Frame of Reference as Subject in Subjective Idealism

[Iggy]

If earth stays the same shape (as all but you agree,... no “morphing”, as Cap ‘n R agreed), it can not be both nearly spherical and very oblate. It must be one or the other.

If it were to be measured as having a diameter of 1000 miles through either the equator or the poles... (length contracted to 1/8th as per Cap 'n R's scenario) rather than the well known and validated 8000 or so miles, the former measurement would be in error.

Again, you can avoid mistakes in logic by changing the subject and/or predicate of your statement and seeing if the logic holds:

 

If earth stays the same velocity (no “accelerating”),

it can not be both moving slow and moving very fast

. It must be one or the other.

If it were to be measured as having a velocity of 65,000 miles per hour relative to the sun rather than the well known and validated zero miles per hour, the former measurement would be in error.

 

You know that the logic of the above statement does not hold because you have said,

 

velocity requires specificity as to "moving how fast relative to what."

It is a false dichotomy because "morph" and "accelerate" both clearly refer to changes in a single frame of reference but you then try to refute differences between frames. But, even if you don't know what a false dichotomy is or what a frame of reference is you still should be able to see that the logic is flawed.

 

Even after so much repetition, as above, the basic challenge has not been addressed.

If you ignore the refutation that doesn't mean it doesn't exist.

[owl]

Iggy:

change the property "shape" for the property "velocity":

 

Does reality require that it is measured or not? If not, then you grant that earth has a velocity independent of how it is observed/measured. You can not have it both ways, logically speaking.

You have already rejected the idea that earth has "a velocity" so you clearly have a false dichotomy

Please get a grip. You even quoted me as follows:

velocity requires specificity as to "moving how fast relative to what.

 

Shape, which is intrinsic to objects according to realism, and velocity, which is always relative to some reference point, as I have often belabored, are not logically interchangeable.

 

I have said that earth has one velocity relative to the sun and another relative to galactic center. I also went into detail about the velocity of a car relative to the road and another relative to the center of earth, etc. It is very difficult to communicate with someone with such a short memory, let alone such a weak grasp of logic.

You say:

It is a false dichotomy because "morph" and "accelerate" both clearly refer to changes in a single frame of reference...

... as if the rigid shape of a body (not changing with observational perspective) were logically interchangeable with velocity or change in velocity (acceleration), which, as above is relative to point of reference. (another repeat for clarity.)

 

If you ignore the refutation that doesn't mean it doesn't exist.

There has been no refutation of realism. Earth is not both very oblate and nearly spherical It is one or the other, and the unverified theory of large scale length contraction is not even close to a possible contender for an accurate description of earth's shape. It does not, in fact, have a diameter of 1000 miles, no matter how you look at it.

[Cap'n Refsmmat]

owl, do you agree that numerous experiments have shown the speed of light to be the same in all reference frames?

[owl]

Swansont:

You have flunked the class on relativity.

 

I am specifically critical of certain aspects of relativity, like spacetime curvature in GR and objects morphing out of shape, depending on how they are observed, as per the empirically unverified length contraction theory of SR.

You can flunk the whole Society for the Advanced Study of Spacetime for criticizing spacetime, if it makes you feel superior, but that doesn't make them (or me) wrong.

 

Your error (or at least one of them) is that "there are properties independent of observation and measurement" is not the same as "length is a property that is independent of observation and measurement." Several of us have pointed out that there are invariant properties. It's just that length is not one of them.

 

You state as a fact that length is not invariant based on the unverified hypothesis (for objects like earth and rods and distances like the AU) of length contraction. This is not science. It is conjecture based on an untested hypothesis. You seem totally blind to this fallacy.

Taking earth's diameter as a contracted length, you must contend that an earth with a 1000 mile diameter is equally as accurate as an earth with an 8000 mile diameter. This is total nonsense.

 

Objects have properties independent of observation and measurement

Length is a property

Therefore length is independent of observation and measurement

 

Surely you can identify this as faulty logic, right?

 

Substitute "earth's diameter" for "length" in the above. (It is equivalent in meaning.) Can you now identify the absurdity of your "logic?" Yes, earth's diameter is independent of observation and measurement.

It's less than 24 hours from your post, and since you still haven't figured out how to properly use the quote tags (that point to the user and post), I didn't get a notification that there was a pending response.

 

I know how to hit the framed "reply" button to get a stamped quote. I choose not to do so quite often for the result above. I can interject comments specific to each quoted point rather than having the whole post in one block to sort out.

I am not concerned about the convenience of your automatic notification.

[Cap'n Refsmmat]

I know how to hit the framed "reply" button to get a stamped quote. I choose not to do so quite often for the result above. I can interject comments specific to each quoted point rather than having the whole post in one block to sort out.

I am not concerned about the convenience of your automatic notification.

When you hit the "reply" button, you get something like this:

 

I know how to hit the framed "reply" button to get a stamped quote.

 

...where the quote tag has the username and timestamp in it. If you want to split up the post and interject comments, you just copy and paste that initial quote tag, like so:

 

I know how to hit the framed "reply" button to get a stamped quote.

 

(your message here)

 

I can interject comments specific to each quoted point rather than having the whole post in one block to sort out.

 

(more comments here)

 

Works just fine and lets people know they've been quoted.

[owl]

owl, do you agree that numerous experiments have shown the speed of light to be the same in all reference frames?

Yes.

I also see that light can not be pushed faster than 'C' by a high speed light source, if this is relevant to your point. And it doesn't go slower than 'C' relative to an observer if the source is speeding away.

Constant 'C' does not make solid objects or astronomical distances in the "real cosmos" shorter.

[Cap'n Refsmmat]

Hm. So the speed of light is the same in all reference frames. So suppose I have a flashlight. I turn it on. The photons travel ahead of me at the speed of light. If I measured their position compared to mine, I'd see that it increases at the speed of light.

 

So far, so good.

 

Now suppose someone is flying past me at half the speed of light. They're flying in the direction opposite to where the flashlight is pointed.

 

Now, do you agree that the person flying past very fast can measure the light's position compared to his, and see that it increases at the speed of light? That's what "the speed of light is the same in all reference frames" means, of course.

[Iggy]

Shape... and velocity... are not logically interchangeable.

Then you should agree -- this statement:

 

If earth stays the same shape (as all but you agree,... no “morphing”, as Cap ‘n R agreed), it can not be both nearly spherical and very oblate. It must be one or the other.

If it were to be measured as having a diameter of 1000 miles through either the equator or the poles... (length contracted to 1/8th as per Cap 'n R's scenario) rather than the well known and validated 8000 or so miles, the former measurement would be in error.

is not logical except that "shape" is special. What makes it true is that 'length' is unlike other properties. This is what you are saying, yes?

 

A personal attack immediately takes points off in a logic debate.

It is very difficult to communicate with someone with such a short memory, let alone such a weak grasp of logic.

I understand. I am not a university professor of logic, so I should defer to your authority on the subject. By the way, I was asked the other day to show why this is either a contradiction or not:

 

[latex]\lnot(A \lor \lnot(A \wedge B))[/latex]

 

I wasn't sure if the associative law was needed. Could you please help me out. Thank you.

Edited September 2, 2011 by Iggy

[moth]

Ontologically speaking, can nothing have properties?

Space has properties like permitivity, permeability, and zero point energy, how could it be nothing?

[owl]

Hm. So the speed of light is the same in all reference frames. So suppose I have a flashlight. I turn it on. The photons travel ahead of me at the speed of light. If I measured their position compared to mine, I'd see that it increases at the speed of light.

 

So far, so good.

 

Now suppose someone is flying past me at half the speed of light. They're flying in the direction opposite to where the flashlight is pointed.

 

Now, do you agree that the person flying past very fast can measure the light's position compared to his, and see that it increases at the speed of light? That's what "the speed of light is the same in all reference frames" means, of course.

I'll go a piece at a time.

Hm. So the speed of light is the same in all reference frames. So suppose I have a flashlight. I turn it on. The photons travel ahead of me at the speed of light. If I measured their position compared to mine, I'd see that it increases at the speed of light.

Yes.

Light doesn't "care" from which frame of reference it is observed. It goes from here to there at the constant rate we all know, no matter from where it is observed... (and that makes no intuitive sense, even though it is true from empirical observation.))

 

So "the photons" above are the front of the beam of light. So far OK?... and they are going at 186,000 mps away from the flashlight.

 

So far, so good.

I think so.

 

Now suppose someone is flying past me at half the speed of light. They're flying in the direction opposite to where the flashlight is pointed.

 

Now, do you agree that the person flying past very fast can measure the light's position compared to his, and see that it increases at the speed of light? That's what "the speed of light is the same in all reference frames" means, of course.

 

Not sure, because I don't know what you mean by " the light's position." The moving bodies ("someone and me") will see both see a light before they see the emitter of the light in each case.

 

Damn! another interruption which I can not ignore.

[Cap'n Refsmmat]

Yes.

Light doesn't "care" from which frame of reference it is observed. It goes from here to there at the constant rate we all know, no matter from where it is observed... (and that makes no intuitive sense, even though it is true from empirical observation.))

 

So "the photons" above are the front of the beam of light. So far OK?... and they are going at 186,000 mps away from the flashlight.

That's exactly what I was thinking, yes.

 

Not sure, because I don't know what you mean by " the light's position." The moving bodies ("someone and me") will see both see a light before they see the emitter of the light in each case.

Well, the light is traveling at 186,000 mps. So suppose we look at the front of the light pulse. If the observer has a way to measure where the front of that pulse is -- perhaps some kind of light detector attached to his spaceship -- he can measure its velocity.

 

So, for example, he might measure that after one second, the front edge of the light pulse is a certain distance away from the flashlight, and after another second it's much farther away, and so on.

 

Does that make more sense?

[swansont]

You state as a fact that length is not invariant based on the unverified hypothesis (for objects like earth and rods and distances like the AU) of length contraction. This is not science. It is conjecture based on an untested hypothesis. You seem totally blind to this fallacy.

Taking earth's diameter as a contracted length, you must contend that an earth with a 1000 mile diameter is equally as accurate as an earth with an 8000 mile diameter. This is total nonsense.

Do you really mean to imply that a theory is invalid if it is not specifically tested at a value that is in question? That one cannot extrapolate under any circumstances? Or test one part of a theory and gain confidence that the theory is correct? I don't know what you taught of the scientific method, but this doesn't reflect what happens in actual application by actual scientists.

 

You have disregarded the muon experiments, but really all you have done is dismiss them because they conflict with your philosophy. How does that fit? Does the scientific method allow for ideology to dictate truth? Does it permit you to cherry-pick evidence and accept only evidence you like, while dismissing evidence you don't like? Do you really contend that science has no predictive power?

 

Objects have properties independent of observation and measurement

Length is a property

Therefore length is independent of observation and measurement

 

Surely you can identify this as faulty logic, right?

Substitute "earth's diameter" for "length" in the above. (It is equivalent in meaning.) Can you now identify the absurdity of your "logic?" Yes, earth's diameter is independent of observation and measurement.

 

I can't help but notice that you did not actually answer my question. Some properties are independent of observation and measurement. That does not mean length is one of them. The burden of proof is upon you to show that it is. Argument from personal incredulity doesn't count.

 

I know how to hit the framed "reply" button to get a stamped quote. I choose not to do so quite often for the result above. I can interject comments specific to each quoted point rather than having the whole post in one block to sort out.

I am not concerned about the convenience of your automatic notification.

 

Then don't whine about not getting a response.

[owl]

First, I agree that 'C' is constant regardless of frame of reference from which it is observed, so maybe your argument is unnecessary.

Anyway, backing up a bit:

Cap 'n R:

Now suppose someone is flying past me at half the speed of light. They're flying in the direction opposite to where the flashlight is pointed.

Now, do you agree that the person flying past very fast can measure the light's position compared to his, and see that it increases at the speed of light?

 

Not sure what "increases." "It" meaning "light's position?" Your beam still approaches him at 'C' even though he is approaching you at half 'C.' Is this what you mean?

You continued:

Well, the light is traveling at 186,000 mps. So suppose we look at the front of the light pulse. If the observer has a way to measure where the front of that pulse is -- perhaps some kind of light detector attached to his spaceship -- he can measure its velocity.

So, for example, he might measure that after one second, the front edge of the light pulse is a certain distance away from the flashlight, and after another second it's much farther away, and so on.

Does that make more sense?

 

So, the apparent paradox is that, even though he measures light at 'C' velocity relative to your flashlight, it is also approaching him at 'C' velocity, even though he is approaching you at half 'C' velocity.

 

I still don't see how all of the above illustrates anything more than that 'C' is constant from all frames, to which I agreed up front.

 

Then the question is, "How does that fact make solid objects like metal meter rods and earth's diameter shorter?"

[swansont]

I still don't see how all of the above illustrates anything more than that 'C' is constant from all frames, to which I agreed up front.

 

Then the question is, "How does that fact make solid objects like metal meter rods and earth's diameter shorter?"

 

You could work through the math. It's a matter of how coordinate transformations work under that restriction.

http://en.wikipedia.org/wiki/Lorentz_transformation#From_physical_principles

 

IOW, once you have agreed that c is invariant, you really have no choice in the matter.

[Cap'n Refsmmat]

So, the apparent paradox is that, even though he measures light at 'C' velocity relative to your flashlight, it is also approaching him at 'C' velocity, even though he is approaching you at half 'C' velocity.

So from the perspective of the holder of the flashlight, after one second the light pulse has moved 186,000 miles away, since he has to observe it moving at c. That makes sense.

 

From the perspective of the observer, after one second the light has moved 186,000 miles and the flashlight 93,000 miles, since the observer is getting closer at half the speed of light. So the light is only 93,000 miles away from the flashlight, since the flashlight is "chasing" it.

 

The two distances are different. How does that work?

[owl]

Ontologically speaking, can nothing have properties?

Space has properties like permitivity, permeability, and zero point energy, how could it be nothing?

If space is the vacuum (no-thing-ness) in which things and forces exist, there is no need to make some-thing out of no-thing. My point is that things and forces exist in and travel through space ( permitivity, permeability) without making space into an expandable medium. Is emptiness/void a "property" or a lack of properties? Properties are usually assigned to things and forces.

 

Einstein said that if all energy and matter disappeared from the cosmos, that space and time would also disappear.

I can see that being true for time, because of my definition: event duration for physical processes. No physical processes, no time. But, with nothing left in the cosmos, it would leave empty space, no-thing-ness. Just an ontological distinction.

On small scale, take all objects out of a box and you have an empty box, empty space (ignoring air for this point.)

 

So from the perspective of the holder of the flashlight, after one second the light pulse has moved 186,000 miles away, since he has to observe it moving at c. That makes sense.

 

From the perspective of the observer, after one second the light has moved 186,000 miles and the flashlight 93,000 miles, since the observer is getting closer at half the speed of light. So the light is only 93,000 miles away from the flashlight, since the flashlight is "chasing" it.

 

The two distances are different. How does that work?

The first paragraph does make sense.

From the perspective of the observer, the flashlight beam has traveled toward him at 186,000 miles in a second and he has traveled toward the flashlight (or the latter toward him, same thing) 93,000 miles in the same second.

So the flashlight did not "push" the light beam to give it a cumulative speed of 279,000 miles per second, as if it were a bullet shot from a gun. No matter how fast the flashlight travels (under 'C'), or the observer approaches the flashlight, its beam can only go light's speed limit.

 

Now, put this scenario in "the real world." It is 93 million miles from sun to earth. That will not change while the above observer approaches your flashlight and its beam. Say you and your flashlight are in space close to earth and the observer is a few light seconds further out between earth and sun approaching you at half 'C.' It the second discussed above, he gets 93,000 miles closer to you, and your light beam gets 186,000 miles closer to him.

Meanwhile, no segment of the distance between earth an sun has shortened.

The Mystery of Constant Lightspeed (granted) does not make distances between objects in the real cosmos shorter... or solid meter rods, or earth's diameter.

[Cap'n Refsmmat]

The first paragraph does make sense.

From the perspective of the observer, the flashlight beam has traveled toward him at 186,000 miles in a second and he has traveled toward the flashlight (or the latter toward him, same thing) 93,000 miles in the same second.

So the flashlight did not "push" the light beam to give it a cumulative speed of 279,000 miles per second, as if it were a bullet shot from a gun. No matter how fast the flashlight travels (under 'C'), or the observer approaches the flashlight, its beam can only go light's speed limit.

I did not make the claim that anyone would observe the light beam to travel at 279,000 miles per second. I said that from the perspective of the flashlight, the light beam would travel away at 186,000 miles per second. (If the flashlight were attached to a 186,000 mile long yardstick, the light would reach the end in one second.) The distance between the flashlight and the light beam increases by 186,000 miles in a second. You agreed.

 

Now, from the perspective of the observer, the flashlight is approaching at 93,000 miles in a second and the light at 186,000 miles per second -- because he has to observe the light beam traveling at c. So in a second, the light gets 186,000 miles closer and the flashlight 93,000 miles closer. The distance between them increases 93,000 miles.

 

How does that work?

Edited September 2, 2011 by Cap'n Refsmmat
corrected numerical typo

[owl]

Me:

I still don't see how all of the above illustrates anything more than that 'C' is constant from all frames, to which I agreed up front.

 

Then the question is, "How does that fact make solid objects like metal meter rods and earth's diameter shorter?"

 

Swansont:

You could work through the math. It's a matter of how coordinate transformations work under that restrictions.

 

Thanks a lot, considering you know that I am not a mathematician. But the meaning of the concepts involved does not require math, as I've pointed out (and quoted from the Ross paper) many times.

 

Coordinates are the map, right, not the territory. Transformations convert the light speed measurements requiring mathematically ‘shorter distances’ (as required by the scenario above) into actual distance traveled through the ‘territory’ like between earth and sun above, right?

 

The alternative is that solid rods, earth’s diameter and earth-sun distance is like silly putty at the whim of those coordindinate systems, Right? If the cosmos is real, with or without our measurements (or humans, for that matter... see my thought experiment awhile back), then actual objects and distances are not dependent on how they are measured, Right?

 

I did not make the claim that anyone would observe the light beam to travel at 279,000 miles per second. I said that from the perspective of the flashlight, the light beam would travel away at 186,000 miles per second. (If the flashlight were attached to a 186,000 mile long yardstick, the light would reach the end in one second.) The distance between the flashlight and the light beam increases by 93,000 miles in a second. You agreed.

 

Now, from the perspective of the observer, the flashlight is approaching at 93,000 miles in a second and the light at 186,000 miles per second -- because he has to observe the light beam traveling at c. So in a second, the light gets 186,000 miles closer and the flashlight 93,000 miles closer. The distance between them increases 93,000 miles.

 

How does that work?

I was using the 279,000 mps as an illustration that lightspeed is not cumulative as beamed from a moving source or as seen from an approaching source... not attributed to you.

 

I really don’t know how the “great mystery” of constant ‘C’ works except to reiterate that light can not be pushed faster than ‘C.’

 

So, lets let the flashlight be moving at half lightspeed (for simplicity sake) and shining ahead in the direction of travel. As above, that does not boost the beam to 279,000 mps, so the flashlight must be moving through the tail end of the beam at half lightspeed even as the front of the beam continues at 186,000 mps relative to a distant target (at which the light is aimed.)

Does this make sense? Now I’ve got to go back and study the details of the Michelson/ Morely experiment and later verifications.

(Just completed a brief review. Created more questions about equipment and experimental design than answers, of course. More homework... ah, the adventure of science!)

 

What do you think of my reply to swansont above?

 

Ps: Oopse, just caught a glitch. You said:

The distance between the flashlight and the light beam increases by 93,000 miles in a second. You agreed.

I agreed that the distance between the photons at the front of the light beam and the flashlight increases at lightspeed, 186,000 mps.

The observer was approaching at half 'c', seeing the flashlight getting 93,000 miles closer every second.

Why don't we maximize complexity and have two light sources speeding toward each other at half 'c' (combined velocity, 'c') while shining their lights at each other. Who sees what when then?... or not!

Edited September 2, 2011 by owl

[Cap'n Refsmmat]

So, lets let the flashlight be moving at half lightspeed (for simplicity sake) and shining ahead in the direction of travel. As above, that does not boost the beam to 279,000 mps, so the flashlight must be moving through the tail end of the beam at half lightspeed even as the front of the beam continues at 186,000 mps relative to a distant target (at which the light is aimed.)

Does this make sense? Now I’ve got to go back and study the details of the Michelson/ Morely experiment and later verifications.

Yes, that makes perfect sense. So you'd agree that from the perspective of the observer, the light only goes 93,000 miles away from the flashlight each second, because the flashlight is moving through the tail end of the beam at half lightspeed?

 

The light is still moving at light speed relative to the observer, of course; I'm asking about how the observer would see its velocity compared to the flashlight.

[owl]

Yes, that makes perfect sense. So you'd agree that from the perspective of the observer, the light only goes 93,000 miles away from the flashlight each second, because the flashlight is moving through the tail end of the beam at half lightspeed?

 

The light is still moving at light speed relative to the observer, of course; I'm asking about how the observer would see its velocity compared to the flashlight.

All of this of course requires a high tolerance for ‘cognitive dissonance’, as we call it in psychology.

As a realist, this seems like a mind game full of trick questions. The base line reality check lies in the answer to the question:

 

“Can light have a constant velocity *AND* can solid objects’ shapes/lengths and distances between cosmic bodies remain un-affected by measurement, both true at once?”

 

This is the philosophical question. Now back to your brain teaser/ trick question. (In gaming mode here.)

The observer, any observer, will measure the speed of light he sees to be 186,000 mps regardless of how fast its source is going. That is SR.

But I think that ”how the observer would see its velocity compared to the flashlight” would depend on whether he had a fix on the whole beam from those far end photons at the front of the beam to those continually being emited from the flashlight. It is very complex, and no arbitrary frame of reference has a perspective on the whole situation, transcending the local points of view.

 

So, I will have to go with not accepting the limitations of the frames of reference employed in the thought experiment. As a realist, I try to stay out of that “box*” anyway. (* Everything depends on frame of reference.")

 

I did run the numbers on my little game mentioned in last post.

 

Why don't we maximize complexity and have two light sources speeding toward each other at half 'c' (combined velocity, 'c') while shining their lights at each other. Who sees what when then?

Here is what i came up with:

A and B are one AU apart (lets call it a nice round 8 light minutes.) They each flick on a laser aimed at the other as they miraculously take off toward each other, each traveling at one half lightspeed.

 

The game question is, how long before they see each other’s light and where are they along the one AU length?

 

Ans: Progressively, A and B would both reach the half way point (X) and run into each other in 8 min at half lightspeed, and their lights would each have gone the whole AU distance.

 

So to answer the question, a little “rewind” reveals that each traveler would have traveled for 4 minutes to reach the quarter AU mark (from their respective starting points) while each of their laser lights traveled to the half way point and met in the same time. (Not there yet to see the other’s light.)

Six minutes of light travel from either laser will reach the 3/4 AU mark away from each starting point. (No push from either traveler's velocity.). The same six minutes brings each traveler to a point 3/8ths AU from their starting points, an 1/8th past other's 3/4 out mark, having just past the point of seeing ther other's light. I'll leave the precise math to hair splitters who love the math.

 

A long way around to this point:

 

Neither the AU nor any part of it “contracted” during the operation. And the creator of the scenario gets to see the whole thing from transcendental perspective, not limited to either A or B’s frame of reference.

[moth]

Here is what i came up with:

A and B are one AU apart (lets call it a nice round 8 light minutes.) They each flick on a laser aimed at the other as they miraculously take off toward each other, each traveling at one half lightspeed.

 

The game question is, how long before they see each other’s light and where are they along the one AU length?

 

Forget one of the ships for a second, it's just the same problem going the other direction.

Replace one ship with a light source that turns on exactly when the remaining ship is traveling .5c and 8 light minutes away heading directly towards the light source.

For every unit of distance the ship moves toward the light source the light from the source moves 2 units towards the ship.

The distance from the ship to the light decreases by 3 units for every unit of distance the ship travels - so the ship moves 1/3 of the way and light travels 2/3 of the distance. They meet after the ship travels 8/3 light minutes.

But we all agree the speed of light is constant from any frame of reference and in this scenario the closing distance decreases by 1.5 times the speed of light and the ship "sees" the light going too fast.

some sort of correction is needed to keep lightspeed a constant.

 

but then i'm just a mutt with a screw loose so i could be wrong ;-)

[swansont]

Thanks a lot, considering you know that I am not a mathematician. But the meaning of the concepts involved does not require math, as I've pointed out (and quoted from the Ross paper) many times.

 

Neither am I. It's only algebra, though. Quoting Ross is all well and good, but you assume that means something. What if he's wrong? Math is the language of physics. Concepts and math are not as orthogonal as Ross (and you) are contending — there is some truth to the statement, but the two cannot really be separated; there's very little physics that can be conveyed without math. (Keep in mind that math is also a concept — it's more than just equations). It's not coincidence that people who lack math skills end up foundering when trying to understand physics concepts. There are plenty of examples right here on SFN.

 

Coordinates are the map, right, not the territory. Transformations convert the light speed measurements requiring mathematically ‘shorter distances’ (as required by the scenario above) into actual distance traveled through the ‘territory’ like between earth and sun above, right?

 

The alternative is that solid rods, earth’s diameter and earth-sun distance is like silly putty at the whim of those coordindinate systems, Right? If the cosmos is real, with or without our measurements (or humans, for that matter... see my thought experiment awhile back), then actual objects and distances are not dependent on how they are measured, Right?

 

No, wrong. That's your philosophy and I don't agree.

 

If we can't trust measurements, then you don't really know the earth is a sphere. It could really (inherently) be a polyhedron or some odd shape. Or maybe it really is very oblate and the sphere is an illusion. How can you tell?

[Cap'n Refsmmat]

This is the philosophical question. Now back to your brain teaser/ trick question. (In gaming mode here.)

The observer, any observer, will measure the speed of light he sees to be 186,000 mps regardless of how fast its source is going. That is SR.

But I think that ”how the observer would see its velocity compared to the flashlight” would depend on whether he had a fix on the whole beam from those far end photons at the front of the beam to those continually being emited from the flashlight. It is very complex, and no arbitrary frame of reference has a perspective on the whole situation, transcending the local points of view.

 

So, I will have to go with not accepting the limitations of the frames of reference employed in the thought experiment. As a realist, I try to stay out of that “box*” anyway. (* Everything depends on frame of reference.")

Hang on a second. This is a thought experiment. I can have whatever detectors and measurement devices I need to get a perspective on the whole situation. It's not very hard: strap some photodetectors to the front of the flashlight at various distances, and strap other photodetectors to the observer.

 

But that's not very relevant, either. It doesn't matter how it's measured: light will move at c, so all I have to know is the velocity of the flashlight and the observer in each reference frame. We know by experiment how fast the light will be moving.

 

Maybe I can make a diagram to help visualize this problem, because switching between observer and flashlight reference frames can be confusing.

 

Here's the picture from the flashlight's perspective:

 

 

Time is on the vertical axis, position on the horizontal. As time progresses (goes upward), the flashlight stays in the same place and the observer moves closer. The light pulse moves to the right until it reaches the observer. The observer moves closer to the flashlight at a high speed.

 

Does that diagram make sense, or do I need to clarify things?

 

I apologize for dragging out the point, but I need to make it crystal clear.

[Iggy]

Ans: Progressively, A and B would both reach the half way point (X) and run into each other in 8 min at half lightspeed, and their lights would each have gone the whole AU distance.

The ships are approaching each other and light goes the whole distance?

[owl]

Hang on a second. This is a thought experiment. I can have whatever detectors and measurement devices I need to get a perspective on the whole situation. It's not very hard: strap some photodetectors to the front of the flashlight at various distances, and strap other photodetectors to the observer.

 

But that's not very relevant, either. It doesn't matter how it's measured: light will move at c, so all I have to know is the velocity of the flashlight and the observer in each reference frame. We know by experiment how fast the light will be moving.

 

Maybe I can make a diagram to help visualize this problem, because switching between observer and flashlight reference frames can be confusing.

 

Here's the picture from the flashlight's perspective:

 

 

Time is on the vertical axis, position on the horizontal. As time progresses (goes upward), the flashlight stays in the same place and the observer moves closer. The light pulse moves to the right until it reaches the observer. The observer moves closer to the flashlight at a high speed.

 

Does that diagram make sense, or do I need to clarify things?

 

I apologize for dragging out the point, but I need to make it crystal clear.

Yes, it's crystal clear. The observer sees the light after about 8 units of time have passed and he has traveled a little over 8 units of distance.

I agree that: "It doesn't matter how it's measured: light will move at c,..."

But your point about length contraction would be more clear to me if you abandoned the graph and laid it out, as I suggested, "in the real world", say between sun and earth for reference points.

 

That was my intent with the laser-jousters scenario above, and the point was that neither the whole AU distance nor any part of it contracted during the journeyers' six minutes of approaching each other at half lightspeed while firing lasers at each other.

 

To my exchange with swansont;

Me:

If the cosmos is real, with or without our measurements (or humans, for that matter... see my thought experiment awhile back), then actual objects and distances are not dependent on how they are measured, Right?

 

Swansont;

No, wrong. That's your philosophy and I don't agree.

 

If we can't trust measurements, then you don't really know the earth is a sphere. It could really (inherently) be a polyhedron or some odd shape. Or maybe it really is very oblate and the sphere is an illusion. How can you tell?

 

The cosmos is not real without our measurements? That is a form of idealism, with "frame of reference" substituted for "subjective" in "subjective idealism."

This philosophy goes all the way back to the absurd (cliche') claim of idealism that a tree falling in the forest doesn't make a sound if it is not heard. Iow, the world has no reality of its own but rather reality is totally dependent on perception and measurement.

 

I have repeatedly argued that we can trust measurements at rest with what is measured "hands down" over all those theoretical, extreme, near-light-speed frames of reference upon which the unverified theory of macro length contraction depends.

The former gives the 'earth science' description of earth, while the latter gives us an earth of a 1000 mile or so diameter, which is, by all accounts (save the above extreme) wrong.

 

Moth:

Forget one of the ships for a second, it's just the same problem going the other direction.

 

Hey! Like Cap 'n R said about his, this is my thought experiment. You are making it way too complicated. Please reconsider my closing "point."

To Iggy's question;

Me:

Ans: Progressively, A and B would both reach the half way point (X) and run into each other in 8 min at half lightspeed, and their lights would each have gone the whole AU distance.

Iggy:

The ships are approaching each other and light goes the whole distance?

Yes, in this phase, before the "rewind." They both began firing lasers and took off toward each other at the same time. Their lasers would have gone the whole 8 light minute AU distance (past each other) while the travelers, at half lightspeed went half the distance. I just started simple before backing up to the shorter segments (fractions of the AU) to see when they would have seen each others' lights.

 

Note: I'm gone for the weekend again.

Edited September 3, 2011 by owl