"Science vs. Religion: What Scientists Really Think"

[humble brother]

polymath257 wrote:

Past acceleration is irrelevant.
...
If both the earth and the twin accelerate the same amount, then they will age the same amount.

So... Past acceleration is irrelevant...

Earth accelerates to 0.25*c to direction-X. This is now in the past and we are all in the rest frame of Earth. Then ship-X accelerates to from Earth 0.5*c to the direction opposite of direction-X.

Is the past acceleration irrelevant for determining rates of ageing on Earth and ship-X? If the past acceleration is irrelevant then your accounting for ship-1 past acceleration previously is FALSE.

[polymath257]

humble brother wrote:

<quoted text>
It is all trivial. You just want to straw man. I said they are in the same rest frame from which the other ship accelerates.
So stop whining.

No, you said they were in the same rest frame when they were moving. That is wrong.

[polymath257]

humble brother wrote:

<quoted text>
So... Past acceleration is irrelevant...
Earth accelerates to 0.25*c to direction-X.

With respect to what? Again, you give a velocity without a reference for it.

This is now in the past and we are all in the rest frame of Earth.

There are two 'rest frames' here: the one before the earth accelerated and the one after. Which do you mean?

Then ship-X accelerates to from Earth 0.5*c to the direction opposite of direction-X.

Unclear what you mean here. So the ship is going away from the earth and is at rest in the original frame?

Is the past acceleration irrelevant for determining rates of ageing on Earth and ship-X?

Yes.

If the past acceleration is irrelevant then your accounting for ship-1 past acceleration previously is FALSE.

Why do you say that? Exactly what do you think is false in what I said?

[humble brother]

polymath257 wrote:

No, you said they were in the same rest frame when they were moving. That is wrong.

Like I said, you like to take obvious trivial things and twist them into a straw man. I said that ship B accelerates from the ship 1 frame, until it accelerated they were in the same frame. That much is trivial.

[Subduction Zone]

humble brother wrote:

<quoted text>
Like I said, you like to take obvious trivial things and twist them into a straw man. I said that ship B accelerates from the ship 1 frame, until it accelerated they were in the same frame. That much is trivial.

It is fairly obvious that you do not know what a "frame of reference" is. It is nonsensical to say that an object is not in a frame of reference. Everything in the universe is in each and every frame of reference.

[humble brother]

polymath257 wrote:

With respect to what? Again, you give a velocity without a reference for it.

With respect everything else in the universe. A ship with fuel in space can just accelerate towards any direction, they feel the acceleration.

polymath257 wrote:

There are two 'rest frames' here: the one before the earth accelerated and the one after. Which do you mean?

What the heck are you talking about? We are all on Earth, at rest. Who was left in the previous rest frame from which Earth accelerated???

That acceleration is in the past, we felt some acceleration on Earth but they now the old frame is lost in history.

polymath257 wrote:

Unclear what you mean here. So the ship is going away from the earth and is at rest in the original frame?

It is quite simple and trivial. The ship was at rest on Earth when Earth accelerated. Before the ship accelerates it is in the same rest frame with Earth. Then the ship accelerates towards direction opposite of Earth's initial acceleration.

polymath257 wrote:

Yes.
<quoted text>
Why do you say that? Exactly what do you think is false in what I said?

Oh no... Lets try this even more simply.

Earth accelerates to speed 0.25*c towards direction-X with the ship-X on Earth, they are in the same rest frame. Then later ship-X accelerates to 0.5*c from Earth's rest frame towards direction opposite to direction-X. The relative velocity between Earth and ship-X is now 0.5*c.

What will be the rate of ageing on ship-X compared to Earth?

If Earth had not first accelerated to 0.25*c, would that rate be different?

[humble brother]

Subduction Zone wrote:

It is fairly obvious that you do not know what a "frame of reference" is. It is nonsensical to say that an object is not in a frame of reference. Everything in the universe is in each and every frame of reference.

Yawn. How can you be this lost?

They are not at rest in each and every frame of reference.

Do you understand what it means for two observes to be at rest in the same frame of reference?

[-Skeptic-]

Subduction Zone wrote:

<quoted text>
It is fairly obvious that you do not know what a "frame of reference" is. It is nonsensical to say that an object is not in a frame of reference. Everything in the universe is in each and every frame of reference.

Don't waste your time with this idiot. I assure you he will run around in circles.

[The Dude]

-Skeptic- wrote:

<quoted text>
Don't waste your time with this idiot. I assure you he will run around in circles.

Ah. He was your teacher!

:-)

[polymath257]

humble brother wrote:

Oh no... Lets try this even more simply.
Earth accelerates to speed 0.25*c towards direction-X

So it is now going .25*c in a certain direction with respect to the frame in which it started (frame 1).

with the ship-X on Earth, they are in the same rest frame.

So at this point, the ship is also moving at .25*c with respect to the frame in which the earth started. It is also at currently rest with respect to the earth (frame 2).

Then later ship-X accelerates to 0.5*c from Earth's rest frame towards direction opposite to direction-X.

OK, so now it is going .5*c with respect to frame 2. It also is going .286*c in frame 1 in the direction opposite the earth.

The relative velocity between Earth and ship-X is now 0.5*c.

Yes.

What will be the rate of ageing on ship-X compared to Earth?

The earth measures the ships clocks as running at 87% of 'normal'. The ship measures the earth's clocks as running at 87% of 'normal'.

If Earth had not first accelerated to 0.25*c, would that rate be different?

No. All that is relevant in this scenario is the relative velocities of the earth and the ship.

[polymath257]

humble brother wrote:

<quoted text>
With respect everything else in the universe. A ship with fuel in space can just accelerate towards any direction, they feel the acceleration.

Yes, but when you say a velocity of .5*c, you have to say in which reference frame that velocity is measured. In the frame that the ship was in before it accelerated?

What the heck are you talking about? We are all on Earth, at rest.

And yet, you were talking about the earth accelerating.

Who was left in the previous rest frame from which Earth accelerated???

Irrelevant. Are you measuring the new velocity of the earth with respect to the old frame?

That acceleration is in the past, we felt some acceleration on Earth but they now the old frame is lost in history.

So it is now irrelevant to any local measurements. it is irrelevant to how much time dilation there is between the earth and any ships nearby.

[humble brother]

polymath257 wrote:

The earth measures the ships clocks as running at 87% of 'normal'. The ship measures the earth's clocks as running at 87% of 'normal'.

And then the ship returns to Earth. Will the people on the ship have aged exactly as much as people on Earth?

[Subduction Zone]

humble brother wrote:

<quoted text>
And then the ship returns to Earth. Will the people on the ship have aged exactly as much as people on Earth?

No. Can you tell us why or do you want to wait for polymath to attempt to try to explain it to you?

[humble brother]

Subduction Zone wrote:

No. Can you tell us why or do you want to wait for polymath to attempt to try to explain it to you?

No? Are you sure?:D

There is no symmetry?

Relative to anything left (lets say the moon was left behind) in the initial rest frame Earth accelerated to 0.25*c and relative to that same thing the ship accelerated to 0.25*c to the opposite direction of Earth.

So, no symmetry? Is that your final answer?

[humble brother]

By now Polymath has probably realized that his horse is dead. I expect we will not see an answer from him.

[humble brother]

Perhaps I need to assist you a bit...

Lets say that instead of the ship returning to Earth, both Earth and the ship return to where the moon was left. They both travel back at 0.25*c.

When they're both back, do you think they still haven't aged exactly as much?:D

[polymath257]

humble brother wrote:

<quoted text>
And then the ship returns to Earth. Will the people on the ship have aged exactly as much as people on Earth?

It depends on how much the earth and the ship accelerate between the time the ship leaves and the time it returns.

If the ship and the earth accelerate the same amount, then they will age exactly as much.

If the earth does not accelerate and the ship does, then the ship will age less.

If the ship does not accelerate and the earth does, then the earth will age less.

Now, you have already said that the ship will accelerate, so the whole question is whether the earth will *also* accelerate between when the ship leaves and when it returns. If not, then the ship ages less. If the earth also accelerates, then the details of the acceleration are required to say which ages less.

[polymath257]

humble brother wrote:

<quoted text>
No? Are you sure?:D
There is no symmetry?
Relative to anything left (lets say the moon was left behind) in the initial rest frame Earth accelerated to 0.25*c and relative to that same thing the ship accelerated to 0.25*c to the opposite direction of Earth.
So, no symmetry? Is that your final answer?

In this, there is a symmetry and they will age the same.

Once again,

CASE I: for twins that are together at one time, move apart, and are together again at a later time,

1) if both accelerate the same amounts (even if in different directions), they will age the same.

2) if one accelerates and the other does not *during the time they are apart*, then the one that accelerates ages less.

3) if they both accelerate, then the details of the accelerations by both are required to know which ages less or if both age the same.

On the other hand,

CASE II: if we have twins that are in uniform motion, they will NOT meet each other twice and both will measure the other as aging less.

Remember this post, I will refer back to it.

[polymath257]

humble brother wrote:

Perhaps I need to assist you a bit...
Lets say that instead of the ship returning to Earth, both Earth and the ship return to where the moon was left. They both travel back at 0.25*c.
When they're both back, do you think they still haven't aged exactly as much?:D

They cannot begin at the moon and end at the moon without one of them accelerating. In other words, they cannot *both* travel at a uniform speed of .25*c in a straight line the whole time.

The answer will depend on the acceleration felt by the earth and the ship during the time between when they meet. See the post above.

[humble brother]

It is funny how blind you are in this case.

Lets say that billions of years ago Earth accelerated to 0.25*c to direction-X and now is on that path. Your logic is that that acceleration is in the past and no longer matters.

A ship which is at rest on Earth accelerates to 0.5*c to direction that happens to be perfectly opposite to direction-X.

There is now 0.5*c relative movement between Earth and the ship. When the distance between them is one light week both the ship and Earth accelerate equally towards each other so that they end up in the same rest frame.

Then both the ship and Earth accelerate to 0.25*c towards each other to meet up (0.5*c relative movement). When they get close they both decelerate equally and stop so that they end up in the same rest frame again.

The simple question to you is:
Is the above situation symmetrical so that both have aged equally?