A Serious Question from an Educated Layman

[AgnosticPriest]

Point 1. All speed is relative to an observer and is never absolute (because there is no absolute frame of reference from which one can observe and measure).

Point 2. The laws of physics hold true for all frames of reference (i.e., an inch is an inch no matter how fast you are traveling).

Point 3. An object in motion will remain so until interfered with (by gravity, air friction, collision with another object, et cetera).

I have been struggling with the logic behind the theory that light speed cannot be achieved by matter nor exceeded by anything. Using these three points, it doesn’t add up. I would like to illustrate my reasoning herein for a moment and submit it for a sort of peer review. I do not speak the language of tensor calculus, so my line of reasoning will come from my logical deduction. I conceptualize abstract ideas in my mind visually as opposed to mathematically, so please bear with me.

The atomic clock aboard the fast airplane which fell behind its land-based twin seems to prove the theory that motion somehow affects time. The problem I see with this is that (point 1) motion is relative and cannot be absolutely measured, therefore motion itself cannot be the factor which causes the time dilation.

But time dilation does occur…so something has to be the factor. There has to be interference because (point 3) objects in motion remain unaffected unless acted upon. Obviously there is gravity to consider. It constantly pulls down on the plane and the atomic clock as it travels over earth’s surface. Also, there is the earth’s magnetic field which the plane and clock are passing through at high speeds. And magnetic fields are well known for causing strange things to happen to atoms who pass through them at high speeds.

Perhaps time dilation and length shortening of objects approaching the speed of light only occur because the things we have observed and experimented with were passing through magnetic and gravitic fields. It just doesn’t make sense logically that mere motion (which is not absolutely measurable) would have absolute effects. It is unfortunate we do not have a pure vacuum in which we can experiment outside the influence of gravity and magnetism.

Perhaps photons going from the back of the plane to the front of the plane only appear to be making the distance at the speed of light because (A) the length of the plane is being shortened by passing through the magnetic/gravitic fields, or (B) the photons themselves are being hindered by the increased motion through the magnetic/gravitic fields. I’ve never heard of anyone creating a chamber which is void of geomagnetic or gravitic interference, so I know that no one has been able to prove or disprove the theory…which is obviously why it is still a theory and not a law.

So, considering these three points and the above illustration, my questions to the scientific community are as follows:

I. If light speed cannot be exceeded (or even achieved by matter without converting it to energy in the process), where is the absolute frame of reference which is being used to determine this?
II. What is the factor which is interfering with the atoms that are in motion that causes the observable effects such as time dilation and length shortening if not magnetic and gravitic fields?
III. What is to stop an object of matter from achieving or even exceeding the speed of light, provided the object has the fuel needed and is traveling through a perfect void where gravity and magnetism are not even factors?
IV. How do we know there isn’t something out there beyond the reach of our universe which is right now traveling beyond the speed of light?

I am posing these questions seriously because I want a straight answer—in layman’s terms, without the mathematics—which either disproves my logic point-for-point, or explains to me how some other genius physicist has also come to this conclusion and is trying right now to create the proper formulae to prove it mathematically (which would mean I’m not completely crazy by thinking this way and I should consider myself worthy of at least some credit for having sound logical deduction as my biggest talent).

 

[El Hombre Invisible]

Point 2. The laws of physics hold true for all frames of reference (i.e., an inch is an inch no matter how fast you are traveling).

I think that's all inertial frames of reference, i.e. ones at which the object is at rest or traveling in a straight line with constant velocity. You could easily conceive of an experiment which yields different results at rest and in an accelerating vehicle.

The problem I see with this is that (point 1) motion is relative and cannot be absolutely measured, therefore motion itself cannot be the factor which causes the time dilation.

Ah, but the time dilation is also relative. The object in motion would not feel time pass any differently in its frame of reference, but to another frame of reference in which it is moving, there would be disagreement about how much time had passed. A third frame of reference would lead to a third value for how much time had passed. Time dilation is a consequence of relative motion.

Perhaps time dilation and length shortening of objects approaching the speed of light only occur because the things we have observed and experimented with were passing through magnetic and gravitic fields.

That would be amazingly coincidental, as Special Relativity does not touch on either, and yet the conclusions of it are remarkably accurate.

Perhaps photons going from the back of the plane to the front of the plane only appear to be making the distance at the speed of light because (A) the length of the plane is being shortened by passing through the magnetic/gravitic fields,

? You're quickly abandoning a theory supported by observed phenomena and proposing one that isn't.

or (B) the photons themselves are being hindered by the increased motion through the magnetic/gravitic fields.

I think you're forgetting that photons are both massless and chargeless. The photon has relativistic mass, so will obey the laws of gravity, but the effect on a photon moving from one end of the plane to the other will be so close to zero you can call it zero. It still doesn't have charge though.

I. If light speed cannot be exceeded (or even achieved by matter without converting it to energy in the process), where is the absolute frame of reference which is being used to determine this?

ANY frame of reference. In the frame of reference in which a particle is at rest, it will undergo no mass increase. In a frame of reference in which it is moving near to the SoL, it will have a large mass increase (large amount of energy). A third, different FoR will yield a different relativistic mass (a different amount of energy). This is not derived from any absolute frame, but is derived differently in all inertial frames.

II. What is the factor which is interfering with the atoms that are in motion that causes the observable effects such as time dilation and length shortening if not magnetic and gravitic fields?

Again, nothing is interfering with the atoms themselves. It's varying velocity across varying frames of reference will show that time has passed less for the object than for something at rest in those frames of reference. The amount depends on the velocity of the object in that frame of reference alone. A different frame may always be chosen and different values yielded.

III. What is to stop an object of matter from achieving or even exceeding the speed of light, provided the object has the fuel needed and is traveling through a perfect void where gravity and magnetism are not even factors?

First, if you're talking about an object traveling with a given velocity, you must be doing so relative to a frame of reference in which that object has that velocity. In this frame of reference, by nature of the object's velocity the object will appear to increase in relativistic mass, and does so more and more the faster the object travels. In a sense, when you provide energy to an object with a given velocity, in the frame of reference in which the object has that velocity, more of that energy will be converted to relativistic mass rather than kinetic energy the faster that object is travelling.

IV. How do we know there isn’t something out there beyond the reach of our universe which is right now traveling beyond the speed of light?

Relative to what?

 

[quantumdude]

Point 1. All speed is relative to an observer and is never absolute (because there is no absolute frame of reference from which one can observe and measure).

Not quite: The speed of light is absolute.

Point 2. The laws of physics hold true for all frames of reference (i.e., an inch is an inch no matter how fast you are traveling).

Point 3. An object in motion will remain so until interfered with (by gravity, air friction, collision with another object, et cetera).

That's correct. Although if you want to avoid tensor calculus you have to specify that the frames are inertial, as Hombre points out.

I have been struggling with the logic behind the theory that light speed cannot be achieved by matter nor exceeded by anything. Using these three points, it doesn’t add up.

Naturally, it won't add up if you look at them only as a set of premises without regard for their content. Requiring the corrected Point 1 as well as Point 2 above leads inexorably to the Lorentz transformation, from which the light speed barrier is predicted.

I would like to illustrate my reasoning herein for a moment and submit it for a sort of peer review. I do not speak the language of tensor calculus, so my line of reasoning will come from my logical deduction. I conceptualize abstract ideas in my mind visually as opposed to mathematically, so please bear with me.

It's OK if you don't know tensor calculus. Einstein deduced it with algebra and some basic calculus.

I'd like to stop here and ask you if the correction to Point 1 changes your argument at all.

 

[DaveC426913]

Point 2. The laws of physics hold true for all frames of reference (i.e., an inch is an inch no matter how fast you are traveling).

Need clarification as to your expectation here.

An inch is an inch when measured by an observer making a measurement of something that's at rest with respect to her. But an inch measured of an object moving with respect to her will not measure an inch.

Agree? Disagree?

 

[AgnosticPriest]

With regard to all the Points, these were quoted from the theories/laws. They mean whatever the author meant.

In point 1, it seems quite clear that ANYTHING in motion can equally call its observer the one who is in motion. If this is true, we are all traveling light speed right now, relative to the photon's point of view. It's an impossible paradox! On a smaller scale, we are the ones traveling thousands of miles per hour away from the Cassini probe, so it is OUR clocks which should be going slower...but only from the perspective of the probe.

In point 2, the words say one thing (that an inch is an inch and a minute is a minute, no matter what frame you are in) but they seem to be getting interpreted to mean another (an inch is an inch only to an observer WITHIN his own particular frame, not outside it). Has anyone proved that items shorten in length as motion is increased? If so, everything we see should be constantly shortening in length from the perspective of thousands of travelers in the airspace right now. Again, a seemingly impossible paradox.

In point 3, I try to give some sort of rational explanation for the results science is giving us. Atoms shouldn't be affected by nothing more than motion (which is relative and means nothing without a relatively stationary observer), but they most definitely ARE affected by gravity and magnetism. Why would an atom on a plane act a certain way while the atoms on the ground refuse to? The atoms on the ground have just as much a reason to slow time and shorten in length as the ones on the plane, if the theory is to be considered. Because the ground is moving the speed of the plane in the opposite direction. Paradox!

As I understand inertia, it refers to the effect caused by changes in motion...not by motion itself. That would be a whole different animal. When I speak of motion, I refer to the abstract idea of an object moving from A to B, even though in reality there is no A or B except what an observer dictates. From the "moving" observer, he is standing still while it is A and B which are moving. Both are right and wrong at the same time, so why should the atoms on one be affected differently than the atoms on another? It doesn't make sense logically.

(And thanks for your polite responses. It's refreshing to not be shunned.)

 

[selfAdjoint]

I don't think your author correctly represented relativity. This can be derived rigorously from two postulates that sound a little like your author's, but the devil is in the details.

1) ("Galilian relativity") Physics is the same in every unertial frame. Falling bodies, clocks, all physical experiments all come out the same for every observer who isn't accelerated.
2) The speed of light is measured the same in every inertial frame. This is really an extension of the first, because measuring the speed of light is a physics experiment. But it has to be stated explicitly because it is contrary to Newtonian expectations.

From these two postulates, or principles, you can derive the Lorentz transformations which describe length contraction, time dilation, and the relativity of simultenaity.

 

[DaveC426913]

In point 1, it seems quite clear that ANYTHING in motion can equally call its observer the one who is in motion. If this is true, we are all traveling light speed right now, relative to the photon's point of view.

OK, couple of points to clarify:
1] "anything in inertial motion (i.e not accelerating) can equally call its observer the one who is in motion". As soon as one of the objects is under the influence of a force that alters its velocity, it is no longer relative. We can determine which one is which. Remeber, relativity applies only in inertial frames of reference.

2] "If this is true, we are all traveling light speed right now, relative to the photon's point of view." Photons do not have a 'point of view'. This is not merely mincing words. Nothing that has mass can be moving at the speed of light. Nothing. No object of any sort that could conceivably have a point of view is capable of moivng at the speed of light. What do photons experience? They do not experience anything at all. Photons quite simply do not experience the passage of time.

 

[AgnosticPriest]

OK, couple of points to clarify:
1] "anything in inertial motion (i.e not accelerating) can equally call its observer the one who is in motion". As soon as one of the objects is under the influence of a force that alters its velocity, it is no longer relative. We can determine which one is which. Remeber, relativity applies only in inertial frames of reference.

2] "If this is true, we are all traveling light speed right now, relative to the photon's point of view." Photons do not have a 'point of view'. This is not merely mincing words. Nothing that has mass can be moving at the speed of light. Nothing. No object of any sort that could conceivably have a point of view is capable of moivng at the speed of light. What do photons experience? They do not experience anything at all. Photons quite simply do not experience the passage of time.

This is what I meant: objects in an unchanging state of relative motion.

And as for photon's points of view, let's forget photons. Say an observer on a ship traveling 99% light speed relative to a planet. Why would the traveler experience time dilation and length shortening while the planet does not? Why would the atoms on the ship act differently than the atoms on the planet if both can say that the other is the one in motion and both would be correct? It doesn't make sense! There is no physical difference between the atoms on the ship and the atoms on the planet. Everything is relative to everything else when it comes to defining objects in an unchanging state of motion. You CAN'T have the effect on one plane and not the other without some outside influence. It's impossible!

 

[arildno]

I'll see if I can straighten this out for you:

"There is no physical difference between the atoms on the ship and the atoms on the planet. "

Correct; but given say a rod at rest with respect to the ship frame, it doesn't follow that the length of that rod measured by a ship observer will equal the length of the rod as measured by a planet observer.
In this case, the planet observer's length measurement of the rod will be smaller than the ship observer's length measurement of this rod.
.


Similarly, consider a rod at rest with respect to the planet frame (which, obviously, is a different object than the rod at rest in the ship frame).
In this case, the ship observer's length measurement will be less than the planet observer's length measurement.

 

[AgnosticPriest]

I'll see if I can straighten this out for you:

"There is no physical difference between the atoms on the ship and the atoms on the planet. "

Correct; but given say a rod at rest with respect to the ship frame, it doesn't follow that the length of that rod measured by a ship observer will equal the length of the rod as measured by a planet observer.
In this case, the planet observer's length measurement of the rod will be smaller than the ship observer's length measurement of this rod.
.


Similarly, consider a rod at rest with respect to the planet frame (which, obviously, is a different object than the rod at rest in the ship frame).
In this case, the ship observer's length measurement will be less than the planet observer's length measurement.

If that's true, there is no physical effect at all. It's all a matter of skewed perspective. They would only APPEAR to change in length. So what about time dilation? The same thing is true there as well, is it not?

 

[arildno]

Same thing with time dilation; however, you ought to be a bit careful when you use the word "skewed perspective":
Example:

In its own rest frame, muons have an exteremely short life-time "t" (half-life value, if you like).
When they enter the Earth's atmosphere, they have a velocity measured in the Earth frame very close to the speed of light.
The Earth observer can, on basis of the muon's observed velocity, and the distance the Earth observer measures from the entrance point in the atmosphere to the ground estimate the time "T" it takes for the muon to reach the ground.

Now, if we proceeded in a Newtonian manner, we would calculate the fraction of muons actually reaching the ground by comparing "t" and "T", i.e, regarding "t" as the correct life-time value of the (moving) muons as seen from the Earth.
But that fractional value we'd get is totally false!

What we need to do, in the Earth frame, is to take into account the time dilation factor, which in the muon/Earth case amounts to that for the Earth observer, the muon lives about 22 times longer than its rest frame life-time "t".
If we do this, we get the right answer.

From the muon perspective, it is the distance from the entrance point to the ground which has contracted by the same factor, yielding the same final fractional value of how many muons actually reaches the ground as when we do the computation in the Earth frame.

 

[Janus]

If that's true, there is no physical effect at all. It's all a matter of skewed perspective. They would only APPEAR to change in length. So what about time dilation? The same thing is true there as well, is it not?

You are falling into the trap of trying to attach a "mechanistic" cause for the effects of Relativity. Relativity is about the nature of time and space and how we measure them.

Frames in motion relative to each other simply do not measure distances and times the same. One meter as measured by me would be 1/2 meter as measured by someone moving at 0.866c relative to me, and vice versa. One second measured by me would be 2 sec as measured by him, and vice versa.

A third effect mentioned earlier, the "relativity of simultaneity", adds another wrinkle. The two frames will not agree as to whether events happen at the same time or not.

Consider two events separated by a distance that lies along the axis of the relative motion. In one frame these events are simultaneous. From a frame in relative motion, they will not be. Again this effect is reciprical, events simulataneous in the seconf frame will not be so in the first.

Using the muon example: according to the Earth clock, the muon enters the atmosphere at 0.00 and reaches the surface at time some time later t.

The muon undergoes a time dilation by a factor of 22 and thus ages t/22 during the trip.

From the muon's point of view, the Earth's atmosphere is only 1/22 the thickness it is as measured form the Earth and thus it only takes 1/22 the time to cross the atmosphere by the muon's clock to reach the surface, or t/22. Thus both the muon and Earth observer agree as to how much the Muon ages crossing the atmosphere.

However, according to the muon, it is the Earth clock that undergoes time dilation by a factor of 22, and thus ages by an amount of t/484 in the time it takes for the muon to cross the atmosphere.

This is where the relativity of simultaneity comes into play. While according to the Earth clock, the event of the muon entering the atmosphere and the clock reading 0.00 are simultaneous, they are not so for the muon. According to the muon, the Earth clock reads a time of t(1-1/484) at the instant the muon enters the atmosphere.

The upshot is that while both the muon and Earth observer agree as the both the age of the muon and what time the Earth clock reads when the muon reaches the surface, they do not agree as to why this result happens and neither's viewpoint on the sequence of events is any more valid than the other.

 

[arildno]

Note that Janus' and my posts do not contradict each other; rather, we're looking at the same problem in distinct, yet equally valid ways.

 

[JO 753]

About the simultanieity thing.

What stops someone from taking his own velocity into account?

The spaceship you are on is going 100,000 mps relative to the sun & you see a meteor strike on Mars in front of you and then another on Earth behind you a few seconds later. Why could you not calculate your speed relative to the planets to determin 'when' each strike happened ?

 

[arildno]

Given the data established in one inertial frame (the time&space-coordinates of some event), you may calculate what the coordinates of the same event would be in another inertial frame by using a suitable Lorentz transformation.

 

[Janus]

About the simultanieity thing.

What stops someone from taking his own velocity into account?

The spaceship you are on is going 100,000 mps relative to the sun & you see a meteor strike on Mars in front of you and then another on Earth behind you a few seconds later. Why could you not calculate your speed relative to the planets to determin 'when' each strike happened ?

You can, that's the whole point. Assume there is an observer at the midpoint between Earth and Mars and at rest with respect to the Sun. He sees the two meteor strikes at the same time, and knowing the distance to each is equal, determines that they occurred simultaneously. You reach the midpoint at the same instant as he sees the strikes, so you also see them at the same time.

You, however, taking into account your relative velocity to the Sun and the fact that light travels at c wrt yourself, "backtrack" the light signals back to the strikes, and determine that in order for you to have seen the light from each strike at the same time, the two strikes would have had to have occurred at different times and not simultaneously.

 

[nwall]

OK, couple of points to clarify:
1] "anything in inertial motion (i.e not accelerating) can equally call its observer the one who is in motion". As soon as one of the objects is under the influence of a force that alters its velocity, it is no longer relative. We can determine which one is which. Remeber, relativity applies only in inertial frames of reference.

This was only true for the special theory of relativity; the general theory of relativity got rid of the need to make the distinction between an accelerating body and a body in uniform motion. Both can be said to be at rest:

All Gaussian co-ordinate systems are essentially equivalent for the formulation of the general laws of nature.

- Albert Einstein, Relativity: The Special and General Theory, Section 28

 

[AgnosticPriest]

Frames in motion relative to each other simply do not measure distances and times the same. One meter as measured by me would be 1/2 meter as measured by someone moving at 0.866c relative to me, and vice versa. One second measured by me would be 2 sec as measured by him, and vice versa.

Exactly my point. Both perspectives cancel each other out.

However, according to the muon, it is the Earth clock that undergoes time dilation by a factor of 22, and thus ages by an amount of t/484 in the time it takes for the muon to cross the atmosphere.

This is where the relativity of simultaneity comes into play. While according to the Earth clock, the event of the muon entering the atmosphere and the clock reading 0.00 are simultaneous, they are not so for the muon. According to the muon, the Earth clock reads a time of t(1-1/484) at the instant the muon enters the atmosphere.

But according to the traveling muon, it is the Earth's atmosphere and surface which are traveling rather than it. It doesn't make sense that any special calculation need be made from either perspective that cannot be canceled out by a complete change of perspective. The Earth is moving toward the muon just as the muon is moving toward the earth. The muon is aging just the same as the Earth is. The length of the muon craft is shortening by a factor exactly the same as the Earth's atmosphere is. Any changes in time or length or distance that one observer measures will be the same for the other. If not, there is some third factor involved which applies to one and not the other. Thickness of atmosphere doesn't seem to cut it...that's just a matter of distance and has to be accounted for from both perspectives equally.

Why would the Earth be different just because it has an atmosphere? The muon's spacecraft or meteor also has physical features that have to be taken into account!

 

[Janus]

Exactly my point. Both perspectives cancel each other out.



But according to the traveling muon, it is the Earth's atmosphere and surface which are traveling rather than it.

right, that is why from the Muon's frame it is the Earth and it's atmosphere that undergoes length contraction

It doesn't make sense that any special calculation need be made from either perspective that cannot be canceled out by a complete change of perspective.

This statement doesn't make any sense. Within any frame the measurements in that frame do not change, only measurements of objects moving with respect to that frame change. There is nothing to "cancel out.

The Earth is moving toward the muon just as the muon is moving toward the earth. The muon is aging just the same as the Earth is. The length of the muon craft is shortening by a factor exactly the same as the Earth's atmosphere is.

The muon is not moving as far as the muon is concerned and thus does not contract or undergo time dilation in that frame.

Any changes in time or length or distance that one observer measures will be the same for the other.

Rule 1: Time dilation and length contraction only happen to the "other guy".

If not, there is some third factor involved which applies to one and not the other. Thickness of atmosphere doesn't seem to cut it...that's just a matter of distance and has to be accounted for from both perspectives equally.

Why would the Earth be different just because it has an atmosphere? The muon's spacecraft or meteor also has physical features that have to be taken into account!

Again.
According to the Muon it is the Earth and its atmosphere that undergo time dilation and length contraction.
According to the Earth is the muon that undergoes time dilation and length contraction.

According to the Earth, the muon hits the atmosphere when it clock reads 0.00

According to the muon it hits the atmosphere when the Earth clock read t(1-1/484) where t is the time the Earth clock reads when the muon reaches the surface.

According to both, the Earth clock reads t when the muon reaches the surface.

You can analyse the situation from either the Earth's frame or the muon's. But whichever you choose, you do not take the other's frames perspective into account. The muon does not care or is affected by how events appear to the Earth and the Earth does not care or is affected by how events appear to the Muon

 

[nwall]

Exactly my point. Both perspectives cancel each other out.

But according to the traveling muon, it is the Earth's atmosphere and surface which are traveling rather than it. It doesn't make sense that any special calculation need be made from either perspective that cannot be canceled out by a complete change of perspective. The Earth is moving toward the muon just as the muon is moving toward the earth. The muon is aging just the same as the Earth is. The length of the muon craft is shortening by a factor exactly the same as the Earth's atmosphere is. Any changes in time or length or distance that one observer measures will be the same for the other. If not, there is some third factor involved which applies to one and not the other. Thickness of atmosphere doesn't seem to cut it...that's just a matter of distance and has to be accounted for from both perspectives equally.

Why would the Earth be different just because it has an atmosphere? The muon's spacecraft or meteor also has physical features that have to be taken into account!

Let me take a stab at providing a suitable explanation. If you are only thinking in terms of time dilation and length contraction, then, no, relativity makes absolutely no sense. The "third factor" which you are searching for, as has been pointed out by others (although not plainly), is what is called relativity of simultaneity, and including this makes everything else make sense. Since we are in Michio Kaku's forum it seems quite fitting to quote from his book, Hyperspace. He gives a good, easy to understand example of how the apparent paradox you are confused about can be solved with the relativity of simultaneity.

Kaku starts by describing a train moving at nearly the speed of light. As it speeds down the tracks, we would see it squished in the direction of its motion. We would also see everyone moving in slow motion on the train, because time will tick slower for people on the train from our perspective. But how does this look to someone moving on the train? According to the principle of relativity, any reference body can be chosen to be called "at rest" and all velocities can be based on that (ie: someone sitting on the train is justified in saying he is sitting still and the Earth is hurtling toward him--although this does seem to be a bit weird way of thinking of things, since we're used to thinking of trains as being the body in motion). Because of this, we know that someone sitting on the train would see a squished version of the Earth and everything on it. A passenger on the train would also see everything in the outside, squished world moving in slow motion, because the Earth's time would move slower than his, due to the velocity of the Earth moving toward him. This is where the paradox arises. How can they both claim the other is squished and how can both of their clocks be moving slower than each other? The answer lies in the relativity of simultaneity, as Kaku explains:

Normally, it is absurd to think that two people can each be taller than the other. However, in this situation we have two people, each correctly thinking that the other has been compressed. This is not a true contradiction because it takes time in which to perform a measurement, and time as well as space has been distored. In particular, events that appear simultaneous in one frame are not simultaneous when viewed in another frame.

For example, let's say that people on the platform take out a ruler and, as the train passes by, drop the measuring stick onto the platform. As the train goes by, they drop the two ends of the stick so that the ends hit the platform simultaneously. In this way, they can prove that the entire length of the compressed train, from the front to the back, is only 1 foot long.

Now consider the same measuring process from the point of view of the passengers on the train. They think they are at rest and see the compressed subway station coming toward them, with compressed people about to drop a compressed ruler onto the platform. At first it seems impossible that such a tiny ruler would be able to measure the entire length of the train. However, when the ruler is dropped, the ends of the ruler do not hit the floor simultaneously. One end of the ruler hits the floor just as the station goes by the front end of the train. Only when the station has moved completely by the length of the entire train does the second end of the ruler finally hit the floor. In this way, the same ruler has measured the entire length of the train in either frame.

- Michio Kaku, Hyperspace, Notes: Chapter 4, note 3

Since you seem to be interested, I recommend reading a few books about relativity and the universe in general. Hyperspace is a great book to start with; it covers a wide range of ideas and Kaku explains things using very easy to understand analogies.

 

[AgnosticPriest]

Since you seem to be interested, I recommend reading a few books about relativity and the universe in general. Hyperspace is a great book to start with; it covers a wide range of ideas and Kaku explains things using very easy to understand analogies.

I have. I've read just about all of the ones available in layman form. And none of the explanations in them or in this thread have yet explained the difference which separates the moving object from the stationary observer. I understand everything which has been illustrated so far, and have read similar examples before. But they can still all be applied equally from both perspectives, and therefore cancel out.

There still hasn't been a concise explanation of what factor in the vehicle is different than the observer which ultimately makes the vehicle have effects which the observer does not experience equally.

 

[nwall]

I have. I've read just about all of the ones available in layman form. And none of the explanations in them or in this thread have yet explained the difference which separates the moving object from the stationary observer. I understand everything which has been illustrated so far, and have read similar examples before. But they can still all be applied equally from both perspectives, and therefore cancel out.

There still hasn't been a concise explanation of what factor in the vehicle is different than the observer which ultimately makes the vehicle have effects which the observer does not experience equally.

I must have misunderstood your question. I apologize.

 

[DaveC426913]

I have. I've read just about all of the ones available in layman form. And none of the explanations in them or in this thread have yet explained the difference which separates the moving object from the stationary observer. I understand everything which has been illustrated so far, and have read similar examples before. But they can still all be applied equally from both perspectives, and therefore cancel out.

There still hasn't been a concise explanation of what factor in the vehicle is different than the observer which ultimately makes the vehicle have effects which the observer does not experience equally.

At the risk of sounding glib, it would be well worth your while to do some more reading. The thing is, this is not a topic that can easily be explained in a few paragraphs - it is that different from our normal understanding of reality. That's why we're failing to explain it concisely here. To do so would require a chapter of a book.

 

[AgnosticPriest]

I must have misunderstood your question. I apologize.

No harm, no foul. Hard to display proper emotions through text. Didn't mean to come off as upset...I'm not. Just trying to get to the bottom of this quandry.

Peace.

 

[Doc Al]

But they can still all be applied equally from both perspectives, and therefore cancel out.

Just because relativistic effects apply equally to both frames does not mean that they cancel out. Each inertial observer sees the same effect when observing the other, but the effect is quite "real".

There still hasn't been a concise explanation of what factor in the vehicle is different than the observer which ultimately makes the vehicle have effects which the observer does not experience equally.

You seem to be looking for a mechanical, frame-independent factor that would explain the relativistic effects. There is none!

I highly recommend that you obtain a copy of Space and Time in Special Relativity by N. David Mermin.

 

[skeptic]

At the risk of being pedantic, could I point out 2 things. 1) The simplistic idea of 'back-tracking' signals, knowing the distances and the speed of light, is insufficient to explain relativistic effects properly. It works with sound, but it is a dangerous analogy to use with light. 2) There have been references to 'seeing' various objects squashed in their direction of motion. It has been known for some 60 years that the length contraction would not be visible, in such a literal sense. One is more likely to see an apparent rotation of the object. The squashing fallacy seems to have been originated by Gamow's Mr Tompkin's book.

 

[Doc Al]

At the risk of being pedantic, could I point out 2 things. 1) The simplistic idea of 'back-tracking' signals, knowing the distances and the speed of light, is insufficient to explain relativistic effects properly. It works with sound, but it is a dangerous analogy to use with light.

On the contrary, it's the only way to understand what's going on. What's simplistic about it?

2) There have been references to 'seeing' various objects squashed in their direction of motion. It has been known for some 60 years that the length contraction would not be visible, in such a literal sense. One is more likely to see an apparent rotation of the object. The squashing fallacy seems to have been originated by Gamow's Mr Tompkin's book.

Yes, the visual appearance of rapidly moving objects will not demonstrate length contraction in a simple way. But that does not mean that length contraction doesn't exist.

 

[skeptic]

1) I shall look up a suitable explanatory reference for you (it is easier than writing it all out here).
2) I did not say that the contraction does not occur. I merely wanted to combat the common misconception that one would be able to 'see' it, in the usual sense of the word. Because relativity is often explained by reference to ordinary objects (bicycles, trains, etc.), there is often a tendency to imply that ordinary methods of observation can be used - rather than the careful 'signal exchanges', etc., used by Einstein.

 

[selfAdjoint]

1) I shall look up a suitable explanatory reference for you (it is easier than writing it all out here).
2) I did not say that the contraction does not occur. I merely wanted to combat the common misconception that one would be able to 'see' it, in the usual sense of the word. Because relativity is often explained by reference to ordinary objects (bicycles, trains, etc.), there is often a tendency to imply that ordinary methods of observation can be used - rather than the careful 'signal exchanges', etc., used by Einstein.

If a body, say an asteroid, was moving through the solar system at a large fraction of c, and it was big enought to see with a telescope, then you could see the contraction that way. Physicists in accelerator experiments can take pictures of relativistically distorted particle clouds. It doesn't only show up under recondite signal interchanges.

 

[skeptic]

1) I do not believe that you could: all of the existing theory on the 'photography' of relativistic objects shows that one would see only an unexpectedly rotated view of the object; not a contraction. And if one did not know what it was 'supposed' to look like (as in the case of a strange asteroid), one would not even notice the rotation.
2) The reference which I was thinking of is: R.E.Scherr et al. Amer. J. Phys. 2001, 69[7] S24 [Phys. Ed. Res. Suppl.], and the point which I was trying to make is the same as in this quote from the paper: "Many students interpret the phrase 'relativity of simultaneity' as implying that the simultaneity of events is determined by an observer on the basis of the reception of light signals. They often attribute the relativity of simultaneity to the difference in signal travel time for different observers. In this way, they reconcile statements of the relativity of simultaneity with a belief in absolute simultaneity and fail to confront the startling ideas of special relativity." I am sure that you are not making this error, but I am also sure that some of the other relativity 'gurus' in these fora are doing so.

 

[AgnosticPriest]

Just because relativistic effects apply equally to both frames does not mean that they cancel out. Each inertial observer sees the same effect when observing the other, but the effect is quite "real".

If the exact same level of dilation and contraction is occurring from both perspectives, they HAVE to cancel each other out for all practical purposes! Neither would arrive one second younger than the other. It would all be attributable to skewed perspectives during motion which corrected itself once both frames were stopped relative to one another.

You seem to be looking for a mechanical, frame-independent factor that would explain the relativistic effects. There is none!

Unless you are going to use metaphysics to explain it, there HAS to be a mechanical factor. Something external to the frame in motion would have to be affecting it. Motion itself (the unchanging steady motion) is incalculable without an observer, which is meaningless except to the observer and is still incalculable from any absolute point of view...because there is none!

I highly recommend that you obtain a copy of Space and Time in Special Relativity by N. David Mermin.

I will, now that I'm aware of it. I love reading such books. I've read so many already, I thought I'd got them all. Dr. Kaku's, Stephen Hawkins', Einstein's, and on and on. But in all their wisdom and skill, they have never answered this question I've posted. They seem to dance around the issue by saying "it just is", which sounds like a cop-out for those who don't know how to put it into layman's terms...much like parents will do to their children who don't get the complexities of adult life.

I don't want to be disrespectful and I don't mean to come off as rude (again, the text is incapable of expressing tones of voice), but I really would like a complete layman's explanation for this.

 

[Doc Al]

If the exact same level of dilation and contraction is occurring from both perspectives, they HAVE to cancel each other out for all practical purposes!

Why would measurements made by different observers "cancel out"? As Janus explained, each inertial observer measures the other frame's sticks to be shorter and clocks to run slower. (Please reread Janus's post.)

To see how this works and why it is not self-contradictory, you must learn a bit of relativity. There are three effects that must be understood together: time dilation, length contraction, and the relativity of simultaneity. (For details, see Mermin.)

Unless you are going to use metaphysics to explain it, there HAS to be a mechanical factor. Something external to the frame in motion would have to be affecting it. Motion itself (the unchanging steady motion) is incalculable without an observer, which is meaningless except to the observer and is still incalculable from any absolute point of view...because there is none!

Nothing metaphysical about it. The effect is a kinematic one, due to the nature of space-time itself, which becomes evident when something moves with respect to something else. No absolute motion necessary.

Nothing "mechanical" happens to your clocks just because someone else moves with respect to you. (That would be really weird!) But observers in relative motion (each using their own perfectly good clocks and metersticks) will measure different time intervals between the same two events.

I will, now that I'm aware of it. I love reading such books. I've read so many already, I thought I'd got them all. Dr. Kaku's, Stephen Hawkins', Einstein's, and on and on. But in all their wisdom and skill, they have never answered this question I've posted. They seem to dance around the issue by saying "it just is", which sounds like a cop-out for those who don't know how to put it into layman's terms...much like parents will do to their children who don't get the complexities of adult life.

Sorry to disappoint you again, but the best physics can do is show how something works. You can often get to the next level of detail, or reveal a more fundamental principle or viewpoint, but sooner or later you just have to say that things just are the way they are. I would say that the ultimate "reason" for why relativity works the way it does is due to an inherent symmetry built into the structure of the world. (But why is there such a symmetry? Beats me!)

I don't want to be disrespectful and I don't mean to come off as rude (again, the text is incapable of expressing tones of voice), but I really would like a complete layman's explanation for this.

I am curious as to what kind of explanation you would find satisfying. The best I can do is refer you again to Mermin's work. (Here I recommend a few others: https://www.physicsforums.com/showpost.php?p=255747&postcount=114) But don't expect some secret mechanism to be revealed that will make you slap your head and say "so that's why clocks behave that way". But if you work your way through it, you will "understand" special relativity.

 

[εllipse]

I don't want to be disrespectful and I don't mean to come off as rude (again, the text is incapable of expressing tones of voice), but I really would like a complete layman's explanation for this.

Imagine a standard Cartesian coordinate system (K). The horizontal axis will be our measure of space (x) and the vertical axis will be our measure of time (t). If we draw a second, shrunken coordinate system (K') on top of it, and place a point (A) at an arbitrary spot on the plane, we'll find that someone who uses this second coordinate system (K') to state the coordinates of the point (A) will give larger values for the coordinates of the point than a person who uses the first coordinate system (K). However, someone who uses the first coordinate system (K) will not give larger values for the coordinates of a second point (A') than a person who uses the second coordinate system (K'). In fact, the person who uses the second coordinate system (K') as his basis for judgement will always measure larger times and distances than the person who uses the first coordinate system (K), with the exception of the point at (0, 0). This is where the paradox seems to arize. (Take note that any two points, separated by a distance (x), that have same time coordinate as judged by the person using the first coordinate system (t) will also have the same time coordinate as judged by the person using the second coordinate system (t'). Although each person will state that the events happened at different times, both will agree that the events happened simultaneously.)

Now we will replace the second coordinate system with a new (K') coordinate system. This coordinate system is not shrunken, however, but rotated (see the attached diagram). The blue dots along the t-axis represent successive ticks of a clock (B). This clock is stationary (along the x-axis) as judged from the first coordinate system (K), but changes with respect to time (t). The pink dots along the t'-axis represent successive ticks of a second clock (B'). This clock is stationary (along the x'-axis) as judged from the second coordinate system (K'). A person who uses the first coordinate system (K) will state that the second clock (B') is ticking faster than his clock because it will take only slightly more than 3 ticks of his clock (the blue dots) before the second clock (the pink dots) ticks 4 times. The green line along the t-axis is a mark of "elapsed time" that two people using the different coordinate systems may use to discuss their results. We'll give the green line a finite value to make discussion easier, say 10 seconds. As you can see, the person using the first coordinate system (K) will claim the second clock (B') finished its 4 ticks in about 5 or 6 seconds, but he will claim that his clock (B) didn't finish its 4 ticks until a second or two later. But the person using the second coordinate system (K') will make a similar claim. He will state that the first clock (B) finished ticking at around 5 or 6 seconds and his clock (B') didn't finish until a second or two later. Thus, both believe that each others' times are moving faster than their own, and they're both correct in stating so.

Notice also, the two red dots. The person using the first coordinate system (K) will claim they happen simultaneously (at the same moment in time (t)). However, the person using the second coordinate system (K') will claim they happened at different times.

So the paradox is solved. Hopefully, this answers your confusion as to how it's possible for two people to each claim the other is experiencing time slower in a visualizable Euclidean example. Although it isn't a valuable diagram of the relationship between two realistic relativistic coordinate systems, it does do an adequate job of explaining the paradox in question in an extremely easy way.

 

[AgnosticPriest]

Not quite following your word-logic.

I can see how, using your drawing, two observers in separate frames can view each other differently. But a mile is a mile, and it will always take a certain amount of time to travel that mile based on a fixed speed. Regardless of what each observer's perspective on each other may be during the travel, they will inevitably end up at the same distance (1 mile) at the same time if they travel the same speed. Neither will suddenly become the other's elder...not even in microseconds.

When two separate planes equal in size and age emerge from one common one, then remerge again, they must equal each other in age and length...unless an outside influence occurs to one and not the other.

Imagine a point in space (for reference) called "x". There are two spacecraft (A and B respectively) which are exactly ten feet in diameter, perfectly spherical, and containing one twenty-year-old male passenger each. Both spacecraft (for reasons of simplicity) have the capacity to jump directly to any given speed instantaneously and stop from any given speed instantaneously, without any sensation of inertia.
Objects A and B both simultaneously travel at half the speed of light in exact opposite directions and stop exactly one light year away. They then make the trip back to point "x" and compare notes.
Although they saw different things when each passenger looked at their buddy's ship:
Both passengers aged the exact same amount.
Both ships measure the exact same diameter and remain perfectly spherical.
Both ship clocks still tick at the same time second for second.

There is no difference in this scenario and any other scenario with A being stationary and the size of a planet and B being in relative motion and the size of a meteor or spacecraft . All speed is relative, so therefore the airplane with the atomic clock MUST have been experiencing outside influence...such as magnetism or gravity, or both.

 

[arildno]

If you are talking of the twin paradox, you are simply wrong.

Let A remain on the planet; "B" leaving in a space-craft, and then return.

While "A" can determine that A's own rest frame was an INERTIAL frame during the entire episode, "B" can determine that B's own frame was a NON-INERTIAL frame.
This is where the asymmetry effectively lies.