Re: Does anyone really know the physical cause for time dilation and length contraction?

From	Sylvia Else <sylvia@not.at.this.address>
Newsgroups	sci.physics
Subject	Re: Does anyone really know the physical cause for time dilation and length contraction?
Date	2016-05-17 12:53 +1000
Message-ID	<dpvfclFh8n4U1@mid.individual.net> (permalink)
References	(2 earlier) <e0cc2aeb-8f2d-4ea2-af63-03e7695120a4@googlegroups.com> <dpsmi1FuddbU1@mid.individual.net> <10429c21-1547-4eda-ad2b-3bc133eee9be@googlegroups.com> <dpt2fdF1teqU1@mid.individual.net> <1e18e60c-8828-470d-b3db-1bca6d34e91b@googlegroups.com>

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On 17/05/2016 5:47 AM, xxein1@att.net wrote:
> On Monday, May 16, 2016 at 1:00:33 AM UTC-4, Sylvia Else wrote:
>> On 16/05/2016 2:45 PM, xxein1@att.net wrote:
>>> On Sunday, May 15, 2016 at 9:37:11 PM UTC-4, Sylvia Else wrote:
>>>> On 16/05/2016 1:31 AM, xxein1@att.net wrote:
>>>>> On Sunday, May 15, 2016 at 9:05:22 AM UTC-4, Sylvia Else
>>>>> wrote:
>>>>>> On 14/05/2016 5:17 AM, xxein1@att.net wrote:
>>>>>>> Can we have a discussion about the root physical cause of
>>>>>>> TD and LC? We all know the math, so skip that.  What is
>>>>>>> it about velocity that becomes a cause?  What about
>>>>>>> gravity as a cause?  How are they a cause?  Stick to
>>>>>>> principles of cause and effect or start your own thread
>>>>>>> for all else.
>>>>>>>
>>>>>>> Btw.  Just because 'we measure' doesn't answer the
>>>>>>> question of how it affects.
>>>>>>>
>>>>>>
>>>>>>
>>>>>> It's a mistake to think of this as cause and effect.
>>>>>> Velocity does not cause time dilation and length
>>>>>> contraction. They are simply manifestations of how
>>>>>> different observers see the universe.
>>>>>>
>>>>>> When I move along (even slowly), I observe the world moving
>>>>>> the other way. Yet it is not sensible to suggest that my
>>>>>> motion has had some strange effect on the world. I just
>>>>>> observe the world from a different perspective.
>>>>>>
>>>>>> Similar thoughts apply to gravity.
>>>>>>
>>>>>> Sylvia.
>>>>>
>>>>> xxein:  So according to you, it's no big deal and why should
>>>>> anyone care?
>>>>>
>>>>
>>>> No, that's not what I said. But you're looking for a cause
>>>> when nothing is being caused.
>>>>
>>>> Sylvia.
>>>
>>> xxein:  You know the clocks those twins have?  Whenever I see
>>> them side by side, they never have the same time.  Did I lose
>>> half my perspective?
>>>
>>
>> So you never look at them side by side just as they set out on
>> their journeys?
>>
>> The travel by different routes. There's no reason to expect their
>> clocks to say the same when they get back.
>>
>> Sylvia.
>
> xxein:  So I have a reason to expect them to be different?  (Let's
> skip gravity for a moment.)  I set their clocks before they left.
> One twin came back an hour slow and the other was two hours slow.
> They each went directly to the same place and stayed a day before
> returning - although one came back before the other.  Why were their
> clocks different from one another?  Did they forget to oil their
> clocks?  What caused their clocks to have different times - both
> slower than mine?
>

In the scenario you describe, they've taken different paths through 
space time, consequently there's no reason to expect their clocks to 
show the same when they get back.

This is not fundamentally different from having them drive cars on a 
round trip, but via different routes, and observing different numbers on 
the trip meters that show distance travelled when they get back.

A journey through space-time is more difficult to visualise, but that's 
the only essential difference.

Sylvia.

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