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Who's familiar with the conversion? - "In 15 years' ship-time they could reach Andromeda

 
 
maxdancona
 
  3  
Reply Tue 17 Nov, 2015 06:40 pm
@layman,
You are missing the point Layman. The train example works just fine with open windows... the reason we suggest closing the windows in the thought experiment is that people who have grown up on the Earth are programmed to believe that the Earth is stationary.

By looking at fence posts to determine your motion you are assuming that the Earth is stationary. The fence posts only give you your motion from the Earth's frame of reference. If you can prove, by experiment that the Earth is stationary... then comparing your motion to the fence posts is a valid way to find absolute truth.

You haven't proposed an experiment to show this though.

The two spaceship example is a simpler example to discuss. How can person A in the spaceship example prove that he is actually the one who is motionless? I have given you the challenge and I will repeat it again.

If you provide me an experiment that can prove that someone is truly motionless (that can't be replicated by someone moving relative to them) then you win the argument. That is all you have to do.

To make a scientific claim, you have to provide an experiment to test it.

0 Replies
 
layman
 
  0  
Reply Tue 17 Nov, 2015 06:57 pm
@maxdancona,
Quote:
Your challenge is to come up with such an experiment that can tell us that one person is absolutely correct, and another is wrong in their claim that they are "truly" stationary.
That's not even relevant, Max. As Newton has proved, you don't have to know a damn thing about "absolute" motion in order to do physics.

YOUR example of "Galilean relativity" was comprised of JUST TWO objects. YOUR claim was that neither could know, AS BETWEEN THE TWO OF THEM, which one was moving.

Yet you are ALSO the one to say this, aren't you?:

Quote:
I just want to point out that the basic point that someone in a spaceship travelling at near C will experience less time going to the nearest star than someone on Earth watching is not theoretical.


That's correct. And you KNOW it is the spaceship moving. That's why it experiences less time PER THE DICTATES OF THE LORENTZ TRANSFORMATION. That's also what the "twin paradox" tells you.

The GPS tells us that, relative to the earth, the satellites, not the earth, are moving. It does that without purporting to know, and without having to know, the "absolute speed" of either.

Using the CMB as a "cosmic rest frame," we now know that the entire solar system (indeed the entire galaxy) is moving at the rate of about 2 million mph toward the "great attractor." That doesn't affect the relationship between the earth and the satellites one bit, though.

For the last time, the question of ABSOLUTE MOTION is totally irrelevant to the issues we've been discussing. Those are questions of relative motion, not absolute motion.

THIS is false:

Quote:
In order to truly prove that you are right you need to propose an experiment that one person can use to prove that they are truly stationary.


Being "truly stationary," or not, is irrelevant to question of who is moving relative to the other.

Get it yet? (I'm sure the answer is "no," but I pose the rhetorical question to you anyway).

maxdancona
 
  2  
Reply Tue 17 Nov, 2015 08:16 pm
@layman,
Quote:
Being "truly stationary," or not, is irrelevant to question of who is moving relative to the other.


No I don't get it. You might want to explain what you mean here. It doesn't make sense to me.

It seems to me that if Person A is moving relative to Person B, then Person B is also moving relative to Person A.

Let me suggest an experiment to prove this point.

We could easily get two cars, car A and car B and drive them so that a passenger in Car A says that car B is moving relative to Car A. By increasing the speed of Car A, we could get in a state where Car B is moving backwards relative to car A we could then stop accelerating so that car A is in constant speed for the experiment. (Car B would remain at constant speed throughout the experiment).

I predict that in this state, a passenger in car B would observe car A moving forward relative to car B.

If my prediction is correct, this will prove my point that both cars are moving relative to each other.



layman
 
  0  
Reply Tue 17 Nov, 2015 08:44 pm
@maxdancona,
Quote:
No I don't get it. You might want to explain what you mean here. It doesn't make sense to me.


I have explained it repeatedly. If you can't see the difference between relative motion between two objects and the absolute speed, through "space" of any one object by now, then I guess you never will.

Quote:
It seems to me that if Person A is moving relative to Person B, then Person B is also moving relative to Person A.


You mean it can be viewed that way? So what? I'm talking about what's happening physically, not what some subject wants to "think."

If I mash down on the gas pedal of a dragster at a raceway, I can choose to "see" myself as motionless and everyone in crowd as rushing past me. So what? If we are ever to believe any part of what we think we know about physics, then we KNOW that's not what's happening, however delusional I might be.

maxdancona
 
  3  
Reply Tue 17 Nov, 2015 08:48 pm
@layman,
You seem to be changing your position Layman. At first you were arguing against relativity... now you are saying that "the question of ABSOLUTE MOTION is totally irrelevant to the issues we've been discussing. Those are questions of relative motion, not absolute motion."

If you now are saying that only relative motion matters (not absolute motion) then I think that now you are agreeing with me (or maybe I misunderstood what you were saying all along).

All motion is relative motion.

The CMB rest frame is very interesting. For those that don't know... if from our frame of reference (as people on Earth) we look at the background radiation we notice that the radiation is redshifted on one side of us and blueshifted on the other side. This is because we are moving away from the radiation "source" on one side and toward it on the other.

This is a pretty straightforward experiment to do if you have the equipment to measure the background radiation in every direction.

Of course there is a frame of refererence that is at rest relative to the CMB... and cosmologists tell us that this was the original frame of reference of the Big Bang.

Sure it is as good a frame of reference, and as valid, as any other. If you are studying cosmology it is an important one. But since all of the laws of physics work the same in our frame of reference (and any other), there are generally simpler frames of reference to use.
0 Replies
 
maxdancona
 
  3  
Reply Tue 17 Nov, 2015 08:50 pm
@layman,
Quote:
If we are ever to believe any part of what we think we know about physics, then we KNOW that's not what's happening, however delusional I might be.


No, we don't know anything in science until we have defined an experiment to show that it is correct.

What experiment can you do that proves that the dragster isn't motionless at any instant of time? The obvious experiment is based on the assumption that the track, and the Earth it is attached to, are motionless. I don't think this is a valid assumption to make.

If you are going to make a claim and call it "science", then please propose an experiment that would back it up. If you can't do that, then whatever you "KNOW" isn't science.


layman
 
  0  
Reply Tue 17 Nov, 2015 09:02 pm
@maxdancona,
Quote:
What experiment can you do that proves that the dragster isn't motionless at any instant of time? The obvious experiment is based on the assumption that the track, and the Earth it is attached to, are motionless. I don't think this is a valid assumption to make.


Oh, that's a tough one. How about the "experiment" of NOT mashing down on the pedal. How about the experiment of taking all the gas out of the tank first? How about calculating the amount of energy it would take to accelerate the entire crowd to 200 mph, and see if the gas in the car is enough to do that, because, maybe mashing down on the pedal is what causes the crowd to move, eh? Physics couldn't tell us anything about that, now, could it? No one knew anything about physics when the internal combustion engine which motivates the dragster was built, eh? Physics tells us NOTHING. Only the mind of a delusional dragster driver can tell us the TRUTH.
maxdancona
 
  3  
Reply Tue 17 Nov, 2015 09:06 pm
@layman,
I also don't know how you got your CMB numbers. The speed of our Sun in the CMB frame is 368 km/s which by my calculations is about 823,000 miles per hour.

Are you going to use this frame of reference in your dragster example? I propose there are much simpler frames of reference to use.

0 Replies
 
maxdancona
 
  3  
Reply Tue 17 Nov, 2015 09:10 pm
@layman,
In the CMB rest frame you proposed the crowd is certainly already moving (along with the earth and the track and everything else you have ever seen)... and the car would have accelerate hundreds of thousands of miles per hour in the opposite direction (relative to the track) to get to the point that it is motionless in the CMB frame of reference.

This is getting silly again.... sometimes you go with the Earth frame, sometimes with the CMB frame, and yet you can't accept the basic precept of special relativity that you seem to be relying on to make whatever argument you are trying to make.

I will let Oristar tell me what part of this discussion interests him.
layman
 
  0  
Reply Tue 17 Nov, 2015 09:24 pm
@maxdancona,
Quote:
In the CMB rest frame you proposed the crowd is certainly already moving (along with the earth and the track and everything else you have ever seen)... and the car would have accelerate hundreds of thousands of mile per hour in the opposite direction (relative to the track) to get to the point that it is motionless in the CMB frame of reference.


Right, and I have already said that. And I have already said that it is irrelevant.

Back to the car and the crowd. The "assumption" is NOT that the earth is motionless. Nor is it that the car, before it hits the gas is "motionless." The plain, empirical FACT is simply that, at that point in time, NEITHER is moving with respect to (relative to) the other.

Then things suddenly change. The driver mashes down on the pedal. Now there is relative motion between the two that didn't exist before (even though they were all orbiting the sun, revolving on the earth's axis, rotating around the galactic barycenter, travelling through the CMB, etc., the moment before). Something has changed. NOW they are moving relative to each other. Is there any way to known which one (or perhaps both) started a "new" movement for this to occur? Hmmmm?
maxdancona
 
  4  
Reply Tue 17 Nov, 2015 09:40 pm
@layman,
Quote:
NOW they are moving relative to each other. Is there any way to known which one (or perhaps both) started a "new" movement for this to occur? Hmmmm?


Of course. This is just Newton's laws. Students in any good high school Physics course do exactly this.

Newton's laws can accurately predict the location and velocity of the car in any inertial frame of reference (given torque over time). These predictions can be made and then confirmed with measurement in any inertial frame of reference. If you took a high school physics class, you would have done exactly that.

This is another example of science being based on the ability to make predictions and confirm them with experiment.

There is a good reason physicists are hired to work (and paid good money) in drag racing.
layman
 
  0  
Reply Tue 17 Nov, 2015 10:12 pm
@maxdancona,
I asked:

Quote:
Is there any way to known which one (or perhaps both) started a "new" movement for this to occur?


You answered:
Quote:
Of course. This is just Newton's laws. Students in any good high school Physics course do exactly this.


Thank you for the answer.

So, if the dragster driver insisted that he never moved an inch relative to the crowd, but instead the crowd just suddenly started accelerating past him, you would say the dragster was WRONG, right?
maxdancona
 
  4  
Reply Tue 17 Nov, 2015 10:22 pm
@layman,
In Galilean relativity, we are restricted to inertial frames. In this example there is no inertial frame where the crowd accelerates.

The principle is that the laws of physics work in any inertial frames. Let me propose three different inertial frames.

1) The Earth frame, where the crowd is motionless, and the car starts out as motionless and ends up moving at 60mph (for the sake of example) with constant acceleration over 3 seconds.

2) The CMB rest frame you proposed where the crowd is moving at 823,000 miles per hour and the car starts at 823,000 miles per hour and ends up moving at 823,060 mile per hour. (This frame of reference of course depends on the orientation on earth, and the rotation of the earth and the current position of earth in its orbit around the sun... but I think we could get close).

3) The "end of acceleration" frame of reference where the crowd is moving at 60 miles per hour (throughout the example), the car starts out moving at 60 miles per hour (along with the crowd) and ends up motionless.

All three of these are inertial frames of reference. Newton's laws work perfectly to predict the location and speed of the care (given torque/acceleration) at any time in the example. In each of these example the crowds does not accelerate and the car has a constant acceleration of 20 miles per hour per second.

There is no experiment you can suggest that can show that one of these frames of reference is more valid than the other (since we can make accurate predictions with any one of them).

If you dispute this... then please provide an experiment that would favor one over the other.
layman
 
  0  
Reply Tue 17 Nov, 2015 10:32 pm
@maxdancona,
I don't understand your third explanation at all, but you end up saying this:

Quote:
All three of these are inertial frames of reference. In each of these example the crowds does not accelerate and the car has a constant acceleration of 20 miles per hour per second.


So, then, you would agree, I take it, that no matter what frame of reference is used, if the dragster claimed that HE did not accelerate, but that the crowd did, then he would be WRONG, right?


maxdancona
 
  3  
Reply Tue 17 Nov, 2015 10:35 pm
@layman,
That would be true for any inertial frame of reference in this particular problem.

You should try to understand my third example. It is rather illustrative. If it would help... imagine that the drag race, crowd and all, were on a train... and that the train were going West at 60 mph (relative to the Earth) and the racecar was starting at the speed of the train (60mph west) and then accelerating (to the East) until it was motionless relative to the Earth.

If you can imagine that... now just get rid of the train... and look at the problem with the Earth going West at 60mph.

In any of these cases, the same laws of physics apply.
layman
 
  0  
Reply Tue 17 Nov, 2015 10:41 pm
@maxdancona,

Quote:
You should try to understand my third example. It is rather illustrative. If it would help... imagine that the drag race, crowd and all, were on a train... and that the train were going West at 60 mph (relative to the Earth) and the racecar was starting at the speed of the train (60mph west) and then accelerating (to the East) until it was motionless relative to the Earth.

If you can imagine that... now just get rid of the train... and look at the problem with the Earth going West at 60mph


OK, but that wasn't the question, was it? The question was, as between the crowd and the car, which one initiated the NEW relative movement which suddenly occurred. The answer to that question would be the same, right?

0 Replies
 
layman
 
  0  
Reply Wed 18 Nov, 2015 12:00 am
@maxdancona,
Quote:
That would be true for any inertial frame of reference in this particular problem.


Your reference is a little vague here.

I understand you to be saying that, in ANY inertial frame of reference, the dragster driver would be wrong if he claimed it was not him, but rather the crowd, that was moving and thereby causing the appearance of relative motion between them. Am I understanding you right?
layman
 
  0  
Reply Wed 18 Nov, 2015 12:16 am
@maxdancona,
Quote:
There is no experiment you can suggest that can show that one of these frames of reference is more valid than the other (since we can make accurate predictions with any one of them).


No, I'm not saying that at all. What I'm saying is that this frame:

Quote:
The Earth frame, where the crowd is motionless, and the car starts out as motionless and ends up moving at 60mph (for the sake of example) with constant acceleration over 3 seconds.


is more valid, for the purpose of determining who is "really moving" as between the car and the crowd than any "frame" which says the car is not moving.

What frame(s) is(are) more valid than others for other purposes is a separate question.

Remember, this all started with you suggesting that the driver's "frame" was just as valid for that purpose. Or, before that, when you began "instructing" Oris, that there was no way to tell which of two frames could be the one moving (relative to the other).

You quoted me as saying:

Quote:
If we are ever to believe any part of what we think we know about physics, then we KNOW that's not what's happening, however delusional I might be
.

The reference to "that's not what's happening" was to the driver's claim that HE was not moving. In response, you said:

Quote:
No... The obvious experiment is based on the assumption that the track, and the Earth it is attached to, are motionless. I don't think this is a valid assumption to make.


I'm saying it IS a valid assumption to make when asking which is the one moving. For that purpose, the earth's frame is the "correct" frame.

You appear to agree (now).



layman
 
  0  
Reply Wed 18 Nov, 2015 12:50 am
@layman,
Quote:
I'm saying it IS a valid assumption to make when asking which is the one moving. For that purpose, the earth's frame is the "correct" frame.


Any frame which "claims" that the earth is moving, vis a vis the car, would have to demonstrate a "force" that accelerates the entire crowd (or more broadly, the entire earth--i.e. something that's makes the earth start to "turn backwards"). That aint there. Unless there's some "magic" going on, maybe.

On the other hand, it's easy to see and understand the forces which accelerate the car so that IT begins moving relative to the crowd rather than vice versa.

Any claim by the driver of the car to the contrary would simply be wrong.
maxdancona
 
  2  
Reply Wed 18 Nov, 2015 05:40 am
@layman,
Quote:
I understand you to be saying that, in ANY inertial frame of reference, the dragster driver would be wrong if he claimed it was not him, but rather the crowd, that was moving and thereby causing the appearance of relative motion between them. Am I understanding you right?


You are using the terms "caused the appearance of relative motion" and "caused initial motion" which is a little strange. I kind of get what you are getting at... but if you want to use this idea you need to define an experiment that will define which one is correct. If you can define an experiment with which we can determine which object "caused the appearance of relative motion"... then we can use this term in a scientific discussion.

Newton did exactly that. He talked about force, impulse and momentum... and he defined each in a way that it could be measured in an experiment.

If you are making claims that can't be unambiguously tested by experiment, then they aren't scientific claims.
 

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