If there is no end to the space

[Sisyphus]

Woops, you are sliding from a subject to another. If we cannot even agree on what distance is, it is useless to jump into further considerations.

 

Unfortunately it's difficult to consider one aspect without the other. Kinetic energy, like distance, time, and relativistic mass, depends on frame of reference. Relative to someone sitting inside it, the plane has no kinetic energy. Relative to the ground, it has a lot. Relative to Mars, it has a lot more than that.

 

Excellent.

I don't expect you to argue that the small dots left & right are actually dancing like that just because an observer happened to travel accelerating rapidly?

 

 

Of course nothing is changing. But no perspective is more real than another. That's the point.

 

There is one reality, but one reference frame is only a slice of that reality. The image is cycling through a range of slices.

[michel123456]

(...) But no perspective is more real than another. That's the point.

 

To me, the one who keeps the rod in his hands knows better than the others.

 

Of course nothing is changing. (...)

 

Does that mean that space contraction & time dilation do not actually happen?

[Sisyphus]

To me, the one who keeps the rod in his hands knows better than the others.

 

I don't know how to respond to that. It's not true. What difference does holding in the hand make?

 

Or, ok, how about this. I'm holding two identical boxes in my hand, containing the same number of hydrogen atoms. However, the hydrogen atoms in box A are moving around faster than in box B. Box A will be heavier. Relativity, right in the palm of your hand!

 

Does that mean that space contraction & time dilation do not actually happen?

 

It actually exists. "Happen" implies that something is changing, so no. Though certainly you can have changes if you involve acceleration between frames, as with the twin paradox, etc.

[Iggy]

I guess Iggy's post was intended to make me change my mind...

 

Those with a good understanding of relativity have no conceptual problem with the reality of length contraction. My post was intended to give you a better understanding.

 

From the .pdf provided page 2:

"The student in the

study classified certain relativistic effects

(including length contraction) as distortions

of perception. Posner et al. report similar

results in interviews with introductory

students and their instructors."

 

It seems I agree with the student.

 

That is what I said. I said "I agree that your understanding is common--even among those studying physics." The paper reports on how common misconceptions are in those learning relativity.

 

Woops, you are sliding from a subject to another.

 

It would be helpful to discuss more than one frame dependent quantity.

 

What is the kinetic energy of a plane? Does the plane have only one "real" value of kinetic energy and many other "apparent" values?

 

O.K. distances in space are relative to reference frame.

It means from some other FOR, the rod I have in my hand can be observed as contracted.

Can you define some FOR where the rod in my hand is expanding?

 

Both you and the rod in your hand are expanding in a coordinate system which is decelerating relative to your coordinate system.

 

Length contraction will not make sense as a physically real process until you stop thinking of length as an inherent property of objects. Length depends on velocity. The distance to the Andromeda galaxy depends on velocity. From our perspective the length is 2.5 million light years. From the perspective of someone traveling between galaxies at near the speed of light the distance is only a few thousand light years. Neither perspective is any more physically meaningful than the other.

[michel123456]

Both you and the rod in your hand are expanding in a coordinate system which is decelerating relative to your coordinate system.

 

Can you show me a concrete example of such a coordinate system?

How is it possible to decelerate from an "at rest" situation?

Edited February 9, 2011 by michel123456

[Iggy]

Can you show me a concrete example of such a coordinate system?

How is it possible to decelerate from an "at rest" situation?

 

Let me put it another way: both you and the rod you are holding are expanding in a coordinate system in which the velocity is approaching your velocity.

 

What is the kinetic energy of a plane? Does the plane have only one "real" value of kinetic energy and many other "apparent" values?

 

Edited to add:

 

I'm sorry, you asked for an example and I forgot to answer. An example is that the space shuttle expands as it lands from our perspective. In orbit it is about 37.189999987484 meters long and on the ground it is about 37.19 meters long. It expands about 0.0000000125 meters relative to the ground.

 

From the shuttle's perspective the united states expands by about .16 centimeters.

Edited February 9, 2011 by Iggy

[michel123456]

(...)Edited to add:

 

I'm sorry, you asked for an example and I forgot to answer. An example is that the space shuttle expands as it lands from our perspective. In orbit it is about 37.189999987484 meters long and on the ground it is about 37.19 meters long. It expands about 0.0000000125 meters relative to the ground.

 

From the shuttle's perspective the united states expands by about .16 centimeters.

 

I was asking for an example where the shuttle is larger than 37,19 meters long.

[Iggy]

I was asking for an example where the shuttle is larger than 37,19 meters long.

 

I see. No, an object is never longer than in its rest frame. Why do you ask? Must the largest length be the realest?

 

What is the kinetic energy of a plane? Does the plane have only one "real" value of kinetic energy and many other "apparent" values?

[Spyman]

No, an object is never longer than in its rest frame.

If the shuttle is in uprised position as like before a take off, would the shuttle's height be longer or shorter if it was standing on the Moon?

(and measured from Earths "rest frame")

[michel123456]

If the shuttle is in uprised position as like before a take off, would the shuttle's height be longer or shorter if it was standing on the Moon?

(and measured from Earths "rest frame")

 

I see you whish to introduce gravity by the means of the equivalence principle.

 

I see. No, an object is never longer than in its rest frame. Why do you ask? Must the largest length be the realest?

 

Why do I ask? Because it is a starting point.

An object observed at rest can never be observed longer, no matter the state of motion (underlined for Spyman).

In other words, it exists an infinite set of FOR that will measure an infinite set of dimensions for a specific object, dimensions going from from infinitely small to D. (not to infinitely big)

D is the dimension of the object as measured at rest.

What do you think ?

That all FOR are equal beween them? or that there is something special in D ?

[Sisyphus]

Why do I ask? Because it is a starting point.

An object observed at rest can never be observed longer, no matter the state of motion (underlined for Spyman).

In other words, it exists an infinite set of FOR that will measure an infinite set of dimensions for a specific object, dimensions going from from infinitely small to D. (not to infinitely big)

D is the dimension of the object as measured at rest.

What do you think ?

That all FOR are equal beween them? or that there is something special in D ?

 

It's special in that it's the rest frame. It's not special in that it's somehow more real. The bus speeding down the street has a rest frame, too. In that rest frame, it has zero kinetic energy. In yours, standing on the sidewalk, it has a lot. Step in front of it, and then tell me frame dependent properties are just an illusion.

[michel123456]

(...)The bus speeding down the street has a rest frame, too. In that rest frame, it has zero kinetic energy. In yours, standing on the sidewalk, it has a lot. Step in front of it, and then tell me frame dependent properties are just an illusion.

 

You are messing things IMHO.

The smash between the bus & me will have to do with acceleration. The bus will produce a force on me in order to make me change velocity. This change will be done in a too small period of time, and that will kill me.

Sorry Iggy, I don't answer to your kinetic energy question because I want to remain on space contraction question.

 

It's special in that it's the rest frame. It's not special in that it's somehow more real.

 

That's the question.

[Sisyphus]

And how does it exert that force, if it has no kinetic energy?

[michel123456]

That is not the question.

 

O.K. I'll bite.

 

The bus has no kinetic energy.

But the infinite set of FOR that move around the bus observe & measure that relatively to them, the bus has kinetic energy.

 

You have an infinite set of FOR that measure a set of values from infinite to zero (not to minus infinite).

What do you choose?

Edited February 10, 2011 by michel123456

[Sisyphus]

Oh, but it is.

[Iggy]

If the shuttle is in uprised position as like before a take off, would the shuttle's height be longer or shorter if it was standing on the Moon?

(and measured from Earths "rest frame")

 

I'm not sure. I think it depends on how you define length, or the radial distance. The Schwarzschild r coordinate, for example, is not the same as a shell observer's r coordinate. Section 4 of this lecture talks about it: http://www.uio.no/studier/emner/matnat/astro/AST1100/h10/undervisningsmateriale/lecture15.pdf

 

The bus has no kinetic energy.

But... the bus has kinetic energy.

 

Someone could object, "which is it? There is only one reality".

 

You have an infinite set of FOR that measure a set of values from infinite to zero (not to minus infinite).

What do you choose?

 

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".

[owl]

Hi folks,

I've been sick, sometimes better, sometimes "worser" for awhile now, so I'm left with a lot of loose ends here which I could not follow up on with good speed. Many gaps for me still remain from my discussions with Spyman and Iggy starting in page two. But rather than try to bactrack to each point for which I need clarification, I'll go to your point, Iggy, on the distance to Andromeda.

You say (sorry, I don't have the single quote tool down yet):

 

"If a person travels the distance with a velocity 0.9999c relative to the galaxy then it will take them 35,357.99 years. Distance is speed times time. The distance to the Andromeda galaxy is therefore 0.9999 lightyears / year times 35,357.99 years = 35,354.5 light years.

 

We on earth measure the distance at 2.5 million light years."

 

Am I confused (as you have previously assumed) or does relativity deny a cosmos independent of observational frames of reference? (I like that FOR also applies to "for abserver A vs for observer B" but never mentions a "beyond the frames" perspective... the actual distance in an objective sense.

 

As I said to Spyman earlier, seems to me such an objectve distance can be designated by the universal constant 'C', and since we use years as time units and light years as a standard cosmic distance measure, that 2.5 million of them is the actual distance.

Since your travelers are going nearly lightspeed, not faster than light by whatever multiple of the difference and fraction of journey time, how is it that the "FOR" of the travelers is now on equal footing with standard measure, as science uses to designate all cosmic distances?

 

This makes "FOR" and relativity into to a kind of subjective idealism, with FOR as the subject.

You have previously misunderstood my philosopical rejection of such idealism as a misunderstanding of relativity. This is usually the case for those who disagree on this very fundamental level. If you disagree, then you don't understand.

Even my "Thought experiment" is dismissed as another misunderstanding of relativity. (If there were no intelligent life, light speed would still be constant and take precisely the same time to travel between objects... with no observers... no frames of reference.)

Rods (naurally occurring, let's say!) would not keep changing length either, as this form of subjective idealism claims.

 

There were other gaps of great interest to me, but I'm out of steam again for now. Oh... the "What is space?" question. Please tell me how this is wrong. A line describes one dimension... a plane, two... and a volume is three dimensional. Space is volume regardless of what exists in space, where, and how moving. There can be no "end of space,*" so, beyond all "defined volumes" is infinite, endless space.(See my comments to spyman in page two in this regard. What boundary... what beyond any imagined boundary?) There is no "it" to space.

So where did the non-Euclidean concept of curved space and four dimensional space come from. (Rhetorical question! I've studied the transition from Euclid to beyond in depth for years.)

I line requires a plane to display curvature. A plane requires volume for same. There is no pretending that great circles or arcs therof are "straight lines" by re-defining curvature as intrinsic to this manifold and extrinsic to that manifold. We can not devise a four dimensional space by a trick of language. Volume has three axes. What would a fourth designate in "the real world?"

 

My fever is climbing again. (Figuratively and literally.) Gotta go. Appreciated the mental exercise.

[michel123456]

Someone could object, "which is it? There is only one reality".

 

 

 

You don't have to choose one. They are all real. (...)

 

If you replace kinetic energy with money, saying that the bus has kinetic energy is like to say the bus is full of money. The problem is that the amount of money is 10 dollars for you, 1000 dollars for another, 10 billions dollars for another observer. But when you step on the bus searching for the pactole, what do you find? No money.

 

Kinetic energy is not on the bus. Kinetic energy is somewhere else, hidden by a trick in spacetime, that makes it relative to motion. So, if you want to understand kinetic energy, I mean understand, not only calculate, you must understand motion. If you want to understand motion, you must understand space and time. That is where I focus.

[Sisyphus]

But quantity of money is not frame-dependent. It's not even physical. Velocity clearly is.

[Iggy]

Hi folks,

I've been sick, sometimes better, sometimes "worser" for awhile now, so I'm left with a lot of loose ends here which I could not follow up on with good speed. Many gaps for me still remain from my discussions with Spyman and Iggy starting in page two. But rather than try to bactrack to each point for which I need clarification, I'll go to your point, Iggy, on the distance to Andromeda.

You say (sorry, I don't have the single quote tool down yet):

 

"If a person travels the distance with a velocity 0.9999c relative to the galaxy then it will take them 35,357.99 years. Distance is speed times time. The distance to the Andromeda galaxy is therefore 0.9999 lightyears / year times 35,357.99 years = 35,354.5 light years.

 

We on earth measure the distance at 2.5 million light years."

 

Am I confused (as you have previously assumed) or does relativity deny a cosmos independent of observational frames of reference? (I like that FOR also applies to "for abserver A vs for observer B" but never mentions a "beyond the frames" perspective... the actual distance in an objective sense.

 

As I said to Spyman earlier, seems to me such an objectve distance can be designated by the universal constant 'C', and since we use years as time units and light years as a standard cosmic distance measure, that 2.5 million of them is the actual distance.

 

To say "c is constant" means that every observer will measure the speed of light as c.

 

In the thought experiment with the Andromeda galaxy the earthlings measure light traveling 2.5 million light years in 2.5 million years. The speed of light as we measure it is 2.5 / 2.5 or 1c. The rocket traveling .9999c relative to us measures the same light traveling 35,354.5 light years in 35,354.5 years. They measure the speed of light as 35,354.5 / 35,354.5 or 1c.

 

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

 

Kinetic energy is not on the bus. Kinetic energy is somewhere else, hidden by a trick in spacetime, that makes it relative to motion.

 

Right. If you think of length in the same way then length contraction makes sense. If you think of either length or kinetic energy as properties of the bus then their relative nature does not make sense.

[michel123456]

To say "c is constant" means that every observer will measure the speed of light as c.

 

In the thought experiment with the Andromeda galaxy the earthlings measure light traveling 2.5 million light years in 2.5 million years. The speed of light as we measure it is 2.5 / 2.5 or 1c. The rocket traveling .9999c relative to us measures the same light traveling 35,354.5 light years in 35,354.5 years. They measure the speed of light as 35,354.5 / 35,354.5 or 1c.

 

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

 

 

 

Right. If you think of length in the same way then length contraction makes sense. If you think of either length or kinetic energy as properties of the bus then their relative nature does not make sense.

 

The difference is that when you step on the bus, you find no money, no kinetic energy. But the bus has a length. And it happens that it is the maximum observable length. Coincidence?

Because I am persuaded that only one reality exists (that's the question), I choose this length as THE length of the bus. I call that length "Reality". All measurements made by other observers from other FOR are paramophosis of observation, not a true contraction of the object.

That's the way I see things.

 

I may be wrong. But the option to consider that an object can have simultaneously multiple lengths looks like total crap to me.

 

The last option, to consider length as a relative concept could be acceptable if all values for length were available. But the absence of length dilation suggests this hypothesis is not correct. Unless length dilation exists...

Edited February 12, 2011 by michel123456

[Sisyphus]

The difference is that when you step on the bus, you find no money, no kinetic energy. But the bus has a length. And it happens that it is the maximum observable length. Coincidence?

Because I am persuaded that only one reality exists (that's the question), I choose this length as THE length of the bus. I call that length "Reality". All measurements made by other observers from other FOR are paramophosis of observation, not a true contraction of the object.

That's the way I see things.

 

I may be wrong. But the option to consider that an object can have simultaneously multiple lengths looks like total crap to me.

 

The last option, to consider length as a relative concept could be acceptable if all values for length were available. But the absence of length dilation suggests this hypothesis is not correct. Unless length dilation exists...

 

And when you step on the bus, it has the minimum observable kinetic energy: zero. And it has the minimum velocity, etc. A frame in which an object is at rest is going to be a limiting case in several ways, because there is no such thing as negative velocity. However, if you think all other measured properties are somehow illusory, I once again invite you to step in front of a speeding bus to test that hypothesis.

 

There is "one reality." And in that reality, things like length, duration, velocity, etc. are dependent on reference frame. If you can't come up with a reason for why you have a problem with some of those properties (like length) but not others (like velocity) besides that it "looks like total crap," then there really isn't anything left to discuss, is there?

[michel123456]

I have no problem with velocity.

I have no problem with duration.

Because those concepts are somehow "outside" of an object. they are not the object itself.

 

I have problem with length.

There is a distinction between rest mass & relativistic mass. Why don't we consider "rest length" and "relativistic length"?

[Iggy]

I have no problem with velocity.

I have no problem with duration.

Because those concepts are somehow "outside" of an object. they are not the object itself.

 

That's what I'm saying. The same thing should be considered true in regards to distance or length.

 

Length (of an object or any other kind) is a function of two points and the frame of reference that those points are taken with respect to. It is not only a static property, but is itself relative to velocity just as much as kinetic energy and velocity are.

 

"the distance of the object is two meters" is not a complete statement any more than "the velocity of the object is two meters per second". Distance and velocity are relative, so we must say "the distance of the object is two meters relative to a specific FOR" and "the velocity of the object is two meters per second relative to a specific FOR"

 

I have problem with length.

There is a distinction between rest mass & relativistic mass. Why don't we consider "rest length" and "relativistic length"?

 

Actually, the term relativistic mass is avoided exactly because it implies what you think it implies. John Taylor and Archibald Wheeler write in their book, "Spacetime physics -- Introduction to special relativity":

 

"The concept of "relativistic mass" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass - belonging to the magnitude of a 4-vector - to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself."

[owl]

OK, so my "thought experiment" above gets no comment, based apparently on the premise... yes, as I said, relativity does deny a cosmos independent of observational frames of reference.

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."

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. Neat trick!

 

Maybe an explanation is just too much to expect.... or is "all is relative, there is no 'objective cosmos'"... the explanation?

Yes, relativity is based on subjective idealism with the subject being the frame of reference and no possibility of an "objective perspective" like the more obvious distance to the sun at just over eight light minutes.

Edited February 15, 2011 by owl