seeing events in reverse order???

[michel123456]

Alright so we know what different observers measured. What really happened though, if not what was measured?

You are free to make the experiment.

[md65536]

1.So, there exist a "nice" FOR that smart scientists can use to easily measure the longest dimension of an object. In no other FOR can such a length be observed.

Just like the last time I remember this "rest frame is a preferred frame" topic was discussed, I must ask: How do you measure the distances between sets of moving objects? What is your "nice" FOR to measure distances that are changing?

[Schneibster]

My position is not against Relativity, it goes about the interpretation.of Relativity.

 

Yes, I understand. Your current interpretation is not useful. We are trying to show you correct ones. (Technically we're all saying the same thing; just from different points of view. This is useful because it makes it more likely one POV will "click" with your other knowledge and you will learn something new.)

[md65536]

You are free to make the experiment.

Suppose I do the experiment and measure what happens. Now how do I determine what really happened?

[michel123456]

 

That frame is called an "inertial frame." And yes, such a frame is always perceived by an observer in it to be experiencing undilated time. However, you must also understand that two such frames can be moving relative to one another; there is no one "master frame" or any reference from which to measure "absolute motion."

 

No, just as you cannot observe a length contraction less than zero due to motion, you also cannot observe time compression due to motion, only time dilation.

O.K.

There is a "nice" FOR in which measured mass is minimal, in which length is maximal and in which time is minimal relatively with all other FORs around the Universe.

Suppose I do the experiment and measure what happens. Now how do I determine what really happened?

If you hear a crash it means reality won against observation. If you hear no crash it means the meter stick passed without touching the posts. In this case, only the meter stick was moving, only the meter stick was contracting, the posts were not contracting ,the observer on the meter stick was wrong.

 

Do you have another alternative?

Edited April 5, 2014 by michel123456

[Schneibster]

O.K.

There is a "nice" FOR in which measured mass is minimal, in which length is maximal and in which time is minimal relatively with all other FORs around the Universe.

 

No. You've forgotten the results of one observer looking at another observer in a non-comoving frame. Every unaccelerated observer sees their own frame as inertial. Only acceleration/gravity is absolute.

 

Later: There are an infinity of frames in which measured mass is minimal, length is maximal, and time is not dilated. They are all special. That's why it's called "special relativity," actually.

Edited April 5, 2014 by Schneibster

[timeless]

I'm most probably being a bit silly here but unfortunately relativity doesn't come as easy to me as it does to others.

[...]

(I'm a second year undergrad in physics so don't shy away from the maths if it's needed)

 

No you are not silly. You see contradictions and you ask the question risking to be ridiculed.

 

There are serious cognitive problems when learning relativity. In the article:

Rachel E. Scherr1, Peter S. Shaffer1 and Stamatis Vokos "Student understanding of time in special relativity: Simultaneity and reference frames" Am. J. Phys. 69, S24 (2001);

The authors state:"The results [of the research] indicate that after standard instruction students at all academic levels have serious difficulties with the relativity of simultaneity and with the role of observers in inertial reference frames. Evidence is presented that suggests many students construct a conceptual framework in which the ideas of absolute simultaneity and the relativity of simultaneity harmoniously co-exist."

 

You have to pursue your questions for as long as you mind is not satisfied with the absence of contradiction on logical grounds. It make take a lifetime but it is worth pursuing.

[Strange]

1.So, there exist a "nice" FOR that smart scientists can use to easily measure the longest dimension of an object. In no other FOR can such a length be observed.

 

2. It is the same FOR in which smart scientists measure the rest mass ("invariant mass") of an object.

 

3. Does this FOR also have some "nice" particularity about time?

 

Question: Is there a FOR for which an observed time interval is less than a time interval as measured in the FOR of the object? (I mean, instead of time dilation, time contraction)

 

This is not a single preferred frame of reference. There are an infinite number frames of reference with the same properties. Therefore there is no preferred frame.

My position is not against Relativity, it goes about the interpretation.of Relativity.

 

There is no interpretation involved. Your computer works. It continues to work despite your attempts to "interpret" relativity differently. Therefore relativity works and you are wrong.

[swansont]

O.K.

There is a "nice" FOR in which measured mass is minimal, in which length is maximal and in which time is minimal relatively with all other FORs around the Universe.

 

 

The problem is that motion is always measured with respect to something, so you have two things to consider. A moves relative to B, and B moves relative to A, so there are two frames in which these things hold.

 

Now, how do you decide which one represents the "truth"?

[michel123456]

 

The problem is that motion is always measured with respect to something, so you have two things to consider. A moves relative to B, and B moves relative to A, so there are two frames in which these things hold.

 

Now, how do you decide which one represents the "truth"?

If A moves relative to B, the length, mass and time in A are true as observed from A.

Mass, time and length of B are true as observed from B.

[swansont]

If A moves relative to B, the length, mass and time in A are true as observed from A.

Mass, time and length of B are true as observed from B.

 

It's incredibly inefficient to do physics that way. The corrections you have to make for what you are observing to respect the "truth" of the other frame are then un-done when you apply the physics from your own frame. Just as if the physics is right in every frame.

 

The implication (supported by Occam's razor) supports the idea behind science: what we observe is objectively true. However, relativity tells us that inertial frames are equivalent and there is no absolute rest frame. Relativity works, so if you disagree, fine, but you are in conflict with science. You can't have it both ways.

[michel123456]

 

It's incredibly inefficient to do physics that way. The corrections you have to make for what you are observing to respect the "truth" of the other frame are then un-done when you apply the physics from your own frame. Just as if the physics is right in every frame.

 

The implication (supported by Occam's razor) supports the idea behind science: what we observe is objectively true. However, relativity tells us that inertial frames are equivalent and there is no absolute rest frame. Relativity works, so if you disagree, fine, but you are in conflict with science. You can't have it both ways.

Could you please explain your statement, It is not clear to me.

[Strange]

If A moves relative to B, the length, mass and time in A are true as observed from A.

Mass, time and length of B are true as observed from B.

 

The correct term for what you are calling "true" values is proper length, mass, etc.; i.e. the value measured in the objects own frame of reference.

 

You still haven't answered the point that there are infinite number of frames of reference and therefore none of them can be considered preferred.

[michel123456]

 

The correct term for what you are calling "true" values is proper length, mass, etc.; i.e. the value measured in the objects own frame of reference.

 

You still haven't answered the point that there are infinite number of frames of reference and therefore none of them can be considered preferred.

You are correct.

"Nice" is the correct scientific term, not "preferred", I apologize.

 

This was sarcasm.

 

The "value measured in the objects own frame of reference" is not simply that.

It is also the extreme value (minimum or maximum). That is not negligeable.

Maybe you can answer my question in post #55?

[Lizzie L]

Temporal order illusions are also possible.

[swansont]

Temporal order illusions are also possible.

 

That's an excellent point (though illusion is not a description I'd use), and one which does not resolve the same way as length and elapsed time.

Could you please explain your statement, It is not clear to me.

 

If I want to do a physics calculation or experiment in my frame of reference, I need to know how the object behaves when observed in my frame. How it behaves in its own frame is of no use unless I apply the proper transform. Doing a calculation in its own frame requires that I transform values of objects that are in my frame. Not doing this will give the wrong answer. GPS satellites, for example: you can't just put an atomic clock on board a GPS satellite and expect the system to work, because what matters is that the timing agrees with what happens in the frame of the earth's surface. Those clocks do actually run at a different rate when we measure them on earth, and all we care about is what happens on the earth's surface.

[Sensei]

You still haven't answered the point that there are infinite number of frames of reference and therefore none of them can be considered preferred.

 

If there is finite quantity of galaxies, therefor finite quantity of stars, therefor finite quantity of baryons and other particles, then there is finite quantity of frames of reference.

For human brain 10^100 or 10^1000 is like infinity, too large to grasp anyway.

 

On the other hand, if velocity is at some level (very small so not easily detectable like f.e. 1 picometer per second) quantized, there will be also finite quantity of frames of reference (but it might even exceed above one FOR quantity).

 

I think so oil drop experiment performed in very long time (months or years), could be used to find whether velocity, distance and time, power and energy are quantized (and much cheaper than building particle collider)

Imagine oil drop that traveled to middle between top & bottom plates. Then ionized and attracted by top plate. At some point it appears staying in place. But what if we will keep it this way for months or years, can we see little movement to up or down?

When it will be really fixed in place for years, we have found minimum energy needed to move particle. Minimum energy more or less = movement to up/down of oil drop in months/years.

 

Just a thought.

[Dekan]

Having read through the thread, the thing which strikes me is this:

 

Swansont, in #14, claims that "something moving at .999c doesn't just look shortened, it actually is that short"

 

And that seems to agreed to by Scheibster in #32 : " a stick appearing shorter or longer is not an illusion, but the actual state of affairs".

 

Whereas Michel in #33, says that the shortening of the stick is just an illusion, caused by the way we observe things. We observe by the medium of light, and light has a finite velocity. So of course, that affects the way we subjectively perceive things.

But it doesn't mean that our subjective perceptions, correspond to objective reality.

 

Michel's interpretation seems intuitively more likely, but could it be put to the test, in this thought-experiment:

 

Suppose the "stick" is actually a hollow tube, 1-metre long. At each end of the tube, is a lump of Uranium 235, Each lump is half the critical mass. And while the two lumps are kept separated by this distance of 1 metre, they remain inert. They won't cause a nuclear explosion. This is carefully monitored by an astronaut, who's sitting on the tube. The tube is floating in interstellar space.

 

The tube has an ion-drive unit attached, which the astronaut switches on. The drive steadily increases the tube's speed, until eventually it's bulleting along at .999+c. This doesn't perturb the astronaut. She sees the tube remaining resolutely 1-metre in length. Which keeps the two sub-critical masses a safe distance apart. So no nuclear detonation. All is serene.

 

However, suppose the tube encounters an alien spaceship, and rushes closely past it. What do the aliens see? Do they see a tube contracted from 1-metre, to perhaps 0.001-millimetre - the two masses of Uranium in virtual contact - violent sizzling of neutrons between the two masses - and a resultant nuclear explosion which destroys their ship?

 

Are the aliens dead, or not? And would if make a difference if they'd evolved from a feline species. .

[swansont]

 

Michel's interpretation seems intuitively more likely, but could it be put to the test, in this thought-experiment:

 

Suppose the "stick" is actually a hollow tube, 1-metre long. At each end of the tube, is a lump of Uranium 235, Each lump is half the critical mass. And while the two lumps are kept separated by this distance of 1 metre, they remain inert. They won't cause a nuclear explosion. This is carefully monitored by an astronaut, who's sitting on the tube. The tube is floating in interstellar space.

 

The tube has an ion-drive unit attached, which the astronaut switches on. The drive steadily increases the tube's speed, until eventually it's bulleting along at .999+c. This doesn't perturb the astronaut. She sees the tube remaining resolutely 1-metre in length. Which keeps the two sub-critical masses a safe distance apart. So no nuclear detonation. All is serene.

 

However, suppose the tube encounters an alien spaceship, and rushes closely past it. What do the aliens see? Do they see a tube contracted from 1-metre, to perhaps 0.001-millimetre - the two masses of Uranium in virtual contact - violent sizzling of neutrons between the two masses - and a resultant nuclear explosion which destroys their ship?

 

Are the aliens dead, or not? And would if make a difference if they'd evolved from a feline species. .

 

You are assuming the safe separation distance of the masses is a frame-independent quantity.

 

If there is finite quantity of galaxies, therefor finite quantity of stars, therefor finite quantity of baryons and other particles, then there is finite quantity of frames of reference.

 

 

One can map a frame onto a speed. There are an infinite number of values of speed, thus there are an infinite number of frames of reference.

[Dekan]

 

You are assuming the safe separation distance of the masses is a frame-independent quantity.

 

I'm asking whether there'd be a nuclear explosion, or not?

[swansont]

I'm asking whether there'd be a nuclear explosion, or not?

 

If an event happens in one frame, it happens in all of them.

[md65536]

If you hear a crash it means reality won against observation. If you hear no crash it means the meter stick passed without touching the posts. In this case, only the meter stick was moving, only the meter stick was contracting, the posts were not contracting ,the observer on the meter stick was wrong.

 

Do you have another alternative?

Okay here's an alternative:

- There is no concept of reality battling against observation. Or equivalently: Reality always wins.

- What is measured is representative of reality.

 

 

How about that? SR and GR then fit. It's simple, also consistent.

 

Yours seems to be an interpretation of a misunderstanding of relativity. It's not the worst by far. It is probably fine if you intend to never use or understand relativity. It might even be especially useful for avoiding understanding relativity, because it puts up a wall where further understanding clashes with beliefs (eg. "length contraction's not real!"), and allows for inconsistency with a simple explanation that what it models and what is real are not the same (eg. "contradictions caused by length contraction's unreality are okay; this observer's measurements are simply wrong").

 

 

 

(If you meant specifically an alternative explanation of the meter stick through the posts, the basic explanation is something along the lines of: the stick makes it through the posts, and this happens in all frames. In the posts' frame, the stick passes through lengthwise, and is contracted enough to fit. In the stick's frame, it doesn't pass both posts simultaneously. The posts are contracted but also skewed allowing the stick to slip through not all at once, as though on an angle. I understand if this is not personally aesthetically appealing, but it is consistent and it works.)

Edited April 6, 2014 by md65536

[Lizzie L]

 

That's an excellent point (though illusion is not a description I'd use), and one which does not resolve the same way as length and elapsed time.

Well, I may not have been making such an excellent point as you credited me with! I did mean "illusion" i.e. people report a different temporal order to events to that indicated by objective measures (or for that matter, manipulated by an experimenter) just as the "moon illusion" is when people report that the moon at the horizon is "bigger" than the moon at the zenith, when it can be readily demonstrated that they subtend the same angle.

 

In contrast, I don't call "free will" and "illusion" (as some do) - it's a perfectly good model. I'd say the difference between an "illusion" and a perfectly good model lies in the degree to which it conflicts (makes different predictions than) predictions based on more objective (i.e. measured by independent observers) measures.

 

But I do think it's interesting - because it tells us that our association of temporal order and causality runs both ways - we think that if something precedes something else, it can have caused it, whereas if it follows it, it can't. However, it turns out that if we think A caused B, that can fool us into thinking A preceded B, even though it didn't (by more objective measures).

[swansont]

Well, I may not have been making such an excellent point as you credited me with! I did mean "illusion" i.e. people report a different temporal order to events to that indicated by objective measures (or for that matter, manipulated by an experimenter) just as the "moon illusion" is when people report that the moon at the horizon is "bigger" than the moon at the zenith, when it can be readily demonstrated that they subtend the same angle.

 

In contrast, I don't call "free will" and "illusion" (as some do) - it's a perfectly good model. I'd say the difference between an "illusion" and a perfectly good model lies in the degree to which it conflicts (makes different predictions than) predictions based on more objective (i.e. measured by independent observers) measures.

 

But I do think it's interesting - because it tells us that our association of temporal order and causality runs both ways - we think that if something precedes something else, it can have caused it, whereas if it follows it, it can't. However, it turns out that if we think A caused B, that can fool us into thinking A preceded B, even though it didn't (by more objective measures).

 

Separated causal events must have the proper order but that doesn't hold for acausal events. Simultaneity is relative, so two observers can see them in reverse order, as the thread started out discussing, and there is no "inherent" ordering to such events. Alice can see event 1 happen before event 2 while Bob sees 2 before 1, and there's no way for one ordering to be called real while the other is called an illusion.

[Schneibster]

If A moves relative to B, the length, mass and time in A are true as observed from A.

Mass, time and length of B are true as observed from B.

 

So you're saying you can only measure the "true" length, mass/energy, and time from a frame that is comoving with what you observe?

 

It's incredibly inefficient to do physics that way. The corrections you have to make for what you are observing to respect the "truth" of the other frame are then un-done when you apply the physics from your own frame. Just as if the physics is right in every frame.

 

The implication (supported by Occam's razor) supports the idea behind science: what we observe is objectively true. However, relativity tells us that inertial frames are equivalent and there is no absolute rest frame. Relativity works, so if you disagree, fine, but you are in conflict with science. You can't have it both ways.

 

You're going the same place I did. I'm going to try leading michel step by step.