to an object in its new frame. From Es frame that second unit of energy didn't accelerate A as much as the first one did, but from As perspective it did because of length contraction and time dilation. So if the same energy is needed to move over a relatively smaller amount of space-time then the mass of A has increased from Es frame, and Es has from As frame as well. So the others energy requirement to accelerate increases from both perspectives as their velocity relative to each other increases, so your mass increases the faster you move relative to something else from their perspective. Energy becomes mass as you accelerate relative to the speed of light from the perspective of other frames of reference. That's how matter and energy are interchangeable, E = mc^2. What separates them is the fact that A has accelerated and E hasn't. If E were to accelerate into As new frame then they'd be the same age again. Length contraction and time dilation would lessen as their speeds become relatively closer to each other. When their relative velocities match they'll be in the same frame again and the only apparent time lag will be caused by how long it takes for light to cover the distance separating them (light hours/days/years).
You can effectively travel as fast as you like, there's no such thing as absolute velocity and there's no speed limit because you will be in a new frame every time you stop using energy to accelerate and the speed of light and your energy requirement for acceleration relative to c is always the same in every possible inertial frame. You can go anywhere in as short an amount of time as you like if you have enough energy, it's just that objects can't reach the speed of light relative any other objects, so space and time make up the difference by being relative rather than fixed. If you accelerated to half the speed of light from your starting frame then you'd be in a new frame when you stop accelerating and you'd now be static from your own perspective and the energy requirement to accelerate to half speed of light would be the same as it was in your starting frame. If accelerated again up to half the speed of light relative to an object in your new frame then you wouldn't be travelling at the speed of light from your starting frame because you are length contracted and time dilated from the perspective of your starting frame and so you're moving slower through time and space. Time and space aren't fixed. As you accelerate towards something, it gets closer to you beyond what you would expect from the increased velocity. You can move infinitely fast, but as far as the rest of the universe is concerned you can't. So if you were to accelerate away from Earth and then return, you would be younger than your twin who stayed home because you were travelling slower through time and space from Earths perspective.
Gravitys strength is directly proportional to mass and inversely proportional to the square of the distance to the mass. That just means that its strength is divided by four if the distance is doubled and multiplied by four if the distance is halved. In zero dimensions (point/singularity) would be infinite. In one spatial dimension (straight line) its strength would remain constant over any distance. In two spatial dimensions (flat plane) it would be directly proportional to the distance. In three spatial dimensions it's an inverse square. It's proportional to the space it fills. We feel our own weight on Earth but it's not gravity that we feel, it's the electro-magnetic force between the atoms that are resisting gravity and pushing us upwards by the same amount that gravity is pulling us down. Neutron stars are heavy enough to collapse past this resistance and are held up by the resistance of the neutrons. Black holes are so heavy for their size that nothing can hold them up and they collapse completely. We feel the difference in the amount of force being applied to our points of contact with the ground and the rest of our bodies, which is why it's more comfortable when this difference is spread over a larger area when we lay down. The difference in the strength of a gravitational field is also all that can be felt rather than the strength of the field itself, because it's relative. The relative difference in the strength of gravity is called tidal force. On Earth that difference is very small and can't be felt but in a strong enough gravitational field it's enough to rip solid objects apart.
Relativity explains how electricity and magnetism are actually the same force (electro-magnetism). A magnetic field can turn into an electric field if you accelerate relative to it because length contradiction moves the electrons closer together giving the field a negative charge, so the magnetism from the previous frame is felt here as electricity.
Later addition:
If you're an intertial object then you're not moving though space at all and moving through time at the speed of light from your own perspective, and the same applies to any object at rest relative to you. If an object is moving though space at a constant velocity relative to you then it's moving through time at less than the speed of light to keep its overall velocity at the speed of light. This situation is symmetric though because they would see you moving through space at the same rate as you observe them moving through, and the same applies to time so that you're moving through space-time at the speed of light from their perspective as well.
Let's say that person A accelerates to half the speed of light, then accelerates by exactly the same amount again. Now, length contraction and time dilation mean that person A didn't accelerate by as much as they did during the first acceleration despite using the same amount of energy. This is why an objects mass increases as its relative velocity increases. Object As mass didn't increase from it's own perspective of course. After the first burst of acceleration it became inertial again, but length contraction and time dilation mean than it finds itself in a new frame of reference where time and space in the dimension that it accelerated in are now shorter than they are from Bs perspective, but of course the situation is symmetric, so how can that be true?
I'm going to have to bring in a third object to explain this. Object C is some distance away from Earth in the same direction that A accelerated in so that you can draw a straight line through all three objects and object C is at rest relative to Earth. The distance between object B and object C is less from object As perspective than it is from the perspectives of objects B and C. If there were another object in the same straight line at rest relative to object A and some distance away from it then that distance would be less in the object B and object Cs frame than it is in the frame of object A and the other object.
The second burst of acceleration from object A accelerates it just as much as the first did from its own perspective, but in space that's length contracted and time that's dilated from the perspective of its original frame. This means that A is travelling through space at a different velocity from it's own perspective than it is from the perspective of object B and the difference increases the more it accelerates in total, and because all objects travel through space-time at the speed of light it means that it's travelling through time at a different rate than it is in object Bs frame which is responsible for the difference in age when A returns to Earth. Because object A is doing all the accelerating it means that when it gets back to Earth it's ended up in a frame where it was moving through space and therefore not moving as quickly through time.
CharlesChandler
Re: Relativity
Sain84 wrote: They are quite correct but they do not say they do not use relativity. At low speeds and large distances from the Sun Newtonian dynamics is fine, there GR reduces to Newtonian dynamics. If you took the time to actually read what I posted you would see plain and simple, the use of relativistic post-Newtonian physics. The JPL ephemerides in particular strive for maximum possible accuracy, hence why relativistic factors are used which only become important in some situations.
They use GR alright. It just doesn't do anything, because at non-relativistic velocities, you're not supposed to get relativistic effects. And if you're going to argue that they're doing such accurate work that they feel compelled to compute even near-infinitesimal effects at non-relativistic velocities, I'll feel compelled to wonder why G is only accurate to 4 places past the decimal point, and GMsun only to 9 places. At orbital velocities, which are nowhere near relativistic, if they're worried about relativistic effects, I'd expect accuracy to dozens of places past the decimal point. But that's not what I'm hearing. So I "think" that what I'm hearing is nothing but BS.
As concerns special relativity, I don't have a use for that either. Why rewrite the physics textbooks to accommodate the rare exceptions? How much of the physics that actually gets used in this world actually requires relativity? Almost none of it. And rare exceptions make bad rules. Any decent scientist will tell you that, as well as any decent engineer. I wouldn't see much utility to something like that, even if we had already solved all of the other mysteries that are a lot closer to home. In that we haven't solved all of the other mysteries, such as how to predict earthquakes and geomagnetic storms, relativity isn't just a waste of time/money. It's taking time/money away from real projects.
A-wal
Re: Relativity
CharlesChandler wrote:
Sain84 wrote: They are quite correct but they do not say they do not use relativity. At low speeds and large distances from the Sun Newtonian dynamics is fine, there GR reduces to Newtonian dynamics. If you took the time to actually read what I posted you would see plain and simple, the use of relativistic post-Newtonian physics. The JPL ephemerides in particular strive for maximum possible accuracy, hence why relativistic factors are used which only become important in some situations.
They use GR alright. It just doesn't do anything, because at non-relativistic velocities, you're not supposed to get relativistic effects.
That's SR, not GR.
CharlesChandler wrote: And if you're going to argue that they're doing such accurate work that they feel compelled to compute even near-infinitesimal effects at non-relativistic velocities, I'll feel compelled to wonder why G is only accurate to 4 places past the decimal point, and GMsun only to 9 places. At orbital velocities, which are nowhere near relativistic, if they're worried about relativistic effects, I'd expect accuracy to dozens of places past the decimal point. But that's not what I'm hearing. So I "think" that what I'm hearing is nothing but BS.
Relativity is not BS. If the speed of light is constant then the only way that can work is if space and time are relative. Velocity is a measurement of distance in space over time. Time and space have to shorten from the perspective of an observer as they accelerate to keep the speed of light the same once they've stopped accelerating. There's no way around it.
CharlesChandler wrote: As concerns special relativity, I don't have a use for that either. Why rewrite the physics textbooks to accommodate the rare exceptions?
Seriously? It's the most profound thing ever discovered and it's stunningly beautiful.
CharlesChandler
Re: Relativity
A-wal wrote: If the speed of light is constant then the only way that can work is if space and time are relative.
Check your assumptions before locking down on your conclusions. The speed of light in a vacuum is (supposedly) constant. Unfortunately, a perfect vacuum has never been achieved, much less on the scale necessary for measuring the speed of light. Yet all kinds of conclusions concerning the relativity of time and space have become accepted as "discoveries" (as if they are incontrovertibly true). I require more than preformed conclusions. And no, that isn't a preformed conclusion on my part, that something is definitely wrong. It's just an insistence on clear reasoning, and well-documented tests. When I don't get this, that's when I start to think that something is wrong. As concerns relativity, for me that was several years ago.
A-wal wrote: Velocity is a measurement of distance in space over time. Time and space have to shorten from the perspective of an observer as they accelerate to keep the speed of light the same once they've stopped accelerating. There's no way around it.
The sound of a train whistle travels at the speed of sound, regardless of the speed of the train. There will be a Doppler Effect if the train is moving relative to the observer. But this doesn't affect the wave transmission speed. No warping of time and/or space is necessary for these physical laws to hold true.
A-wal wrote: [SR] is stunningly beautiful.
So is the Mona Lisa. So what?
Sain84
Re: Relativity
CharlesChandler wrote: They use GR alright. It just doesn't do anything, because at non-relativistic velocities, you're not supposed to get relativistic effects. And if you're going to argue that they're doing such accurate work that they feel compelled to compute even near-infinitesimal effects at non-relativistic velocities, I'll feel compelled to wonder why G is only accurate to 4 places past the decimal point, and GMsun only to 9 places. At orbital velocities, which are nowhere near relativistic, if they're worried about relativistic effects, I'd expect accuracy to dozens of places past the decimal point. But that's not what I'm hearing. So I "think" that what I'm hearing is nothing but BS.
As concerns special relativity, I don't have a use for that either. Why rewrite the physics textbooks to accommodate the rare exceptions? How much of the physics that actually gets used in this world actually requires relativity? Almost none of it. And rare exceptions make bad rules. Any decent scientist will tell you that, as well as any decent engineer. I wouldn't see much utility to something like that, even if we had already solved all of the other mysteries that are a lot closer to home. In that we haven't solved all of the other mysteries, such as how to predict earthquakes and geomagnetic storms, relativity isn't just a waste of time/money. It's taking time/money away from real projects.
It does do things. In order to gather all the observations GR is important. It might not be large but these people strive for accuracy. It will be more accurate than Newtonian dynamics. The precision of the simulation is limited by the precision of the initial parameters obtained from observations. I didn't state it was huge, it stated correctly it was used to put a lander on Mars. Neither you nor I can say what the error would be if you started neglecting parts of physics.
Special relativity was written because Newtonian dynamics is wrong. How does a constant speed of light from Maxwell's equations affect dynamics as we know it? It creates contradictions. You have to change mechanics or you have contradictory physics. There is no logical argument for leaving theory broken. Newtonian dynamics does work pretty well in most cases, that's why it's taught but you can't abandon the search for better theory because it inconveniences you. Better theory is not a waste of time, it provides answers. Without relativity we wouldn't know why gold was yellow. Without relativity we wouldn't understand one of the sources of error for orbital clocks. We can fund more than one avenue of physics at one time.
The sound of a train whistle travels at the speed of sound, regardless of the speed of the train. There will be a Doppler Effect if the train is moving relative to the observer. But this doesn't affect the wave transmission speed.
It travels at the speed of sound with respect to the air but an observer moving with respect to the air will not measure it at the same speed. The speed of light however is constant regardless of what frame you're in. We get that from Maxwell's equations which are empirically tested.
Aardwolf
Re: Relativity
Sain84 wrote: I didn't state it was huge, it stated correctly it was used to put a lander on Mars. Neither you nor I can say what the error would be if you started neglecting parts of physics.
The more you post the further you reveal the ignorance of what you are posting about.
Mars Science Laboratory wrote: Cruise
The cruise phase begins soon after separation from the launch vehicle when the spacecraft completes the launch phase. Cruise ends when the spacecraft is 45 days from entry into the Martian atmosphere, when the approach phase begins. Major activities during the cruise phase • health checks and maintenance of the spacecraft in its cruise configuration • monitoring and calibration of the spacecraft and subsystems • attitude correction turns (spins to maintain the antenna pointing toward Earth for communications and to keep the solar panels pointed toward the Sun for power) • navigation activities, including trajectory correction maneuvers, for determining and correcting the vehicle´s flight path and for training navigators prior to approach • preparation for entry, descent, and landing and surface operations, including communication tests used during entry, descent, and landing
Mars Science Laboratory wrote: Approach
To ensure a successful entry, descent, and landing, engineers began intensive preparations during the approach phase, 45 days before the spacecraft entered the Martian atmosphere. It lasted until the spacecraft entered the Martian atmosphere, which extends 3522.2 kilometers (2,113 miles) as measured from the center of the red planet. The activities that engineers typically focus on during the approach phase include: • the final trajectory correction maneuvers, which are used to make final adjustments to the spacecraft's incoming trajectory at Mars • attitude pointing updates, as necessary, for communications and power • frequent "Delta DOR" measurements that monitor the spacecraft's position and ensure accurate delivery • start of the entry, descent, and landing behavior software, which automatically executes commands during that phase • entry, descent, and landing parameter updates • spacecraft activities leading up to the final turn to the entry attitude and separation from the cruise stage • the loading of surface sequences and communication windows needed for the first several sols (a "sol" is a martian day)
During the approach phase, the amount of requested tracking by the Deep Space Network was substantially increased to allow engineers to determine more accurate trajectory solutions in the final weeks before arrival at Mars. This tracking supported the safe delivery of the Mars Science Laboratory landing system to the surface of Mars. The Deep Space Network's 34-meter and 70-meter antennas provided tracking coverage of the spacecraft during the approach phase.
The craft is actively steered all the way there. They can't even rely on Newtonian calculations due to numerous large and unpredictable perturbations. To state they need to account for tiny relativistic adjustments is pure BS.
That proves nothing, and it rules out nothing. Good numeric models can "predict" new observations by interpolation, but they tend to extrapolate poorly, and they typically leave the physical forces unidentified. So if all you have is numeric models, you're liable to be surprised every time a new type of data is collected, because your numeric model was fitted to the existing data, but that didn't give it the ability to extrapolate out into new territory. And how often do you hear scientists say that they were surprised at the results that they got when they tried something new? This is where physical models outshine numeric models. Once the causal factors are identified, the full range of behaviors can be derived a priori. For example, using the atomic theory, chemists can now predict the properties of chemicals that have never been observed before. And the economy of accurate extrapolations is the whole reason to engage in theory in the first place. If you just want to do fit curves after the fact, you don't need (or want) theory — you just go with whatever works numerically. If interpolations are all that you need, that's the way to go. Just expect to be surprised if you ever try something new. IMO, we've passed the point of diminishing returns with that strategy. I'm tired of hearing how proud scientists are of the accuracy of their after-the-fact numeric modeling, while being very comfortable with being surprised every time they collect a new type of data. Those are people who just like playing with numbers, and see no need in pursuing the economy of physical modeling. It's good money if you can get it. But in no sense does the accuracy of numeric modeling preclude debates over the actual physical forces behind the observations.
If the speed of light is constant then the only way that can work is if space and time are relative. Velocity is a measurement of distance in space over time. Time and space have to shorten from the perspective of an observer as they accelerate to keep the speed of light the same once they've stopped accelerating. There's no way around it.
CharlesChandler wrote:Seriously? It's the most profound thing ever discovered and it's stunningly beautiful.As concerns relativity, for me that was several years ago.
A-wal wrote:The sound of a train whistle travels at the speed of sound, regardless of the speed of the train. There will be a Doppler Effect if the train is moving relative to the observer. But this doesn't affect the wave transmission speed. No warping of time and/or space is necessary for these physical laws to hold true.