Relativity

[Sain84]

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.

No, I never said that. What you claimed was that they didn't use GR, I have proven that totally false, now you're moving the goalpost. I never claimed they were significant, I said GR is what was used to put a rover on Mars. That is correct. You can argue whether or not you think they need to do it all you like but there it is, a hard fact, they take account of it.

Tell me this. Even if you knew the complete dynamics of the solar system to perfect precision would you need to adjust the spacecraft? Yes, because the burns used to get there are only so accurate. Deep space maneuvers are usually either planned from day one or are done to correct for errors in initial flight path. You're rocket and spacecraft propulsion system is only so accurate. The longer you let it fly the more precisely you know what the errors are so corrections are easier to implement. The bulk of the uncertainty will lie in the trajectory of the spacecraft not the planet. They say nothing about "unpredictable perturbations".

[A-wal]

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.

My assumptions are fine. A perfect vacuum isn't needed to demonstrate that the rate that energy/information propagates is the same for every inertial observer. Space is more than diffuse enough to show that this is the case. Not getting it is not a good enough justification for rejecting it. It's very simple...

If the rate that information travels is the same for every inertial observer then their measurements of distances in space and time can't be. It really is that simple. When your watching an object moving at half the speed of light relative to you you're seeing light moving away from them at half the speed of light. They're seeing it moving away from themselves at the full speed of light. The only way that makes sense is if their view of time and space are contracted from your perspective. This makes your view of time and space extended relative to their, which is why an object moving at a high velocity relative to you looks stretched in space and in time. They would say the same of you because from their point of view light is moving away from you at half the speed of light.

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.

NO! No, no, no! The speed of sound is not constant. It's doesn't move away from a moving train at the same velocity that it moves away from someone standing on the platform. You can vary your speed relative to sound, you can overtake it. You can't gain on the speed of light at all! It's moves away from the moving train from the trains perspective at the same velocity that it moves away from someone standing on the platform from the perspecive of that person. Sound doesn't do that. Sounds velocity depends on the relative velocity of the source, light doesn't.

The way you change the velocity of light relative to you is through acceleration. As acceleratation increases, lights velocity slows relative to the accelerater. You can still never catch up to it though because it takes more acceleration to close the gap by the same amount as acceleration increases approaching infinity at the speed of light. It's identicle to the way that it more of an increase in velocity to move closer to the speed of light relative to another object as relative velocity increases. Acceleration is velocity relative to energy rather than mass. It's also exactly the same rate that distance between an object and the event horizon of a black hole shortens at a slower rate the closer you get to it preventing any object from reaching because event horizons are moving away from external objects at the speed of light locally and slower as distance between them and the horizon increases, because of length contraction and time dilation. It's also exactly the same rate that the Rindler horizon (the point past which a signal moving at the speed of light can never catch up to an accelerating object as long as they continue to accelerate at at least the same rate) gets closer to an accelerating object at a progresively slower rate as their acceleration increases.

[SR] is stunningly beautiful.

So is the Mona Lisa. So what?

You don't think beauty is important? Oh dear.

[CharlesChandler]

When your watching an object moving at half the speed of light relative to you you're seeing light moving away from them at half the speed of light.

And how was this demonstrated? By a thought experiment in the mind of Einstein? Which you found to be really profound, so now you speak of it as if it is fact? And you require that I accept it as fact? Dr. Who episodes can be profound, to whatever extent you're predisposed to believe in them. The connection to reality hasn't been demonstrated, which means that the "proof" is in the predisposition.

[SR] is stunningly beautiful.

So is the Mona Lisa. So what?

You don't think beauty is important? Oh dear.

Beauty is very important. And sophistry can be beautiful. That doesn't make it true.

[A-wal]

When your watching an object moving at half the speed of light relative to you you're seeing light moving away from them at half the speed of light.

And how was this demonstrated? By a thought experiment in the mind of Einstein? Which you found to be really profound, so now you speak of it as if it is fact? And you require that I accept it as fact? Dr. Who episodes can be profound, to whatever extent you're predisposed to believe in them. The connection to reality hasn't been demonstrated, which means that the "proof" is in the predisposition.

No, it was first demonstrated by measuring light from the sun I think. Einsteins thought experiments where based on that information, not the other way round. The relative velocity of energy doesn't behave in the same way as the relative velocities of mass. Why should it? It actually wouldn't make sense if it did.

[SR] is stunningly beautiful.

So is the Mona Lisa. So what?

You don't think beauty is important? Oh dear.

Beauty is very important. And sophistry can be beautiful. That doesn't make it true.

Beauty is truth. It's true, I checked. Look it up.

[Aardwolf]

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.

No, I never said that. What you claimed was that they didn't use GR, I have proven that totally false

I didn't claim they didn't use GR, I provided a link from NASA JPL that said they didn't use GR. Where's your link that says they do calculate relativistic adjustments to the spacecraft manoeuvres etc?

As for your proof, those papers are calculating theoretical epheremis of planets and are nothing to do with spacecraft manoeuver/trajectories. And how accurate are they? Here's what is says about Mars on the first page in the abstract;

Because of perturbation of the orbit of Mars by asteroids, frequent updates are needed to maintain the current accuracy into the future decade

Their predictive abilities with or without GR are garbage.

I never claimed they were significant, I said GR is what was used to put a rover on Mars. That is correct. You can argue whether or not you think they need to do it all you like but there it is, a hard fact, they take account of it.

Then provide a relevant link please.

Tell me this. Even if you knew the complete dynamics of the solar system to perfect precision would you need to adjust the spacecraft? Yes, because the burns used to get there are only so accurate. Deep space maneuvers are usually either planned from day one or are done to correct for errors in initial flight path. You're rocket and spacecraft propulsion system is only so accurate. The longer you let it fly the more precisely you know what the errors are so corrections are easier to implement. The bulk of the uncertainty will lie in the trajectory of the spacecraft not the planet. They say nothing about "unpredictable perturbations".

You're just confirming that making GR adjustments are entirely useless whether you dogma says they should be included or not.

[CharlesChandler]

I said GR is what was used to put a rover on Mars.

Did they use GR to calculate ever so precisely how fast the smoke would dissipate when they burned up 193.1 million USD in the Martian atmosphere...

On November 10, 1999, the Mars Climate Orbiter Mishap Investigation Board released a Phase I report, detailing the suspected issues encountered with the loss of the spacecraft. Previously, on September 8, 1999, Trajectory Correction Maneuver-4 was computed and then executed on September 15, 1999. It was intended to place the spacecraft at an optimal position for an orbital insertion maneuver that would bring the spacecraft around Mars at an altitude of 226 kilometers on September 23, 1999. However, during the week between TCM-4 and the orbital insertion maneuver, the navigation team indicated the altitude may be much lower than intended at 150 to 170 kilometers. Twenty-four hours prior to orbital insertion, calculations placed the orbiter at an altitude of 110 kilometers; 80 kilometers is the minimum altitude that Mars Climate Orbiter was thought to be capable of surviving during this maneuver. Post-failure calculations showed that the spacecraft was on a trajectory that would have taken the orbiter within 57 kilometers of the surface, where the spacecraft likely disintegrated because of atmospheric stresses.

The primary cause of this discrepancy was that one piece of ground software produced results in an Imperial unit, while a second system that used those results expected them to be in metric units. Software that calculated the total impulse produced by thruster firings calculated results in pound-seconds. The trajectory calculation used these results to correct the predicted position of the spacecraft for the effects of thruster firings. This software expected its inputs to be in newton-seconds.

The discrepancy between calculated and measured position, resulting in the discrepancy between desired and actual orbit insertion altitude, had been noticed earlier by at least two navigators, whose concerns were dismissed. A meeting of trajectory software engineers, trajectory software operators (navigators), propulsion engineers, and managers, was convened to consider the possibility of executing Trajectory Correction Maneuver-5, which was in the schedule. Attendees of the meeting recall an agreement to conduct TCM-5, but it was ultimately not done.

If I'm reading that correctly, they had already done 4 "Trajectory Correction Maneuvers". How did they do 4 burns with mismatched imperial/metric units, and still come within 116 km of the target, after following a 669 million km trajectory? Anyway, a discrepancy between the calculated and measured positions was noticed, but the concerns were dismissed. So they cancelled the last scheduled burn (?) and the satellite disintegrated in the Martian atmosphere. (Oops.) Forgive me for confessing that I don't fully understand how this could have happened the way they tell it. If I was smart enough to understand GR, would I be smart enough to believe NASA press reports like this?

[Maol]

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.

NO! No, no, no! The speed of sound is not constant. It's doesn't move away from a moving train at the same velocity that it moves away from someone standing on the platform. r.

Charles is right. The speed of sound is constant (in the medium, for the local atmospheric conditions) irrespective of the direction the train is moving or how fast or what directions the train or observer are moving. However, unlike light (as light’s behavior is currently assumed), if the air is moving relative to a stationary observer, the velocity of the medium affects the relative velocity of the sound. Charles example is the classic which implies the observer is in a static medium in which the sound travels.

Did you get your mords wixed, or did I?

[CharlesChandler]

Charles example is the classic which implies the observer is in a static medium in which the sound travels.

Yes.

When your watching an object moving at half the speed of light relative to you you're seeing light moving away from them at half the speed of light.

And how was this demonstrated? By a thought experiment in the mind of Einstein?

No, it was first demonstrated by measuring light from the sun I think. Einsteins thought experiments where based on that information, not the other way round.

So you're talking about Earth-based measurements of the speed of light from the Sun. This means that the instrumentation was swimming in a static medium -- the Earth's atmosphere. So how was the effect of the medium ruled out?

[Sparky]

NO! No, no, no! The speed of sound is not constant.

It is as useless to fight against the interpretations of ignorance as to whip the fog.

GEORGE ELIOT, Middlemarc

[A-wal]

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.

NO! No, no, no! The speed of sound is not constant. It's doesn't move away from a moving train at the same velocity that it moves away from someone standing on the platform. r.

Charles is right. The speed of sound is constant (in the medium, for the local atmospheric conditions) irrespective of the direction the train is moving or how fast or what directions the train or observer are moving. However, unlike light (as light’s behavior is currently assumed), if the air is moving relative to a stationary observer, the velocity of the medium affects the relative velocity of the sound. Charles example is the classic which implies the observer is in a static medium in which the sound travels.

Did you get your mords wixed, or did I?

The speed of sound is certainly not constant. It does not move at the same velocity relative to every observer. Imagine a light shone from the Earth that passes a ship that’s at rest relative to the Earth. Then that same beam of later passes another ship that’s moving away from the Earth and the first ship at half the speed of light. It passes both ships at the same relative velocity. Sound behaves nothing like this. It couldn’t work if to types of waves with different velocities both behaved like this. The light passes passes both ships at the same velocity because their measurement of space and time aren't the same. If we look at the ship that's moving away from Earth at half the speed of light it has to mearsure the same amount of time and space as shorter than the other ship does so that light gets the boost it needs to pass them at the full speed of light, because the distance it has to traverse is less from the perspective of this from as viewed from the other frame. The ship that's at rest relative to Earth see the other ship as stretched across time and space because this ship measure the same distance as having a greater value. Now the bit where most people get lost is the fact the the situation is symetric. From the perspective of the ship that's moving away the Earth at half the speed of light it's the ship that's at rest relative to Earth that's stretched ocross time and space and so appears to be length extended and moving through time in slow motion because from this frame it's the other frame that measures the same distance as having a greater value. People think this is a contradiction but it really isn't, it just takes a bit of getting used to. It really hepls to think of it in four dimensions or imagine yourself outside of the system somehow so you're able to see it from the perspective of both frames and see that there's no contradiction, and it is in fact so beautiful and cool. It's what got me interested in physics.

It would really help the EU cause if there weren't so many of its supporters trying to falsify something truly amazing just because they don't understand it. Any relativity doubters have to come up with an different explanation of how light could have a the same velocity relative to all inertial observers. Good luck, there isn't one.

Charles example is the classic which implies the observer is in a static medium in which the sound travels.

Yes.

When your watching an object moving at half the speed of light relative to you you're seeing light moving away from them at half the speed of light.

And how was this demonstrated? By a thought experiment in the mind of Einstein?

No, it was first demonstrated by measuring light from the sun I think. Einsteins thought experiments where based on that information, not the other way round.

So you're talking about Earth-based measurements of the speed of light from the Sun. This means that the instrumentation was swimming in a static medium -- the Earth's atmosphere. So how was the effect of the medium ruled out?

It wasn't. The point is that relative the velocity of the source of the light has no influence on the relative velocity of the light coming from and is also unaffected by the relative velocity of the observer.

NO! No, no, no! The speed of sound is not constant.

It is as useless to fight against the interpretations of ignorance as to whip the fog.

GEORGE ELIOT, Middlemarc

Have you even heard of a sonic boom?

[Sain84]

I didn't claim they didn't use GR, I provided a link from NASA JPL that said they didn't use GR. Where's your link that says they do calculate relativistic adjustments to the spacecraft manoeuvres etc?

As for your proof, those papers are calculating theoretical epheremis of planets and are nothing to do with spacecraft manoeuver/trajectories. And how accurate are they? Here's what is says about Mars on the first page in the abstract;

Because of perturbation of the orbit of Mars by asteroids, frequent updates are needed to maintain the current accuracy into the future decade

Their predictive abilities with or without GR are garbage.

No you provided a link which said they "can" use Newtonian dynamics to put a spacecraft on Mars. They may have back in the days of Viking and Mars. It did not say they did not use GR.

I've already given you the link that say's they use relativistic adjustments.

Planetary ephemeris DE424 for Mars Science Laboratory early cruise navigation

There it is all you had to do was look.That does not say their predictive abilities are "rubbish", what it says is small errors grow over time. We know this, that's why there are so many versions. Again I never made any claims about the accuracy of this system.

[CharlesChandler]

Any relativity doubters have to come up with an different explanation of how light could have a the same velocity relative to all inertial observers. Good luck, there isn't one.

You're assuming the conclusion, and insisting that we do the same, or we must be wrong.

Can you demonstrate the proof that the speed of light is independent of the medium in which it is traveling?

Somewhere in here, something just has to be said. I'm asked to accept relativity. I ask about the methods by which the conclusions were made. I'm accused of being stupid, or even that I'm giving the EU a bad name, because I don't understand relativity. How am I to understand the conclusions except in the terms by which they were derived? I tend to think that many people who claim to "understand" relativity don't understand it at all. My reason for saying that is that when questioned, they cannot provide the derivations. Without those, there isn't any understanding. There is only blind faith. Similarly, if you tell me that in a right triangle, a^2 + b^2 = c^2, I'll ask you to show me the proof, which I'll inspect, and if it sounds reasonable, now I'll understand it too. If you cannot produce the proof, you don't "understand" it -- somebody told it to you, and you blindly accepted it. That might be beautiful, and it might be profound. But it isn't understanding. And I'd rather question, and be thought a fool, than to keep my mouth shut, blindly accepting what I'm told, and BE a fool!!!

So if you're going to insist that I accept relativity, first I'll have to understand it, and for that to happen, you have to show the derivations. So, how is the speed of light measured, and how was it determined that it is constant, regardless of the medium? I want to understand...

[A-wal]

I never said the that the speed of light is idependent of the medium though which it's moving. It isn't. That's not the point. The constistancy of the speed of light regarless of the relative velocity of both the sourse and of the observer has been varified many times. One of the ways is by measuring light coming from moons as they're moving away from and towards us. Guess what, the directly and velocity of the moon relative to us doesn't alter the speed of light that's coming it relative to us, imagine that. I'll make this as simple as I know how.

An object, let's say Earth, shines a light out into space, which pass a spaceship(A) that's at rest relative to the Earth. A second spaceship(B) leaves Earth and travels away from at half the speed of light. Now, let's look at the two frames of reference at the moment the second ship passes the first one at half the speed of light.

1. The ships pass each other at half the speed of light from the perspective of both ships.

2. The light beam passes the ship(A) that's at rest relative to Earth at the speed of light from the perspective of the ship(A) that's at rest relative to Earth.

3. The light beam passes the ship(B) that's moving away from Earth at the speed of light from the perspective of the ship(B) that's moving away from Earth.

4. The light beam passes the ship(B) that's moving away from Earth at half the speed of light from the perspective of the ship(A) that's at rest relative to Earth.

5. The light beam passes the ship(A) that's at rest relative to Earth at 1.5 times the speed of light from the perspective of the ship(B) that's moving away from Earth.

How do we reconcile all five? Velocity is nothing more than a measurement of distance over time. Let's say the ship(A) that's at rest relative to Earth measures the distance between the ships and Earth (remember we're using the moment they pass each other so they're both the same distance away from Earth) as one light year. It takes a year from the perspective of Earth and the ship(A) that's at rest relative to Earth for the beam to travel from Earth to pass the the ship at the speed of light, and so it sees the light beam pass the other ship at half the speed of light (because they're travelling in the same directio). Now we'll switch to the perspective of the ship(B) that's moving away from Earth at half the speed of light. In this frame of reference the other ship (and Earth) are moving away at half the speed of light and this ship is now stationary. It sees the same light beam passing itself at the speed of light and passing the other ship at 1.5 times the speed of light (because they're travelling in opposite directions).

For both frames of reference to be consistant with each other each of them has to measure the distance between Earth and the ships and/or the time it takes the light to reach them as shorterned. It's actually both because like I said, velocity is a measurememt of distance over time and any two objects are seperated in space by a one dimensional straight line, so we have one dimension of space and one dimension of time. If only one of them were shortend then it would be halved at half the speed of light to keep the speed of light constant, but both are shortened by the same amount so it's much lees than that to keep the distance over time the same. That's why the graph for this showing length contraction and time dilation as an object approaches the speed of light goes up slowly to start with and gradual increases at a faster rate as relative speed increases at a constant rate.

The ship that's at rest relative to the Earth sees the ship(B) that's moving away from Earth at half the speed of light as length extened and slowed through time so that the light that the ship(B) that's moving away from Earth at half the speed of light sees passing themselves at the speed of light passes the ship(B) that's moving away from Earth at half the speed of light at half the speed of light from the perspective of the ship(A) that's at rest relative to Earth. Similarly the ship(B) that's moving away from Earth at half the speed of light sees the ship(A) that's at rest relative to Earth as length extened and slowed through time so that the light that the ship that's at rest relative to the Earth sees passing themselves at the speed of light passes the ship that's at rest relative to the Earth at 1.5 times the speed of light from the perspective of the ship(B) that's moving away from Earth at half the speed of light.

Don't accuse me of not understanding something when I've shown countless and accurate examples of how it works. It's not stupid to not get how relativity works, it can seem a bit tripper. What's stupid is to assume it isn't true just because you don't get it. This is how it works regardless of your opinion on the matter because it doesn't give a crap whether you understand or not. If you're with me so far and you want me to I'll explain how acceleration works and how it resolves the twin paradox.

[CharlesChandler]

I never said the that the speed of light is idependent of the medium though which it's moving. It isn't. That's not the point. The constistancy of the speed of light regarless of the relative velocity of both the sourse and of the observer has been varified many times. One of the ways is by measuring light coming from moons as they're moving away from and towards us. Guess what, the directly and velocity of the moon relative to us doesn't alter the speed of light that's coming it relative to us, imagine that.

If two pebbles are tossed into a pond, and hit the surface at points equidistant from an observer, with one pebble traveling away from the observer, and the other traveling towards the observer, and both make waves in the pond, do the waves 1) reach the observer at the same time, 2) reach the observer at different times, depending on the relative velocity of the pebbles?

Try to make your explanation of this as simple as possible, so even stupid people can understand.

[A-wal]

This is getting very silly. Do you think you've just managed to refute the most profound and beautiful theory ever conceived with an analogy of ripples on a bloody pond? If two pebbles are tossed into a pond, and hit the surface at points equidistant from an observer, with the observer traveling towards one of the stones at half the speed of the waves, does the observer; 1, measure the waves coming from the stone they're heading towards passing them at the same velocity as the waves coming from the stone they're heading away from, or 2, measure the relative velocities of the waves coming from the stone they're heading towards and of the stone they're heading away from passing at different relative velocities, depending on the relative velocity of the observer?