## Dark Energy

In article <dg0qo6$hmt$1@online.de>,
helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to

> > The question in my mind is where does this energy come from and it would
> > seem that more and more of it is needed in order to increase the expansion
> > rate.

>
> It doesn't have to come from anywhere. The Friedmann-Lemaître equations
> allow for such a term, and apparently it has been observed. Note that
> there is not a problem with energy conservation, since energy isn't
> conserved in general relativity anyway. (Imagine a universe consisting
> only of radiation. It expands. The number of photons remains the same,
> but the energy of each decreases due to the redshift. No, this lost
> energy does not do the work of expanding the universe.)
>

What, if any, conserved quantities are there in General Relativity? I
recall there is an Energy-Momentum tensor, but I know little beyond
that. Is that conserved or involved in a conservation law? If so, what
does it mean?

thanks.

-- Lou Pecora (my views are my own) REMOVE THIS to email me.

 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 In article , helbig@astro.multiCLOTHESvax.de (Phillip Helbig---remove CLOTHES to reply) wrote: > > The question in my mind is where does this energy come from and it would > > seem that more and more of it is needed in order to increase the expansion > > rate. > > It doesn't have to come from anywhere. The Friedmann-Lemaître equations > allow for such a term, and apparently it has been observed. Note that > there is not a problem with energy conservation, since energy isn't > conserved in general relativity anyway. (Imagine a universe consisting > only of radiation. It expands. The number of photons remains the same, > but the energy of each decreases due to the redshift. No, this lost > energy does not do the work of expanding the universe.) > What, if any, conserved quantities are there in General Relativity? I recall there is an Energy-Momentum tensor, but I know little beyond that. Is that conserved or involved in a conservation law? If so, what does it mean? thanks. -- Lou Pecora (my views are my own) REMOVE THIS to email me.
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm
 >> My understanding is that the Universe is expanding and that >> this expansion is speeding up. What is fuelling this expansion >> rate increase that is working against the force of gravity? >> >> The answer seems to be Dark Energy. Correct. > Whatever that is! Dark energy may be modelled by adding a constant to Einstein's equations; hence the term "cosmological constant". >> The question in my mind is where does this energy come from >> and it would seem that more and more of it is needed in order >> to increase the expansion rate. Correct. The energy comes from the expansion (a form of gravitational or geometric energy) which is negative. As the universe expands the positive energy locked as dark energy increases (density is constant, but volume increases); this is offset by the negative energy in the Hubble expansion which decreases (becomes more negative). In the case of dark energy this process can continue for ever; it's a slow form of inflation. > > It doesn't have to come from anywhere. The Friedmann-Lemaître > equations allow for such a term, and apparently it has been observed. > Note that there is not a problem with energy conservation, since > energy isn't conserved in general relativity anyway. That is not true. Energy is conserved in GR, with the obvious caveat that we have to adopt a sensible definition of energy. http://www.physics.adelaide.edu.au/~...energy_gr.html > (Imagine a universe consisting only of radiation. It expands. > The number of photons remains the same, but the energy of each > decreases due to the redshift. No, this lost energy does not do > the work of expanding the universe.) Then why does a radiant-filled universe decelerate faster than a matter-filled universe? Because the energy lost in the redshift cancels some of the negative energy tied up in the Hubble expansion. Cheers, Michael C Price ---------------------------------------- http://mcp.longevity-report.com http://www.hedweb.com/manworld.htm