Distances of deep space objects

[UncleJoe]

Forgive me if this is an obvious, or simplistic question but I am completely new to the field. Thank you.

 

CONFUSED:

 

When we see images of deep space, or something like therecent "Ultra Deep Space Field," I believe it's called, we are seeingan area of space not as it is now, but as it was millions of years ago,correct? We are essentially, seeingBACK IN TIME.

 

But if that is the case then, what we are seeing has been altered by millionsof years of expansion, so that the objects we do see are, AT PRESENT, muchfarther away. Is that correct? Now, when we are given the numbersdescribing the distances of these objects, do those number reflect the distancesas they WERE millions of years ago, which we are only NOW observing, or, dothose number reflect the distances the objects actually are from us, which wecannot see?

 

 

 

Does this question even make sense? I'm so confused, I'm not sure myself. <br style="mso-special-character:line-break"><br style="mso-special-character:line-break">

[michel123456]

There are many distances in cosmology.

See http://en.wikipedia.org/wiki/Distance_measures_(cosmology)

[Spyman]

When we see images of deep space, or something like therecent "Ultra Deep Space Field," I believe it's called, we are seeingan area of space not as it is now, but as it was millions of years ago,correct?

Yes, except that is was several billions and not millions years ago for the farthest objects.

 

 

We are essentially, seeingBACK IN TIME.

Yes, we see objects as they appeared a very long time ago.

 

 

But if that is the case then, what we are seeing has been altered by millionsof years of expansion, so that the objects we do see are, AT PRESENT, muchfarther away. Is that correct?

Yes, they are now farther away due to expansion and they have also aged a lot since then.

 

 

Now, when we are given the numbersdescribing the distances of these objects, do those number reflect the distancesas they WERE millions of years ago, which we are only NOW observing, or, dothose number reflect the distances the objects actually are from us, which wecannot see?

Neither, as you have already figured out the expansion has moved them further away while the light from them was travelling to us, but what you have missed is that since space is expanding during the time light is making its journey, the actual distance light have to travel to reach us gets extended.

 

Therefor there are three different distances involved: the past distance to the objects when light was emitted, the distance light has travelled through space to reach us and the distance to where the objects are assumed to be today.

 

The normal figure given in popular science articles is the distance light has travelled through space to reach us, but they where closer when they emitted that light and they are further away now when we see it.

[questionposter]

Given that the hubble constant is, well, constant, we can calculate where they are now at this very second by knowing where they were millions of years ago, which for us is the present, based on how fast those objects are moving and the time it took the light to reach us.

Edited March 20, 2012 by questionposter

[Spyman]

The Hubble constant is time dependent.

[questionposter]

The Hubble constant is time dependent.

 

Doesn't it portray the constant speed at which celestial objects are moving away from us? If we know the speed that galaxies have been travel for that billion years to get to us, then we can project where they are now at this very second.

[Spyman]

The expansion of space doesn't have a constant rate.

[questionposter]

The expansion of space doesn't have a constant rate.

 

Then why is the red-shift normally constant?

 

https://www.cfa.harv.../huchra/hubble/

 

Something's expanding at least, and since matter follows the path of the distortion of space, if space expands, matter will try to follow that distortion, and since we see matter following the same relative path throughout the universe, that distortion must also be relatively the same throughout the universe.

Hubble's constant also seems pretty...constant.

I suppose the acceleration for the expansion of space and not the actual rate itself is constant if you were just being that picky.

There also just isn't really another explanation for why we see this dramatic acceleration either, the only thing we can think of is that something is causing space to expand.

Edited March 21, 2012 by questionposter

[Spyman]

Then why is the red-shift normally constant?

The increase in redshift relative distance is constant today but it was a different constant one billion year ago. The Hubble constant is the constant ratio of how fast a distant object is receding depending on its distance right now, but it changes over time.

 

The Hubble constant is constant throughout the Universe but NOT throughout history.

 

According to current Big Bang theory the Universe expanded rapidly at first, but since the Universe was much denser in the past gravity was much stronger and affected the expansion more, therefore gravity has been slowly braking the expansion until around 6 billion years ago when the Universe got to spread out and dark energy got the upper hand causing the rate of expansion to accelerate.

 

 

The expansion or contraction of the universe depends on its content and past history. With enough matter, the expansion will slow or even become a contraction. On the other hand, dark energy drives the universe towards increasing rates of expansion. The current rate of expansion is usually expressed as the Hubble Constant (in units of kilometers per second per Megaparsec, or just per second).

http://map.gsfc.nasa.gov/universe/uni_expansion.html

 

The Hubble constant H is one of the most important numbers in cosmology because it may be used to estimate the size and age of the Universe. It indicates the rate at which the universe is expanding. Although the Hubble "constant" is not really constant because it changes with time (and therefore should probably more properly be called the "Hubble parameter").

http://csep10.phys.utk.edu/astr162/lect/cosmology/hubble_constant.html

 

H₀ is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent and which can be expressed in terms of the scale factor) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving time.

(...)

Since the Hubble "constant" is only a constant in space, not in time, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today. Current evidence suggests the expansion of the universe is accelerating (see Accelerating universe), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.

http://en.wikipedia.org/wiki/Hubble's_law

 

 

Timeline of the Big Bang

(...) The earliest phases of the Big Bang are subject to much speculation. (...) Approximately 10⁻³⁷ seconds into the expansion, a phase transition caused a cosmic inflation, during which the Universe grew exponentially. (...) After inflation stopped (...) The Universe continued to grow in size and fall in temperature (...) with less space and everything closer together, gravity had the upper hand, and it was slowly braking the expansion. But eventually, after numerous billion years of expansion, the growing abundance of dark energy caused the expansion of the Universe to slowly begin to accelerate.

http://en.wikipedia.org/wiki/Big_Bang

 

The current scientific consensus of most cosmologists is that the ultimate fate of the universe depends on its overall shape, how much dark energy it contains, and on the equation of state which determines how the dark energy density responds to the expansion of the universe. Recent observations have shown that, from 7.5 billion years after the Big Bang onwards, the expansion rate of the universe has actually been increasing, commensurate with the Open Universe theory.

http://en.wikipedia.org/wiki/Ultimate_fate_of_the_universe

[questionposter]

The increase in redshift relative distance is constant today but it was a different constant one billion year ago. The Hubble constant is the constant ratio of how fast a distant object is receding depending on its distance right now, but it changes over time.

 

The Hubble constant is constant throughout the Universe but NOT throughout history.

 

According to current Big Bang theory the Universe expanded rapidly at first, but since the Universe was much denser in the past gravity was much stronger and affected the expansion more, therefore gravity has been slowly braking the expansion until around 6 billion years ago when the Universe got to spread out and dark energy got the upper hand causing the rate of expansion to accelerate.

 

 

The expansion or contraction of the universe depends on its content and past history. With enough matter, the expansion will slow or even become a contraction. On the other hand, dark energy drives the universe towards increasing rates of expansion. The current rate of expansion is usually expressed as the Hubble Constant (in units of kilometers per second per Megaparsec, or just per second).

http://map.gsfc.nasa..._expansion.html

 

The Hubble constant H is one of the most important numbers in cosmology because it may be used to estimate the size and age of the Universe. It indicates the rate at which the universe is expanding. Although the Hubble "constant" is not really constant because it changes with time (and therefore should probably more properly be called the "Hubble parameter").

http://csep10.phys.u...e_constant.html

 

H₀ is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent and which can be expressed in terms of the scale factor) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving time.

(...)

Since the Hubble "constant" is only a constant in space, not in time, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today. Current evidence suggests the expansion of the universe is accelerating (see Accelerating universe), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.

http://en.wikipedia.org/wiki/Hubble's_law

 

 

Timeline of the Big Bang

(...) The earliest phases of the Big Bang are subject to much speculation. (...) Approximately 10⁻³⁷ seconds into the expansion, a phase transition caused a cosmic inflation, during which the Universe grew exponentially. (...) After inflation stopped (...) The Universe continued to grow in size and fall in temperature (...) with less space and everything closer together, gravity had the upper hand, and it was slowly braking the expansion. But eventually, after numerous billion years of expansion, the growing abundance of dark energy caused the expansion of the Universe to slowly begin to accelerate.

http://en.wikipedia.org/wiki/Big_Bang

 

The current scientific consensus of most cosmologists is that the ultimate fate of the universe depends on its overall shape, how much dark energy it contains, and on the equation of state which determines how the dark energy density responds to the expansion of the universe. Recent observations have shown that, from 7.5 billion years after the Big Bang onwards, the expansion rate of the universe has actually been increasing, commensurate with the Open Universe theory.

http://en.wikipedia....of_the_universe

 

Ok, so I see how the exact rate isn't constant, but isn't there a specific pattern or equation that models "how" that constant changes? At first, it was fast, now it's leveling off, that seems kind like some square root function.

Also, what else would be causing the distance between galaxies to increase at the rate they currently are?

 

 

 

[questionposter]

The increase in redshift relative distance is constant today but it was a different constant one billion year ago. The Hubble constant is the constant ratio of how fast a distant object is receding depending on its distance right now, but it changes over time.

 

The Hubble constant is constant throughout the Universe but NOT throughout history.

 

According to current Big Bang theory the Universe expanded rapidly at first, but since the Universe was much denser in the past gravity was much stronger and affected the expansion more, therefore gravity has been slowly braking the expansion until around 6 billion years ago when the Universe got to spread out and dark energy got the upper hand causing the rate of expansion to accelerate.

 

 

The expansion or contraction of the universe depends on its content and past history. With enough matter, the expansion will slow or even become a contraction. On the other hand, dark energy drives the universe towards increasing rates of expansion. The current rate of expansion is usually expressed as the Hubble Constant (in units of kilometers per second per Megaparsec, or just per second).

http://map.gsfc.nasa..._expansion.html

 

The Hubble constant H is one of the most important numbers in cosmology because it may be used to estimate the size and age of the Universe. It indicates the rate at which the universe is expanding. Although the Hubble "constant" is not really constant because it changes with time (and therefore should probably more properly be called the "Hubble parameter").

http://csep10.phys.u...e_constant.html

 

H₀ is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent and which can be expressed in terms of the scale factor) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving time.

(...)

Since the Hubble "constant" is only a constant in space, not in time, the radius of the Hubble sphere may increase or decrease over various time intervals. The subscript '0' indicates the value of the Hubble constant today. Current evidence suggests the expansion of the universe is accelerating (see Accelerating universe), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.

http://en.wikipedia.org/wiki/Hubble's_law

 

 

Timeline of the Big Bang

(...) The earliest phases of the Big Bang are subject to much speculation. (...) Approximately 10⁻³⁷ seconds into the expansion, a phase transition caused a cosmic inflation, during which the Universe grew exponentially. (...) After inflation stopped (...) The Universe continued to grow in size and fall in temperature (...) with less space and everything closer together, gravity had the upper hand, and it was slowly braking the expansion. But eventually, after numerous billion years of expansion, the growing abundance of dark energy caused the expansion of the Universe to slowly begin to accelerate.

http://en.wikipedia.org/wiki/Big_Bang

 

The current scientific consensus of most cosmologists is that the ultimate fate of the universe depends on its overall shape, how much dark energy it contains, and on the equation of state which determines how the dark energy density responds to the expansion of the universe. Recent observations have shown that, from 7.5 billion years after the Big Bang onwards, the expansion rate of the universe has actually been increasing, commensurate with the Open Universe theory.

http://en.wikipedia....of_the_universe

 

Ok, so I see how the exact rate isn't constant, but isn't there a specific pattern or equation that models "how" that rate changes? At first, it was fast, now it's leveling off, that seems kind like some square root function. I thought you had meant though that the acceleration isn't uniform, because if that was true scientists couldn't have come up with a model for the expansion of the entire universe.

Also, what else would be causing the distance between galaxies to increase at the rate they currently are?

Edited March 22, 2012 by questionposter

[Spyman]

Ok, so I see how the exact rate isn't constant, but isn't there a specific pattern or equation that models "how" that rate changes? At first, it was fast, now it's leveling off, that seems kind like some square root function. I thought you had meant though that the acceleration isn't uniform, because if that was true scientists couldn't have come up with a model for the expansion of the entire universe.

Also, what else would be causing the distance between galaxies to increase at the rate they currently are?

There are several models that describes the expansion of space but the basic is the Friedmann-Lemaître-Robertson-Walker metric and the current standard model in big bang cosmology is the Lambda-CDM model.

 

At first the rate was fast, then leveling off and now it is accelerating, and don't see how you can call that unvarying.

 

Dark energy is named "dark" because we don't know what it is and how it works.

[questionposter]

There are several models that describes the expansion of space but the basic is the Friedmann-Lemaître-Robertson-Walker metric and the current standard model in big bang cosmology is the Lambda-CDM model.

 

At first the rate was fast, then leveling off and now it is accelerating, and don't see how you can call that unvarying.

 

Dark energy is named "dark" because we don't know what it is and how it works.

 

Ok, as long as it's uniform.

[Spyman]

The rate of expansion is not uniform, but the underlying principle in nature causing this phenomenon might be consistent.

[questionposter]

The rate of expansion is not uniform, but the underlying principle in nature causing this phenomenon might be consistent.

 

If it's not uniform, how can scientists model the expansion of the "entire" universe?

[Spyman]

If it's not uniform, how can scientists model the expansion of the "entire" universe?

I am sorry but in the context your question doesn't make any sense, you are either playing silly word games or I am failing to understand you. Could you please rephrase your question without using the word "uniform" and explain further why you think scientists should be unable to model expansion.

[questionposter]

I am sorry but in the context your question doesn't make any sense, you are either playing silly word games or I am failing to understand you. Could you please rephrase your question without using the word "uniform" and explain further why you think scientists should be unable to model expansion.

 

If the expansion is not consistant throughout most if not all of the 3-dimensional coordinates of the universe, how can scientists model how the universe has changed? Without a consistency, the universe would expand at random rates and random amounts everywhere.

[Spyman]

If the expansion is not consistant throughout most if not all of the 3-dimensional coordinates of the universe, how can scientists model how the universe has changed? Without a consistency, the universe would expand at random rates and random amounts everywhere.

In post #9 I said: The Hubble constant is constant throughout the Universe but NOT throughout history.

 

The expansion is thought to be equal everywhere inside 3D space of the Universe but not equal through different durations of time.

 

Scientists examine the observed pattern of how the Universe have been expanding through history by looking further away and compare with their models of the Universe.

 

EDIT: The laws of nature causing the expansion are assumed to be consistent.

Edited March 23, 2012 by Spyman

[questionposter]

In post #9 I said: The Hubble constant is constant throughout the Universe but NOT throughout history.

 

The expansion is thought to be equal everywhere inside 3D space of the Universe but not equal through different durations of time.

 

Scientists examine the observed pattern of how the Universe have been expanding through history by looking further away and compare with their models of the Universe.

 

EDIT: The laws of nature causing the expansion are assumed to be consistent.

 

Ok, I just got confused because you said

 

The rate of expansion is not uniform,

 

 

But I guess you were talking about the acceleration vs speed.

Edited March 23, 2012 by questionposter

[JohnStu]

Forgive me if this is an obvious, or simplistic question but I am completely new to the field. Thank you.

 

CONFUSED:

 

When we see images of deep space, or something like therecent "Ultra Deep Space Field," I believe it's called, we are seeingan area of space not as it is now, but as it was millions of years ago,correct? We are essentially, seeingBACK IN TIME.

 

But if that is the case then, what we are seeing has been altered by millionsof years of expansion, so that the objects we do see are, AT PRESENT, muchfarther away. Is that correct? Now, when we are given the numbersdescribing the distances of these objects, do those number reflect the distancesas they WERE millions of years ago, which we are only NOW observing, or, dothose number reflect the distances the objects actually are from us, which wecannot see?

 

 

 

Does this question even make sense? I'm so confused, I'm not sure myself. <br style="mso-special-character:line-break"><br style="mso-special-character:line-break">

 

 

The Ultra Deep Space Field is actually 13 something billion years + light years old.

 

I believe it said that on the NASA website which I read 3 months ago.