Distance to the Furthest Visible Objects

[litespeed]

I often read light from distant these objects took such-and-such billions of light years to reach us. However, it seems to me the objects themselves must be very much further away then light years mentioned.

This is because we have been speeding away from these objects for billions of years, all the while light emitted from them has been chasing and passing us the entire time.

Does anyone know how FAR away such objects are TODAY? Or put another way, how far have we traveled away from them in the billions of years it has taken the current visible light to reach us.

[Essay]

Scientists Detect "Dark Flow:" Matter From Beyond the Visible Universe | Universe Today

Originally Posted by Sept. 2008

Scientists believe the cause is the gravitational attraction of matter that lies beyond the observable universe, and they are calling it "Dark Flow," in the vein of two other cosmological mysteries, dark matter and dark energy.

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How Can We See Galaxies 47 Billion Light Years Away When the Universe is Only 13 Billion Years Old?

Originally Posted by buff.com

What all of this means is that whenever you discuss the size of the universe, you need to apply a scale factor that is relevant TO THE TIME you are interested in. The issue of when is very important because the size of the universe, and the rate at which it was expanding has changed since the universe began.

So, for RIGHT NOW, the size of the universe has expanded to roughly 46.5 billion light years since the Big Bang.

...and here's a cool link:
NASA's Observatorium -- Observation of the Week
"Gravitationally lensed quasars like the one shown above...."

Discussing the Accelerating Expansion of the Universe - Science in the Metaverse - T. Troy McConaghy's blog on Nature Network
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...and here's a great discussion on the whole topic of "space" vs. "the void."

http://www.astro.princeton.edu/~aes/...onsBigBang.pdf
"But because the universe is expanding, the space traversed by a photon expands behind it during the voyage. Consequently, the current distance to the most distant object we can see is about three times farther, or 46 billion light-years."
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"...space traversed by a photon expands behind it during the voyage."
...geee, sounds kinda like a "wake."

~

[LogicTech]

Yes, the time it took light to reach us should not be confused with the actual distance the source is. Because the universe expands, the source would now be much further away, even though the light itself only traveled for a few billion years. That's why we rely on redshifts.

[Essay]

Originally Posted by Essay

"...space traversed by a photon expands behind it during the voyage." -princeton.edu
...geee, sounds kinda like a "wake."

I was just being silly, based on their choice of words "behind it," but of course one can't help but think about "in front" of the photon also.

It would be the expansion of that "in front" space, that causes the red-shift, wouldn't it?

~

p.s. Though from the photon's POV, it's just it's own timeless, static space that is relaxing a bit, allowing it to vibrate more freely (red-shifting). ...maybe?

[LogicTech]

Originally Posted by Essay

I was just being silly, based on their choice of words "behind it," but of course one can't help but think about "in front" of the photon also.

It would be the expansion of that "in front" space, that causes the red-shift, wouldn't it?

~

Well, a photon is both a particle and a wave, so when space itself expands, it stretches the wavelength. Since objects further away are receding faster than objects that are closer (i.e. Hubble's Law), they tend to have a greater redshift, which is why we use them to help determine distance.

Photons will only reach their destination if the galaxy is close enough to begin with, that is, if it isn't beyond the cosmological horizon. If the galaxy is too far away, then it will never reach it, because of both Hubble's Law dictates that it is receding too fast, and recent observations have concluded that this expansion is accelerating.

p.s. Though from the photon's POV, it's just it's own timeless, static space that is relaxing a bit, allowing it to vibrate more freely (red-shifting). ...maybe?

Since photons travel at the speed of light, I can't really say that there exists a frame of reference for the photon itself. The speed of light is constant in all frames of reference.

[litespeed]

RE Red Shift

Thanks for the posts; they have been very helpful. However, it now seems to me that Red Shift can be caused by TWO things. First, the expansion of space itself seems the most important. Second, I believe Red Shift can also be induced by motion where space expansion would not be too small to notice.

For instance, many space objects are moving towards us. Specifically, galaxies in the local group or cluster moving towards us would, it seems to me, exhibit a blue(?) shift. This, even though the SPACE between us is expanding, they are moving faster towards us then space between us is expanding.

Incidentally, can anyone tell me when the current understanding of Red Shift was developed? If I recall correctly, for many decades Red Shift was simply accounted for by motion itself. In the same way a train whistle changes pitch as the train passes ( the speed of sound is not violated). Or in the probable Blue Shift of approachjing stars and galaxies.

[modest]

Originally Posted by litespeed

RE Red Shift

Thanks for the posts; they have been very helpful. However, it now seems to me that Red Shift can be caused by TWO things. First, the expansion of space itself seems the most important. Second, I believe Red Shift can also be induced by motion where space expansion would not be too small to notice.

While redshift is single value, it is commonly attributed to three things:

1. Cosmological expansion. Over cosmological distances, everything is expanding away from everything else. This is the scale factor in FLRW cosmology.

2. Relativistic doppler effect. The scale factor mentioned above assumes nothing has any peculiar motion, but as you point out—astronomical objects do have (often very small) motion peculiar to the Hubble flow. In these cases, there is an additional factor affecting the redshift between two objects, it is the relativistic doppler effect.

3. Gravitational redshift. The scale factor in FLRW cosmology assumes the universe is homogeneous with no variations in local gravity, but this is an approximation and not always the case. A photon moving from a stronger area of gravity to a weaker area of gravity (e.g. from the sun to the earth) is redshifted.

These are all three in a way related to each other and they are explained in depth at wikipedia's article on redshift.

Originally Posted by litespeed

For instance, many space objects are moving towards us. Specifically, galaxies in the local group or cluster moving towards us would, it seems to me, exhibit a blue(?) shift. This, even though the SPACE between us is expanding, they are moving faster towards us then space between us is expanding.

Yes. Galaxies that are relatively close to us such as Andromeda or some galaxies in the Virgo cluster are blueshifted meaning they are getting closer to us over time. Hubble's law, which describes how fast the universe is expanding, is an average which is closer and closer to real values over greater and greater distances. Over small distances (such as two stars in the same galaxy or two galaxies in the same group), doppler redshift and gravitational redshift are most meaningful.

Originally Posted by litespeed

Incidentally, can anyone tell me when the current understanding of Red Shift was developed? If I recall correctly, for many decades Red Shift was simply accounted for by motion itself. In the same way a train whistle changes pitch as the train passes ( the speed of sound is not violated). Or in the probable Blue Shift of approachjing stars and galaxies.

The general relativistic model of the universe that explains redshift as an expanding spacetime metric was developed before Hubble noticed galaxies were receding in 1929. In this respect, the explanation for cosmic redshift has existed for as long as the observations were available.

~modest

[simcha]

I often read light from distant these objects took such-and-such billions of light years to reach us. However, it seems to me the objects themselves must be very much further away then light years mentioned.

This is because we have been speeding away from these objects for billions of years, all the while light emitted from them has been chasing and passing us the entire time.

Does anyone know how FAR away such objects are TODAY? Or put another way, how far have we traveled away from them in the billions of years it has taken the current visible light to reach us.

hi !, Litespeed,
... Top-Marks! ... top! marks! in what you say/suggest.
... Excellent point you bring up. Ha'Kavod ! ["(with) The'Honor(s!)"]
i thought that I understood "Space/Time-Dilation" as well as anyone else, but i suppose not. It's obvious to me now that you and others have a greater appreciation & understanding of the topic & subject-matter.
... I don't really know whether or not "Black-holes" (or infinite-points of singularity) are "hollow" ,... but i certainly hope so
Simcha.

[simcha]

oke`! Essay ,... i see your stuff.
You're a 'sharpy' !
... don't, respond to me with this "Dark-Void" in the universe we have just recently detected.
... my "Yahoo-Chess" ratings have already been discussed.

(so has my phone bill)

there's always ways to get around even this.
Simcha.

Cops are so-o pathetically s////////

/////wait someone's banging really hard this time