Relativity - Oh dear, here we go again!

[BillyJoe]

...and, Myriad, that is a really good explanation.
I hope ynot doesn't miss it.

 

[Ziggurat]

As I understand it the periods of acceleration of the travelling twin aren’t what causes the time dilation but it’s that the travelling twin is travelling faster than the other that does.

Acceleration itself does not cause time dilation. But the fact that one twin accelerated and another did not does matter. Let's look at the triplet problem (two traveling siblings moving in opposite directions, one earthbound) in three different inertial reference frames (space is horizontal axis, time is vertical, black lines are a lightcone, colored lines are paths of siblings):



In all frames, moving twins experience time dilation relative to unmoving ones, and which ones are moving and which aren't changes. But note what happens in reference frames where the earthbound triplet (red) is moving: the traveling siblings move even faster, for more than half the journey, than the earth-bound twin, and so experience more total time dilation regardless of which reference frame we examine the problem in - provided that we are looking from an inertial reference frame. Handling it in a non-inertial frame is possible (and you'll get the same final answer if you do it right), but it gets ugly, so let's not do that for now.

 

[sol invictus]

There's no way to find out what the predictions of Newton's theory of gravity are without treating his assumptions as if they were correct.

Not so. For example, we can define Newtonian gravity as the weak-field limit of GR. No Newtonian assumptions are necessary.

I'm not sure why it bothers you that I think it's OK to think of that as "pretending" that the inverse square law is correct while we're doing the calculation. Anyway, it's clear that we only disagree about the semantics.

Yes, but semantics are important. To say we must pretend makes it sound like we're willfully deceiving ourselves. But that's nonsense - we are simply making a controlled approximation. We know it's not exact, we know what to do if we need more precision, and we know when the errors become large. It has nothing whatsoever to do with pretense.

When a store adds tax to a price and rounds it off to the nearest cent, are they "pretending" the tax always adds up to a whole number? When you say the temperature is 29, are you "pretending" it's exactly 29.000000.... degrees?

 

[ynot]

Of course they're not exactly the same thing. It's an analogy. But they're very very similar.

Imagine you were a member of an isolated tribe that never invented perspective drawing. So in your whole life you've never seen a drawing with perspective, or a photograph. Then, someone comes along and shows you photographs of the Brooklyn Bridge taken from different angles. Your tribe uses rope suspension bridges, so with a bit of explanation you understand the bridge, but what you can't understand is why the bridge looks different in pictures from different angles.

You tell the stranger: "In this picture, the tower at one end is higher. In this picture, the tower at the other end is higher. And yet you're claiming that they're both the same height, like in this third picture here. Each picture shows the bridge having different properties, and yet you claim they're all the same bridge. That's a contradiction. What you must really mean is that the bridge exists in many different realities, and each picture shows a different reality."

The analogy goes fairly deep, because both our tribesman looking at perspective photographs for the first time, and you when you contemplate relativistic effects, are mistaking the effects of a rotation of viewpoint as changes in the actual properties of the observed object/event. For the bridge photos, the rotation is of the camera position in 3-space relative to the bridge; for relativistic observations, the rotation is of the observer in 4-dimensional spacetime relative to the event observed.

One key point is that just as the camera angle from which it's photographed is not an intrinsic property of a bridge, a reference frame is not an intrinsic property of a moving object. A reference frame is a property of the observer.

It's a language shortcut, and therefore potentially misleading, to speak of "an object observed from its own reference frame." What that really means is "an object observed from a reference frame in which the object's velocity is zero."

It becomes really misleading when you start describing a change in velocity (an acceleration) of an object as the object "changing reference frames." Since a reference frame is not a property of the object, it doesn't change when the object accelerates. It's up to the person evaluating the subsequent events whether to keep the same reference frame and calculate the effects of the acceleration within that reference frame, or change reference frames and calculate the effects of that change in reference frame. This will lead to two different ways of doing the math, but the results will be the same.

In one reference frame, a clock ticks faster than it does in another. In one reference frame, a rocket is longer than it is in another. Not different realties. The same reality, observed from different angles in spacetime.

Respectfully,
Myriad

Point of observation and distance can cause perception anomalies and delayed observation but I don’t see how any of this changes the actual reality of anything. The far end of the bridge appears smaller than the near one but in reality they are always the same size. A clock one light second away appears to be running one second slow but it isn’t. How does where or how a thing is observed (or even if it’s observed) have any actual effect on an thing?

 

[ynot]

I am sorry, but I do not understand what this means. They have taken different paths from point A to point B, which means that they have experienced different distances between point A and point B. Does that means they have experienced different realities of that distance?

If you would say that they have, then I guess the above statement is right. However, I am not sure what it is supposed to show. It seems like you are just using a non-standard definition of the word "reality".

Do you understand “According to Relativity the twins experience different realities of time” any better if I say they experience different “proper” times?

I also don’t understand what you mean. What path did the “stay home” twin travel if it stayed home?

A and B are on a long conveyor belt travelling at 2X. B travels against the motion of the belt at X and is still travelling in the same direction as A but at half the speed. B then travels back to A at X and 2X (the speed of the belt). When A and B are back together the net result of the speed and distance they have both independently travelled is exactly equal. B always travelled in the same direction as A and never “turned around“. Given it can’t be said that the “stay home” twin is actually stationary in an absolute or universal sense how can it be said that both twins don’t travel exactly the same distance and speed as A and B did on the belt? Relatively stationary isn’t absolutely stationary and acceleration can’t be correctly (absolutely) defined as being either an increase or decrease in speed.

 

[Reality Check]

Point of observation and distance can cause perception anomalies and delayed observation but I don’t see how any of this changes the actual reality of anything. The far end of the bridge appears smaller than the near one but in reality they are always the same size. A clock one light second away appears to be running one second slow but it isn’t. How does where or how a thing is observed (or even if it’s observed) have any actual effect on an thing?

"Point of observation and distance" do not have any effect in Special Relativity. The "clock one light second away appears" appears to be running at exactly the same rate as any other clock that is moving at the same velocity as the clock.

The relative velocity of observers does have effects, e.g time dilation.

The longer lifetime of muons is an example (probably in this thread already). We measure the lifetime of muons in experiments where their velocity is low and get one value. We measure the lifetime of muons produced by high energy cosmic rays and get higher value for the lifetime.

 

[Reality Check]

I also don’t understand what you mean. What path did the “stay home” twin travel if it stayed home?

I can answer this: You have forgotten about the time bit of spacetime. The "stay at home" twin did not move in space from point A in spacetime to point B in spacetime. But their time coordinate went from point A to point B.
That is the first diagram in Ziggurat's previous post about triplets. Remember that the images are 2D slices through a 4D space with "space is horizontal axis, time is vertical, black lines are a lightcone, colored lines are paths of siblings".

 

[ynot]

"Point of observation and distance" do not have any effect in Special Relativity. The "clock one light second away appears" appears to be running at exactly the same rate as any other clock that is moving at the same velocity as the clock.

I didn’t say the clock would appear to run at a slower rate. I said it would appear to be showing time one second slower than it actually showed because the information took a second to reach the observer. The observation would be time delayed by one second.

 

[Reality Check]

I didn’t say the clock would appear to run at a slower rate. I said it would appear to be showing time one second slower than it actually showed because the information took a second to reach the observer. The observation would be time delayed by one second.

Then you are right - a clock one light second away will appear to be one second behind another (previously synchronized) clock with an observer.
However this is just basic Newtonian physics - nothing to do with relativity.

Of course what Myraid has stated is an analogy: "Of course they're not exactly the same thing. It's an analogy. But they're very very similar."

 

[ynot]

I can answer this: You have forgotten about the time bit of spacetime. The "stay at home" twin did not move in space from point A in spacetime to point B in spacetime. But their time coordinate went from point A to point B.
That is the first diagram in Ziggurat's previous post about triplets. Remember that the images are 2D slices through a 4D space with "space is horizontal axis, time is vertical, black lines are a lightcone, colored lines are paths of siblings".

When I tell a theist that I don’t accept their claim that a god exists they invariably start quoting from the bible. This is totally pointless as the bible is only valid if a god exists. When I tell people that I don’t accept Relativity because I can’t accept some of the basic building blocks it’s constructed on then it’s equally pointless to use Relativity to validate the building blocks.

 

[ynot]

Then you are right - a clock one light second away will appear to be one second behind another (previously synchronized) clock with an observer.
However this is just basic Newtonian physics - nothing to do with relativity.

Of course what Myraid has stated is an analogy: "Of course they're not exactly the same thing. It's an analogy. But they're very very similar."

I can’t see them as being similar at all so I don‘t get the analogy.

ETA - Perhaps I should say that I can see that the claimed effects of Relativity are similar to the actual effects of perception and observation anomalies. In fact to me Relativity seems to take the effects of perception and observation anomalies and claim they are actual and lasting effects on things.

 

[Reality Check]

When I tell a theist that I don’t accept their claim that a god exists they invariably start quoting from the bible. This is totally pointless as the bible is only valid if a god exists. When I tell people that I don’t accept Relativity because I can’t accept some of the basic building blocks it’s constructed on then it’s equally pointless to use Relativity to validate the building blocks.

Your acceptance of The "building blocks" of Relativity is not needed, especially since my post did not even mention the two "building blocks" of relativity.
The scientific acceptance of relativity comes when the theory matches the experimental data which it has for over 100 years.

 

[Reality Check]

I can’t see them as being similar at all so I don‘t get the analogy.

What can you not get?
In one case an optical effect makes measurements different to different observers.
In another case a velocity effect makes measurements different to different observers.
Seems similiar to me.

 

[ynot]

What can you not get?
In one case an optical effect makes measurements different to different observers.
In another case a velocity effect makes measurements different to different observers.
Seems similiar to me.

We are cross posting. Did you see this addition to my previous post? - ETA - Perhaps I should say that I can see that the claimed effects of Relativity are similar to the actual effects of perception and observation anomalies. In fact to me Relativity seems to take the effects of perception and observation anomalies and claim they are actual and lasting effects on things.”

 

[Reality Check]

We are cross posting. Did you see this addition to my previous post? - ETA - Perhaps I should say that I can see that the claimed effects of Relativity are similar to the actual effects of perception and observation anomalies. In fact to me Relativity seems to take the effects of perception and observation anomalies and claim they are actual and lasting effects on things.”

Relativity does not assume that there are "effects of perception and observation anomalies". That is the terminology used in the anology.

SR starts with its 2 postulates and deduces that observers will see different things, e.g. two observers at different velocities will see each others clock running slower. These are not observation anomalies. They are actual observed facts.

 

[ynot]

Your acceptance of The "building blocks" of Relativity is not needed, especially since my post did not even mention the two "building blocks" of relativity.
The scientific acceptance of relativity comes when the theory matches the experimental data which it has for over 100 years.

More ice cream is eaten in summer months and more murders are committed in summer months. This doesn’t mean that eating ice cream turns people in to murderers.

As I said earlier in the thread - “From a sceptical perspective Relativity seems to use a lot of terms that are “user friendly”. I don’t think this is any form of conscious conspiracy but perhaps there is an ongoing subconscious confirmation bias. Collective subconscious confirmation bias could also apply to experimental data (I know it’s not likely but it‘s possible). Not every academic in the world accepts Relativity or the experiments that are claimed to prove it (I‘m not an academic).

I also said - “It’s most likely however that I simply don’t fully understand the language and how it’s correctly applied to reality”.

 

[ynot]

Relativity does not assume that there are "effects of perception and observation anomalies". That is the terminology used in the anology.

SR starts with its 2 postulates and deduces that observers will see different things, e.g. two observers at different velocities will see each others clock running slower. These are not observation anomalies. They are actual observed facts.

I have no disgreement or argument with “observers will see different things” and “two observers at different velocities will see each others clock running slower” because they will see effects of perception and observation anomalies. I don’t understand how this means each other’s clocks actually will run slower however.

 

[ynot]

A couple of questions . . .

Has it been experimentally proven (non-math) that light always travels at c regardless of the speed of the observer?

What problem does Relativity fix?

 

[Reality Check]

More ice cream is eaten in summer months and more murders are committed in summer months. This doesn’t mean that eating ice cream turns people in to murderers.

As I said earlier in the thread - “From a sceptical perspective Relativity seems to use a lot of terms that are “user friendly”. I don’t think this is any form of conscious conspiracy but perhaps there is an ongoing subconscious confirmation bias. Collective subconscious confirmation bias could also apply to experimental data (I know it’s not likely but it‘s possible). Not every academic in the world accepts Relativity or the experiments that are claimed to prove it (I‘m not an academic).

I also said - “It’s most likely however that I simply don’t fully understand the language and how it’s correctly applied to reality”.

Ice cream also has nothing to do with special relativity .

Why do you expect SR to use non-user friendly terms?

I would say that SR terms are not applied to reality. What they are applied to is a scientific model that is close to reality.
The way I look at it is that the scientific method does not start with an assumption of a specific kind of reality. The scientific process starts with the assumption that the universe can be measured and that these measurements can be modeled mathematically to form a picture of reality. That picture is not the actual, one and only reality (assuming that there is a reality and that there is only one). It is an approximation that gets closer to reality as the scientific process continues.

 

[Reality Check]

A couple of questions . . .
Has it been experimentally proven (non-math) that light always travels at c regardless of the speed of the observer?

Yes: What is the experimental basis of Special Relativity?

What problem does Relativity fix?

Lots of problems, e.g.

• Particle accelerators do not work unless you account for SR effects in their design.
• GPS does not work unless you account for SR effects in its design.