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Mass creates gravity. At the moment of the big bang and for a short time after, all that existed was energy and energy without mass has no gravity. Without gravity the universe would have inflated until such time as matter and antimatter were created.The curvature of space by gravity is possibly what creates time. Therefore the inflation would have taken place possibly outside of time as without mass, gravity and therefore time did not yet exist.The above does not contradict the idea of inflation. It just explains the cause.Is this a reasonable explanation?

Mike - energy causes curvature of space-time; ie gravity. it does not need to be matter - energy and mass are equivalent.

The special theory of relativity has led to the conclusion that inert masa is nothing more or less than energy..

We make a distinction hereafter between "gravitational field" and "matter" in ths way that we denote everything but the gravitational field as "matter." Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field.

I disagree. Einstein defined "gravity" quite differently, as many modern scientists do today. He wrote in his 1916 paper, page 148QuoteThe special theory of relativity has led to the conclusion that inert masa is nothing more or less than energy..Om page 143 Einstein wroteQuoteWe make a distinction hereafter between "gravitational field" and "matter" in ths way that we denote everything but the gravitational field as "matter." Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field.

PMB - how would you and other modern scientists define it then?Quote from: Pmb on 24/10/2011 15:24:28I disagree. Einstein defined "gravity" quite differently, as many modern scientists do today. He wrote in his 1916 paper, page 148QuoteThe special theory of relativity has led to the conclusion that inert masa is nothing more or less than energy..Om page 143 Einstein wroteQuoteWe make a distinction hereafter between "gravitational field" and "matter" in ths way that we denote everything but the gravitational field as "matter." Our use of the word therefore includes not only matter in the ordinary sense, but the electromagnetic field.

Quote from: imatfaal on 24/10/2011 11:17:58Mike - energy causes curvature of space-time; ie gravity. it does not need to be matter - energy and mass are equivalent. ImatfaalEnergy and mass are only equivalent, in that matter is created from energy. In many respects they can be thought of as opposites.

Gravity causes curvature of space-time but gravity is not energy. Mass creates gravity, energy does not. If you have any arguments or links to the contrary I would be interested to know.

Quote from: MikeS on 25/10/2011 08:22:29Quote from: imatfaal on 24/10/2011 11:17:58Mike - energy causes curvature of space-time; ie gravity. it does not need to be matter - energy and mass are equivalent. ImatfaalEnergy and mass are only equivalent, in that matter is created from energy. In many respects they can be thought of as opposites. In which cases? QuoteGravity causes curvature of space-time but gravity is not energy. Mass creates gravity, energy does not. If you have any arguments or links to the contrary I would be interested to know.Gravity does not curve space time - gravity is (simplistically) the effect of space time being curved. The einstein field equations and the stress energy tensor that determine how space time are curved are notoriously complex but quite clearly include energy. The stress energy tensor has multiple blocks of components which contribute - two of such are energy density and energy flux (along with momentum flux and density)

Matter is lumpy, solid and sticks together. Energy likes to dissipate. It requires energy to make 'things'. It takes energy to power 'things'. The universe is essentially made of matter but fuelled by energy.I can't agree with that. Space time being curved is due to gravity, not gravity being an effect of curved space-time. If gravity does not curve space-time, what does? We know that mass (matter) curves space time, the greater the mass, the greater the curvature.This would seem to imply that if energy is included then gravity must be a force? As I understand it, gravity is geometry.

Quote from: MikeS on 26/10/2011 07:35:26Matter is lumpy, solid and sticks together. Energy likes to dissipate. It requires energy to make 'things'. It takes energy to power 'things'. The universe is essentially made of matter but fuelled by energy.I can't agree with that. Space time being curved is due to gravity, not gravity being an effect of curved space-time. If gravity does not curve space-time, what does? We know that mass (matter) curves space time, the greater the mass, the greater the curvature.This would seem to imply that if energy is included then gravity must be a force? As I understand it, gravity is geometry."Mike you are talking nonsense. matter is lumpy? energy likes? the universe is fuelled?"This may not be the correct terminology but is never the less true.spacetime is curved by mass/energy not by gravity. gravity emerges from freefalling bodies following geodesics in curved spacedtime. Please try and read up on this before contradicting everything. the wikipedia page on gravitation would be a good place to start. ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN

Gravity and acceleration are equivalent and it requires energy to accelerate an object. Does this mean that energy by itself creates gravity. Not as I understand it. To accelerate an object up to relativistic speed requires a lot of energy. This energy is stored as relativistic mass. So it's the mass that creates the additional gravity, not the energy per se. As I understand it mass is the sole cause of gravity. Energy only has the roll of producing mass. Energy by itself does not produce gravity.

Space-time is curved by mass, I agree and said so

If you actually read my posts you would realise that I am not "contradicting everything in fact I am contradicting very little.",

My whole point being that to the best of my knowledge, mass is the only source of gravity.

(Mass and acceleration being the same.)

Energy is not a source of gravity other than it can be converted into mass. Energy, by itself does not produce a gravitational field. Either it does or it does not. If it does then I would like to know how?

Quote from: MikeS on 27/10/2011 09:20:36Space-time is curved by mass, I agree and said so But you also said this " Gravity causes curvature of space-time but gravity is not energy." and "The curvature of space by gravity ...." which are completely false. Go back and re-read your posts.QuoteIf you actually read my posts you would realise that I am not "contradicting everything in fact I am contradicting very little.", "I can't agree with that. Space time being curved is due to gravity, not gravity being an effect of curved space-time. " This is a direct contradiction of what I posted and completely against all that is taught.Quote My whole point being that to the best of my knowledge, mass is the only source of gravity. Then unfortunately your knowledge is lacking - try reading the introduction to gravity on ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN that I posted and you might start to understand and gain the required knowledge. Quote(Mass and acceleration being the same.) No! Mass and energy are equivalent - gravity and acceleration can be equivalent on a local scale, but mass and acceleration are not the same. Just look at the units - mass is kg or even eV/c^2 (cos mass and energy are equivalent) acceleration is ms^-2 they are just not the sameQuoteEnergy is not a source of gravity other than it can be converted into mass. Energy, by itself does not produce a gravitational field. Either it does or it does not. If it does then I would like to know how? Converted into is not quite the same as equivalent. Energy and its flux will warp spacetime and this will be experienced as gravity. How? that's the best and worst question of the lot. We do not know - we dont even know what spacetime is! What we do know is that we have an incredibly accurate model consisting of 10 equations which relate the einstein tensor (which describes spacetime geometry) with the stress energy tensor (which describes momentum and energy density and fluxes). This mad situation of incredibly nasty maths does however allow us to get mercury's orbit and perihelion correct, and it predicted correctly gravitational time dilation and redshift. Physics can never really answer how or why - it merely creates models that accurately parallel reality to greater and finer extents

imatfaalThat was obviously a mistake and should have read "gravity and acceleration are the same".

What is the reasoning behind the hypothesis that energy has gravity and what experimental evidence is there to confirm it?

I know that Einstein's field equations talk about the stress-energy tensor but what does this mean in non mathematical jargon. There must have been some logic that led up to it?

The alleged gravity of energy (light) being so weak that it cannot be measured. If so, then it is conceivable that energy does not have gravity?

Quote from: MikeS on 30/10/2011 07:55:31imatfaalThat was obviously a mistake and should have read "gravity and acceleration are the same". Locally yes - gravity will always have a tidal component tho.QuoteWhat is the reasoning behind the hypothesis that energy has gravity and what experimental evidence is there to confirm it? The "hypothesis" is now generally accepted as a well tested theory - it is called General Relativity. It is as well tested as any theory in science.QuoteI know that Einstein's field equations talk about the stress-energy tensor but what does this mean in non mathematical jargon. There must have been some logic that led up to it? well yes the logic is based upon mass/energy equivalence QuoteThe alleged gravity of energy (light) being so weak that it cannot be measured. If so, then it is conceivable that energy does not have gravity? Who says it cannot be measured? And no with physics as it is it is inconceivable that energy does not cause spacetime to warp.

Quote from: imatfaal on 31/10/2011 10:23:46Quote from: MikeS on 30/10/2011 07:55:31imatfaalThat was obviously a mistake and should have read "gravity and acceleration are the same". Locally yes - gravity will always have a tidal component tho.QuoteWhat is the reasoning behind the hypothesis that energy has gravity and what experimental evidence is there to confirm it? The "hypothesis" is now generally accepted as a well tested theory - it is called General Relativity. It is as well tested as any theory in science.QuoteI know that Einstein's field equations talk about the stress-energy tensor but what does this mean in non mathematical jargon. There must have been some logic that led up to it? well yes the logic is based upon mass/energy equivalence QuoteThe alleged gravity of energy (light) being so weak that it cannot be measured. If so, then it is conceivable that energy does not have gravity? Who says it cannot be measured? And no with physics as it is it is inconceivable that energy does not cause spacetime to warp.General Relativity covers a lot of ground and I was specifically asking if energy has gravity. I have not been able to find any research confirming that it has been measured. All I have found are articles saying it is too weak to be measured. I agree that when looking at it from the mass/energy equivalence principle mass can be seen as energy and hence energy has mass and therefore gravity. But that is when looked at from the energy equivalence of mass. Energy is equivalent to mass but energy is not mass. I still don't see why energy by itself should have gravity. I can't see the logic behind it. What am I missing?

You say that "it is inconceivable that energy does not cause spacetime to warp". Does that not imply that if it is energy that causes spacetime to warp that gravity is a force, not geometry?

I am sorry to labour the point but I really am trying to understand. If energy has gravity then at the moment of the big-bang, the universe was born with gravity. If energy does not have gravity then the universe was born initially without gravity.

Quote from: MikeS on 02/11/2011 08:06:55Quote from: imatfaal on 31/10/2011 10:23:46Quote from: MikeS on 30/10/2011 07:55:31imatfaalThat was obviously a mistake and should have read "gravity and acceleration are the same". Locally yes - gravity will always have a tidal component tho.QuoteWhat is the reasoning behind the hypothesis that energy has gravity and what experimental evidence is there to confirm it? The "hypothesis" is now generally accepted as a well tested theory - it is called General Relativity. It is as well tested as any theory in science.QuoteI know that Einstein's field equations talk about the stress-energy tensor but what does this mean in non mathematical jargon. There must have been some logic that led up to it? well yes the logic is based upon mass/energy equivalence QuoteThe alleged gravity of energy (light) being so weak that it cannot be measured. If so, then it is conceivable that energy does not have gravity? Who says it cannot be measured? And no with physics as it is it is inconceivable that energy does not cause spacetime to warp.General Relativity covers a lot of ground and I was specifically asking if energy has gravity. I have not been able to find any research confirming that it has been measured. All I have found are articles saying it is too weak to be measured. I agree that when looking at it from the mass/energy equivalence principle mass can be seen as energy and hence energy has mass and therefore gravity. But that is when looked at from the energy equivalence of mass. Energy is equivalent to mass but energy is not mass. I still don't see why energy by itself should have gravity. I can't see the logic behind it. What am I missing?What you are missing I am afraid is a full physics education and a solid grounding in maths. Your argument from personal incredulity is not convincingQuote You say that "it is inconceivable that energy does not cause spacetime to warp". Does that not imply that if it is energy that causes spacetime to warp that gravity is a force, not geometry?That is a complete non-sequitur. Mass/energy cause space time to curve - curved space time gives rise to the effects of gravityQuoteI am sorry to labour the point but I really am trying to understand. If energy has gravity then at the moment of the big-bang, the universe was born with gravity. If energy does not have gravity then the universe was born initially without gravity.Yes both your if..thens are correctly constructed - however the only one with experimental evidence to back it up is that energy curves space time and gives rise to gravitational attraction; but this is experimental evidence from a very different, colder, less denser and mass-dominated universe