1

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 15/06/2012 13:39:18 »

Going back to basics and the original question

Do we need acceleration to define the concept of mass?

"The kilogram or kilogramme (SI symbol: kg), also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram (IPK), which is almost exactly equal to the mass of one liter of water."

The IPK is made of a platinum–iridium alloy and is stored in a vault at the International Bureau of Weights and Measures in Sèvres, France.  It is known as Le Grand K.
http://en.wikipedia.org/wiki/Kilogram

The kilogram is by definition what the IPK weighs and is not a constant in the sense that the speed of light is a constant.

Weight
From Wikipedia, the free encyclopedia

"A spring scale measures the weight of an object (according to the operational definition)

In science and engineering, the weight of an object is the force on the object due to gravity.[2][3] Its magnitude (a scalar quantity), often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g;[4] thus: W = mg. When considered a vector, weight is often denoted by a bold letter W. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, about one-sixth as much on the Moon, and very nearly zero when in deep space far away from all bodies imparting gravitational influence."
http://en.wikipedia.org/wiki/Weight

The Newton
"Definition

The newton is the SI unit for force; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one metre per second squared. Newton's second law of motion states: F = ma, multiplying m (kg) by a (m/s2), The newton is therefore:[1]

N=kg x m/s²

Units used:
N = newton
kg = kilogram
m = metre
s = second

http://en.wikipedia.org/wiki/Newton_(unit)

“Le Grand K has been losing weight — or, by the definition of mass under the metric system, the rest of the universe has been getting fatter. The most recent comparison, in 1988, found a discrepancy as large as five-hundredths of a milligram, a bit less than the weight of a dust speck, between Le Grand K and its official underlings.

This state of affairs is intolerable to the guardians of weights and measures. “Something must be done,” says Terry Quinn, director emeritus of the International Bureau of Weights and Measures, the governing body of the metric system. Since the early 1990s, Quinn has campaigned to redefine the kilogram based not on a physical prototype but on a constant of nature, something hardwired into the circuitry of the universe. In fact, of the seven fundamental metric units — the kilogram, meter, second, ampere, kelvin, mole, and candela — only the kilogram is still dependent on a physical artifact. (The meter, for example, was redefined 30 years ago as the distance traveled by light in a given fraction of a second.)”
http://www.wired.com/magazine/2011/09/ff_kilogram/all/1

What is the point of the above?  The point is the "The kilogram or kilogramme (SI symbol: kg), also known as the kilo, is the base unit of mass in the International System of Units” is defined by measuring its acceleration (weighing it). “Its magnitude (a scalar quantity), often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g;[4] thus: W = mg.”  “ The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton.”   “The newton is the SI unit for force; it is equal to the amount of net force required to accelerate a mass of one kilogram at a rate of one metre per second squared.”  “In science and engineering, the weight of an object is the force on the object due to gravity.[2][3] Its magnitude (a scalar quantity), often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g;[4] thus: W = mg.”  So, going back to the original question “Do we need acceleration to define the concept of mass?”  From the above it is obvious that we do.

As Le Grand K has been loosing weight in comparison to the rest of the Universe it is necessary to find a way of defining mass by using some constant of nature as opposed to using an artifact.  “So two decades ago, as Quinn’s campaign to switch the kilo to a physical constant began to gain traction, Becker and his colleagues decided to tackle the problem from the opposite direction. Building upon their earlier work, they decided to create a 1-kilogram sphere, not from hydrogen, but from silicon. The sphere would be identical in mass to the international prototype. Then, because Becker’s x-ray experiments had shown that the atoms were arranged in a regular pattern, they could use basic geometry to deduce how many silicon atoms the crystalline sphere contained. Once the number of atoms was determined with sufficient precision, that figure would forever define the mass of the kilogram. In other words, they set out to make a new artifact superior to Le Grand K — but only so that they could count its atoms and then eliminate all kilogram artifacts in perpetuity.”

The other approach is to use an apparatus called a watt balance, which compares electrical and mechanical power.  “On the upper floor is a room-sized scale dominated by a wheel fabricated of milled aluminum. Below the wheel is a hand-sized pan supporting a platinum-iridium mass positioned like an apple on a produce scale. One floor below, superconducting electromagnets counteract the downward tug of the platinum-iridium. In other words, the gravitational force on the mass is balanced with the electrical force produced by current in the copper coil. Once calibrated against the international prototype, the electronic kilogram can be defined in terms of the voltage required to levitate Le Grand K — a numerical value, governed by a natural constant, that can be used to calibrate any future watt balance — and the international prototype can at last be sent into retirement.” 
http://www.wired.com/magazine/2011/09/ff_kilogram/all/1

Both of the above alternatives of defining a kg of mass require weighing the object.  In the first case knowing the weight of a silicon atom and counting (calculating) the number of atoms.  In the second case weighing the object by knowing the amount of energy required to levitate it.  Both scenarios require weighing the object and that requires the use of a non-inertial (accelerating) reference frame.

2

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 15/06/2012 11:12:29 »

mass is only a function of speed (magnitude of velocity), not of acceleration.

How does that relate to

quote lightarrow
 
Reply #2 on: 24/05/2012 21:52:40
Quote
"The best way is to consider the object...still 
An oject's mass is its energy (divided c2) when the object is still."

and
The question was not about what mass is a function of but "Do we need acceleration to define the concept of mass?"

3

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 15/06/2012 11:02:34 »

It is when talking about the acceleration of a massive body like the Earth.  A steady push is the steady application of energy.  The steady application of energy (as in a rocket for example) causes a steady acceleration.  A 'push' changes the velocity of the object.  That change in velocity is acceleration.

We do know what the acceleration is it's 1 g.  There must be travel as the Earth is travelling through space-time.  Because we do not understand how to take the measurements does not make it any the less true.

Mike, if you are going to argue using GR, I strongly suggest you study Classical Mechanics and basic Thermodynamics first. What you are suggesting here is that there is a continuous transfer of energy from the Earth to your backside when you are sitting in a chair. That is patently ridiculous. There is no change in energy of the Earth, you, or the chair, and even String Theory won't support the idea that there is.
 
 Standard Gravity on Earth is an approximation. It is not constant with location which is why weight varies depending on where you are on the Earth.

Is it ridiculous?  Let me see if I understand you correctly.  What you are saying is if You are sitting in a chair in a rocket accelerating at one g and approaching the speed of light you will not have gained mass?

My point was a push causes a change in velocity which involves acceleration. 

It costs the Earth nothing extra to accelerate anything on its surface (other than maybe meteorites) as everything is part of the Earths mass.

Whether or not the Earths acceleration in space-time (gravity) involves the expenditure or energy we simply do not know.  We do know that the Earth warps or bends space-time locally.  Maybe the Earth extracts energy from that. I am not postulating that it does, I am simply saying it remains a possibility until proven otherwise.

4

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 15/06/2012 10:00:42 »

1) The increase in heat of the water is equivalent to the loss of mass.  So presumably you are referring to the equivalence principle E=mc².  The ² in c² represents acceleration.

velocity squared DNE acceleration

2) The energy produced is unknown until it is measured which involves obliterating the photons making them give up their energy as momentum and re-radiating some photons at a lower energy level.  The increase in momentum of the target is acceleration.

E = h.nu

3) Presumably this relies upon knowing initially both the volume and mass of 1 molecule.
Knowing the mass of 1 molecule relies upon counting the total number of protons and neutrons and knowing the weight of a proton.
“Because atoms are exceptionally small, scientists typically work with atoms in larger quantities called moles. A mole is the amount of a substance with as many atoms as there would be in 12 grams of the isotope carbon-12. This number is roughly 600 sextillion (6 times 10 to the 23rd power) atoms, and is known as Avogadro's number for the scientist who defined it.”
http://www.wikihow.com/Calculate-Atomic-Mass

This method of calculating the mass depends upon initially knowing the atomic weight of one molecule and that requires ‘weighing’ it.  Weighing it requires a non-inertial (accelerating) reference frame.  It’s a calculation based upon a measurement taken in an accelerating reference frame.

  volume of molecule no need to know.  mass of molecule is calculable as well as measurable
 

4) Is essentially the same answer as 3 but substituting atom for molecule.

  i never mentioned molecule btw.  And three is easily done - whereas 4 is v difficult

What does that mean?

To know the frequency or wavelength involves obliterating the photon which gives up its momentum by transferring it to something else.  That transfer involves a change in velocity which is acceleration.

How do you calculate it without first knowing the weight of either one molecule or constituent parts?  Weighing involves using a non-inertial (accelerating) reference frame.

5

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 12/06/2012 07:39:43 »

The Earth pushes the scale.  The scale pushes the mass.  This results in a change of momentum for the mass.  This is acceleration.

Sorry, but that's not right either.  The only change in momentum is caused by the rotation of the Earth and the rotation of the object, and the amount of the change is very small.

A tripple balance compares an unknown mass with a known mass and the difference in gravity (acceleration) on different planets is compensated for by affecting both the known and unknown mass in the same proportion.  The mass remains the same but the weight changes.

Yes, mass is constant, but you are ignoring the fact that gravity on Earth is not constant, so the weight of an object on Earth varies with location.

Whether you apply acceleration to the mass by the Earth pushing it or anything else pushing it, its the same thing, acceleration.

Pushing is NOT the same as acceleration. Acceleration requires a change in velocity. In Classical Mechanics, gravity produces an accelerative force that acts on all matter, but there is only acceleration with change in velocity, hence a change in momentum.

There is no difference between accelerating a mass by applying a force to it and the Earth accelerating the same mass by applying a pseudo-force to it (gravity).  They are equivalent.

But the object is not accelerating. Your argument only applies if you allow the object to free-fall, but then you will find that all objects accelerate at the same rate regardless of their mass. Treating gravity as a pseudo-force only works if you apply General Relativity. That means you have to analyze the entire problem using General Relativity.

There is no difference in measuring a force applied to a mass and the distance it travels than measuring the pseudo-force the Earth applies to the same mass and the distance it travels.

Except that you don't know what the gravitational force actually is, and there isn't any "travel".

That's not true.  According to Einstein, gravity and acceleration are equivalent.  It is the acceleration of the Earth that endows us with weight.

True but irrelevant to the discussion.

It is when talking about the acceleration of a massive body like the Earth.  A steady push is the steady application of energy.  The steady application of energy (as in a rocket for example) causes a steady acceleration.  A 'push' changes the velocity of the object.  That change in velocity is acceleration.

If you choose to ignore General Relativity then there is little point in discussing gravity.

We do know what the acceleration is it's 1 g.  There must be travel as the Earth is travelling through space-time.  Because we do not understand how to take the measurements does not make it any the less true.

6

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 11/06/2012 11:26:16 »

If you use a spring type scale, or an accelerometer, you are determining weight, not mass. You could use a "known mass" to determine the intensity of a gravitational field by this method then do a comparison to determine the relative mass of another object, but then you are back to only establishing a comparitive arbitrary mass.

The acceleration of the Earths surface and hence the scale applies acceleration and hence change of momentum to the mass.  (The Earth pushes the scale.  The scale pushes the mass.  This results in a change of momentum for the mass.  This is acceleration)

A tripple balance compares an unknown mass with a known mass and the difference in gravity (acceleration) on different planets is compensated for by affecting both the known and unknown mass in the same proportion.  The mass remains the same but the weight changes.

Whether you apply acceleration to the mass by the Earth pushing it or anything else pushing it, its the same thing, acceleration.

There is no difference between accelerating a mass by applying a force to it and the Earth accelerating the same mass by applying a pseudo-force to it (gravity).  They are equivalent. 

There is no difference in measuring a force applied to a mass and the distance it travels than measuring the pseudo-force the Earth applies to the same mass and the distance it travels.

7

Physics, Astronomy & Cosmology / Re: How and Why Does Light Carry an Image?

« on: 11/06/2012 09:48:59 »

Light interacts so strongly with matter that it is actually not the best technique for seeing some astronomical phenomena.
 

I guess it depends upon what you mean by light and what you mean by interact.  Individual photons to the best of my knowledge can not interact in any way and survive. 

8

Physics, Astronomy & Cosmology / Re: How and Why Does Light Carry an Image?

« on: 11/06/2012 09:40:37 »

• Estimates vary, but it is said that it can take of the order of a million years for light energy to percolate from the center of the sun to the visible surface, so it tells astronomers very little about what is happening in the sun now.
  
  

Light energy probably.  Individual original photons probably not and it is individual photons that carry that information. 

9

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 11/06/2012 08:38:35 »

It's not arbitrary as it is comparing an unknown mass with a known mass.

All three cases involve acceleration and acceleration costs energy.  In the case of the spring and triple balance the energy comes from gravitational potential energy.  It makes little difference where the energy comes from it still causes acceleration and gives "some idea of the relationship between mass and energy".

As Evan points out, the known mass is completely arbitrary, so the compared mass is also completely arbitrary. Consequently, any form of balance isn't really telling you anything about the mass.

If you use a spring type scale, or an accelerometer, you are determining weight, not mass. You could use a "known mass" to determine the intensity of a gravitational field by this method then do a comparison to determine the relative mass of another object, but then you are back to only establishing a comparitive arbitrary mass.

On the other hand, if you actually alter the momentum of an object, there are methods of directly quantifying the energy conversion.

I agree it does not tell you anything about mass itself but it is not really arbitrary if you do the comparison with a known mass. Anyway that argument is beside the point.

The question was “Do we need acceleration to define the concept of mass?"

How do you propose to "alter the momentum of an object" without accelerating it?

If you accept that it accelerates then presumably you accept that you "Do .. need acceleration to define the concept of mass?" Which is what I said in the first place and repeated in post #40 of this thread.
"For example imagine a big rock floating in space. Give it a slap with a calibrated hand so you know exactly how much energy you gave it. Now measure how fast the rock is moving."
http://education.jlab.org/qa/mass_01.html
"That's one way of measuring the mass and it involved acceleration of the mass."

10

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 10/06/2012 11:49:00 »

1. Put super-critical lump of mixed radioactive Pu and U in large water pool  - measure rise in temperature - do maths - get mass lost.

2. measure energy of photons given off by matter/anti-matter annihilation - do maths - get mass of pair

3. measure volume of ideal gas at stp - do maths - get mass

4. count atoms - do maths - get mass (ok that one is silly)

5. take complex hydrocarbon - burn to buggery - do maths - know mass of result (without measuring energy given off)


(and I know BC or JP will haul me over the coals for the liberties I have taken in the above)

imatfaal
Thanks for the input.  I will try to address all of your points.
1) I need to consider some more.
5) How do you know the starting and final mass without weighing it?  (Without using a non-inertial reference frame)

1) The increase in heat of the water is equivalent to the loss of mass.  So presumably you are referring to the equivalence principle E=mc².  The ² in c² represents acceleration.

2) The energy produced is unknown until it is measured which involves obliterating the photons making them give up their energy as momentum and re-radiating some photons at a lower energy level.  The increase in momentum of the target is acceleration.

3) Presumably this relies upon knowing initially both the volume and mass of 1 molecule.
Knowing the mass of 1 molecule relies upon counting the total number of protons and neutrons and knowing the weight of a proton.
“Because atoms are exceptionally small, scientists typically work with atoms in larger quantities called moles. A mole is the amount of a substance with as many atoms as there would be in 12 grams of the isotope carbon-12. This number is roughly 600 sextillion (6 times 10 to the 23rd power) atoms, and is known as Avogadro's number for the scientist who defined it.”
http://www.wikihow.com/Calculate-Atomic-Mass

This method of calculating the mass depends upon initially knowing the atomic weight of one molecule and that requires ‘weighing’ it.  Weighing it requires a non-inertial (accelerating) reference frame.  It’s a calculation based upon a measurement taken in an accelerating reference frame.

4) Is essentially the same answer as 3 but substituting atom for molecule.

11

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 10/06/2012 11:38:07 »

it still requires acceleration by way of a non-inertial reference frame to evaluate it.  That is, we can weigh it or use an accelerometer.

No - that won't work.

If you weigh an object in a gravitational field using the deflection of a spring (as in a bathroom scale or an accelerometer), you cannot properly evaluate the mass because you are only measuring the deflection of a spring, and the deflection will vary according to the intensity of the gravitational field.

If you weigh an object using a comparison with another mass (as in a beam balance) you are using an arbitrary object for comparison, but that's not getting you any closer to "the concept of mass".

On the other hand, if you apply a quantity of energy to an object so that its momentum changes, you can get some idea of the relationship between mass and energy.

I have already explained above how that can be used to measure mass.

It's not arbitrary as it is comparing an unknown mass with a known mass.

All three cases involve acceleration and acceleration costs energy.  In the case of the spring and triple balance the energy comes from gravitational potential energy.  It makes little difference where the energy comes from it still causes acceleration and gives "some idea of the relationship between mass and energy".

12

Physics, Astronomy & Cosmology / Re: How and Why Does Light Carry an Image?

« on: 09/06/2012 11:40:00 »

For a photon image to degrade, somehow the photons that make up the image would have to interact with each other or something else and that implies an interaction over time.  Any interaction en-route obliterates those photons.  Only un-interacted photons survive to make up the image and they (the survivors) have no sensation of the passage of either time or distance.

The image can only degrade through
Photons being obliterated.
Red-shift.
Photon density decrease per unit space volume.
Non of the above degrades the image other than it looses intensity.

The warping of space-time by passing close to a large mass can distort the image by distorting the 'grid' the geodesics that the photons follow but this is a distortion of the 'fabric' of space-time not individual photons.  (This is similar to the distortion of the 'fabric' of a child's balloon as the balloon is inflated or distorted by poking it with a finger which is analogous to gravity.)

13

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 09/06/2012 10:27:21 »

Yes it does. 

Other than the fact that you assert that it does, why does it help answer the question?

 The question was “Do we need acceleration to define the concept of mass?"  My answer was  "... it still requires acceleration by way of a non-inertial reference frame to evaluate it.  That is, we can weigh it or use an accelerometer."

"For example imagine a big rock floating in space. Give it a slap with a calibrated hand so you know exactly how much energy you gave it. Now measure how fast the rock is moving."
http://education.jlab.org/qa/mass_01.html
That's one way of measuring the mass and it involved acceleration of the mass.
"There are a couple of ways to measure mass. The most common method is to use a balance."  " If you go to a different planet, the balance weights change by the same factor as the object you are measuring. Your mass measured with a balance would be the same on the moon as it is on Earth."
http://education.jlab.org/qa/mass_01.html
This way of measuring mass relies upon comparing a known mass with an unknown mass in a non-inertial (accelerating) reference frame.
A spring balance can also measure mass but strictly speaking only measures weight.  The weight on the Moon would be 1/6 that of Earth although the mass remains the same.  Again it relies upon a non-inertial reference frame.

To the best of my knowledge that is self evident.  I don't know of any other way of evaluating or measuring mass and if you can't measure it you can't fully define it.  In that way I believe it does help to answer the question.

Does anyone know of any way of measuring mass that does not rely upon acceleration?

14

Physics, Astronomy & Cosmology / Re: Electromagnetic Force Field

« on: 08/06/2012 13:19:49 »

The Earths magnetosphere stops most harmful radiation from reaching the surface of the Earth.

I guess, if you took a projectile from a mag-lev gun and fired it back down the barrel at the same time as the gun was fired (less normal projectile), the field would maybe stop and then reverse the trajectory of the projectile.  Presumably, it would only work on metal or super-cooled objects.

15

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 08/06/2012 12:56:10 »

which was acceleration and gravity are equivalent.

Who cares! It doesn't help answer the question.

Well I do and Einstein did.

Yes it does. 

  The question was “Do we need acceleration to define the concept of mass?"  "... it still requires acceleration by way of a non-inertial reference frame to evaluate it.  That is, we can weigh it or use an accelerometer.

Unless you know differently of course.

16

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 07/06/2012 13:53:03 »

The same mass accelerating at 1g in low gravity (far away from the Earths surface) still weighs 1kg.  That is due to gravity and acceleration being equivalent.

Right - which proves that mass and gravity are independent.

Could you explain the logic of that please?

You can accelerate a mass without any gravitational field by using, for example, a chemical energy source. A rocket would work.

The point is that mass could care less about gravity. Mass remains with, or without, gravity. 

You can't have mass without a gravitational 'field' but apart from that, this is true and I never said otherwise but it is missing my point, which was acceleration and gravity are equivalent.

That’s not strictly speaking correct.  Mass warps space-time.  That interaction is what we call gravity and it involves time-dilation.  You can’t have mass without gravity.  If you try to accelerate mass in a gravitational field (other than its own), it certainly "cares" as evidenced by the variable amounts of energy required to change velocity (in the sense of direction).

That mass remains is almost certainly true (and I have never said otherwise), or it would cause problems for the conservation of mass/energy but that is not what we have been debating.  The question was “Do we need acceleration to define the concept of mass?"  Whether or not mass remains (and it almost certainly does), it still requires acceleration by way of a non-inertial reference frame to evaluate it.  That is, we can weigh it or use an accelerometer.

17

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 06/06/2012 21:28:55 »

The same mass accelerating at 1g in low gravity (far away from the Earths surface) still weighs 1kg.  That is due to gravity and acceleration being equivalent.

Right - which proves that mass and gravity are independent.

Could you explain the logic of that please?

18

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 06/06/2012 10:54:23 »

I am talking about the acceleration due to gravity of a massive object like the Earth, not acceleration of an object in free fall.

It makes no difference. A massive object like the Earth is in free-fall as it orbits the Sun.

Anyway, as I said earlier, a gravitational field won't allow you to evaluate mass. It will only allow you to evaluate weight. You can infer the mass from the weight if you know the acceleration produced by the gravitational field, but that has nothing to do with the weight.

That's true but it is still not the same as the gravitational acceleration produced by mass.  An accelerometer in free fall does not register acceleration, an accelerometer on the surface of the Earth does. It's the reference frame that is different.

You say that a gravitational field wont allow you to evaluate mass but then you go on to explain how a gravitational field can be used to evaluate mass?

We seem to be at cross purposes here.  You keep mentioning weight and I am not quite sure why.  You need a non-inertial reference frame (accelerating) to be able to measure weight or mass.  The non-inertial reference frame needed to evaluate weight is due to the gravity (acceleration) of the surface of the Earth.  To evaluate mass in a low gravity environment still requires acceleration (which is equivalent to gravity).  Both require a non-inertial reference frame.  A 1kg mass weighs 1kg on the Earths surface as the Earths surface is accelerating at 1g.  The same mass accelerating at 1g in low gravity (far away from the Earths surface) still weighs 1kg.  That is due to gravity and acceleration being equivalent.

19

Physics, Astronomy & Cosmology / Re: Do we need acceleration to define the concept of mass?

« on: 05/06/2012 10:24:31 »

Mass can be evaluated quite easily without any gravitational field by measuring acceleration. Weight is the measurement of the interaction between mass and gravity.

Gravitational acceleration has not the slightest thing to do with the mass of an object because the acceleration is completely independent of the mass.

Mass creates its own gravitational field therefore you can’t have mass without a gravitational field.  So you can’t measure mass without a gravitational field because a gravitational field is associated with mass.  Likewise, you can’t have acceleration without gravity because they are equivalent, although in the case of a small mass the gravitational component is not so obvious until the acceleration is approaching the speed of light.


This is true but what is your point?

 “In science and engineering, the weight of an object is the force on the object due to gravity. Its magnitude (a scalar quantity), often denoted by an italic letter W, is the product of the mass m of the object and the magnitude of the local gravitational acceleration g; thus: W = mg.”
http://en.wikipedia.org/wiki/Weight

_{added 06 June}
As I see it, a weighing machine measures weight because it is in a non-inertial reference frame, that is, it is in an accelerating reference frame.  As the acceleration of that reference frame is constant, so is the measure of weight.  Therefore, a non-inertial reference frame (accelerating) is required to be able to measure weight.   
_{end of edit}

This is only true when considering an object in free fall in a gravitational field.  It’s not true for the mass (Earth) that is generating that gravitational field.  See reply #12 in this thread.

Gravitational acceleration of the Earth (gravity) or any other massive gravitating body is entirely dependent upon mass, as it is mass that bends space-time.  (Assuming velocity to be insignificant)

I am talking about the acceleration due to gravity of a massive object like the Earth, not acceleration of an object in free fall.

Where Einstein said that energy and mass are equivalent he meant equivalent not exactly the same.  You can make things from mass (matter) but you need energy to do it.  Although equivalent, they are not the same.  When he said that gravity and acceleration are equivalent, I believe he meant they are the same thing, identical.

20

Physics, Astronomy & Cosmology / Re: Could the universe be like a seed that will grow into a final product?

« on: 01/06/2012 20:48:37 »

Is there a predetermined end game to our universe such as a say an apple seed one day turning into an apple tree only to throw out new seeds or as in this analogy new universes. With this in mind that seed has DNA, which it must be somehow possible to work out how it will end up being that tree. So does our universe have some kind of DNA from which we could work out how it will end up?

Any thoughts

Cheers Ace

It is certainly evolving and will, like all things eventually die.

I think so.  The universes DNA is the Laws of Nature, The Laws of Physics, the structure of atoms and the various forces.  Those things dictate how to build this universe.  If we perfectly understood those things and could measure accurately all we need to measure then in theory I see no reason why we could not predict how the Universe will end.  But it's not life Jim, not as we know it.

_{added 5th June}
The Universe produced us, so I guess it must in some sense have included the instructions for that or the possibility but those instructions are much broader and less restrictive than DNA.