The Twins Paradox in Relativity...

[Joe Gwinn]

It turns out there is a long history, with many parallel explanations:

..<https://en.wikipedia.org/wiki/Twin_paradox>

Joe Gwinn

 

[Martin Brown]

On 15/05/2022 12:05, Dimiter_Popoff wrote:

On 5/15/2022 0:35, Joe Gwinn wrote:
It turns out there is a long history, with many parallel explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

Joe Gwinn

And it explains why clocks at the equator and on the poles run
the same without involving gravity.

Actually they don\'t.

One of Einstein\'s minor errors in his 1905 paper on special relativity
was to predict how much slower a clock at the equator would tick when
compared to one at the pole (due to the extra rotational speed of a
clock at the equator). Every now and then someone points it out... eg

https://physicstoday.scitation.org/doi/10.1063/1.1897562#

They only run at the same speed when *both* the GR and SR corrections
are applied simultaneously and only then at mean sea level.

It is hard to get your head round but everybody\'s clock ticks at a
different speed. Your head ages marginally more quickly than your feet.

The best clocks in the world at NIST are now sensitive and stable enough
to detect a vertical shift of about 30cm or a foot in old money.

https://www.nist.gov/news-events/news/2010/09/nist-pair-aluminum-atomic-clocks-reveal-einsteins-relativity-personal-scale

This isn\'t a bad introduction by Brian Cox for BBC science series.

https://www.bbc.co.uk/iplayer/episode/m000x9v4/brian-coxs-adventures-in-space-and-time-series-1-4-what-is-time

(you might have to spoof a UK address to see it)

--
Regards,
Martin Brown

 

[Sylvia Else]

On 15-May-22 6:46 pm, Jeff Layman wrote:

But what happens with the Triplet Paradox where the moving triplets are
accelerating away from each other? Once they\'ve \"exceeded\" C in relation
to each other, <snip

That doesn\'t happen.

Sylvia.

 

[Dimiter_Popoff]

On 5/16/2022 16:07, Martin Brown wrote:

On 15/05/2022 12:05, Dimiter_Popoff wrote:
On 5/15/2022 0:35, Joe Gwinn wrote:
It turns out there is a long history, with many parallel explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

Joe Gwinn

And it explains why clocks at the equator and on the poles run
the same without involving gravity.

Actually they don\'t.

One of Einstein\'s minor errors in his 1905 paper on special relativity
was to predict how much slower a clock at the equator would tick when
compared to one at the pole (due to the extra rotational speed of a
clock at the equator). Every now and then someone points it out... eg

https://physicstoday.scitation.org/doi/10.1063/1.1897562#

They only run at the same speed when *both* the GR and SR corrections
are applied simultaneously and only then at mean sea level.

It is hard to get your head round but everybody\'s clock ticks at a
different speed. Your head ages marginally more quickly than your feet.

The best clocks in the world at NIST are now sensitive and stable enough
to detect a vertical shift of about 30cm or a foot in old money.

https://www.nist.gov/news-events/news/2010/09/nist-pair-aluminum-atomic-clocks-reveal-einsteins-relativity-personal-scale


This isn\'t a bad introduction by Brian Cox for BBC science series.

https://www.bbc.co.uk/iplayer/episode/m000x9v4/brian-coxs-adventures-in-space-and-time-series-1-4-what-is-time


(you might have to spoof a UK address to see it)

I have been digging into physics just as much as it takes to do what I
do so me being naive with that sort of thing is no surprise. I am
vaguely aware of what your references say, I think I may have read some
of these some time ago.
What I don\'t get though is the flashing light on the train thing.
Looks obvious to me that the observed period depends on the movement
direction (assuming gravity is constant, i.e. it is no factor).
In fact this should be easily measurable (not that I would go into
it, just wondering if you or someone else has an explanation, I am
not the \"out there to challenge the science\" type, more the \"curious
until things get clarified for me\" sort).

 

[Martin Brown]

On 16/05/2022 14:38, Dimiter_Popoff wrote:

I have been digging into physics just as much as it takes to do what I
do so me being naive with that sort of thing is no surprise. I am
vaguely aware of what your references say, I think I may have read some
of these some time ago.

What I don\'t get though is the flashing light on the train thing.
Looks obvious to me that the observed period depends on the movement
direction (assuming gravity is constant, i.e. it is no factor).

The bit you are missing is that to be able to meaningfully compare times
between two different moving objects they *have* to be at the same
location. That means a round trip back to the stay at home.

In fact this should be easily measurable (not that I would go into
it, just wondering if you or someone else has an explanation, I am
not the \"out there to challenge the science\" type, more the \"curious
until things get clarified for me\" sort).

One of the classic illustrations is to draw a world lines diagram for
bleep who stays put and booster who goes off at 4c/5 (3,4,5 triangle).

This illustration says it more clearly than words ever can. It was a
diagram of this sort that convinced me to give up on common sense where
relativity was concerned and trust the mathematics.

<https://www.google.com/url?sa=i&url=https%3A%2F%2Faapt.scitation.org%2Fdoi%2F10.1119%2F1.4947152&psig=AOvVaw2kQVy1xGR-cIehmwjR9R5y&ust=1652796475815000&source=images&cd=vfe&ved=0CAkQjRxqFwoTCLialeiY5PcCFQAAAAAdAAAAABAE>

It points to this article (behind a paywall )
https://aapt.scitation.org/doi/10.1119/1.4947152

Be a miracle if that works so Google keywords
\"world lines signal twin paradox illustration\"

--
Regards,
Martin Brown

 

[Phil Hobbs]

Jeff Layman wrote:

On 14/05/2022 22:35, Joe Gwinn wrote:
It turns out there is a long history, with many parallel explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

It can be expanded to the Triplets Paradox, for example
http://www.mysearch.org.uk/website1/html/251.Triplets.html

SRT is well above me, I\'m afraid. Some of the explanation of the Twins
Paradox refers to the twins\' clocks transmitting their time to the other
twin (the clock signal is transmitted at the speed of light). Even
allowing for the travelling twin\'s speed when approaching the speed of
light, and the relativistic effect it has on each clock\'s perceived
time, as the travelling twin\'s speed doesn\'t exceed that speed, each
twin will, eventually, receive the clock time of the other.

But what happens with the Triplet Paradox where the moving triplets are
accelerating away from each other? Once they\'ve \"exceeded\" C in relation
to each other, although they can receive the stationary triplet\'s clock
reading (and he can receive theirs), can one moving triplet still
receive the other moving triplet\'s clock signal? If there is such a
moment when they can no longer receive each other\'s signal, when they
finally stop moving away and start moving towards each other again, will
there be a moment when they suddenly start receiving that \"missing\"
clock signal as they catch up with it (or perhaps it catches up with
them)? Will there be a specific moment when they not only receive a
missing clock time, but coincidentally receive the \"accurate\" time as
transmitted by the other moving triplet, so appear to be receiving two
different clock readings at the same time?

If you shine your laser pointer at two points 180 degrees apart in the
sky, the relative speed of the light pulses in your frame of reference
is 2c. No paradox is involved.

Also, there\'s no simultaneity between separated objects moving at
different speeds. The relativistic garage illustrates this.

Say you have a 1927 Bugatti Type 41, which is 252 inches long. Your
garage is the standard 20 feed (240 inches) long, and has a very fast
automatically-controlled door at each end. The doors are designed to
open and close automatically to allow the car to enter and leave.

Because the Bugatti is so fast, you drive towards the open end of the
garage at 0.5c. You measure the length of the garage as

240 inches * sqrt(1-0.5**2) = 207.8 inches.

The hood of the car passes through the open door, then the closed door
opens before the back bumper has passed through the doorway. No
collision occurs, because the second door opens before the first one closes.

Your spouse, waiting for you to come home from your drive, measures the
length of the car as

252 inches * sqrt(1-0.5**2) = 218.2 inches.

The car fits into the garage, so as it enters, the first door closes
before the second door opens. Once again no collision occurs, because
the car is shorter than the garage.

The math works out fine in both English and metric, and no paradoxes are
involved.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[corvid]

On 5/16/22 07:18, Phil Hobbs wrote:

Jeff Layman wrote:
On 14/05/2022 22:35, Joe Gwinn wrote:
It turns out there is a long history, with many parallel
explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

It can be expanded to the Triplets Paradox, for example
http://www.mysearch.org.uk/website1/html/251.Triplets.html

SRT is well above me, I\'m afraid. Some of the explanation of the
Twins Paradox refers to the twins\' clocks transmitting their time
to the other twin (the clock signal is transmitted at the speed of
light). Even allowing for the travelling twin\'s speed when
approaching the speed of light, and the relativistic effect it has
on each clock\'s perceived time, as the travelling twin\'s speed
doesn\'t exceed that speed, each twin will, eventually, receive the
clock time of the other.

But what happens with the Triplet Paradox where the moving triplets
are accelerating away from each other? Once they\'ve \"exceeded\" C
in relation to each other, although they can receive the stationary
triplet\'s clock reading (and he can receive theirs), can one
moving triplet still receive the other moving triplet\'s clock
signal? If there is such a moment when they can no longer receive
each other\'s signal, when they finally stop moving away and start
moving towards each other again, will there be a moment when they
suddenly start receiving that \"missing\" clock signal as they catch
up with it (or perhaps it catches up with them)? Will there be a
specific moment when they not only receive a missing clock time,
but coincidentally receive the \"accurate\" time as transmitted by
the other moving triplet, so appear to be receiving two different
clock readings at the same time?


If you shine your laser pointer at two points 180 degrees apart in
the sky, the relative speed of the light pulses in your frame of
reference is 2c. No paradox is involved.

Also, there\'s no simultaneity between separated objects moving at
different speeds. The relativistic garage illustrates this.

Say you have a 1927 Bugatti Type 41, which is 252 inches long. Your
garage is the standard 20 feed (240 inches) long, and has a very
fast automatically-controlled door at each end. The doors are
designed to open and close automatically to allow the car to enter
and leave.

Because the Bugatti is so fast, you drive towards the open end of the
garage at 0.5c. You measure the length of the garage as

240 inches * sqrt(1-0.5**2) = 207.8 inches.

The hood of the car passes through the open door, then the closed
door opens before the back bumper has passed through the doorway. No
collision occurs, because the second door opens before the first one
closes.

Your spouse, waiting for you to come home from your drive, measures
the length of the car as

252 inches * sqrt(1-0.5**2) = 218.2 inches.

The car fits into the garage, so as it enters, the first door closes
before the second door opens. Once again no collision occurs,
because the car is shorter than the garage.

The math works out fine in both English and metric, and no paradoxes
are involved.

Cheers

Phil Hobbs

But, but... the bottom of the tires are in contact with the garage
floor. Shouldn\'t that anchor the Bugatti and garage into the same frame?

 

[Dimiter_Popoff]

On 5/16/2022 17:18, Phil Hobbs wrote:

Jeff Layman wrote:
On 14/05/2022 22:35, Joe Gwinn wrote:
It turns out there is a long history, with many parallel explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

It can be expanded to the Triplets Paradox, for example
http://www.mysearch.org.uk/website1/html/251.Triplets.html

SRT is well above me, I\'m afraid. Some of the explanation of the Twins
Paradox refers to the twins\' clocks transmitting their time to the
other twin (the clock signal is transmitted at the speed of light).
Even allowing for the travelling twin\'s speed when approaching the
speed of light, and the relativistic effect it has on each clock\'s
perceived time, as the travelling twin\'s speed doesn\'t exceed that
speed, each twin will, eventually, receive the clock time of the other.

But what happens with the Triplet Paradox where the moving triplets
are accelerating away from each other? Once they\'ve \"exceeded\" C in
relation to each other, although they can receive the stationary
triplet\'s clock reading (and he can receive theirs), can one moving
triplet still receive the other moving triplet\'s clock signal? If
there is such a moment when they can no longer receive each other\'s
signal, when they finally stop moving away and start moving towards
each other again, will there be a moment when they suddenly start
receiving that \"missing\" clock signal as they catch up with it (or
perhaps it catches up with them)? Will there be a specific moment when
they not only receive a missing clock time, but coincidentally receive
the \"accurate\" time as transmitted by the other moving triplet, so
appear to be receiving two different clock readings at the same time?


If you shine your laser pointer at two points 180 degrees apart in the
sky, the relative speed of the light pulses in your frame of reference
is 2c.  No paradox is involved.

This is obvious enough. I refer to the case where the laser pointer is
moving towards us; no RTT involved, we just measure the period at which
it flashes. Since the light speed is always c and every next flash will
have less distance to travel until it reaches us it seems obvious
we will see a period shorter than it is for an observer moving together
with the pointer. And vice versa, if the pointer moves away from us
each next flash will have more distance to travel at c to reach us
so the period we will see will be longer than at the pointer (the
latter being the example Einstein gives in some of the papers, IIRC).
Should not be too hard to test experimentally nowadays (the direction
dependence, that is). At the moment I can\'t see how the period of an
approaching pointer will be longer for the observer.
I\'ll better switch to doing something useful, it is not that I don\'t
have enough to do .

 

[Dimiter_Popoff]

On 5/16/2022 17:13, Martin Brown wrote:

On 16/05/2022 14:38, Dimiter_Popoff wrote:

I have been digging into physics just as much as it takes to do what I
do so me being naive with that sort of thing is no surprise. I am
vaguely aware of what your references say, I think I may have read some
of these some time ago.

What I don\'t get though is the flashing light on the train thing.
Looks obvious to me that the observed period depends on the movement
direction (assuming gravity is constant, i.e. it is no factor).

The bit you are missing is that to be able to meaningfully compare times
between two different moving objects they *have* to be at the same
location. That means a round trip back to the stay at home.

In fact this should be easily measurable (not that I would go into
it, just wondering if you or someone else has an explanation, I am
not the \"out there to challenge the science\" type, more the \"curious
until things get clarified for me\" sort).

One of the classic illustrations is to draw a world lines diagram for
bleep who stays put and booster who goes off at  4c/5 (3,4,5 triangle).

This illustration says it more clearly than words ever can. It was a
diagram of this sort that convinced me to give up on common sense where
relativity was concerned and trust the mathematics.

https://www.google.com/url?sa=i&url=https%3A%2F%2Faapt.scitation.org%2Fdoi%2F10.1119%2F1.4947152&psig=AOvVaw2kQVy1xGR-cIehmwjR9R5y&ust=1652796475815000&source=images&cd=vfe&ved=0CAkQjRxqFwoTCLialeiY5PcCFQAAAAAdAAAAABAE


It points to this article (behind a paywall )
https://aapt.scitation.org/doi/10.1119/1.4947152

Be a miracle if that works so Google keywords
\"world lines signal twin paradox illustration\"

I am not talking about the \"twin paradox\", I had not heard the
phrase until this post (or did not remember I had). It involves
acceleration so things get more complex.
I refer only to the blinking object moving towards us and away from
us, no acceleration (I put that into more detail in my post to
Phil).
I\'ll try to switch to doing useful work now though. Thanks for
the links and explanations, once I get bugged again I\'ll probably
be heard of .

 

[Phil Hobbs]

corvid wrote:

On 5/16/22 07:18, Phil Hobbs wrote:
Jeff Layman wrote:
On 14/05/2022 22:35, Joe Gwinn wrote:
It turns out there is a long history, with many parallel
explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

It can be expanded to the Triplets Paradox, for example
http://www.mysearch.org.uk/website1/html/251.Triplets.html

SRT is well above me, I\'m afraid. Some of the explanation of the
Twins Paradox refers to the twins\' clocks transmitting their
time to the other twin (the clock signal is transmitted at the
speed of light). Even allowing for the travelling twin\'s speed
when approaching the speed of light, and the relativistic effect
it has on each clock\'s perceived time, as the travelling twin\'s
speed doesn\'t exceed that speed, each twin will, eventually,
receive the clock time of the other.

But what happens with the Triplet Paradox where the moving
triplets are accelerating away from each other? Once they\'ve
\"exceeded\" C in relation to each other, although they can receive
the stationary triplet\'s clock reading (and he can receive
theirs), can one moving triplet still receive the other moving
triplet\'s clock signal? If there is such a moment when they can
no longer receive each other\'s signal, when they finally stop
moving away and start moving towards each other again, will there
be a moment when they suddenly start receiving that \"missing\"
clock signal as they catch up with it (or perhaps it catches up
with them)? Will there be a specific moment when they not only
receive a missing clock time, but coincidentally receive the
\"accurate\" time as transmitted by the other moving triplet, so
appear to be receiving two different clock readings at the same
time?


If you shine your laser pointer at two points 180 degrees apart in
the sky, the relative speed of the light pulses in your frame of
reference is 2c. No paradox is involved.

Also, there\'s no simultaneity between separated objects moving at
different speeds. The relativistic garage illustrates this.

Say you have a 1927 Bugatti Type 41, which is 252 inches long.
Your garage is the standard 20 feed (240 inches) long, and has a
very fast automatically-controlled door at each end. The doors
are designed to open and close automatically to allow the car to
enter and leave.

Because the Bugatti is so fast, you drive towards the open end of
the garage at 0.5c. You measure the length of the garage as

240 inches * sqrt(1-0.5**2) = 207.8 inches.

The hood of the car passes through the open door, then the closed
door opens before the back bumper has passed through the doorway.
No collision occurs, because the second door opens before the first
one closes.

Your spouse, waiting for you to come home from your drive,
measures the length of the car as

252 inches * sqrt(1-0.5**2) = 218.2 inches.

The car fits into the garage, so as it enters, the first door
closes before the second door opens. Once again no collision
occurs, because the car is shorter than the garage.

The math works out fine in both English and metric, and no
paradoxes are involved.

Cheers

Phil Hobbs

But, but... the bottom of the tires are in contact with the garage
floor. Shouldn\'t that anchor the Bugatti and garage into the same
frame?

And the pistons are going up and down pretty good too.

Just stick with the front and rear bumpers for present purposes.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[corvid]

On 5/16/22 13:26, Phil Hobbs wrote:

Also, there\'s no simultaneity between separated objects moving at
different speeds. The relativistic garage illustrates this.

Say you have a 1927 Bugatti Type 41, which is 252 inches long.
Your garage is the standard 20 feed (240 inches) long, and has a
very fast automatically-controlled door at each end. The doors
are designed to open and close automatically to allow the car to
enter and leave.

Because the Bugatti is so fast, you drive towards the open end
of the garage at 0.5c. You measure the length of the garage as

240 inches * sqrt(1-0.5**2) = 207.8 inches.

The hood of the car passes through the open door, then the closed
door opens before the back bumper has passed through the
doorway. No collision occurs, because the second door opens
before the first one closes.

Your spouse, waiting for you to come home from your drive,
measures the length of the car as

252 inches * sqrt(1-0.5**2) = 218.2 inches.

The car fits into the garage, so as it enters, the first door
closes before the second door opens. Once again no collision
occurs, because the car is shorter than the garage.

The math works out fine in both English and metric, and no
paradoxes are involved.

Cheers

Phil Hobbs

But, but... the bottom of the tires are in contact with the garage
floor. Shouldn\'t that anchor the Bugatti and garage into the same
frame?

And the pistons are going up and down pretty good too.

Just stick with the front and rear bumpers for present purposes.

Cheers

Phil Hobbs

Now I want to tweak the car and garage lengths, and the speed, so that
the car goes thru unscathed in one frame but gets smashed in the other.
Is it possible?

 

[Clifford Heath]

On 17/5/22 12:18 am, Phil Hobbs wrote:

then the closed door opens before the back bumper has passed through the
doorway.  No collision occurs

Umm, sorry? \"before\"? Is that a slip? Did you mean \"as the back bumper
passes through the doorway?

Very cool illustration BTW. I want to use it, but want to make sure I
have it correct first.

Clifford Heath.

 

[Phil Hobbs]

Clifford Heath wrote:

On 17/5/22 12:18 am, Phil Hobbs wrote:
then the closed door opens before the back bumper has passed through
the doorway.  No collision occurs

Umm, sorry? \"before\"? Is that a slip? Did you mean \"as the back bumper
passes through the doorway?

No, the point is that seen from a point in the car\'s reference frame,
the events happen *in a different order* from what you\'d see in the
garage\'s frame.

Very cool illustration BTW. I want to use it, but want to make sure I
have it correct first.

Clifford Heath.

I picked the Bugatti because I\'m a fan, and looked up the standard
length of a garage on the net--the fact that it worked out well with a
speed of c/2 was fortuitous. (I\'m very far from the first to use that
general sort of illustration, of course, but it\'s a fun one.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

corvid wrote:

On 5/16/22 13:26, Phil Hobbs wrote:

Also, there\'s no simultaneity between separated objects moving at
 different speeds.  The relativistic garage illustrates this.

Say you have a 1927 Bugatti Type 41, which is 252 inches long. Your
garage is the standard 20 feed (240 inches) long, and has a very
fast automatically-controlled door at each end.  The doors are
designed to open and close automatically to allow the car to enter
and leave.

Because the Bugatti is so fast, you drive towards the open end
of the garage at 0.5c.  You measure the length of the garage as

240 inches * sqrt(1-0.5**2) = 207.8 inches.

The hood of the car passes through the open door, then the closed
 door opens before the back bumper has passed through the
doorway. No collision occurs, because the second door opens
before the first one closes.

Your spouse, waiting for you to come home from your drive, measures
the length of the car as

252 inches * sqrt(1-0.5**2) = 218.2 inches.

The car fits into the garage, so as it enters, the first door closes
before the second door opens.  Once again no collision occurs,
because the car is shorter than the garage.

The math works out fine in both English and metric, and no paradoxes
are involved.



But, but...  the bottom of the tires are in contact with the garage
 floor. Shouldn\'t that anchor the Bugatti and garage into the same
frame?

And the pistons are going up and down pretty good too.

Just stick with the front and rear bumpers for present purposes.


Now I want to tweak the car and garage lengths, and the speed, so that
the car goes thru unscathed in one frame but gets smashed in the other.
Is it possible?

Nope. When a collision occurs, it\'s because the two objects moving at
different speeds are trying to be in the same place at once. If there\'s
no difference in position, you can have simultaneity, same as if there\'s
no difference in speed.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Clifford Heath]

On 17/5/22 9:42 am, Phil Hobbs wrote:

Clifford Heath wrote:
On 17/5/22 12:18 am, Phil Hobbs wrote:
then the closed door opens before the back bumper has passed through
the doorway.  No collision occurs

Umm, sorry? \"before\"? Is that a slip? Did you mean \"as the back bumper
passes through the doorway?

No, the point is that seen from a point in the car\'s reference frame,
the events happen *in a different order* from what you\'d see in the
garage\'s frame.

Oh ok, I get it.

Very cool illustration BTW. I want to use it, but want to make sure I
have it correct first.

Clifford Heath.

I picked the Bugatti because I\'m a fan,

My grandfather had a Type 40 for a while - it\'s now restored and living
in a garage 15km from here. But his really interesting car that I\'d like
to find more about was a Lea-Francis \"Hyper\" - the first supercharged
British production car. He used to race that at the Albert Park track
and the Philip Island track, which are both current or previous F1
tracks. I don\'t think he ever entered F1, but I have a number of photos
he took while flag marshalling at Phillip Island in 1933.

Clifford Heath.

 

[Clive Arthur]

On 16/05/2022 14:38, Dimiter_Popoff wrote:

<snipped>

I have been digging into physics just as much as it takes to do what I
do so me being naive with that sort of thing is no surprise. I am
vaguely aware of what your references say, I think I may have read some
of these some time ago.
What I don\'t get though is the flashing light on the train thing.
Looks obvious to me that the observed period depends on the movement
direction (assuming gravity is constant, i.e. it is no factor).
In fact this should be easily measurable (not that I would go into
it, just wondering if you or someone else has an explanation, I am
not the \"out there to challenge the science\" type, more the \"curious
until things get clarified for me\" sort).

One extra thing - the (very fast) train\'s time is dilated, so if both
stationary you (ie, waiting in the station) and the driver are both
flashing at 1Hz, he\'ll send fewer flashes than you.

Is that right?

--
Cheers
Clive

 

[Phil Hobbs]

Clifford Heath wrote:

On 17/5/22 9:42 am, Phil Hobbs wrote:
Clifford Heath wrote:
On 17/5/22 12:18 am, Phil Hobbs wrote:
then the closed door opens before the back bumper has passed through
the doorway.  No collision occurs

Umm, sorry? \"before\"? Is that a slip? Did you mean \"as the back
bumper passes through the doorway?

No, the point is that seen from a point in the car\'s reference frame,
the events happen *in a different order* from what you\'d see in the
garage\'s frame.

Oh ok, I get it.

Very cool illustration BTW. I want to use it, but want to make sure I
have it correct first.

Clifford Heath.

I picked the Bugatti because I\'m a fan,

My grandfather had a Type 40 for a while - it\'s now restored and living
in a garage 15km from here. But his really interesting car that I\'d like
to find more about was a Lea-Francis \"Hyper\" - the first supercharged
British production car. He used to race that at the Albert Park track
and the Philip Island track, which are both current or previous F1
tracks. I don\'t think he ever entered F1, but I have a number of photos
he took while flag marshalling at Phillip Island in 1933.

Clifford Heath.

Fun!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[RichD]

On May 16, corvid wrote:

Also, there\'s no simultaneity between separated objects moving at
different speeds. The relativistic garage illustrates this.
Because the Bugatti is so fast, you drive towards the open end
of the garage at 0.5c. You measure the length of the garage as
240 inches * sqrt(1-0.5**2) = 207.8 inches.
The hood of the car passes through the open door, then the closed
door opens before the back bumper has passed through the
doorway. No collision occurs, because the second door opens
before the first one closes.
Your spouse measures the length of the car as
252 inches * sqrt(1-0.5**2) = 218.2 inches.
The car fits into the garage, so as it enters, the first door
closes before the second door opens. Once again no collision
occurs, because the car is shorter than the garage.

Now I want to tweak the car and garage lengths, and the speed, so that
the car goes thru unscathed in one frame but gets smashed in the other.
Is it possible?

heh
Einstein skeptics have been trying to do that for a hundred years.

Playing around with the the numbers does make a nice exercise for the student.

You can also gin up variations on this paradox. For instance, the garage
becomes a two lane highway, with north and southbound lanes. Two cars
approach, simultaneously, as seen from the garage. In the garage frame, it\'s
much the same as before, both cars fit inside.

Then work out the various door sequences, as seen from each vehicle, for some
real brain twisting -

--
Rich

 

[Phil Hobbs]

RichD wrote:

On May 16, corvid wrote:
Also, there\'s no simultaneity between separated objects moving at
different speeds. The relativistic garage illustrates this.
Because the Bugatti is so fast, you drive towards the open end
of the garage at 0.5c. You measure the length of the garage as
240 inches * sqrt(1-0.5**2) = 207.8 inches.
The hood of the car passes through the open door, then the closed
door opens before the back bumper has passed through the
doorway. No collision occurs, because the second door opens
before the first one closes.
Your spouse measures the length of the car as
252 inches * sqrt(1-0.5**2) = 218.2 inches.
The car fits into the garage, so as it enters, the first door
closes before the second door opens. Once again no collision
occurs, because the car is shorter than the garage.

Now I want to tweak the car and garage lengths, and the speed, so that
the car goes thru unscathed in one frame but gets smashed in the other.
Is it possible?

heh
Einstein skeptics have been trying to do that for a hundred years.

There\'s a class of things, called _Lorentz_scalars_, that are the same
in all reference frames, i.e. hitting them with a Lorentz transform
doesn\'t change the answer. On example is phase. (It\'s based on
counting, not length measurements.) Whether a collision occurs is one
of those.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Anthony William Sloman]

On Sunday, May 15, 2022 at 7:35:56 AM UTC+10, Joe Gwinn wrote:

It turns out there is a long history, with many parallel explanations:

.<https://en.wikipedia.org/wiki/Twin_paradox

But no reference to the traveling clock experiment,

https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

or the Global Positioning System satellites, where these effects are of practical importance.

Experimental fact is very effective at disciplining theoretical speculation.

--
Bill Sloman, Sydney