Relativity - Oh dear, here we go again!

[BillyJoe]

Observing a thing from different reference frames results in different perceptions of the thing, but I don’t see how this in any way creates different realities of the thing. A thing can only exist how it is, where it is, and it can only have one reality. There is an absolute “is” when it comes to the actual reality of a thing. It still seems to me that relativity is based on anomalies of perception and not on actual reality.

There is a great deal of truth in this and it would be absolutely true except for the inconvient fact that, when they meet up again, the twins really have aged at different rates.

regards,
BillyJoe

 

[Fredrik]

If time stops to create an event, how does it get started again? If an event can’t exist then a universal frame can’t exist either

You are really focusing on the wrong things here. The structure of space-time on very small scales is not what special relativity says it is, but if you want to understand things like time dilation, what you need to understand is special relativity, and space-time diagrams in particular. You do not have to understand what the small-scale structure of space-time really is. (No one understands that yet anyway).

As I see it, reality is represented by events (not an event).

I can agree with that, but it's irrelevant here. When you consider the twin paradox for example, it's perfectly adequate to think of the launching of the rocket followed by a short acceleration phase as an event. You don't lose anything essential by doing so.

Different events create different frames...

That's either not true or doesn't make sense, depending on what you mean. There is however a natural way to associate an inertial frame with each straight line through space-time. (Actually it would be a whole class of inertial frames related to each other by rotations, but let's not get into that right now). Since straight lines represent something moving with a constant velocity, we can think of this inertial frame as representing the point of view of a physical observer whose path through space-time is that straight line.

(One more technical point: I said "each" straight line, but it's actually only true for those lines that are "timelike".)

...and there is never an actual reality where existence shares the same frame.

If you mean that two objects can't occupy the same place in space-time, you're right (if we're talking about objects that can be described by classical physics), but you're using the word "frame" wrong, and you're still focusing on something that's irrelevant. It's perfectly adequate to think of the astronaut twin's return to Earth as an event where the twins' paths through space-time cross.

 

[Fredrik]

It’s only perceived to be running slower when observed from the other frame. How does an anomaly of perception change the actual reality of the clock as it is, where it is?

The answer to this is what I wrote in #326 (answering 69dodge). It is an anomaly of perception, but our "perception" is also more or less forced upon us by the physics, so it's not just an anomaly of perception. In special relativity, we define an inertial observer's point of view as the coordinate system that's naturally associated with his path through space-time, and when we compare the descriptions of the same set of events (the same "reality") made using the coordinate systems naturally associated with two different observers, there are differences, and we have given those differences names like "time dilation" and "Lorentz contraction".

In general relativity there is no natural way to associate a coordinate system with a physical observer's path through space-time, so there are no "points of view" in GR. (The best we can do is to define an approximate point of view that only makes sense in a small region of space-time).

The only reason we can even talk about two "points of view" descriptions of the same set of events in SR is that the properties of space-time allow us to define those points of view mathematically.

This is however a difficult point to get. I didn't really think of it that way myself until I was forced to think about it yesterday when I wanted to answer 69dodge.

 

[Fredrik]

So true. Until Kepler, Newton and Einstein, nobody understood gravity. Things fell, but nobody understood why.

All of those people increased our understanding of gravity by finding theories that agreed with observational and experimental evidence to various degrees. Each new theory was capable of describing a wider range of phenomena than the previous, and did it more accurately.

You can understand that an apple will fall to the ground if you drop it without understanding Newton's theory (because you have experiences that tell you what will happen), but there's no way you can understand that there will be time dilation when speeds get high without understanding the theory of special relativity.

Do you have a reference for who defined "event" like that? I would love to read the paper. And know what genius defined event that way. It would help us all out. Thanks.

It was probably Hermann Minkowski^WP, back in 1907, but you can find the definition in any textbook on special relativity or general relativity.

 

[ynot]

There is a great deal of truth in this and it would be absolutely true except for the inconvient fact that, when they meet up again, the twins really have aged at different rates.

regards,
BillyJoe

Only a “fact” (however inconvenient) and “really have aged” if relativity is a fact and really true. I realise yourself and others think this is so, but my jury is still out.

 

[Paulhoff]

Only a “fact” (however inconvenient) and “really have aged” if relativity is a fact and really true. I realise yourself and others think this is so, but my jury is still out.

May your jury stay out.

The twin that moved is younger, no matter how much and/or how fast, the experiments have been done, scientifically peered reviewed, and has passed all tests so far.

If you knew why, you wouldn’t have a jury.

Paul

 

[BillyJoe]

Ynot,

Only a “fact” (however inconvenient) and “really have aged” if relativity is a fact and really true. I realise yourself and others think this is so, but my jury is still out.

The experiment has been done with very accurate atomic clocks.
It is now established scientific fact.
What remains is for you to overcome your stubborness and accept it.
Whether you can get your head around it is another matter.
But while you are in denial it will be no easy task.

Bummer hey?

BillyJoe

 

[Tumbleweed]

And the moral of the story is that you cannot physically be present in two places ( or frames of reference) at the same time. And the number 101 can never be in a set of numbers that range from 1 to 100 by definition. Whoopee
My twin gets on a rocket and flys away. It blows up and never comes back. Are we saying that my reality is the only one that matters, and since the rocket did not blow up on Earth, it did not blow up at all and he is indeed coming back? Or would we insist that the rocket ship and my brother no longer exist at all since they are no longer in my frame of reference ( or within my defined set of numbers).
Or are we going to say that any and all events that happened to my brother in space are no longer relevant or real when he gets back, and all those Jedi battlescars will disappear once I lay eyes on him

 

[RecoveringYuppy]

@Tumbleweed. You need to re-read the thread. Almost every sentence you wrote contains a misunderstanding that's been addressed multiple times.

 

[ynot]

Obviously there hasn’t been an actual twins experiment done where one twin has travelled away and back and found to be measurably younger than the other. As far as I know the “proof” is either purely mathematical or time discrepancies have been measured in experiments with clocks.

Math is great but it doesn’t create reality and can abstractly express things that aren’t possible as an actual reality (zero for instance).

Clocks are most accurate when they’re in a stable environment. Leaving one clock in a relatively stable environment while the other is placed in an unstable environment of a flight around the world is bound (IMO) to create at least some discrepancies between the clocks that has nothing to do with relativity. In other words, has time slowed, or has the clock slowed?

As I’m not fluent in “relativity speak” let me explain what I mean by “frame”. If things are not moving relative to each other they are in the same frame. If they are moving relative to each other they are in different frames. Not only can a thing not be in two places at the same time, it also can’t move at two speeds or directions at the same time. A thing therefore can only exist in one frame. If an “event” was possible then everything would share the same frame. An event is a theoretical, abstract concept that’s not possible in actual reality, so an “event frame” is not possible either.

 

[sol invictus]

Obviously there hasn’t been an actual twins experiment done where one twin has travelled away and back and found to be measurably younger than the other.

There have been many, many such experiments (using identical atomic clocks as the twins). Here's the first link from a google search:

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/airtim.html

EDIT - by the way, an even more dramatic demonstration of this effect is seen in particle physics experiments every day. There are many kinds of unstable particles in the world - you make them, they exist for a certain lifetime, and then they decay (not unlike people, except that the lifetime is a small fraction of a second). Now make one of these particles and shoot it at high speed in some direction. Guess what happens? It last for much, much longer than its lifetime before it decays, and the extra time is in precise agreement with the relativistic time dilation factor we've been discussing. That experiment is done literally billions of times every day (no exaggeration) at multiple facilities around the world. It's one of the best-tested experimentally and most thoroughly understood theoretically phenomena in all of science.

As I’m not fluent in “relativity speak” let me explain what I mean by “frame”. If things are not moving relative to each other they are in the same frame. If they are moving relative to each other they are in different frames. Not only can a thing not be in two places at the same time, it also can’t move at two speeds or directions at the same time. A thing therefore can only exist in one frame.

If you simply replace "in a frame" with "at rest in an inertial reference frame" you will be able to communicate better with other people.

If an “event” was possible then everything would share the same frame. An event is a theoretical, abstract concept that’s not possible in actual reality, so an “event frame” is not possible either.

I have no idea what that means.

 

[ynot]

There have been many, many such experiments (using identical atomic clocks as the twins). Here's the first link from a google search.

Clocks are interchangeable with humans? Perhaps the clock was “jet-lagged” then.

The point I was trying to make is that a clocks accuracy can (or might) be affected by the unstable environment of a flight around the world. If it does and can, then the experiment hasn’t proven that time per se has been slowed by the flight, but merely the clock has been slowed compared to the other.

 

[ynot]

.I have no idea what that means.

As I understand it - An event is a theoretical “snapshot” of the universe where everything is “frozen” and nothing moves relative to anything else. Does that make it any clearer?

 

[sol invictus]

Clocks are interchangeable with humans? Perhaps the clock was “jet-lagged” then.

The point I was trying to make is that a clocks accuracy can (or might) be affected by the unstable environment of a flight around the world. If it does and can, then the experiment hasn’t proven that time per se has been slowed by the flight, but merely the clock has been slowed compared to the other.

So clocks flying west are always slowed differently than clocks flying east? By exactly the amount predicted by the theory? Those must be pretty smart clocks, or very direction-sensitive planes, huh? And every single time the experiment is done? No matter what kind of clock or plane is used?

And see the comment I added above about unstable particles.

If you don't want to believe in this no matter what the evidence, it's perfectly fine by me. Your loss.

 

[sol invictus]

As I understand it - An event is a theoretical “snapshot” of the universe where everything is “frozen” and nothing moves relative to anything else. Does that make it any clearer?

No - I don't understand what you mean, and that's certainly not how the word is used by everyone else.

An "event" is something that took place at a particular point in space and at a particular point in time. For example, a pion (an unstable particle) decayed into two photons at precisely 12 noon January 3rd 2008 at the exact center of Red Square in Moscow. That's an event.

 

[ponderingturtle]

Clocks are interchangeable with humans?

No for measureing the rate of travel through time they are much more accurate than humans. So we have don far more precise twin paradox experiments than the thought experiment.

 

[ponderingturtle]

Simply read the bible and have faith?

Or reading the dictionary to learn definitions of words. That is for those damn fundamentalist english types.

 

[ynot]

EDIT - by the way, an even more dramatic demonstration of this effect is seen in particle physics experiments every day. There are many kinds of unstable particles in the world - you make them, they exist for a certain lifetime, and then they decay (not unlike people, except that the lifetime is a small fraction of a second). Now make one of these particles and shoot it at high speed in some direction. Guess what happens? It last for much, much longer than its lifetime before it decays, and the extra time is in precise agreement with the relativistic time dilation factor we've been discussing. That experiment is done literally billions of times every day (no exaggeration) at multiple facilities around the world. It's one of the best-tested experimentally and most thoroughly understood theoretically phenomena in all of science.

Thanks. But I can’t help wondering if such an experiments are being correctly observed and interpreted, and how much confirmation bias might be involved. Perhaps I’m too fanatical a sceptic. If the “Theory of Relativity” has been proven as an indisputable fact, why isn’t it called the “Law of Relativity“?

 

[ynot]

Or reading the dictionary to learn definitions of words. That is for those damn fundamentalist english types


No for measureing the rate of travel through time they are much more accurate than humans. So we have don far more precise twin paradox experiments than the thought experiment..

You might find a dictionary handy yourself.

 

[Ziggurat]

Thanks. But I can’t help wondering if such an experiments are being correctly observed and interpreted, and how much confirmation bias might be involved. Perhaps I’m too fanatical a sceptic. If the “Theory of Relativity” has been proven as an indisputable fact, why isn’t it called the “Law of Relativity“?

Laws are concise statements of relationships, usually in the form of single equations. They are not distinct from theory because they are better understood or more correct, but because they are more compact. And they are frequently wrong anyways. Ohm's law doesn't work for transistors. Newton's 2nd law is only a low-velocity approximation. Relativity is not a law because it is a whole body of concepts, not a single one. It can never become a law, no matter how well-established it is. But it is extremely well established. If relativity is ever supplanted by something else, it's only going to be by something which maintains the essential features of relativity (at least in the regimes we've been able to access), just like Newtonian physics remains an excellent approximation of relativistic mechanics at low velocity.