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Does the expansion of the universe increase with distance?
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I read something in a book the other day which has gotten me really confused. They were talking about the expansion of the universe, and if I understood it all, they said that the expansion of the universe increases with distance. I’m wondering if I understood this correctly, because I was reading about Hubble’s law and it said that the redshift if galaxies far away (caused by the expansion of the universe) is proportional to the distance (up to a few hundred megaparsecs away). Doesn’t this mean that the expansion is the same but the redshift increases? (I don’t see why the redshift would be proportional and a linear graph if the universe expanded from us proportionally to the distance, or at least more further away). I hope you understand what I mean by all this.
universe expansion redshift
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MelvinMelvin
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I read something in a book the other day which has gotten me really confused. They were talking about the expansion of the universe, and if I understood it all, they said that the expansion of the universe increases with distance. I’m wondering if I understood this correctly, because I was reading about Hubble’s law and it said that the redshift if galaxies far away (caused by the expansion of the universe) is proportional to the distance (up to a few hundred megaparsecs away). Doesn’t this mean that the expansion is the same but the redshift increases? (I don’t see why the redshift would be proportional and a linear graph if the universe expanded from us proportionally to the distance, or at least more further away). I hope you understand what I mean by all this.
universe expansion redshift
asked 8 hours ago
MelvinMelvin
253
New contributor
Melvin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
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add a comment |
$begingroup$
I read something in a book the other day which has gotten me really confused. They were talking about the expansion of the universe, and if I understood it all, they said that the expansion of the universe increases with distance. I’m wondering if I understood this correctly, because I was reading about Hubble’s law and it said that the redshift if galaxies far away (caused by the expansion of the universe) is proportional to the distance (up to a few hundred megaparsecs away). Doesn’t this mean that the expansion is the same but the redshift increases? (I don’t see why the redshift would be proportional and a linear graph if the universe expanded from us proportionally to the distance, or at least more further away). I hope you understand what I mean by all this.
universe expansion redshift
asked 8 hours ago
MelvinMelvin
253
New contributor
Melvin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
I read something in a book the other day which has gotten me really confused. They were talking about the expansion of the universe, and if I understood it all, they said that the expansion of the universe increases with distance. I’m wondering if I understood this correctly, because I was reading about Hubble’s law and it said that the redshift if galaxies far away (caused by the expansion of the universe) is proportional to the distance (up to a few hundred megaparsecs away). Doesn’t this mean that the expansion is the same but the redshift increases? (I don’t see why the redshift would be proportional and a linear graph if the universe expanded from us proportionally to the distance, or at least more further away). I hope you understand what I mean by all this.
universe expansion redshift
universe expansion redshift
asked 8 hours ago
MelvinMelvin
253
New contributor
Melvin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
MelvinMelvin
253
New contributor
Melvin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 7 hours ago
Melvin
asked 8 hours ago
MelvinMelvin
253
New contributor
Melvin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 8 hours ago
MelvinMelvin
253
asked 8 hours ago
MelvinMelvin
253
253
New contributor
Melvin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
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Check out our Code of Conduct.
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I'm not sure why you say that "expansion is the same" when you also say that "expansion increases with distance", but I wouldn't say the "expansion increases", but rather that "the recession velocity increases".
The recession velocity $v$ of galaxies increases linearly with distance $d$. The constant of proportionality is called the Hubble constant $H_0$. Thus, Hubble's law states that
$$
v = H_0 d,
$$
and currently, $H_0 simeq 70,mathrm{km},mathrm{s}^{-1},mathrm{Mpc}^{-1}$, but in the past it was higher. That means that, for every Mpc (mega-parsec, $simeq 3.26times10^6$ light-years) a galaxy is from us, its speed away from us is roughly $70,mathrm{km},mathrm{s}^{-1}$. This is the speed it has right now, but not the speed we see it have, since we see it in the past.
In fact, we don't really see a speed at all. We measure a galaxy's redshift $z$, and $z$ also increases with distance, but not linearly. Thats's because it depends on how much the Universe has expanded since the light was emitted, and the expansion rate changes with time. But for small enough distances, i.e. for galaxies that are not seen that far into the past, the relation is close to linear, so that $v = cz$, where $c$ is the speed of light.
This is indeed approximately true out to a few hundred Mpc. For larger distances, the linear relation becomes inaccurate, and one must instead apply a cosmological model of the expansion history of the Universe, which depends non-trivially on the densities of its various constituents.
answered 6 hours ago
pelapela
18k3965
$endgroup$
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
add a comment |
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$begingroup$
I'm not sure why you say that "expansion is the same" when you also say that "expansion increases with distance", but I wouldn't say the "expansion increases", but rather that "the recession velocity increases".
The recession velocity $v$ of galaxies increases linearly with distance $d$. The constant of proportionality is called the Hubble constant $H_0$. Thus, Hubble's law states that
$$
v = H_0 d,
$$
and currently, $H_0 simeq 70,mathrm{km},mathrm{s}^{-1},mathrm{Mpc}^{-1}$, but in the past it was higher. That means that, for every Mpc (mega-parsec, $simeq 3.26times10^6$ light-years) a galaxy is from us, its speed away from us is roughly $70,mathrm{km},mathrm{s}^{-1}$. This is the speed it has right now, but not the speed we see it have, since we see it in the past.
In fact, we don't really see a speed at all. We measure a galaxy's redshift $z$, and $z$ also increases with distance, but not linearly. Thats's because it depends on how much the Universe has expanded since the light was emitted, and the expansion rate changes with time. But for small enough distances, i.e. for galaxies that are not seen that far into the past, the relation is close to linear, so that $v = cz$, where $c$ is the speed of light.
This is indeed approximately true out to a few hundred Mpc. For larger distances, the linear relation becomes inaccurate, and one must instead apply a cosmological model of the expansion history of the Universe, which depends non-trivially on the densities of its various constituents.
answered 6 hours ago
pelapela
18k3965
$endgroup$
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
add a comment |
$begingroup$
I'm not sure why you say that "expansion is the same" when you also say that "expansion increases with distance", but I wouldn't say the "expansion increases", but rather that "the recession velocity increases".
The recession velocity $v$ of galaxies increases linearly with distance $d$. The constant of proportionality is called the Hubble constant $H_0$. Thus, Hubble's law states that
$$
v = H_0 d,
$$
and currently, $H_0 simeq 70,mathrm{km},mathrm{s}^{-1},mathrm{Mpc}^{-1}$, but in the past it was higher. That means that, for every Mpc (mega-parsec, $simeq 3.26times10^6$ light-years) a galaxy is from us, its speed away from us is roughly $70,mathrm{km},mathrm{s}^{-1}$. This is the speed it has right now, but not the speed we see it have, since we see it in the past.
In fact, we don't really see a speed at all. We measure a galaxy's redshift $z$, and $z$ also increases with distance, but not linearly. Thats's because it depends on how much the Universe has expanded since the light was emitted, and the expansion rate changes with time. But for small enough distances, i.e. for galaxies that are not seen that far into the past, the relation is close to linear, so that $v = cz$, where $c$ is the speed of light.
This is indeed approximately true out to a few hundred Mpc. For larger distances, the linear relation becomes inaccurate, and one must instead apply a cosmological model of the expansion history of the Universe, which depends non-trivially on the densities of its various constituents.
answered 6 hours ago
pelapela
18k3965
$endgroup$
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
add a comment |
$begingroup$
I'm not sure why you say that "expansion is the same" when you also say that "expansion increases with distance", but I wouldn't say the "expansion increases", but rather that "the recession velocity increases".
The recession velocity $v$ of galaxies increases linearly with distance $d$. The constant of proportionality is called the Hubble constant $H_0$. Thus, Hubble's law states that
$$
v = H_0 d,
$$
and currently, $H_0 simeq 70,mathrm{km},mathrm{s}^{-1},mathrm{Mpc}^{-1}$, but in the past it was higher. That means that, for every Mpc (mega-parsec, $simeq 3.26times10^6$ light-years) a galaxy is from us, its speed away from us is roughly $70,mathrm{km},mathrm{s}^{-1}$. This is the speed it has right now, but not the speed we see it have, since we see it in the past.
In fact, we don't really see a speed at all. We measure a galaxy's redshift $z$, and $z$ also increases with distance, but not linearly. Thats's because it depends on how much the Universe has expanded since the light was emitted, and the expansion rate changes with time. But for small enough distances, i.e. for galaxies that are not seen that far into the past, the relation is close to linear, so that $v = cz$, where $c$ is the speed of light.
This is indeed approximately true out to a few hundred Mpc. For larger distances, the linear relation becomes inaccurate, and one must instead apply a cosmological model of the expansion history of the Universe, which depends non-trivially on the densities of its various constituents.
answered 6 hours ago
pelapela
18k3965
$endgroup$
I'm not sure why you say that "expansion is the same" when you also say that "expansion increases with distance", but I wouldn't say the "expansion increases", but rather that "the recession velocity increases".
The recession velocity $v$ of galaxies increases linearly with distance $d$. The constant of proportionality is called the Hubble constant $H_0$. Thus, Hubble's law states that
$$
v = H_0 d,
$$
and currently, $H_0 simeq 70,mathrm{km},mathrm{s}^{-1},mathrm{Mpc}^{-1}$, but in the past it was higher. That means that, for every Mpc (mega-parsec, $simeq 3.26times10^6$ light-years) a galaxy is from us, its speed away from us is roughly $70,mathrm{km},mathrm{s}^{-1}$. This is the speed it has right now, but not the speed we see it have, since we see it in the past.
In fact, we don't really see a speed at all. We measure a galaxy's redshift $z$, and $z$ also increases with distance, but not linearly. Thats's because it depends on how much the Universe has expanded since the light was emitted, and the expansion rate changes with time. But for small enough distances, i.e. for galaxies that are not seen that far into the past, the relation is close to linear, so that $v = cz$, where $c$ is the speed of light.
This is indeed approximately true out to a few hundred Mpc. For larger distances, the linear relation becomes inaccurate, and one must instead apply a cosmological model of the expansion history of the Universe, which depends non-trivially on the densities of its various constituents.
answered 6 hours ago
pelapela
18k3965
answered 6 hours ago
pelapela
18k3965
answered 6 hours ago
pelapela
18k3965
answered 6 hours ago
pelapela
18k3965
18k3965
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
add a comment |
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
OK, but you said that the recession velocity has been higher before, but doesn’t the universe expand more and more with time? (Or have I got that totally wrong?)
$endgroup$
– Melvin
57 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
$begingroup$
And yeah, I probably meant recession velocity :)
$endgroup$
– Melvin
53 mins ago
add a comment |
Melvin is a new contributor. Be nice, and check out our Code of Conduct.
Melvin is a new contributor. Be nice, and check out our Code of Conduct.
Melvin is a new contributor. Be nice, and check out our Code of Conduct.
Melvin is a new contributor. Be nice, and check out our Code of Conduct.
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