Mixing
Is the term 'matter' in 'dark matter' misleading?
Clash Royale CLAN TAG#URR8PPP
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If the only evidence for dark matter we have is gravitational, why call it 'matter' rather than 'observed space-time geometry that does not match predictions'?
General Relativity tells us that mass distorts local space-time but as far as I know, it doesn't say that it is the only thing that does so - isn't for all we know space-time is more fundamental than mass and can have local distortions caused by the big bang / inflationary epoch / flying-spaghetti-monster blueprints?
general-relativity dark-matter
asked 6 hours ago
AlternativelyBaryonic
113
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up vote
2
down vote
favorite
If the only evidence for dark matter we have is gravitational, why call it 'matter' rather than 'observed space-time geometry that does not match predictions'?
General Relativity tells us that mass distorts local space-time but as far as I know, it doesn't say that it is the only thing that does so - isn't for all we know space-time is more fundamental than mass and can have local distortions caused by the big bang / inflationary epoch / flying-spaghetti-monster blueprints?
general-relativity dark-matter
asked 6 hours ago
AlternativelyBaryonic
113
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
It's not just mass. GR says that stress-energy induces spacetime curvature.
– PM 2Ring
4 hours ago
+1 for invoking the flying-spaghetti-monster. Einstein must have missed that one ;)
– Time4Tea
2 hours ago
Yes, but it doesn't matter.
– Evargalo
1 hour ago
add a comment |Â
up vote
2
down vote
favorite
up vote
2
down vote
favorite
If the only evidence for dark matter we have is gravitational, why call it 'matter' rather than 'observed space-time geometry that does not match predictions'?
General Relativity tells us that mass distorts local space-time but as far as I know, it doesn't say that it is the only thing that does so - isn't for all we know space-time is more fundamental than mass and can have local distortions caused by the big bang / inflationary epoch / flying-spaghetti-monster blueprints?
general-relativity dark-matter
asked 6 hours ago
AlternativelyBaryonic
113
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
If the only evidence for dark matter we have is gravitational, why call it 'matter' rather than 'observed space-time geometry that does not match predictions'?
General Relativity tells us that mass distorts local space-time but as far as I know, it doesn't say that it is the only thing that does so - isn't for all we know space-time is more fundamental than mass and can have local distortions caused by the big bang / inflationary epoch / flying-spaghetti-monster blueprints?
general-relativity dark-matter
general-relativity dark-matter
asked 6 hours ago
AlternativelyBaryonic
113
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
AlternativelyBaryonic
113
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 5 hours ago
asked 6 hours ago
AlternativelyBaryonic
113
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 6 hours ago
AlternativelyBaryonic
113
asked 6 hours ago
AlternativelyBaryonic
113
113
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
AlternativelyBaryonic is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
It's not just mass. GR says that stress-energy induces spacetime curvature.
– PM 2Ring
4 hours ago
+1 for invoking the flying-spaghetti-monster. Einstein must have missed that one ;)
– Time4Tea
2 hours ago
Yes, but it doesn't matter.
– Evargalo
1 hour ago
add a comment |Â
1
It's not just mass. GR says that stress-energy induces spacetime curvature.
– PM 2Ring
4 hours ago
+1 for invoking the flying-spaghetti-monster. Einstein must have missed that one ;)
– Time4Tea
2 hours ago
Yes, but it doesn't matter.
– Evargalo
1 hour ago
1
1
It's not just mass. GR says that stress-energy induces spacetime curvature.
– PM 2Ring
4 hours ago
It's not just mass. GR says that stress-energy induces spacetime curvature.
– PM 2Ring
4 hours ago
+1 for invoking the flying-spaghetti-monster. Einstein must have missed that one ;)
– Time4Tea
2 hours ago
+1 for invoking the flying-spaghetti-monster. Einstein must have missed that one ;)
– Time4Tea
2 hours ago
Yes, but it doesn't matter.
– Evargalo
1 hour ago
Yes, but it doesn't matter.
– Evargalo
1 hour ago
add a comment |Â
2 Answers
2
active
oldest
votes
up vote
8
down vote
As the universe expands you would expect the density of the stuff in it to decrease for the obvious reason that the amount of stuff remains constant while the volume increases. So you'd expect something like:
$$ rho propto frac1V propto frac1a^3 $$
where $a$ is the linear scale factor (i.e. $a^3$ is the volume scale factor).
However things are more complicated than this. For radiation and highly relativistic matter the energy density decreases as $a^-4$, while for a cosmological constant the energy density doesn't decrease at all but remains constant. It is only matter, and specifically pressureless matter, that decreases as $a^-3$.
And the stuff that we call dark matter decreases as $a^-3$ just like regular matter, so whatever it is it behaves like matter. Hence the name dark matter.
answered 6 hours ago
John Rennie
265k41518765
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
1
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
add a comment |Â
up vote
0
down vote
According to the Einstein-Cartan version of gravity, there are two sources which "distort" local space-time:
Mass (or more generally energy-momentum tensor), which induces space-time curvature.
Spin current (from Dirac fermions), which induces space-time torsion.
As an alternative to missing/dark mass, we could attribute the "observed space-time geometry that does not match predictions" to dark spin current (or dubbed as " flying-spaghetti-monster", if you will).
As per Poplawski, the spin current/torsion approach has another nice property that "averts the unphysical big-bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting".
answered 2 hours ago
MadMax
201110
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
8
down vote
As the universe expands you would expect the density of the stuff in it to decrease for the obvious reason that the amount of stuff remains constant while the volume increases. So you'd expect something like:
$$ rho propto frac1V propto frac1a^3 $$
where $a$ is the linear scale factor (i.e. $a^3$ is the volume scale factor).
However things are more complicated than this. For radiation and highly relativistic matter the energy density decreases as $a^-4$, while for a cosmological constant the energy density doesn't decrease at all but remains constant. It is only matter, and specifically pressureless matter, that decreases as $a^-3$.
And the stuff that we call dark matter decreases as $a^-3$ just like regular matter, so whatever it is it behaves like matter. Hence the name dark matter.
answered 6 hours ago
John Rennie
265k41518765
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
1
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
add a comment |Â
up vote
8
down vote
As the universe expands you would expect the density of the stuff in it to decrease for the obvious reason that the amount of stuff remains constant while the volume increases. So you'd expect something like:
$$ rho propto frac1V propto frac1a^3 $$
where $a$ is the linear scale factor (i.e. $a^3$ is the volume scale factor).
However things are more complicated than this. For radiation and highly relativistic matter the energy density decreases as $a^-4$, while for a cosmological constant the energy density doesn't decrease at all but remains constant. It is only matter, and specifically pressureless matter, that decreases as $a^-3$.
And the stuff that we call dark matter decreases as $a^-3$ just like regular matter, so whatever it is it behaves like matter. Hence the name dark matter.
answered 6 hours ago
John Rennie
265k41518765
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
1
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
add a comment |Â
up vote
8
down vote
up vote
8
down vote
As the universe expands you would expect the density of the stuff in it to decrease for the obvious reason that the amount of stuff remains constant while the volume increases. So you'd expect something like:
$$ rho propto frac1V propto frac1a^3 $$
where $a$ is the linear scale factor (i.e. $a^3$ is the volume scale factor).
However things are more complicated than this. For radiation and highly relativistic matter the energy density decreases as $a^-4$, while for a cosmological constant the energy density doesn't decrease at all but remains constant. It is only matter, and specifically pressureless matter, that decreases as $a^-3$.
And the stuff that we call dark matter decreases as $a^-3$ just like regular matter, so whatever it is it behaves like matter. Hence the name dark matter.
answered 6 hours ago
John Rennie
265k41518765
As the universe expands you would expect the density of the stuff in it to decrease for the obvious reason that the amount of stuff remains constant while the volume increases. So you'd expect something like:
$$ rho propto frac1V propto frac1a^3 $$
where $a$ is the linear scale factor (i.e. $a^3$ is the volume scale factor).
However things are more complicated than this. For radiation and highly relativistic matter the energy density decreases as $a^-4$, while for a cosmological constant the energy density doesn't decrease at all but remains constant. It is only matter, and specifically pressureless matter, that decreases as $a^-3$.
And the stuff that we call dark matter decreases as $a^-3$ just like regular matter, so whatever it is it behaves like matter. Hence the name dark matter.
answered 6 hours ago
John Rennie
265k41518765
answered 6 hours ago
John Rennie
265k41518765
answered 6 hours ago
John Rennie
265k41518765
answered 6 hours ago
John Rennie
265k41518765
265k41518765
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
1
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
add a comment |Â
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
1
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
What results are considered to observe this 'stuff' decrease as $a^-3$ rather than not-enough regular matter decreasing as $a^-3$ ?
– AlternativelyBaryonic
5 hours ago
1
1
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
@AlternativelyBaryonic the current best measurements of the dark energy density and behaviour come from the Planck experiment to observe the microwave background.
– John Rennie
4 hours ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
Dark matter or dark energym Is this really dark matter?
– Vladimir F
1 hour ago
add a comment |Â
up vote
0
down vote
According to the Einstein-Cartan version of gravity, there are two sources which "distort" local space-time:
Mass (or more generally energy-momentum tensor), which induces space-time curvature.
Spin current (from Dirac fermions), which induces space-time torsion.
As an alternative to missing/dark mass, we could attribute the "observed space-time geometry that does not match predictions" to dark spin current (or dubbed as " flying-spaghetti-monster", if you will).
As per Poplawski, the spin current/torsion approach has another nice property that "averts the unphysical big-bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting".
answered 2 hours ago
MadMax
201110
add a comment |Â
up vote
0
down vote
According to the Einstein-Cartan version of gravity, there are two sources which "distort" local space-time:
Mass (or more generally energy-momentum tensor), which induces space-time curvature.
Spin current (from Dirac fermions), which induces space-time torsion.
As an alternative to missing/dark mass, we could attribute the "observed space-time geometry that does not match predictions" to dark spin current (or dubbed as " flying-spaghetti-monster", if you will).
As per Poplawski, the spin current/torsion approach has another nice property that "averts the unphysical big-bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting".
answered 2 hours ago
MadMax
201110
add a comment |Â
up vote
0
down vote
up vote
0
down vote
According to the Einstein-Cartan version of gravity, there are two sources which "distort" local space-time:
Mass (or more generally energy-momentum tensor), which induces space-time curvature.
Spin current (from Dirac fermions), which induces space-time torsion.
As an alternative to missing/dark mass, we could attribute the "observed space-time geometry that does not match predictions" to dark spin current (or dubbed as " flying-spaghetti-monster", if you will).
As per Poplawski, the spin current/torsion approach has another nice property that "averts the unphysical big-bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting".
answered 2 hours ago
MadMax
201110
According to the Einstein-Cartan version of gravity, there are two sources which "distort" local space-time:
Mass (or more generally energy-momentum tensor), which induces space-time curvature.
Spin current (from Dirac fermions), which induces space-time torsion.
As an alternative to missing/dark mass, we could attribute the "observed space-time geometry that does not match predictions" to dark spin current (or dubbed as " flying-spaghetti-monster", if you will).
As per Poplawski, the spin current/torsion approach has another nice property that "averts the unphysical big-bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting".
answered 2 hours ago
MadMax
201110
edited 2 hours ago
answered 2 hours ago
MadMax
201110
answered 2 hours ago
MadMax
201110
answered 2 hours ago
MadMax
201110
201110
add a comment |Â
add a comment |Â
AlternativelyBaryonic is a new contributor. Be nice, and check out our Code of Conduct.
AlternativelyBaryonic is a new contributor. Be nice, and check out our Code of Conduct.
AlternativelyBaryonic is a new contributor. Be nice, and check out our Code of Conduct.
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1
It's not just mass. GR says that stress-energy induces spacetime curvature.
– PM 2Ring
4 hours ago
+1 for invoking the flying-spaghetti-monster. Einstein must have missed that one ;)
– Time4Tea
2 hours ago
Yes, but it doesn't matter.
– Evargalo
1 hour ago