Register to reply

Dark Energy

by nc
Tags: dark, energy
Share this thread:
Phillip Helbig---remove CLOTHES to reply
#73
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#74
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#75
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#76
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#77
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#78
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#79
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Phillip Helbig---remove CLOTHES to reply
#80
Oct12-06, 05:08 AM
P: n/a
In article <%ZD4f.3782$cA4.3019@newsfe3-gui.ntli.net>, Michael C Price
<michaelEXCISESPAMprice917@tesco.net> writes:

> >>>> 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.


> >>>> 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).

> >
> > Where did you get this idea from?


> 8 pi G rho + gamma + -3H^2 = 0
>
> ( gamma = cosmological constant, a form of dark energy.
> rho = average matter density
> G = Newton's constant
> H = Hubble's expansion factor. )
>
> The question is: how do we interpret this equation?
>
> Since the first two terms are proportional to energy density then
> it is a reasonable inference that we have an expression of energy
> conservation if the last term is also proportional to energy density;
> in this case the energy of the dynamic geometry.
>
> > Explain how the energy of the
> > cosmological constant "comes from" the expansion. The stuff about
> > "dark energy" is OK, but the claim that it is "offset by the negative
> > energy in the Hubble expansion" is completely bogus.

>
> Yet the above equation shows that the offset is exact with
> complete cancellation or conservation.


> > Also, imagine a universe with NO cosmological constant. There
> > would thus be no "offset".

>
> Correct.
>
> > Are you claiming that such a universe is impossible?

>
> No, at this stage I was only talking about how the dark energy/
> cosmological constant was handled, which was what the original
> query related to. If there is no cosmological constant then set
> gamma = 0 in the above equation.


> >>> (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.)

> >
> > Give a "sensible definition of energy", which is not ad-hoc, which is
> > conserved in this case.

>
> 8piG rho + gamma - 3H^2 .


Let me rephrase my criticism. You say that there is a conservation
equation, and say that the energy of the cosmological constant "comes
from" the expansion and also that the equation is valid if there is no
cosmological constant. So, my question is, if there is no cosmological
constant, then, in the case of no cosmological constant, where does the
energy go which, in the case of a cosmological constant, is transformed
into the cosmological constant?

Imagin the Einstein static universe. There is no expansion. Yet there
is an energy density due to the cosmological constant. How does it
"come from" the (non-existent) expansion in this case? What about a
negative cosmological constant?

I'll reply in more detail later.

Perhaps we are merely using completely different terminology. However,
I think that what you are saying is misleading, or at least confusingly
phrased. You seem to be saying "no mystery where the dark energy comes
from, it comes from expansion". Of course if there is an equation which
holds while the universe expands, then something is conserved; the
question is how this relates to commonly used usages of the term.

I think Edward Harrison has explained rather well what is meant by
"energy is not conserved in the expanding universe". Do you disagree
with his analysis?

This argument might be similar to "cosmological redshift is a Doppler
redshift, and at large redshift one must use the relativistic Doppler
formula". This is not the case if the words have their normal meaning.
One can of course DEFINE a velocity such that it is given by the
relativistic Doppler formula, but I don't see how that is useful.
(Narlikar, in an American Journal of Physics article which Ted Bunn
mentioned here a while back, shows how this can be perhaps useful in a
very unorthodox sense; this might be interesting to experts, but
certainly not to the casual layman interested in cosmology and trying to
get around elementary misunderstandings about Olbers's paradox, what was
before the big bang, where was the big bang etc.)

Michael C Price
#81
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#82
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#83
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#84
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#85
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#86
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#87
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#88
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Michael C Price
#89
Oct12-06, 05:09 AM
P: n/a
Me:
>> 8 pi G rho + gamma + -3H^2 = 0
>>
>> ( gamma = cosmological constant, a form of dark energy.
>> rho = average matter density
>> G = Newton's constant
>> H = Hubble's expansion factor. )
>>
>> The question is: how do we interpret this equation?
>>
>> Since the first two terms are proportional to energy density then
>> it is a reasonable inference that we have an expression of energy
>> conservation if the last term is also proportional to energy density;
>> in this case the energy of the dynamic geometry.
>>

[.......]
Philip:
> Let me rephrase my criticism. You say that there is a conservation
> equation, and say that the energy of the cosmological constant "comes
> from" the expansion and also that the equation is valid if there is no
> cosmological constant. So, my question is, if there is no cosmological
> constant, then, in the case of no cosmological constant, where does the
> energy go which, in the case of a cosmological constant, is transformed
> into the cosmological constant?


Let me answer it this way: the cosmological constant currently dominates
the expansion of the universe. The matter and photons are just being
carried along for the ride. (This wasn't always the case. Earlier the
matter dominated, and before that the photons.) The dominant flow of
energy, today, is from the Hubble expansion to the cosmological constant,
each one growing in magnitude although of opposite sign. Without a
cosmological constant the presently insignificant flow from the photons
(via the red shift) to the Hubble factor would dominate, as it did in the
early universe. i.e. the direction of the energy flow would be reversed.

> Imagine the Einstein static universe. There is no expansion. Yet there
> is an energy density due to the cosmological constant. How does it
> "come from" the (non-existent) expansion in this case? What about a
> negative cosmological constant?


Indeed, as you point out, in Einstein's original static universe the
cosmological constant was negative and its now negative energy offset
the energy in the matter and photons. With no expansion there was no
energy transfer to/from the cosmological constant.
>
> I'll reply in more detail later.
>
> Perhaps we are merely using completely different terminology. However,
> I think that what you are saying is misleading, or at least confusingly
> phrased. You seem to be saying "no mystery where the dark energy comes
> from, it comes from expansion". Of course if there is an equation which
> holds while the universe expands, then something is conserved; the
> question is how this relates to commonly used usages of the term.


True.

> I think Edward Harrison has explained rather well what is meant by
> "energy is not conserved in the expanding universe". Do you disagree
> with his analysis?


Yes. If I understand Harrison's argument it is that pressure and pressure
gradients mediate the transfer of energy in the thermodynamic dE = -P dV
equation (which has a cosmological equivalent), which describes the
expansion of, say, a pressurised gas against its environment. But in the
universe there is no exterior system to push against and hence no transfer
of energy. Instead he concludes the red-shift energy is lost and not
transferred. I think he is being lead astray by the thermodynamic
analogy with pressure. Pressure is the result of particles (including
photons) with momenta, which have de Broglie wavelengths. It is the
stretching of the wavelengths by the Hubble expansion which causes the
loss of momenta and the red-shift. The loss of radiation pressure is a
consequence of this stretching and not a mediating mechanism; no
pressure gradient or exterior system is required.

I agree with your point about definitions and the Doppler effect.

Cheers,
Michael C Price
----------------------------------------
http://mcp.longevity-report.com
http://www.hedweb.com/manworld.htm

Phillip Helbig---remove CLOTHES to reply
#90
Oct12-06, 05:09 AM
P: n/a
In article <ovh5f.5505$cA4.1338@newsfe3-gui.ntli.net>, "Michael C Price"
<michaelEXCISESPAMprice917@tesco.net> writes:

> Let me answer it this way: the cosmological constant currently dominates
> the expansion of the universe. The matter and photons are just being
> carried along for the ride. (This wasn't always the case. Earlier the
> matter dominated, and before that the photons.) The dominant flow of
> energy, today, is from the Hubble expansion to the cosmological constant,
> each one growing in magnitude although of opposite sign. Without a
> cosmological constant the presently insignificant flow from the photons
> (via the red shift) to the Hubble factor would dominate, as it did in the
> early universe. i.e. the direction of the energy flow would be reversed.


You seem to think that this "flow" is some sort of physical
transformation. Can you explain this in more detail?

> > Imagine the Einstein static universe. There is no expansion. Yet there
> > is an energy density due to the cosmological constant. How does it
> > "come from" the (non-existent) expansion in this case? What about a
> > negative cosmological constant?

>
> Indeed, as you point out, in Einstein's original static universe the
> cosmological constant was negative


The cosmological constant in the Einstein static universe is positive.
I was providing two examples: one in which there can be no "flow" since
there is no expansion, and in addition mentioning that the cosmological
constant can, theoretically, be negative while the expansion has the
same sign as it has today. I don't see how you can say that there is a
"flow" in all three cases (static, negative cosmological constant,
positive cosmological constant) or, if you don't claim this (which seems
to be the case), how you can say that in some cases (like the one which
corresponds to our universe), there IS a flow.

Let me EXAGGERATE. Fewer children are born where fewer storks nest.
Does this prove that storks bring children? No. It is due to a common
cause (fewer children are born in industrialised societies, and storks
are less common here as well). Historically, global warming is also
negatively correlated with the number of pirates sailing the seven seas,
but that doesn't mean that pirates prevent global warming. You seem to
be saying a) there is expansion and b) there is a cosmological constant
and then claiming that one "causes" the other in some sense.

> > I think Edward Harrison has explained rather well what is meant by
> > "energy is not conserved in the expanding universe". Do you disagree
> > with his analysis?

>
> Yes. If I understand Harrison's argument it is that pressure and pressure
> gradients mediate the transfer of energy in the thermodynamic dE = -P dV
> equation (which has a cosmological equivalent), which describes the
> expansion of, say, a pressurised gas against its environment. But in the
> universe there is no exterior system to push against and hence no transfer
> of energy. Instead he concludes the red-shift energy is lost and not
> transferred. I think he is being lead astray by the thermodynamic
> analogy with pressure. Pressure is the result of particles (including
> photons) with momenta, which have de Broglie wavelengths. It is the
> stretching of the wavelengths by the Hubble expansion which causes the
> loss of momenta and the red-shift. The loss of radiation pressure is a
> consequence of this stretching and not a mediating mechanism; no
> pressure gradient or exterior system is required.


Harrison (in his textbook) explicitly states that the universe is not
like a steam engine, so I think the disagreement has another cause.



Register to reply

Related Discussions
Dark Matter/Dark Energy Question Cosmology 4
Superb overview of contemporary research/observations in dark matter, dark energy Cosmology 0
Review of Dark Matter and Dark Energy by M. Kamionkowski Cosmology 5
Dark matter, dark energy & gravity Cosmology 45
Dark energy = dark matter*speed of light squared? Astronomy & Astrophysics 14