# If there is no end to the space

## Recommended Posts

And if you look up the distance to Andromeda in lightyears, instead of finding something in the neighborhood of 2.5 million, we should get the fine print version... "depending on observational frame of reference."

I can't assure that every (or any) publication would insert that fine print, but it is true.

By some magic, if a traveler is going there at just under the speed of light, somehow he can make the journey in about 70.7 times less that light going at full speed.

I think you are mixing frames.

The rocket takes just over 2.5 million years to reach the Andromeda galaxy as measured by us here on earth. Light takes 2.5 million years to reach the Andromeda galaxy as measured by us here on earth.

They spend more time traveling between galaxies (as measured by us) than it takes light.

The rocket takes just over 35,354.5 years to reach the Andromeda galaxy as measured by those on the rocket. Light takes 35,354.5 years to reach the Andromeda galaxy as measured by the people on the rocket.

It takes them (as measured by them) longer to reach the galaxy than it takes light (as measured by them) to travel the distance.

In both frames of reference light spends less time traveling the distance than the rocket does.

When you say "by some magic" I think you mean that it is paradoxical. That is not the case.

Maybe an explanation is just too much to expect....

Nothing that I'm saying is beyond an explanation. Time and distance must be relative for the speed of light to be fixed between observers of differing velocity. How else could you explain that the velocity of light is constant? How could the person on the rocket and the person on earth agree about the distance between galaxies and the time spent traveling and measure the speed of the same ray of light and say "it is receding from me at one light year per year"?

The first step is understanding why that is impossible.

Edited by Iggy

• Replies 263
• Created

#### Posted Images

You don't have to choose one. They are all real. Relative to the person on the bus, it has no kinetic energy. Relative to the person on the street, it has kinetic energy. Kinetic energy is real even though it is relative to velocity. Frame dependence does not imply non-realness. If frame dependence does not imply non-realness then that is not a reason to reject length contraction as non-real or "only an optical distortion".

You have to be careful or you will get into an endless and fruitless philosophical debate over what is meant by "real".

Physics is in general invariant, even when described by coordinate quantities that are not invariant,

Take your bus collision, and look at the Newtonian physics. Yes, the absolute and momentum are coordinate-dependent. But momentum will be conserved in any inertial frame. And the net loss of kinetic energy in the collision is independent of the inertial reference frame (do the calculation, which requires conservation of momentum and see for yourself). In particular, if the collision is elastic it is elastic in all inertial frames. In any frame you will be hit by the bus. In any frame you will be dead.

Similarly in relativity, it is the invariants that describe physical events. The real lesson of relativity is that one deals with spacetime, not space and time. What is invariant is the Minkowski norm of a 4-vector. Conventional "length" and "time" are coordinate dependent, not invariant. They are "real", but they are not fundamental. Most of the confusion and so-called "paradoxes" of relativity come from thinking about coordinate dependent quantities as though they were invariant. The Lorentz transformations are important precisely because they preserve the Minkowski inner product and hence the geometry of flat spacetime.

Length "contraction" is real, but it is also nothing more and nothing less than a relationship between two separate coordinate systems. Two distinct observers simply have different rulers, and different clocks. But they see the same physical events. Physical events are invariant.

##### Share on other sites

You have to be careful or you will get into an endless and fruitless philosophical debate over what is meant by "real".

(...) Length "contraction" is real, but it is also nothing more and nothing less than a relationship between two separate coordinate systems. Two distinct observers simply have different rulers, and different clocks. But they see the same physical events. Physical events are invariant.

First of all, this is not a philosophical debate, although it may be fruitless and endless.

How do you conciliate that "Two distinct observers simply have different rulers, and different clocks" (in which I agree)and that "Length "contraction" is real"? (in which I disagree). What is your argument that will me change my mind?

When you say "they see the same physical event" my question is: what is this event? Can you make an invariant description of it? (since you wrote that "Physical events are invariant")

##### Share on other sites

You have to be careful or you will get into an endless and fruitless philosophical debate over what is meant by "real".

Indeed.

Conventional "length" and "time" are coordinate dependent, not invariant.

That is at least one issue. Owl is saying that length is invariant.

Physical events are invariant.

I'm not sure what you mean there. I consider anything I can measure both physical and real. Length and time are physical, but not invariant. My point to Michel is that their relative nature does not make them non-physical or unreal any more than kinetic energy's relative nature in classical mechanics makes it unreal.

Edited by Iggy
##### Share on other sites

First of all, this is not a philosophical debate, although it may be fruitless and endless.

My point is not philosophical. I am talking rigorous special relativity. If you let the debate become philosophical then I can pretty much guarantee that it will be fruitless and endless.

How do you conciliate that "Two distinct observers simply have different rulers, and different clocks" (in which I agree)and that "Length "contraction" is real"? (in which I disagree). What is your argument that will me change my mind?

I have no idea what it takes to change your mind. Try reading a book on relativity, perhaps An Introduction to Special relativity by Wolfgang Rindler.

Rulers and clocks are associated with a particular choice of spacetime coordinates. The very fact that different observers see different coordinate times and different coordinate lengths shows that their clocks and rulers are different (record different values)

That length contraction and time dilation are real are demonstrated by the decay times of relativistic particles. One of the early pieces of evidence for the validity of special relativity is the deep penetration into the Earth's atmosphere by muons formed by cosmic ray collisions high in the atmosphere. I think that meets the criteria for a "real" effect.

When you say "they see the same physical event" my question is: what is this event? Can you make an invariant description of it? (since you wrote that "Physical events are invariant")

A physical event in rigorous relativity is a point in spacetime. Alternately and more loosely a physical event could be a collision, falling into a hole, etc -- something that "happens" at a point in spacetime..

##### Share on other sites

Physical events are invariant.

I'm not sure what you mean there...

After reading it a second time I think I know what you mean. The distance between events in space time (the space time interval) is invariant. If that is what you mean then I agree.

##### Share on other sites

It seems my fundamental inquiry is still not clear. Here it is again.

My most avid interest in science is the philosophy by which relativity claims that 'frame of

reference' (FOR) is the ultimate criterion for what is real and true of the cosmos.

Accordingly, our clocking time becomes the operational definition of what time IS. (No

philosophical consideration of whether time is an artifact of measurement or an entity with

an independent existence all by itself. Likewise, "space,"... since the conceptual leap beyond

common sense Euclidean space... now has 'curvature' and expands, etc., as if it were, like

time, an actual entity.

So, as a philosopher of science, I say that relativity is based on a form of subjective

idealism... like that of Berkely and Hume but for the 'subject' being the abstract

"observer" or frame of reference.

Funny that "FOR" also applies to the common thought experiments that relativity theorists

love... i.e., "for observer A vs for observer B. there is no "for" an objective perspective

transcending local viewpoints... tho we can easily imagine (as a "thought experiment" thinking outside the frames) that cosmos exists independently of local observational perspectives.

In a nutshell, I am asking, as above...

does relativity deny a cosmos independent of observational frames of reference?

Iggy:

"In special relativity, the speed of light is constant. The distance between the two galaxies is not constant."

I take this to assert that there is no "actual, objective distance" between here and Andromeda... nor between here and the sun, because "it all depends on frame of reference."

Just to be absolutely clear, is this what you and relativity are claiming? If so are you and all relativity theorists philosophically persuaded to the belief in subjective idealism. A direct answer would be very much appreciated.

edited to try cleaning up my notepad paste job, and one correction.

Edited by owl
##### Share on other sites

After reading it a second time I think I know what you mean. The distance between events in space time (the space time interval) is invariant. If that is what you mean then I agree.

I mean that and a bit more. Invariance of the spacetime interval is just a re-phrasing of the statement that Lorentz transformations preserve the Minkowski inner product (analogous to orthogonal matrices on a Euclidean space).

When you formulate special relativity as a theory on Minkowski space 4-vectors are invariant and you can write the equations of dynamics in a completely coordinate-free way, without the need to explicitly identify a reference frame. Only when you need to use measurements from some specific reference frame need the frame be identified. The physical events are the same in all reference frames -- the physics is invariant.

You do the same thing in Newtonian mechanics, often without thinking about it. F=ma is not dependent on the specific inertial frame in which F or a are measured. You can pick any convenient inertial frame in which to describe a dynamical system -- the physics is invariant. For instance, an elastic collision in one inertial reference frame is an elastic collision in all reference frames. If you step in front of a bus, the kinetic energy of the bus and the kinetic energy of your body are different if you choose the rest frame of the bus versus your own rest frame, but the kinetic energy lost in the inelastic collision is invariant, and you are dead in either frame.

Coordinate-dependent quantities are useful, but the fundamental physics is embodied in the invariants. You can become very confused with coordinate-dependent quantities -- see any of the "paradoxes" of special relativity. But ultimately these things are just components of some 4-vector that is invariant. This is often easier in concept than in concrete realization since translating a common problem statement into 4-vector language takes some thought. The typical "paradox" involves some problem statement that subtly invokes a notion of "simultaneity" which is not invariant, but which our psyche is prepared to accept as invariant.

The fundamental problem is that neither time nor space are invariants They are very much dependent on a coordinate choice (aka observer's reference frame). Any timelike vector in spacetime (a vector of positive length if one takes the signature of the metric as +,-,-,-) is coordinate "time" for some observer.

Time should really be "proper time". Take two points in spacetime that are joined by a timelike curve (a curve with tangent vectors that are everywhere timelike). The arc length of that curve, called a "world line", using the Minkowski metric, is the proper time of the world line. It is the time that would be measured by a clock having that world line (this is not obvious, but it is true). Proper time is invariant under Lorentz transformations, because the Minkowski norm is invariant. Coordinate time is proper time only in the rest frame of the observer.

A lot of this is perspective, analogous to abstract linear algebra as opposed to matrix theory.. One starts with an abstract vector space and only at the last minute chooses an explicit basis or coordinate system. A vector or a linear transformation is an object with certain properties, and only after a choice of a basis is it an n-tuple or matrix. The fundamental properties of vector spaces and linear transformations are made clear and the confusion that comes with an orgy of superscripts and subscripts for matrix elements is avoided.

##### Share on other sites

When you formulate special relativity as a theory on Minkowski space 4-vectors are invariant and you can write the equations of dynamics in a completely coordinate-free way

Yeah, general covariance, I agree. Good point. I think that is at the heart of the solution to any perceived paradoxes.

as a philosopher of science, I say that relativity is based on a form of subjective

idealism

Philosophy of science involves interpreting scientific theories. To interpret a theory, a working understanding of the theory is necessary.

I believe you need someone to be brutally honest. You do not have even an elementary understanding of relativity. Your posts in this thread show that you would not be able to use the theory and that you don’t understand what makes the theory necessary or what purpose it serves.

A few posts ago you said that the distance between objects is constant in relativity when expressed in light units because the speed of light is constant. In truth, a constant speed of light makes the opposite true. With that kind of misunderstanding of the purpose and application of the theory, you can’t expect a good philosophical interpretation.

I won’t get into a philosophical debate, but special relativity really doesn’t suggest subjective idealism.

In a nutshell, I am asking, as above...

does relativity deny a cosmos independent of observational frames of reference?

A frame of reference is like a two dimensional slice through a three dimensional object. The three dimensional object is the same even if all the two dimensional slices are different.

Imagine a three dimensional object like a tomato. Imagine all the different ways that you could slice it at different angles. The surface of the slices will all look different, but the tomato is still a tomato.

In relativity, frames of reference are three dimensional slices through ‘four dimensional’ space-time. Space time is the same even if all the three dimensional slices, or frames of reference, are different.

If you understood how and why that is true then you would also understand that relativity offers an objective reality independent of the various differing perceptions of reality that come with different frames of reference. You ask if it denies a cosmos independent of observational frames of reference and the answer is that it establishes exactly the opposite. This is what Dr. Rocket has been talking about.

"In special relativity, the speed of light is constant. The distance between the two galaxies is not constant."

I take this to assert that there is no "actual, objective distance" between here and Andromeda... nor between here and the sun, because "it all depends on frame of reference."

The speed of light is constant; which means that it is the same in all inertial frames of reference, while the duration between events and the distance between objects is relative to velocity. This was predicted by special relativity in 1905, but more important, it is confirmed experimentally to very high precision on a daily basis. It is a physical fact that can’t be argued against reasonably.

Characterizing this fact by saying “there is no actual objective distance” doesn’t seem completely correct or useful to me.

Just to be absolutely clear, is this what you and relativity are claiming? If so are you and all relativity theorists philosophically persuaded to the belief in subjective idealism. A direct answer would be very much appreciated.

A player is running from home plate to first base after bunting the ball. He is halfway there going 10 miles per hour relative to the catcher. The catcher grabs the ball and throws it to the first baseman. The catcher who is standing on home plate finds that the ball is moving away from himself and toward the first baseman at 20 miles per hour. Just before the first baseman catches the ball and gets the out the runner asks the question, “how fast is that ball going relative to me?” If the runner measured the speed of the ball as compared to himself while he was running what would be the answer?

How did you come up with the answer?

A second version of the same thing -- The runner travels half the speed of light relative to the catcher (he is a very good runner). The catcher decides to shoot the first baseman with a laser rather than throwing him the ball (he is a very bad catcher). Just before the laser hits and kills the first baseman the runner asks “how fast is that laser beam going relative to me?” If the runner measured the speed of the laser beam as compared to himself while he was running what would be the answer?

How did you come up with the answer?

If you work through this problem recognizing, like you do, that the speed of light is constant for all observers then you should realize that there is a problem. If the runner in the second version of the game assumes that distance is constant and he uses the same method to answer the question as you used in the first version of the game then he cannot come up with the right answer.

Oh Boy! After hitting "preview" I realize that this post ended up way longer than I meant it to. Sorry.

A question for the site administrators if any are reading, is it OK to be so far off topic for so many posts? Should maybe the thread be split up into two threads if that is something you do, or maybe Owl or I should start another thread? I'm not familiar with the usual practice so just want to be sure we're not posting inappropriately.

##### Share on other sites

A question for the site administrators if any are reading, is it OK to be so far off topic for so many posts? Should maybe the thread be split up into two threads if that is something you do, or maybe Owl or I should start another thread? I'm not familiar with the usual practice so just want to be sure we're not posting inappropriately.

I am not part of the staff but IMHO the question in the OP was answered in the very first posts and I personally don't think there is anything wrong with having threads evolve far off into off topic branches, as long as it's not due to a hijacking or otherwise intentionally disrupting tactics.

If the discussion ends up splitted into several different sidetracks then a separation might help keep the discussion cleaner and easier to follow, but so far I think Michel's and Owl's inclinations seems to be close enough related to continue together in the same thread.

AFAIK the usual practice is as long as everyone are happy with the development it's also appropriately to continue. If someone is displeased with the direction of the discussion they can always use the report function and have a moderator look into the situation.

Off course if either you, Owl, Michel or anyone else want to split this thread or make a new fresh start thats good too...

Edited by Spyman
##### Share on other sites

When you formulate special relativity as a theory on Minkowski space 4-vectors are invariant and you can write the equations of dynamics in a completely coordinate-free way, without the need to explicitly identify a reference frame. Only when you need to use measurements from some specific reference frame need the frame be identified. The physical events are the same in all reference frames -- the physics is invariant.

So you say Reality with a big R exists and is invariant when fully described in 4 dimensions.

Is that a fair interpretation of your statement?

##### Share on other sites

First, I agree that this is off topic, but if no objection, I'll continue for the sake of convenience. (BTW, I still haven't figured out individual quote boxes but intend to review the tutorial.)

Iggy wrote:

Philosophy of science involves interpreting scientific theories. To interpret a theory, a working understanding of the theory is necessary.

I believe you need someone to be brutally honest. You do not have even an elementary understanding of relativity. Your posts in this thread show that you would not be able to use the theory and that you don’t understand what makes the theory necessary or what purpose it serves.

A few posts ago you said that the distance between objects is constant in relativity when expressed in light units because the speed of light is constant. In truth, a constant speed of light makes the opposite true. With that kind of misunderstanding of the purpose and application of the theory, you can’t expect a good philosophical interpretation."

I am much better at philosophy of science, as per the subjective idealism inquiry as an implied basis of FOR relativity... than at technical discourse. I do understand that light speed stays constant regardless of the speed of a given lightsource. I get it but can only guess why... someting lame like "light can not be pushed." On the other hand, if cosmos exists in and of itself regardless of FOR measurements/observations, which I believe is true, then the opposite cannot be true, i.e., that observational perspective changes distances observed... which is pure subjective idealism.

I see how my quote above confuses the issue. I just meant that we have a universal instument of distance measure in that lightspeed is constant, so, for instance we can say that the sun is just over eight light minutes away from earth, and that is not going to change because some traveler is is approaching our system at near lightspeed and having to run the well proven relativity formulae to correct for the distortion created by their speed/vector.

As for the ball players: Of course in the first instance the ball is going 10mph relative to the runner, whose speed is 10 mph, tho the ball is is going 20mph relative to the catcher or the ground.

In the second case, SR of course applies, and light is still going at 'C' relative to the runner, who is going 1/2 lightspeed. But the distance between bases does not change in either scenario unless you subscribe to the FOR version of subjective idealism I have proposed as appliicable to relativity.

So far your examples are well worn and frankly quite pedantic, not to say insulting.

You say: "I won’t get into a philosophical debate, but special relativity really doesn’t suggest subjective idealism. " How so... or why not?

Now to the sliced tomato... also quite pedantic. You have two dimensional slices of a 3-D object. Fine. But then you stretch the metaphore as follows:

"In relativity, frames of reference are three dimensional slices through ‘four dimensional’ space-time. Space time is the same even if all the three dimensional slices, or frames of reference, are different.

If you understood how and why that is true then you would also understand that relativity offers an objective reality independent of the various differing perceptions of reality that come with different frames of reference. You ask if it denies a cosmos independent of observational frames of reference and the answer is that it establishes exactly the opposite. This is what Dr. Rocket has been talking about."

Space-time is not an established entity, though it is constantly/routinely treated as such everywhere in relativity. My essay on the subject of that ontology is still under house rule gag order. (I do understand why and OK with the reasoning.)

Space can be fully defined as volume with three coordinates. A fourth axis for space remains a metaphysical concept. Time is a factor (if not a "dimension") because all movement can be said to happen with duration, or "through time." I have often cited an essay by Kelley Ross on the Ontology and Cosmology of Non-Euclidean Geometry in this regard. See my spacetime ontology thread in this regard.

If your second paragraph is true then how is "length contraction" explained? No rod lengths staying the same there. Rod length, like distances between cosmic bodies, according to my understanding of relativity are supposed to change with changes in FOR. Seems to contradict your paragraph above.

##### Share on other sites

I am much better at philosophy of science

Without understanding science, at least at an elementary level, you cannot be good at philosophy of science.

As for the ball players: Of course in the first instance the ball is going 10mph relative to the runner, whose speed is 10 mph, tho the ball is is going 20mph relative to the catcher or the ground.

Thank you so much for answering!

The ball, you say, is going 20 mph and the runner is going 10 miles per hour so the ball is moving away from the runner at 10 miles per hour. You find this by subtracting 10 from 20. Very good. I am very glad you answered this.

In the second case, SR of course applies, and light is still going at 'C' relative to the runner, who is going 1/2 lightspeed.

Here you use a different method to answer the question (you didn't subtract anything from anything)... you actually used no method at all for this one. I'm sure you don't think it is a problem not having any method to answer the second question, so we need to ask another question.

The key question is...

The catcher throws the ball very fast. The runner is running half the speed of light (335 million miles per hour) away from the catcher. Right before the first baseman catches the ball, the runner figures out that the ball is moving away from himself at 0.9 times the speed of light (603 million miles per hour).

How fast is the ball moving away from the catcher? How did you get the answer?

The reason this is the critical question is that you will absolutely not be able to answer it. By trying, and failing, to answer it I believe you could discover the problem with your view of reality.

Right now you obviously don't see why a constant speed of light is incompatible with classical mechanics. If you try to solve some classical mechanical problems while acknowledging that the speed of light is constant then you might discover the incompatibility and the problem with your view of reality.

So far your examples are well worn and frankly quite pedantic, not to say insulting.

The examples are insulting or I'm being insulting? I can understand if you find my description of your misunderstanding insulting, but I don't know what about these examples would be insulting. They are just thought experiments involving velocity.

##### Share on other sites

So you say Reality with a big R exists and is invariant when fully described in 4 dimensions.

Is that a fair interpretation of your statement?

I suspect that the answer is "yes", but am not certain what "Reality with a big R exists" means beyond the obvious. I have no desire for some endless philosophical debate on ontology.

##### Share on other sites

I suspect that the answer is "yes", but am not certain what "Reality with a big R exists" means beyond the obvious. I have no desire for some endless philosophical debate on ontology.

In Pavillon de Breteuil near Paris there exists a metal bar made of platinum & iridium which is the prototype metre not in use after the sixties, but still there.

That is Reality with a big R: the metal bar measures one metre long. Point.

If some astronaut or alien moving, accelerating, rotating, measures this metre as shorter, IMHO it is only a matter of measurement. The metal bar in the Pavillon de Breteuil does not actually contract. It cannot contract a lot for the alien, a little bit for the astronaut, and at all for the visitor at rest. It just like stating 1=2=3. It is simply wrong.

##### Share on other sites

In Pavillon de Breteuil near Paris there exists a metal bar made of platinum & iridium which is the prototype metre not in use after the sixties, but still there.

That is Reality with a big R: the metal bar measures one metre long. Point.

If some astronaut or alien moving, accelerating, rotating, measures this metre as shorter, IMHO it is only a matter of measurement. The metal bar in the Pavillon de Breteuil does not actually contract. It cannot contract a lot for the alien, a little bit for the astronaut, and at all for the visitor at rest. It just like stating 1=2=3. It is simply wrong.

Not at all.

Suppose that we start with two identical such bars. Leave one in Pavillon de Breteuil with a technician and give its twin to the Alien. Now let the Alien come cruising past the technician at a large fraction of c. The technician will compare his bar to the Alien's bar as they pass. And the Alien will do likewise (on the fly). Both will measure the other's bar as being the shorter of the two.

The bars have not "changed", and it is not a matter of measurement technique. It is a matter of the very nature of "space" and "time". That is the nature of relativity. What changes is the very decomposition of spacetime into space and time. It is indeed Reality with a big "R", but it is not the reality of everyday experience. This theory has a mountain of experimental data supporting it.

That solid bar not only can but does "contract a lot for the alien, a little for the (slower) astronaut, and not at all for the visitor at rest". And it most certainly is neither "like stating that 1=2=3" nor is "simply wrong'. It may not match your intuition, but your intuition is what is "simply wrong".

##### Share on other sites

I will never agree on that. Call me stubborn.

There is a common point of vue that states that measurements are identical to reality: if I propulse the one meter metal bar into space at close to light speed and somehow take it back, I will get a metal rod contracted one inch long and can go away with it in my pocket? No.

IMO it is a wrong interpretation of the equations of Relativity. Not that the equations are wrong, but our understanding of it is incorrect. IMVHO of course.

------------------------------------------

Edit;

Sorry I didn't notice the "The bars have not "changed" part. Maybe we do not disagree that much.

-----------------------------------------

(..)

Suppose that we start with two identical such bars. Leave one in Pavillon de Breteuil with a technician and give its twin to the Alien. Now let the Alien come cruising past the technician at a large fraction of c. The technician will compare his bar to the Alien's bar as they pass. And the Alien will do likewise (on the fly). Both will measure the other's bar as being the shorter of the two.

O.K. I have no problem with that. Relativity describes accurately the measurements of both observers.

The bars have not "changed", and it is not a matter of measurement technique. It is a matter of the very nature of "space" and "time".

O.K. It is a matter of the very nature of "space" and "time". No disagreement there.

That is the nature of relativity. What changes is the very decomposition of spacetime into space and time.

Agree again.

It is indeed Reality with a big "R", but it is not the reality of everyday experience.

Is that the stone where we hit?

This theory has a mountain of experimental data supporting it.

Sure. I am not arguing against it. There is an obvious misunderstanding, I ought to improve my wording as it seems.

That solid bar not only can but does "contract a lot for the alien, a little for the (slower) astronaut, and not at all for the visitor at rest".

Here I agree somehow with Owls point of vue. There cannot be "for the alien" or "for anyone" Reality. You were the one who stated that reality is 4D and that in this 4D reality physics are invariant. Or are we lost in translation? What we may agree on is that neither we, neither the alien can have a look at this 4D Reality, and that we all look at deformed 3D+1D measurements.

And it most certainly is neither "like stating that 1=2=3" nor is "simply wrong'.

Sorry, but it is really the effect it makes on me.

It may not match your intuition, but your intuition is what is "simply wrong".

Maybe. I am working on it. Edited by michel123456
##### Share on other sites

Iggy:

"Without understanding science, at least at an elementary level, you cannot be good at philosophy of science."

Here is a little philosophy of science for you... though you continue to avoid comment on it:

Without understanding that frames of reference do not shorten or lengthen "time" or "distance" or create an entity "spacetime"... that cosmos is as it is idependent of frames of reference, you end up being a a subjective idealist without even knowing it, so you continue to avoid this aspect of relativity as a case of subjective idealism.

I will not again go into SR with you. I've seen similar thought experiments dozens of times over the years. Please do not think you have found a new way to express it. We all know that the speed of light is constant no matter the speed of a given lightsource... either in the direction of the source's travel or "looking back" from whence it came.

This does not mean that relative FOR makes distances change, as the subjective idealism aspect of relativity asserts. Like it or not, this is a "philosophy of science" issue, which you still refuse to engage.

I, like most people interested in SR, have asked myself why light does not gain speed in an "add-on" way with its speeding source. My best "explanation" is that light can not be "pushed" faster... ever. This must have to do with its lack of mass... nothing to "push against." But this leaves me wondering why lasers have recoil when fired and why the old "box of mirrors" gains inertia, just as if it gained mass, when light is introduced to bounce around inside.

I am very curious and open to explanation in either or both cases. But I will not play the game of "Owl obviously misunderstands SR" any further.

Thanks for the conversation. If you decide to answer my philosophical challenge, please do so.

Edit: BTW the calculations you continue to demand do not address the philosophical issue here... nor, in more general terms, does the math confer understanding any more than observation creates that which is observed.

Edited by owl
##### Share on other sites

The reason this is the critical question is that you will absolutely not be able to answer it.

I will not again go into SR with you.

As expected.

Until you try, there is no chance you will learn relativity.

I, like most people interested in SR, have asked myself why light does not gain speed in an "add-on" way with its speeding source.

I didn't mention light or the speed of light in my latest question. I guess you didn't read it or consider it.

Here it is in a simplified form: someone is moving left of you at 540 million miles per hour and someone else is moving to your right at 540 million miles per hour. How fast is the second person moving away from the first person? How fast, in other words, would the first person measure or say that the second person is moving away from himself?

Your view of reality involves notions that are not consistent with each other which makes it impossible for you to answer the question I've just asked.

I'm hoping that since you can't answer it you will realize there is a problem and ask, or at least try to figure out, what that problem is.

BTW the calculations you continue to demand do not address the philosophical issue here... nor, in more general terms, does the math confer understanding any more than observation creates that which is observed.

I do not expect you to use relativity to answer the question I just asked. I expect you would use whatever understanding you have of reality to answer it.

More than that, being able to use relativity does not mean a person has a philosophical understanding of it, but it is a prerequisite.

Edited by Iggy
##### Share on other sites

Interesting question, alot of long answers, read page 1 and gave up.

Did anyone mention that visible light is only a small part of the electromagnetic spectrum?

##### Share on other sites

Here I agree somehow with Owls point of vue. There cannot be "for the alien" or "for anyone" Reality. You were the one who stated that reality is 4D and that in this 4D reality physics are invariant. Or are we lost in translation? What we may agree on is that neither we, neither the alien can have a look at this 4D Reality, and that we all look at deformed 3D+1D measurements.

This is the gist of it. What we call "length" and "time" are bound up in the "deformed 3D+1D measurements" which are different for the alien, astronaut and technician. Those measurements are "real" and they are different, but they are observer-dependent. The world lines of the ends of the bar are invariant and are the same for the alien, astronaut and the technician. But those world lines translate differently into "time" and "length/space" for each of them.

That is why I prefer, to avoid confusion, to think about things in terms of invariants and translate back to coordinate-dependent "time" and "space" only at the last minute.

But our senses and measurement apparatus only allow us to directly perceive the 3D+1D picture, so a translation to that picture is necessary at some point.

It seems my fundamental inquiry is still not clear. Here it is again.

My most avid interest in science is the philosophy by which relativity claims that 'frame of

reference' (FOR) is the ultimate criterion for what is real and true of the cosmos.

Accordingly, our clocking time becomes the operational definition of what time IS. .

You need to understand the difference between "coordinate time" and propertime. Proper time is what clocks, all clocks, measure. This is actually more clear in the context of general relativity than in the context of special relativity where the two often coincide.

http://www.scienceforums.net/topic/54990-proper-time/

##### Share on other sites

Even the 3D picture is deformed. Here is my point of vue:

If you take a cube, and look at it from a distance, you will never see it as it "really" is. You cannot observe a cube and see simultaneously its 6 faces as squares. Even with mirrors, I doubt you can do that. What you can do is take a measure and represent on a sheet of paper the 6 faces as different schemes, and say: that's a cube. or you can use 3D virtual representation and make a computerized representation of the 3D cube, and look at "as in reality" hence deformed by perspective. In other words, even without counting the effects of time & motion, what we are used to see as reality is not Reality.

When a physicist try to approach what the cube "is", the dimensions of its sides are not enough. He must know of what material it is made of, what color, what density, and going into the material the physicist inquiry has almost no end.

What the physicist gathers from its search are all measurements. And most of the time, the sum of those measurements hardly correspond to any macroscopic "reality" of the cube. Many physicists do not care at all about what all those measurements put together may "mean" for the layman. Physicists care that all those measurements do not conflict each other , that measurements in cube A can be reproduced in cube B, and that those measurements can be done in any other cube.

So, when the layman will ask the physicist "explain me the reality of this cube?" the scientist will explain about relativistic distances of the sides, of particles jiggeling producing its color or internal temperature or wathever, going into deep mathematical constructs that show the tremendous amount of energy hidden in the cube's mass but say about nothing to the layman.

If you get annoyed and propulse the cube into space, the scientist gets terribly excited and procedes into explanations including length contraction and time dilation.

You can also take the cube and put it in your coffee.

Edited by michel123456
##### Share on other sites

if I propulse the one meter metal bar into space at close to light speed and somehow take it back, I will get a metal rod contracted one inch long and can go away with it in my pocket? No.

If the rest length (the length relative to the rest frame) is one meter then I don't agree that the rest length will be one inch.

##### Share on other sites

One could make the remarkthat it is not a matter of agreement (although I agree with you). It is a matter of calculations.

What do the maths tell? -or is it too much off topic?-

Edited by michel123456
##### Share on other sites

Iggy,

As I said above (the philosophical question you are avoiding):

On the other hand, if cosmos exists in and of itself regardless of FOR measurements/observations, which I believe is true, then the opposite cannot be true, i.e., that observational perspective changes distances observed... which is pure subjective idealism.

I see how my quote above confuses the issue. I just meant that we have a universal instument of distance measure in that lightspeed is constant, so, for instance we can say that the sun is just over eight light minutes away from earth, and that is not going to change because some traveler is approaching our system at near lightspeed and having to run the well proven relativity formulae to correct for the distortion created by their speed/vector. (End if reiteration.)

I was using lightspeed as a constant measure of distance and making the point that a speeding alien's frame of reference is not going to change the actual, objective distance between sun and earth... the subjective idealism point I have relentlessly tried to make here while you throw SR thought experiments at me and demand that I do the calculations.

So now you throw another one at me:

"Here it is in a simplified form: someone is moving left of you at 540 million miles per hour and someone else is moving to your right at 540 million miles per hour. How fast is the second person moving away from the first person? How fast, in other words, would the first person measure or say that the second person is moving away from himself?

Your view of reality involves notions that are not consistent with each other which makes it impossible for you to answer the question I've just asked."

(I said I would not play that anymore, but I will offer a deal: You answer my challenge and I will do the calculations required above.)

Even I can do elementary math, but of course this another SR trick question since nothing can travel faster that lightspeed, which is 671 million miles an hour. So if I add the 540 million mph of the guy going away to my left onto the 540 million mph of the guy going away to my right... I get a billion and 80million mph.... which somewhat exeeds the universal speed limit.... so.... what is your point given that I know what SR means?

And will you now agree that earth stays a bit over eight lights minutes from the sun no matter what speeding travelers see from "far out" frames of reference? And how about those rods? Do they "really" contract in length according to observational frame of reference? Ans: Of course not. If "yes" then, by the same principle, namely subjective idealism, your world will disappear every time you blink! You get my point?

Edited by owl

## Create an account

Register a new account