[net.sf-lovers] Why shouldn't time travel leave you in the same spot?

petrick@lll-crg.ARPA (Jim Petrick) (08/16/85)

>>Everybody goes on and on about how if you time travel, you should end
>>up way out in space because the Earth is whizzing around the sun.
>
>Nice try Brad -- but wrong. The earth orbits the Sun, the solar system
>[rotates] (etc.)
[a few lines removed from the middle]

What's the problem?  If someone was smart enough to build a time machine in
the first place, couldn't they also think of compensating for these
rotations in some manner?  I know it would be nearly impossible to
determine all the effects of different frames of reference, but then I'd
think that the time travel aspect would be a much tougher nut to crack.
Besides, he could experiment to determine these rotational (etc) effects.

This discussion reminds me of an Isaac Asimov story about two scientists;
one a slow and cautious thinker, the other a quick, jump-to-conclusions
type.  The two are jealous rivals out to outdo each other.  The quick one
invents a device for nullifying gravity, and to show up his rival places
the device on the center of a pool table over a hole cut in the surface.
To embarass his rival, the quick guy invites the slow guy to demonstrate
what a great invention he has by shooting a pool ball across the hole in
the table (and through the null-gravity field).  The slow guy thinks a bit,
then makes a bank shot so the ball is headed directly at the fast guy as it
enters the field.  There is a flash, and the quick guy has a hole punched
through him by the ball (all gravity nullified, it was not accellerated
along with everything else in our frame of reference, and stayed put while
the rest of the world whooshed by).  

	Two questions:  Does anyone remember the title of this story?

			How could the slow guy predict which way the ball 
			accelerated?  

	Jim Petrick
	(petrick@lll-crg.ARPA)

peter@baylor.UUCP (Peter da Silva) (08/18/85)

> through him by the ball (all gravity nullified, it was not accellerated
> along with everything else in our frame of reference, and stayed put while
> the rest of the world whooshed by).  

It was accelerated because it was a massless particle and had to travel at 'C',
not because it was suddenly "left behind as the earth moved".

> 	Two questions:  Does anyone remember the title of this story?

Nope.

> 			How could the slow guy predict which way the ball 
> 			accelerated?  

Yeh, he figured it would keep going in the same direction on the absence of
other forces. A perhaps unwarranted generalisation of Neton, but what the
hell.
-- 
	Peter da Silva (the mad Australian werewolf)
		UUCP: ...!shell!neuro1!{hyd-ptd,baylor,datafac}!peter
		MCI: PDASILVA; CIS: 70216,1076

sean@ukma.UUCP (Sean Casey) (08/19/85)

In article <790@lll-crg.ARPA> petrick@lll-crg.UUCP (Jim petrick) writes:
>This discussion reminds me of an Isaac Asimov story about two scientists;
>one a slow and cautious thinker, the other a quick, jump-to-conclusions
>type.  The two are jealous rivals out to outdo each other.  The quick one
>invents a device for nullifying gravity, and to show up his rival places
>the device on the center of a pool table over a hole cut in the surface.
>To embarass his rival, the quick guy invites the slow guy to demonstrate
>what a great invention he has by shooting a pool ball across the hole in
>the table (and through the null-gravity field).  The slow guy thinks a bit,
>then makes a bank shot so the ball is headed directly at the fast guy as it
>enters the field.  There is a flash, and the quick guy has a hole punched
>through him by the ball (all gravity nullified, it was not accellerated
>along with everything else in our frame of reference, and stayed put while
>the rest of the world whooshed by).  

That is ludicrous.  The world would whoosh by only if the ball were
under a force that would cause it to de-accelerate.  If an antigrav
field were maintained upon the ball, it would eventually leave the
earth by centrifugal force, but not very quickly.

For what you decribed to happen, the device would not only have to
nullify gravity, but also place the ball in some relative movement such
that the earth seemed to be whooshing by.



-- 

-  Sean Casey				UUCP:	sean@ukma.UUCP   or
-  Department of Mathematics			{cbosgd,anlams,hasmed}!ukma!sean
-  University of Kentucky		ARPA:	ukma!sean@ANL-MCS.ARPA	

lsr@apple.UUCP (Larry Rosenstein) (08/20/85)

In article <790@lll-crg.ARPA> petrick@lll-crg.UUCP (Jim petrick) writes:
>.....
>
>This discussion reminds me of an Isaac Asimov story about two scientists;
>one a slow and cautious thinker, the other a quick, jump-to-conclusions
>type.  
>..... There is a flash, and the quick guy has a hole punched
>through him by the ball (all gravity nullified, it was not accellerated
>along with everything else in our frame of reference, and stayed put while
>the rest of the world whooshed by).  
>
I don't think that is the right explanation (at least not the
explanation given in the story).  When the gravity was nullified the
ball became massless.  Massless things (eg., photons) travel at the
speed of light, accounting for the ball's velocity.

-- 
Larry Rosenstein
Apple Computer

UUCP:  {nsc, dual, voder, ios, mtxinu}!apple!lsr
CSNET: lsr@Apple.CSNET

pamp@bcsaic.UUCP (pam pincha) (08/21/85)

In article <2063@ukma.UUCP> sean@ukma.UUCP (Sean Casey) writes:
>In article <790@lll-crg.ARPA> petrick@lll-crg.UUCP (Jim petrick) writes:
>>This discussion reminds me of an Isaac Asimov story about two scientists;
>>one a slow and cautious thinker, the other a quick, jump-to-conclusions
>>type.  The two are jealous rivals out to outdo each other.  The quick one
>>invents a device for nullifying gravity, and to show up his rival places
>>the device on the center of a pool table over a hole cut in the surface.
>>To embarass his rival, the quick guy invites the slow guy to demonstrate
>>what a great invention he has by shooting a pool ball across the hole in
>>the table (and through the null-gravity field).  The slow guy thinks a bit,
>>then makes a bank shot so the ball is headed directly at the fast guy as it
>>enters the field.  There is a flash, and the quick guy has a hole punched
>>through him by the ball (all gravity nullified, it was not accellerated
>>along with everything else in our frame of reference, and stayed put while
>>the rest of the world whooshed by).  
>
>That is ludicrous.  The world would whoosh by only if the ball were
>under a force that would cause it to de-accelerate.  If an antigrav
>field were maintained upon the ball, it would eventually leave the
>earth by centrifugal force, but not very quickly.
>
>For what you decribed to happen, the device would not only have to
>nullify gravity, but also place the ball in some relative movement such
>that the earth seemed to be whooshing by.
>-  Sean Casey				UUCP:	sean@ukma.UUCP   or
>-  Department of Mathematics			{cbosgd,anlams,hasmed}!ukma!sean
>-  University of Kentucky		ARPA:	ukma!sean@ANL-MCS.ARPA	

I suggest you send your comments to the "good Doctor" and
see what he has to come up with. He enjoys matching wits and
formulas given half the chance. (He also is a bit of a ham,
and loves attention and mail.)  You can send him a note thru   
his Sci-Fi magazine address.