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Microgravity parable



 
 
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  #81  
Old October 21st 03, 03:05 AM
Stuf4
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Default Microgravity parable

From stmx3:
Stuf4 wrote:
[snip]


"NASA scientists call this microgravity... The term is apt since
Albert Einstein said that acceleration caused by gravity is equivalent
to any other push."

The principle is about _mass_ equivalence, not acceleration
equivalence.

[snip]

That is incorrect. It was the happiest moment in Einstein's life when
he realized that an accelerated reference frame was equivalent to a
frame in a uniform gravitational field. From this basis, Einstein could
later show the equivalence of intertial and gravitational mass. But the
first preceded the second.


It's called a thought experiment. I suspect a primary reason is
because Einstein was well aware that there's no such thing as a
"uniform gravitational field".

Gravity follows an inverse square decay (not uniform linear decay).
Gravity extends radially (not uniformly linear once again).

These are the extremely fine ways to distinguish gravity from uniform
linear acceleration (the "moving elevator"). To repeat the easy way:

Just look out the window.

In the following, Einstein discusses how he came to believe there should
be *no* preferred reference frame for the description of physical phenomena:

"Then there occurred to me the ... happiest though of my life, in the
following form. The gravitational field has only a relative existence
in a way similar to the electric field generated by magnetoelectric
induction. *Because for an observer falling freely from the roof of a
house there exists--at least in his immediate surroundings--no
gravitational field* [his emphasis in italics]. Indded, if the observer
drops some bodies then these remain relative to him in a state of rest
or of uniform motion, independent of their particular chemical or
physical nature (in this consideration the air resistance is, of course,
ignored). The observer therefore has the right to interpret his state
as 'at rest.'


Here are two possible explanations for the above italics:

- Einstein was misquoted.

- Einstein was mistaken.

Let's not fall into the trap that, "Einstein said it then it must be
true". I don't know of anyone who is(/was) infallible.

Of course, a third explanation of the highlighted quote is that the
position I've been backing here is in error and that somehow gravity
ceases to exist when an object is in freefall ("there exists...no
gravitational field" in the immediate surroundings).

Both positions appear to be very well defined. We are all free to
reject what strikes us as absurd and to accept that which seems
logical.

Because of this idea, the uncommonly peculiar experimental law that in
the gravitational field all bodies fall with the same acceleration
attained at once a deep physical meaning. Namely, if there were to
exist just one single object that falls in the gravitational field in a
way different from all others, then with its help the observer could
realize that he is in a gravitational field and is falling in it. If
such an object does not exist, however--as experience has shown with
great accuracy--then the observer lacks any objective means of
perceiving himself as falling in a gravitational field. Rather he has
the right to consider his state as one of rest and his environment as
field-free relative to gravitation.

The experimentally known matter independence of the acceleration of fall
is therefore a powerful argument for the fact that the relativity
postulate has to be extended to coordinate systems which, relative to
each other, are in non-uniform motion."

(Pais, A. (1982). 'Subtle is the Lord...': The Science and the Life of
Albert Einsteing. Oxford: Oxford University Press. p. 178)

So, Einstein would say that an ISS crewmember has the right to say
he/she is in zero gravity.


If Albert isn't turning in his grave over the use (nay, the
popularity) of that term, I am certain that Isaac is.

(my opinion)


~ CT
  #82  
Old October 21st 03, 03:39 AM
Stuf4
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Default Microgravity parable

From Peter Smith:
Mike Hanson wrote...
Out in space and accelerating at
9.81 m/s^2, the man also has weight: he feels exactly the
same force pushing up on the soles of his feet. These two
'forms' of weight are qualitatively identical, and this is
where you have gone wrong: looking out of the window
doesn't count. The key word is 'locally', and the question
is: can you distinguish between the first and second
cases *if you don't know where you are*? And the answer is: no.


Mike, I fail to see your reasoning as to why looking out the window
doesn't count as a simple way to tell that you are in a very strong
gravitational field (due to the planet Earth, the Sun, the Moon, etc)
as opposed to a "zero gravitation" field (no gravity).

You ask whether one can distinguish between gravity and acceleration. But
the question of whether one can distinguish between 'orbital microgravity'
and a 'microgravity field' is a different question.


Peter, please check "orbital microgravity" as a self-contradictory
oxymoron. Orbits require gravity in order to be orbits.

(I would be interested to hear an official explanation of how NASA
resolves this blatant contradiction.)


~ CT
  #83  
Old October 21st 03, 02:22 PM
Peter Smith
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Default Microgravity parable


Stuf4 wrote...

You ask whether one can distinguish between gravity and acceleration.
But the question of whether one can distinguish between 'orbital
microgravity' and a 'microgravity field' is a different question.


Peter, please check "orbital microgravity" as a self-contradictory
oxymoron. Orbits require gravity in order to be orbits.


duuh - that's why I used the quote marks, Stuf4.

I went on to explain how you could (if you were in a sealed box with no
windows and experiencing no obvious gravitational effects), how you could
differentiate between orbit and absence of (significant) gravity.

By the way, if you looked out the window, how would you detect a black
hole?

- Peter


  #84  
Old October 21st 03, 07:41 PM
stmx3
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Default Microgravity parable

Peter Smith wrote:
Stuf4 wrote...


You ask whether one can distinguish between gravity and acceleration.
But the question of whether one can distinguish between 'orbital
microgravity' and a 'microgravity field' is a different question.


Peter, please check "orbital microgravity" as a self-contradictory
oxymoron. Orbits require gravity in order to be orbits.



duuh - that's why I used the quote marks, Stuf4.

I went on to explain how you could (if you were in a sealed box with no
windows and experiencing no obvious gravitational effects), how you could
differentiate between orbit and absence of (significant) gravity.

By the way, if you looked out the window, how would you detect a black
hole?

- Peter



Apparently, according to Stuf4, you can see acceleration, but you can't
see gravitation.

  #85  
Old October 22nd 03, 03:17 AM
Neelix
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Default Microgravity parable

Peter Smith wrote:
I went on to explain how you could (if you were in a sealed box with no
windows and experiencing no obvious gravitational effects), how you could
differentiate between orbit and absence of (significant) gravity.


There are ways to fool the human body into thinking a plane is falling even
though it is still climbing (by gradually reducing climb rate by a certain amount).

There are ways to simulate 0g in a plane even though it isn't in orbit.

On the ISS, your senses may be fooled into thinking that there is no gravity
because you fall at the same rate as the walls, ceiling, floor. But a cell
doesn't really have senses, nor do crystals, light waves etc.

It is only in recent history that we found out that gravity also affects
light. Before that, humans thought gravity only affected "matter" and didn't
think light could be affected.

Until we understand gravity 100%, it is wrong and/or arrogant for anyone to
state that all the effects of gravity are cancelled if you are in the right
spot on the ISS.
  #86  
Old October 22nd 03, 09:04 AM
Peter Smith
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Default Microgravity parable

Neelix wrote...
Until we understand gravity 100%, it is wrong and/or arrogant for
anyone to state that all the effects of gravity are cancelled if
you are in the right spot on the ISS.


Of course.

And a previous post of mine showed how to easily demontrate that they are
*not* cancelled.

- Peter


  #87  
Old October 22nd 03, 11:48 PM
Stuf4
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Default Microgravity parable

From Peter Smith:
Stuf4 wrote...

You ask whether one can distinguish between gravity and acceleration.
But the question of whether one can distinguish between 'orbital
microgravity' and a 'microgravity field' is a different question.


Peter, please check "orbital microgravity" as a self-contradictory
oxymoron. Orbits require gravity in order to be orbits.


duuh - that's why I used the quote marks, Stuf4.


(A perfectly accurate term is "micro-g". No contradiction.)

I went on to explain how you could (if you were in a sealed box with no
windows and experiencing no obvious gravitational effects), how you could
differentiate between orbit and absence of (significant) gravity.


I agree with your point there. There are other ways to tell that an
astronaut is in a strong gravitational field (vice "zero gravity")
beside just the windows.

By the way, if you looked out the window, how would you detect a black
hole?


One way would be to observe the patch of blackness that defines the
black hole's event horizon circled by a haloed grouping of apparent
stars created by the gravitational lens effect.


~ CT
  #88  
Old October 23rd 03, 01:32 PM
Peter Smith
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Default Microgravity parable


Stuf4 wrote...

By the way, if you looked out the window, how would you
detect a black hole?


One way would be to observe the patch of blackness that
defines the black hole's event horizon circled by a haloed
grouping of apparent stars created by the gravitational
lens effect.


If the Sun became a black hole, its event horison would have a 6km
diameter. To see the black disc, I would have to be at most 350km away.
At this distance the gravitational gradient would be significant, and I
would be orbiting at 1.9kHz. I would be feeling like LooseChanj is about
now I guess

Pass me a iBuzz Aldrin/i Hic!

- Peter


  #89  
Old October 24th 03, 03:28 PM
Scott Hedrick
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Default Microgravity parable

"Peter Smith" wrote in message
...
Pass me a iBuzz Aldrin/i Hic!


We know that Drew Carey is a space fan- after all, he named the results from
his garage brewery *Buzz* Beer!
--
If you have had problems with Illinois Student Assistance Commission (ISAC),
please contact shredder at bellsouth dot net. There may be a class-action
lawsuit
in the works.


 




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