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Negative Gravity?

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  Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-08-29 06:53 +1000
    Negative Gravity? "David (Time Lord) Fuller" <fuller.david@hotmail.com> - 2016-08-28 18:08 -0700
    Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-08-28 22:08 -0500
      Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-08-29 21:01 +1000
        Re: Negative Gravity? JanPB <filmart@gmail.com> - 2016-08-30 12:12 -0700
          Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-08-31 07:02 +1000
            Re: Negative Gravity? JanPB <filmart@gmail.com> - 2016-08-30 15:10 -0700
              Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-08-31 10:16 -0500
                Re: Negative Gravity? mlwozniak@wp.pl - 2016-08-31 23:07 -0700
        Re: Negative Gravity? Peter Riedt <riedt1@yahoo.co.uk> - 2016-09-02 19:15 -0700
          Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-09-04 07:59 +1000
      Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-08-31 11:37 -0700
        Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-08-31 21:00 -0500
          Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-09-03 09:31 +1000
            Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-09-02 18:05 -0700
              Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-03 08:19 -0500
                Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-09-03 09:55 -0700
              Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-09-04 08:00 +1000
                Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-09-03 18:36 -0700
            Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-06 12:22 -0500
              Re: Negative Gravity? HGW <hw@....> - 2016-09-14 08:35 +1000
    Re: Negative Gravity? Alan Folmsbee <omnilobe@gmail.com> - 2016-08-28 21:48 -0700
      Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-08-29 21:53 +1000
        Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-08-30 10:11 -0500
          Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-12 10:21 -0700
            Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-12 22:39 -0500
              Re: Negative Gravity? HGW <hw@....> - 2016-09-14 08:16 +1000
                Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-13 18:26 -0500
                  Re: Negative Gravity? HGW <hw@....> - 2016-09-15 08:29 +1000
                    Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-14 23:23 -0500
                    Re: Negative Gravity? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-09-15 15:42 +0000
                      Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-15 12:37 -0500
                        Re: Negative Gravity? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-09-16 03:30 +0000
                          Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-15 23:30 -0500
                            Re: Negative Gravity? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-09-16 16:23 +0000
                      Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-09-16 06:40 +1000
                        Re: Negative Gravity? Odd Bodkin <bodkinodd@gmail.com> - 2016-09-15 16:13 -0500
                        Re: Negative Gravity? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-09-16 03:34 +0000
                          Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-09-17 04:29 +1000
                            Re: Negative Gravity? moroney@world.std.spaamtrap.com (Michael Moroney) - 2016-09-16 21:05 +0000
              Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-13 15:58 -0700
                Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-13 18:40 -0500
                  Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-14 12:56 -0700
                    Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-09-14 13:34 -0700
                    Re: Negative Gravity? Odd Bodkin <bodkinodd@gmail.com> - 2016-09-14 15:40 -0500
                    Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-14 23:53 -0500
                      Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-16 11:37 -0700
                        Re: Negative Gravity? Odd Bodkin <bodkinodd@gmail.com> - 2016-09-16 14:21 -0500
                        Re: Negative Gravity? Odd Bodkin <bodkinodd@gmail.com> - 2016-09-16 14:21 -0500
                        Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-16 22:25 -0500
                          Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-19 12:43 -0700
                            Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-19 17:01 -0500
                              Re: Negative Gravity? Odd Bodkin <bodkinodd@gmail.com> - 2016-09-20 08:37 -0500
                                Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-20 09:23 -0500
                                Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-20 17:54 -0700
                                  Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-09-20 20:15 -0700
                                    Re: Negative Gravity? RichD <r_delaney2001@yahoo.com> - 2016-09-21 12:32 -0700
                                      Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-09-21 15:03 -0700
                                  Re: Negative Gravity? Odd Bodkin <bodkinodd@gmail.com> - 2016-09-21 07:48 -0500
                      Re: Negative Gravity? "HGWilson, DSc." <hgw@....> - 2016-09-17 04:41 +1000
                        Re: Negative Gravity? Tom Roberts <tjroberts137@sbcglobal.net> - 2016-09-19 11:14 -0500
                          Re: Negative Gravity? Koobee Wublee <koobee.wublee@gmail.com> - 2016-10-03 23:20 -0700
    Re: Negative Gravity? kenseto <setoken@att.net> - 2016-08-29 08:59 -0700
    Negative Gravity? "David (Time Lord) Fuller" <fuller.david@hotmail.com> - 2016-08-29 09:57 -0700
    Re: Negative Gravity? numbernumber1964@gmail.com - 2016-08-31 11:48 -0700
      Re: Negative Gravity? Gary Harnagel <hitlong@yahoo.com> - 2016-08-31 14:16 -0700
      Re: Negative Gravity? "David (Time Lord) Fuller" <fuller.david@hotmail.com> - 2016-08-31 14:46 -0700

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#392251

On September 12,  tjrob137 wrote:
>>> A "present day rocket engine" is indeed "fueled by mc^2".
>>> That is, its thrust is generated by the mass difference between
>>> its fuel and its exhaust. It _DOES_ "convert mass into energy".
>
>> What about [a railgun]
>> try Google News, search:  WSJ + supergun
>> Where's the relativistic mass --> energy conversion?
> 
> In the capacitors used to energize it.
> 
> If you look carefully and accurately enough, you'll always find 
> some mass differences when energy is transformed. For instance, in a 
> hydroelectric plant the mass decrease corresponding to the electricity 
> produced is in the total mass of earth+water; but there is a corresponding 
> mass increase in whatever used the electricity 

That's overly simplistic, really hand waving.

Looking into the capacitor, we see an E field across 
a dielectric, due to stored charges.  Then a switch 
is closed, current flows (the conducting band electrons), 
the resulting B field accelerates the iron in the 
projectile.  The electrons eventually settle into the 
other plate, as the fields balance.  The cap's internal 
field evaporates. 

Where and when does the mass decrease?  Are the electrons 
lighter at the end of their journey?


--
Rich

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#392260

On 9/13/16 9/13/16   5:58 PM, RichD wrote:
> Looking into the capacitor, we see an E field across
> a dielectric, due to stored charges.  Then a switch
> is closed, current flows (the conducting band electrons),
> the resulting B field accelerates the iron in the
> projectile.  The electrons eventually settle into the
> other plate, as the fields balance.  The cap's internal
> field evaporates.
>
> Where and when does the mass decrease?  Are the electrons
> lighter at the end of their journey?

A capacitor has more mass when charged than when discharged. This is due to the 
energy contained in the E field inside. This is almost surely too small to be 
directly measured, but in principle it is so.


Tom Roberts

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#392351

On September 13,  tjrob137 wrote:
>> Looking into the capacitor, we see an E field across
>> a dielectric, due to stored charges.  Then a switch
>> is closed, current flows (the conducting band electrons),
>> the resulting B field accelerates the iron in the
>> projectile.  The electrons eventually settle into the
>> other plate, as the fields balance.  The cap's internal
>> field evaporates.
>> Where and when does the mass decrease?  Are the electrons
>> lighter at the end of their journey?
> 
> A capacitor has more mass when charged than when discharged. This is 
> due to the energy contained in the E field inside. 

An E field has an inertial mass? 

Mass measures the amount of an object's inertia.  
OK, let's hypothesize a E-M pulse through a vacuum, 
of very low dispersion.  It occupies a finite volume, 
of finite duration; a 'cloud of radiation', so to speak, 
flying free.

Now, what does inertia mean, in this case, of a 
non-material object?  As gedanken experiment, how 
would one measure its mass?  

--
Rich

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#392357

On Wednesday, September 14, 2016 at 1:56:55 PM UTC-6, RichD wrote:
>
> On September 13,  tjrob137 wrote:
> >
> > A capacitor has more mass when charged than when discharged. This is 
> > due to the energy contained in the E field inside. 
> 
> An E field has an inertial mass? 

Tom said "energy" not inertial mass, but it has that, too, in the sense
that mass can have momentum.

> Mass measures the amount of an object's inertia.  
> OK, let's hypothesize a E-M pulse through a vacuum, 
> of very low dispersion.  It occupies a finite volume, 
> of finite duration; a 'cloud of radiation', so to speak, 
> flying free.
> 
> Now, what does inertia mean, in this case, of a 
> non-material object?  As gedanken experiment, how 
> would one measure its mass?  
> 
> --
> Rich

Maxwell's equations demonstrate that E = p*c, so there's your momentum
(i.e., inertial mass).  They also demonstrate that energy is proportional
to the square of the electric field.  Ergo, it has mass by E = mc^2.

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#392359

On 9/14/2016 2:56 PM, RichD wrote:
> An E field has an inertial mass?

Yes.

For a 5 uC capacitor at 12 V, this energy is CV^2/2 = 0.36 mJ.
The mass for that field is 4E-21 kg.

-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#392405

On 9/14/16 9/14/16   2:56 PM, RichD wrote:
>> A capacitor has more mass when charged than when discharged. This is
>> due to the energy contained in the E field inside.
>
> An E field has an inertial mass?

In some cases, yes; in other cases, no. In particular, "mass" does not apply 
unless the E field is contained by some object made of matter -- without that 
there is no way to "grab onto" the field for it to exhibit inertia.


> Mass measures the amount of an object's inertia.

Yes. The key word here is "object". A capacitor exhibits larger inertia when 
charged than when discharged -- the norm of the capacitor's 4-momentum is larger 
when charged than when discharged, and this affects how it responds to a given 
applied force. In practice this difference is unmeasurably small.


> OK, let's hypothesize a E-M pulse through a vacuum,
> of very low dispersion.  It occupies a finite volume,
> of finite duration; a 'cloud of radiation', so to speak,
> flying free.
> Now, what does inertia mean, in this case, of a
> non-material object?  As gedanken experiment, how
> would one measure its mass?

Such an EM wave has no mass, in that the norm of its 4-momentum is zero. But it 
follows a null geodesic through spacetime, and thus "falls" in gravity. It has 
energy and so influences the geometry of spacetime, and thus can "attract" other 
objects gravitationally. In GR these last two are simply geometry, and there's 
no such thing as "gravitational mass" or "gravitational force".

In GR, the concept "mass" applies only to objects, and an object's mass is the 
norm of its 4-momentum; classical (Newtonian) ideas don't really apply. In 
general it's best to consider how a given object behaves, and not attempt to 
apply outmoded labels from past theories.


Tom Roberts

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#392607

On September 14, tjrob137 wrote:
>>> A capacitor has more mass when charged than when discharged. This is
>>> due to the energy contained in the E field inside.
>
>> An E field has an inertial mass?
> 
> In some cases, yes; in other cases, no. In particular, "mass" does 
> not apply unless the E field is contained by some object made of 
> matter -- without that there is no way to "grab onto" the field 
> for it to exhibit inertia.

Right, to measure a thing, we have to contact it somehow.

>> Mass measures the amount of an object's inertia.
> 
> Yes. The key word here is "object". A capacitor exhibits larger inertia when 
> charged than when discharged -- the norm of the capacitor's 4-momentum 
> is  larger when charged than when discharged, and this affects how it 
> responds to a given applied force. 
> 
>> OK, let's hypothesize a E-M pulse through a vacuum,
>> of very low dispersion.  It occupies a finite volume,
>> of finite duration; a 'cloud of radiation', so to speak,
>> Now, what does inertia mean, in this case, of a
>> non-material object?  As gedanken experiment, how
>> would one measure its mass?
> 
> Such an EM wave has no mass, in that the norm of its 4-momentum is zero. 
> But it follows a null geodesic through spacetime, and thus "falls" in 
> gravity. 
> It has energy and so influences the geometry of spacetime, and thus can 
> "attract" other objects gravitationally. In GR these last two are simply 
> geometry, and there's no such thing as "gravitational mass" or 
> "gravitational force".

But in GR, gravity equals acceleration, which dovetails 
into momentum and inertia, so you could argue this 
entails the mass of the E-M burst.  But still, if this 
can't be measured, you have a problem - 
 
> In GR, the concept "mass" applies only to objects, and an object's 
. mass is the norm of its 4-momentum; classical (Newtonian) ideas 
> don't really apply. In general it's best to consider how a given 
> object behaves, and not attempt to 
> apply outmoded labels from past theories.

What also doesn't apply, is our common sense ideas of 
'contain' or 'inside' or 'object'.  

It's easy to talk about the state of uranium before or 
after fission (though I don't know how to measure mass 
distinct from energy).  Then let's consider the E-M 
cloud.  Let's say it passes through a transparent window, 
and resort to our intuitive ideas of 'inside'... the 
wave transmits, but doesn't interact, as per the quantum 
model...  does the window's inertia increase?  

Or, let's say the window is 50% absorbing.  Now, what 
does 'inside' mean, what's the resulting inertia?   

How does the capacitor know the field is 'contained'?  
Suppose we pop the top, and allow the E-field lines to 
spill out, even though the energy is unaltered.  Is the 
E field still 'inside' the cap? 

See, the notions that 'the field has mass' and 'the 
capacitor is an object which contains the field' are 
thornier than you think -  

--
Rich

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#392613

On 9/16/2016 1:37 PM, RichD wrote:
> Right, to measure a thing, we have to contact it somehow.

And how do we measure the chemical composition of Saturn?

-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#392614

On 9/16/2016 1:37 PM, RichD wrote:
> But in GR, gravity equals acceleration,

Not true.

> which dovetails
> into momentum and inertia, so you could argue this
> entails the mass of the E-M burst.  But still, if this
> can't be measured, you have a problem -


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#392668

On 9/16/16 9/16/16   1:37 PM, RichD wrote:
> On September 14, tjrob137 wrote:
>> Such an EM wave has no mass, in that the norm of its 4-momentum is zero.
>> But it follows a null geodesic through spacetime, and thus "falls" in
>> gravity.
>> It has energy and so influences the geometry of spacetime, and thus can
>> "attract" other objects gravitationally. In GR these last two are simply
>> geometry, and there's no such thing as "gravitational mass" or
>> "gravitational force".
>
> But in GR, gravity equals acceleration,

Where do you get such nonsense? This is wrong. COMPLETELY WRONG.

In GR, gravitation is the geometry of spacetime; nothing more, nothing less.


> the notions that 'the field has mass' and 'the
> capacitor is an object which contains the field' are
> thornier than you think -

Yes, such issues are unexpectedly complex, and I already said so in this thread.

I repeat: In general it's best to consider how a given object behaves, and not 
attempt to apply outmoded labels from past theories.

Tom Roberts

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#392995

On September 16,  tjrob137 wrote:
>>> Such an EM wave has no mass, in that the norm of its 4-momentum is zero.
>>> But it follows a null geodesic through spacetime, and thus "falls" in
>>> gravity.
>>> It has energy and so influences the geometry of spacetime, and thus can
>>> "attract" other objects gravitationally. In GR these last two are simply
>>> geometry, and there's no such thing as "gravitational mass" or
>>> "gravitational force".
>
>> But in GR, gravity equals acceleration,
> 
> Where do you get such nonsense? This is wrong. COMPLETELY WRONG.

"We assume the complete physical equivalence of a gravitational 
field and a corresponding acceleration of the reference system."
—  A. Einstein, "On the relativity principle and the conclusions 
drawn from it",  Jahrbuch der Radioaktivitaet und Elektronik, 1907
 
Before spouting your ill-informed OPINION on a topic,
you REALLY ought to LEARN something about the topic.

As I said, which whooshed over your head, if energy has 
a gravitational effect, we can impute a gravitational 
mass, and then, as that equals inertial mass, we can impute 
inertial mass to a E-M pulse.

However, we can't push a radio wave as we would a car, thus 
we merely observe that it transports momentum, and reason 
from there. 

>> the notions that 'the field has mass' and 'the
>> capacitor is an object which contains the field' are
>> thornier than you think -
> 
> Yes, such issues are unexpectedly complex, and I already said so 
> in this thread.  I repeat: In general it's best to consider how a 
> given object behaves, and not 
> attempt to apply outmoded labels from past theories.

OK, but we're human, and we still wonder how things work.  

Push on a cart loaded with logs, it's heavy.  Of course, 
you feel the weight (mass) of the wood, you're pushing 
both cart and wood! 

Now push the charged cap.  It feels heavier, where's the 
extra mass?  In the E field, hmmm... what does it mean 
to push a field?  Where IS the field, anyhow?  Look in a 
text book, you see lots of little arrows, very nice... 
open the cap, don't see no arrows... what's going on?

Let's look at the window again, and say it's 100% 
transparent.  At the moment the light pulse is inside 
(according to theory), we push on the glass - do we feel 
extra mass (inertia)? I  can't imagine any way to test 
this, but it's an interesting question -

--
Rich

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#393004

On 9/19/16 9/19/16 - 2:43 PM, RichD wrote:
> On September 16,  tjrob137 wrote:
>>>> Such an EM wave has no mass, in that the norm of its 4-momentum is zero.
>>>> But it follows a null geodesic through spacetime, and thus "falls" in
>>>> gravity.
>>>> It has energy and so influences the geometry of spacetime, and thus can
>>>> "attract" other objects gravitationally. In GR these last two are simply
>>>> geometry, and there's no such thing as "gravitational mass" or
>>>> "gravitational force".
>>
>>> But in GR, gravity equals acceleration,
>>
>> Where do you get such nonsense? This is wrong. COMPLETELY WRONG.
>
> "We assume the complete physical equivalence of a gravitational
> field and a corresponding acceleration of the reference system."
> —  A. Einstein, "On the relativity principle and the conclusions
> drawn from it",  Jahrbuch der Radioaktivitaet und Elektronik, 1907

equivalence != equal

Moreover, GR is more subtle than you apparently think.


Tom Roberts

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#393095

On 9/19/2016 5:01 PM, Tom Roberts wrote:

>>
>> "We assume the complete physical equivalence of a gravitational
>> field and a corresponding acceleration of the reference system."
>> —  A. Einstein, "On the relativity principle and the conclusions
>> drawn from it",  Jahrbuch der Radioaktivitaet und Elektronik, 1907
>
> equivalence != equal

Plus, this statement by Einstein is not actually very careful. The 
equivalence is between a UNIFORM gravitational field and a corresponding 
acceleration of the reference system; or between a gravitational field 
and a small region within a reference system that is accelerating. It is 
simply not true that a non-uniform gravitational field is completely 
equivalent to an accelerating reference system.

Such is the problem with sound bites.

>
> Moreover, GR is more subtle than you apparently think.
>
>
> Tom Roberts


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#393101

On 9/20/16 9/20/16   8:37 AM, Odd Bodkin wrote:
> On 9/19/2016 5:01 PM, Tom Roberts wrote:
>>> "We assume the complete physical equivalence of a gravitational
>>> field and a corresponding acceleration of the reference system."
>>> —  A. Einstein, "On the relativity principle and the conclusions
>>> drawn from it",  Jahrbuch der Radioaktivitaet und Elektronik, 1907
>>
>> equivalence != equal
>
> Plus, this statement by Einstein is not actually very careful. The equivalence
> is between a UNIFORM gravitational field and a corresponding acceleration of the
> reference system; or between a gravitational field and a small region within a
> reference system that is accelerating. It is simply not true that a non-uniform
> gravitational field is completely equivalent to an accelerating reference system.
>
> Such is the problem with sound bites.

Yes.

Tom Roberts

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#393160

On September 20, Odd Bodkin wrote:
>>> "We assume the complete physical equivalence of a gravitational
>>> field and a corresponding acceleration of the reference system."
>>> —  A. Einstein, "On the relativity principle and the conclusions
>>> drawn from it",  Jahrbuch der Radioaktivitaet und Elektronik, 1907
> >
> > equivalence != equal
> 
> Plus, this statement by Einstein is not actually very careful. The 
> equivalence is between a UNIFORM gravitational field and a corresponding 
> acceleration of the reference system; or between a gravitational field 
> and a small region within a reference system that is accelerating. It is 
> simply not true that a non-uniform gravitational field is completely 
> equivalent to an accelerating reference system.

Then, inside a closed spaceship, within a non-uniform 
G field, one can distinguish between acceleration and gravity?  
i.e. one can measure the G field?


--
Rich

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#393170

On Tuesday, September 20, 2016 at 6:54:49 PM UTC-6, RichD wrote:
>
> On September 20, Odd Bodkin wrote:
> >
> > Plus, this statement by Einstein is not actually very careful. The 
> > equivalence is between a UNIFORM gravitational field and a corresponding 
> > acceleration of the reference system; or between a gravitational field 
> > and a small region within a reference system that is accelerating. It is 
> > simply not true that a non-uniform gravitational field is completely 
> > equivalent to an accelerating reference system.
> 
> Then, inside a closed spaceship, within a non-uniform 
> G field, one can distinguish between acceleration and gravity?  
> i.e. one can measure the G field?
> 
> 
> --
> Rich

Of course:

https://en.m.wikipedia.org/wiki/Gravity_gradiometry

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#393248

On September 20, Gary Harnagel wrote:
>>> Plus, this statement by Einstein is not actually very careful. The 
>>> equivalence is between a UNIFORM gravitational field and a corresponding 
>>> acceleration of the reference system; or between a gravitational field 
>>> and a small region within a reference system that is accelerating. It is 
>>> simply not true that a non-uniform gravitational field is completely 
>>> equivalent to an accelerating reference system.
> 
>> Then, inside a closed spaceship, within a non-uniform 
>> G field, one can distinguish between acceleration and gravity?  
>> i.e. one can measure the G field?
> 
> Of course:
> https://en.m.wikipedia.org/wiki/Gravity_gradiometry

Doesn't address the equivalence principle of relativity.

--
Rich

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#393263

On Wednesday, September 21, 2016 at 1:32:52 PM UTC-6, RichD wrote:
>
> On September 20, Gary Harnagel wrote:
> >
> > > Then, inside a closed spaceship, within a non-uniform 
> > > G field, one can distinguish between acceleration and gravity?  
> > > i.e. one can measure the G field?
> > 
> > Of course:
> > https://en.m.wikipedia.org/wiki/Gravity_gradiometry
> 
> Doesn't address the equivalence principle of relativity.
> 
> --
> Rich

It addresses your QUESTION.  Do you have Alzheimer's?

Gary

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#393207

On 9/20/2016 7:54 PM, RichD wrote:
> On September 20, Odd Bodkin wrote:
>>>> "We assume the complete physical equivalence of a gravitational
>>>> field and a corresponding acceleration of the reference system."
>>>> —  A. Einstein, "On the relativity principle and the conclusions
>>>> drawn from it",  Jahrbuch der Radioaktivitaet und Elektronik, 1907
>>>
>>> equivalence != equal
>>
>> Plus, this statement by Einstein is not actually very careful. The
>> equivalence is between a UNIFORM gravitational field and a corresponding
>> acceleration of the reference system; or between a gravitational field
>> and a small region within a reference system that is accelerating. It is
>> simply not true that a non-uniform gravitational field is completely
>> equivalent to an accelerating reference system.
>
> Then, inside a closed spaceship, within a non-uniform
> G field, one can distinguish between acceleration and gravity?
> i.e. one can measure the G field?
>

If the ship is large enough or you conduct the experiment long enough, yes.


-- 
Odd Bodkin --- maker of fine toys, tools, tables

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#392608

On 15/09/16 14:53, Tom Roberts wrote:
> On 9/14/16 9/14/16   2:56 PM, RichD wrote:

> Such an EM wave has no mass, in that the norm of its 4-momentum is zero.
> But it follows a null geodesic through spacetime, and thus "falls" in
> gravity. It has energy and so influences the geometry of spacetime, and
> thus can "attract" other objects gravitationally. In GR these last two
> are simply geometry, and there's no such thing as "gravitational mass"
> or "gravitational force".

Crap! Drawing curved lines on a fictitious graph does not create a force!

> In GR, the concept "mass" applies only to objects, and an object's mass
> is the norm of its 4-momentum; classical (Newtonian) ideas don't really
> apply. In general it's best to consider how a given object behaves, and
> not attempt to apply outmoded labels from past theories.

Einstein's 'spacetime' assumes constant light speed and its therefore 
nonsense. Newtonian space/time is a mathematical convenience that tells 
the true story in space over time.

Einstein never explained the existence of gravity. He merely introduced 
a silly error in its ability to attract.

> Tom Roberts

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