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Author Topic: Have We Found Anti-Gravity ?  (Read 11264 times)

Offline DoctorBeaver

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Re: Have We Found Anti-Gravity ?
« Reply #25 on: 05/01/2006 13:35:40 »
But if you take the hypothetical situation where there is only 1 rock in the whole of the universe, there would be nothing to exert a gravitational effect on it yet it would still have mass. At least, I think it would.
 

another_someone

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Re: Have We Found Anti-Gravity ?
« Reply #26 on: 05/01/2006 14:01:25 »
quote:
Originally posted by DoctorBeaver

But if you take the hypothetical situation where there is only 1 rock in the whole of the universe, there would be nothing to exert a gravitational effect on it yet it would still have mass. At least, I think it would.



Mass has two manifestations: 1) inertia, or its resistance to force; 2) gravitational pull.

If there is only one particle in the whole universe, then no other particle can exist to exert a force upon that particle, whether it be a gravitational force or an electromagnetic force or any other force.  Thus, the particle would not be subject to acceleration in any way whatsoever; thus neither gravity nor inertia will manifest itself.
 

Offline DoctorBeaver

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Re: Have We Found Anti-Gravity ?
« Reply #27 on: 05/01/2006 14:35:25 »
quote:
Mass has two manifestations: 1) inertia, or its resistance to force; 2) gravitational pull.

If there is only one particle in the whole universe, then no other particle can exist to exert a force upon that particle, whether it be a gravitational force or an electromagnetic force or any other force. Thus, the particle would not be subject to acceleration in any way whatsoever; thus neither gravity nor inertia will manifest itself.


But I was talking about a rock, not a single particle. The particles comprising the rock all have mass. Therefore, if there  were just 1 rock in the entire universe, its mass would be the sum of its constituent particles.
 

another_someone

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Re: Have We Found Anti-Gravity ?
« Reply #28 on: 05/01/2006 19:29:34 »
quote:
Originally posted by DoctorBeaver

But I was talking about a rock, not a single particle. The particles comprising the rock all have mass. Therefore, if there  were just 1 rock in the entire universe, its mass would be the sum of its constituent particles.



I used the word particle loosely, but intentionally so.  Essentially, if you treat the entity as a single unified particle, then one ignores any internal forces, and neither internal gravitational nor electromagnetic, nor other forces within the internal structure of the body need be taken into account.

If one regards the entity as a clump of matter containing many particles, then it follows that those particles will influence each other and the internal forces between those particles are accepted to exist, including the internal forces of gravity, even where the gravitational force is not the most powerful of forces within the rock.

If the rock is totally stable, and has no internal dynamics, then the inertia of its components parts is irrelevant, and it makes no difference whether you are talking about a single particle or a large rock.

If the rock is in a dynamic state, with internal components continually in motion, then all the internal forces, including gravity, must be taken into account, and inertia of the separate component parts would also be relevant.

From the outside, it matters not what the rock looks like, because there is nothing out there to look at the rock, and determine what its gravity or mass is.
« Last Edit: 06/01/2006 01:49:23 by another_someone »
 

another_someone

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Re: Have We Found Anti-Gravity ?
« Reply #29 on: 06/01/2006 01:30:38 »
quote:
Originally posted by DoctorBeaver

another_someone - if that is the case, would the particle not be able to travel slower than c & therefore be undetectable? Or does travelling faster than c imply travelling backwards in time as I have seen suggested elsewhere here? If so, would all the particles be lurking somewhere near the big bang and have possibly caused expansion?



It does get confusing when you edit messages 39 hours after you first posted it. :)

If a particle has negative mass, then it implies two things:

Firstly, the sqrt(1 v^2/c^2) must be resolved to its negative square root.  This is mathematically legitimate, since any positive number has both a positive and a negative square root, and it is merely arbitrary that we have to date only considered the positive square root.

Secondly, although matter with negative mass can easily resolve to positive energy values (assuming the above condition is met), but the issue with regard to momentum is more problematic.  Either a particle with negative mass must produce negative momentum, or be travelling with negative velocity.

One interesting effect of having negative mass is that, excluding relativistic effects, if two particles with equal and opposite mass were to collide in an elastic collision, they would rebound with infinite velocities.  Clearly relativity will give a different answer, but it should be an interesting answer nontheless.
« Last Edit: 06/01/2006 05:29:17 by another_someone »
 

Offline DoctorBeaver

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Re: Have We Found Anti-Gravity ?
« Reply #30 on: 06/01/2006 12:24:36 »
quote:
It does get confusing when you edit messages 39 hours after you first posted it.


I realised I'd left out the word "near" and had merely put "lurking the big bang". Not really a drastic edit. [:I]
 

Offline DoctorBeaver

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Re: Have We Found Anti-Gravity ?
« Reply #31 on: 06/01/2006 12:32:43 »
quote:
Either a particle with negative mass must produce negative momentum, or be travelling with negative velocity.


Hmmm... I'm not sure I can get my head around those concepts [xx(]
Negative mass just about seems comprehensible to me; but negative momentum and negative velocity? Oo-er, matron!
 

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Re: Have We Found Anti-Gravity ?
« Reply #32 on: 06/01/2006 15:51:14 »
quote:
Originally posted by DoctorBeaver

Hmmm... I'm not sure I can get my head around those concepts [xx(]
Negative mass just about seems comprehensible to me; but negative momentum and negative velocity? Oo-er, matron!



Apologies, it was my stupidity.

After saying that the sign can be manipulated for the energy because the Lorentz factor can be either negative or positive, I ignored that with regard to momentum.[:I]

One can have a positive value even with a positive velocity simply by taking a negative value for the Lorentz factor.
« Last Edit: 06/01/2006 23:11:32 by another_someone »
 

Offline DoctorBeaver

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Re: Have We Found Anti-Gravity ?
« Reply #33 on: 07/01/2006 01:09:53 »
PHEW... that's a relief! [:o)]
My poor little brain was going into meltdown
 

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Re: Have We Found Anti-Gravity ?
« Reply #33 on: 07/01/2006 01:09:53 »

 

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