How Far Away is the Farthest Galaxy?

"Master looks after us now, we don't need you anymore. Leave now and never come back!" -Smeagol, LOTR

You all know how to find the farthest galaxy ever, right? You take the most powerful telescope in the world, put it into space, and have it stare into the darkness for days on end. What do you find?

Image credit: Hubble Ultra Deep Field.

Galaxies! In just a tiny area like this, only about a fiftieth of a single degree on a side, over ten thousand galaxies are visible.

And, as you'll notice if you click through, and zoom in on a small section of these, some of these galaxies are much dimmer and redder than others.

Sure, you might notice the brighter, closer galaxies at first. But take a look at the left-hand-side of this image. Notice that red "dot" about mid-way down? That -- like every other light source in this image -- is a galaxy. But it's very dim and red, not because it's a dim, red galaxy.

It's dim because it's super far away, and it's red because the Universe is expanding!

How so? Let's take a look at (roughly) the same field-of-view, but instead of using a visible light telescope, like Hubble, let's use an infrared space telescope: the ESA's Herschel!

It's pretty spectacular, and almost just as good a resolution, too. (Check out an amazing showcase here.) We can zoom in on the same area of this image as we did on the earlier one, for comparison. What do we find?

Look at that! That galaxy -- once you find it -- which was so dim, red, and point-like with Hubble's eyes, is now just as visible as the other galaxies around it.

Having difficulty finding it? Let me do you the favor of zooming in, incredibly close, to the area I'm talking about on both images, and presenting them side-by-side.

That's Herschel's image on the left, and Hubble's on the right. (Pretty amazing, isn't it?) Notice how the dim, red galaxy, as seen by Hubble, appears just as bright and vibrant as all the others through Herschel's eyes.

Now, what you're looking at is a galaxy whose light is "only" about 10 billion years old.

But our Universe is about 13.7 billion years old, and we can do much better. (For a fantastic example of how you can do even better, check out the brilliant work that reader Dave W. has done!)

Thanks to the Hubble Ultra Deep Field team, they've gone deeper into the Universe than ever before, and managed to pull out a galaxy whose light has been traveling to us for 13.2 billion years. Want to see?

Image credit: NASA, ESA, and the HUDF09 team, Illingsworth et al.

Now, like I said earlier, there's a big reason why a galaxy like this is invisible to your visible-light eyes: the Universe is expanding.

Let's provide you with a visual of how this works.

Image credit:

So, that's the Universe expanding. As you'll notice, the farther away something is from you, the faster away from you it appears to move. The tricky part, of course, is that it isn't actually moving!

What's really going on -- according to General Relativity -- is that the space between these galaxies is expanding. As light travels through this space, the wavelength of that light gets longer, causing it to shift towards the red end of the spectrum. (What we colloquially call redshift.)

Have a look at this beautiful illustration by Rob Knop.

So we need to look with longer and longer wavelength light, and to be sensitive to ever-fainter light sources, to be able to see it!

I can hear the wheels turning in your mind, wondering about this whole 13.2 billion light years thing. What does that actually mean? I recently got this question from Scott Welty, a high school teacher:

Light from a galaxy 13.2 billion light years away is coming from where? That galaxy is no longer where it was, right? Does the galaxy even exist any longer if we're seeing it as it was 13.2 billion years ago? I have this problem in general with deep sky pictures. You can't really take a snap shot of the universe because nothing is standing still and farther away is longer ago!

You can find plenty of illustrations on the web that get it wrong, like this guy. (Sorry,

If you learn General Relativity, you can figure out how the separation distance between any two points evolves over time. For this galaxy in particular, let's take a look at what would happen. (Images stolen from Rob Knop's above video.)

Back when the light from this galaxy -- the light we are seeing now -- was emitted, it was "only" about 1.4 billion light years away from us. This is still a tremendous distance, and it's made all the more impressive by the fact that the Universe is only about 500 million years old at the time!

This should really underscore to you the difference between "this thing is moving away from us faster than the speed of light," which isn't happening, and "the space between things is expanding," which is what's happening. Let's take a look at what happens as the light travels towards us, to better illustrate this.

As the light leaves the distant galaxy, the space between that galaxy and us continues to expand! The light is always getting closer to us; it's never farther than the initial 1.4 billion light years away. (Update: After working it out, galaxies farther away than about 400 million light years, at the time, do have their light get farther away from us before it gets closer to us.) But because of how that space expands, it takes far longer than the expected 1.4 billion years for that light to reach us.

In fact, it takes 13.2 billion years for that light to reach us! When you see figures quoted like "this thing is 13.2 billion light years away," that's actually deceptive. What they usually mean is that the light has been traveling for that long. But by time we come to now...

...that distant galaxy is way farther away than 13.2 billion light years! In this example, the galaxy is more like 32 billion light years away, and the light it's emitting right now will never reach us! (Thanks a lot, dark energy!)

You might ask, then, what's the greatest distance away a galaxy could be from us, in principle, and still be visible today?

Image credit: xkcd.

The answer is about 46 billion light years, although we know that the Universe doesn't have galaxies in it that early on. We are about to go hunting for the new record-breakers with the James Webb Space Telescope; we expect to be able to push that record back until we're possibly seeing the very first galaxies that form in the Universe!

But it's important to look sooner rather than later, at least on a cosmic timescale. This "redding-out" of distant galaxies that I just described to you is real, and it means that our distant future Universe will look like this,

where the actual Universe is in blue, but the part visible to us is in red. The red sphere is growing ever larger, but the Universe is expanding faster than that. Admittedly, we're fine for billions of years longer, but that is our eventual fate, as far as we know it. Lucky for us that we live now, in a Universe full of galaxies, near and far!

More like this

So Ethan, I have to ask: How long is it -from our vantage point in the Milky Way- until the universe has expanded so much that we can no longer see any other galaxies? How far into the future would it be that some Milky Way civilization (if it exists) would look up and only see their own galaxy in the sky? In addition, at that point in time, would the presence of other galaxies still be able to be inferred by other means, such as the CMB?


By Brad Walker (not verified) on 11 May 2011 #permalink

Ethan,great explanation as usual, but problems with the images and your description, or I am being particularly stupid on a cold morning!

"That galaxy -- once you find it -- which was so dim, red, and point-like with Hubble's eyes, is now just as visible as the other galaxies around it." Um, no, it's not, where exactly are you pointing?

"Notice how the dim, red galaxy, as seen by Hubble, appears just as bright and vibrant as all the others through Herschel's eyes." Um, no, it doesn't in what is showing here (two very fuzzy images, and nothing showing in Herschel that seems different).

On a tangent from Brad's question, could this mean that eventually the space within an individual galaxy's stars become so great that the structure dissipates? Could this mean that eventually, in some unimaginably distant future, that the space between nuclear particles expands beyond the limits of the strong & weak forces?
Or could this mean that I shouldn't read awesome science blogs while high?

David, in the first image it's about 1cm from the left edge and just short of halfway down from the top. You should be able to find it easily in the second image based on the pattern in the 3 stars above and to the left of it.

In the first image it is red and barely visible. In the second it is just as visible as all the other non-spectacular galxies.

By Vince whirlwind (not verified) on 11 May 2011 #permalink

Ethan, This is a nice clear explanation of how distances vary with time - best I've seen in 30 years of reading astro articles.
Please tell us what equations(s) you used to calculate the distance (1.4 billion LY) between our galaxy and the observed galaxy, 500 million years after the Big Bang. Since distance = 0 LY at t = 0.0 years, and distance = 1.4 billion LY at t = 0.5 billion years, that means the average rate of the expansion of the space between them was 2.8 LY per year. How is that calculated?? Best regards, GM

By George Monser (not verified) on 11 May 2011 #permalink

When you talk about the farthest galaxy in our universe, you're really talking about the farthest visible galaxy, right? It's not at all clear from the blog post but what you're saying doesn't agree with what I've read elsewhere.

If we are looking back in time, then the very distant galaxies we see are at a time before the universe expanded. So, I would expect that the distant galaxies would be packed close together. But across the width of the sky it appears as though the between distant galaxies 90 degrees apart (from our perspective) are what, 2piR/4? This would seem to say that the distances between distant galaxies are greater than the universe is old. That can't be right. So, if the apparent distances between distant galaxies are a type of optical illusion, then should those galaxies be noticeably apparently larger? Are they?

At Tyro, Yeah I agree with you. I have read other sources and I seem to disagree to Ethan's. Just the title is confusing. But the totality of the information given is very good.

John Hunt, Space between your two distant galaxies is expanding (as well as the Space between them and us). There is no problem with the number of light years between them exceeding the age of the Universe. The space within the galaxies will be expanding too, but as you are looking at a snapshot of a moment in time, what would these galaxies be "apparently larger" than when all such galaxies are at a similar distance?

Tyro, observable is perhaps a better word than visible, as the latter strongly implies the use of the visible part of the spectrum. Anything older than this galaxy would be even further into the infra-red. My understanding from this post is that there is nothing "inside" our universe that can't be theoretically observed at the right frequency, but in billions of years time this will not be the case. The nature of anything "outside" our universe is forever hidden from us. It is wrong to think of this "outside" as simply "more universe" beyond some horizon.

@Brad: This talk by Lawrence Krauss (see about 51:20 - but the whole thing is worth watching)

Puts that horizon at about 100 Bn years. He also states that future civilizations will have no way of knowing anything else is out there.

Uhmm there war a good point about this last picture from Lawrence Krauss. He said that if a civilisation will life at this far future universe and this civilisation will observe their universe they will wrongly find out that their universe is a static one, and that they are the only one out there...strange thing !

lol...i cant believe that... ok sry Chuck C was first ;D

So if the universe is constantly expanding and objects, such as my head, remain the same size, does that mean that the atoms in my head are actually acting against this stretching effect in order to remain the same distance from each other?

"Space exists so that everything doesn't happen in one place." Anonymous, Mens Room, Physics Bldg. Michigan State University.

So does it follow that more stuff happening requires more space, ergo space must expand?

David - thanks for the clarification. It sounds like there's a lot of subtleties. I re-read the article with that in mind and I think I understand more :)

@Artor and @ChrisR: The clumpy bits of the universe, i.e., galaxies and clusters of galaxies, have enough gravity to keep the space close to them from expanding. The expansion only happens in the big spaces between clusters of galaxies where there is not enough mass (and, therefore, gravity) to counteract it.

By Daniel C. Smith (not verified) on 12 May 2011 #permalink

Suriyeâde 15 Martâtan bu yana devam eden protestoları bastırmak için BeÅar Esad yönetimi Åimdi de kendi halkını bombalamaya baÅlarken, Obamaânın çok yakında Suriye Devlet BaÅkanı BeÅar Esadâa koltuÄunu bırakma çaÄrısı yapacaÄı iddia edildi

I understand the consistency of your explanation. But further, within accepted big bang cosmology thinking; how are a couple of questions answered.

1) Is the universe 13.7 billion years old from any point in the visible universe or is 13.7 billiont years the age of the universe as viewed from Earth?
1a) In particular, consider that galaxy "1.4 billion light years away from us... (when) the Universe is only about 500 million years old." I assume at the center of that galaxy, there was a black hole and that black hole or its (merged) descendant black hole still exists. Now from the point of view of the event horizon of such a black hole (since infinite time dilation at an event horizon of a black hole); it would seem that the universe is now at most only 1.4 billion years old (i.e. a cosmic twin paradox). Hence my question 1). Or am I misthinking something basic or complex? Can you point me in the right direction?

2) Does the universe have a topological shape? Or range of possible shapes? By universe, I mean all of the matter and energy visible or dark that originated from the big bang event. I assume all of this remaining matter finite and contained within 46 Billion lightyear radius. And here is the confusion; but if that 46 billion lightyear radius is true for all observers; then how can it be a globe like the Earth; even if 46 Billion lightyear radius froms a 2-sphere (i.e. even if our observed cosmic event horizon is a 2-sphere = a spherical surface). So to repeat my question what is the range of possible universe topological shapes? I assume also the universe (as visible or at the 46 billion lightyear radius is finite not infinite.

OK, any help on wrapping my mind (better) around these two questions will be appreciated.

One can why nature sought fit to locate mankind so far from everything else in the universe, and
in case we do get dangerously close to being able to send an astronaut hit-team to the nearest star, by then the nearest star will have expanded safely out of reach.

To expand on what Daniel described @18, should dark energy become too strong for even gravity and the other three forces hold anything together (even atoms) you would have a Big Rip scenario. Perhaps Ethan will explain it in more detail in a future update.

One the ways I like to look at the Astronomy Picture of Day, when it has suitable pictures of stars or nebulae or nearby galaxies, is to see how many distant galaxies I find.

By NoAstronomer (not verified) on 12 May 2011 #permalink

If you differentiate between apparent observable Universe and Universe as a whole then you'll see that from your vantage point, the limits of your view form a spherical shape (red sphere), but that shape(blue sphere) is an illusion if you wish to relate it to the exspanded Universe as a whole.The spheres in the last photo are to show the relevance of expansion.
The red sphere constantly incorporates information from the blue sphere yet it will never catchup.

The age of the apparent observable Universe (13.7/ B.Y.) and time of light in flight (46 B.L.Y.) two seperate concepts. The first is an age the second is distance the light will travel due to the exspantion of space.

Analysis of data from WMAP implies that on the scale to the surface of last scattering, the density parameter of the Universe is within about 2% of the value representing spatial flatness.a bounded global geometry such as a three sphere is not ruled out, niether is hyperbolic (saddle) or a donut, ect.

Excerpt from following link;

The latest research shows that even the most powerful future experiments (like SKA, Planck..) will not be able to distinguish between flat, open and closed universe if the true value of cosmological curvature parameter is smaller than 10â4. If the true value of the cosmological curvature parameter is larger than 10â3 we will be able to distinguish between these three models even now.

By Sphere Coupler (not verified) on 12 May 2011 #permalink

Ethan, you said: "The light is always getting closer to us; it's never farther than the initial 1.4 billion light years away."

My understanding was that any light that we now see that was emitted in the first ~5Gy of the universe was emitted from regions then (and always since) receding superluminally. The photons initially receded from us; only when the expansion of the Hubble sphere reached those photons did they begin to move towards us.

This is described in section 3.3 of the excellent paper by Davis & Lineweaver (2003) "Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe." (freely available online)

Or do have I compounded my misconceptions by reading this?

Sphere Coupler
Thanks for clarifying my shape of the universe #2)question.

Any thoughts on my #1) in my response 20 above. I don't think your red sphere blue sphere discussion addresses it; unless I am misunderstanding something. Thanks.

Does it strike anyone else as odd that the big bang and inflation took place just at the event horizon? It seems a bit like looking out over the ocean and saying that just a few yards beyond the horizon the ocean was incredibly dense and incredibly small but suddenly it got incredibly big incredibly fast.

Not sure I understand the question, perhaps reread Ethans post and/or rephrase...sorry I'm a little dense today.

By Sphere Coupler (not verified) on 13 May 2011 #permalink

That infrared image is NOT from Herschel. It's also from Hubble, using its new infrared camera (WFC3) installed by astronauts during the latest servicing mission.

And strictly speaking, galaxies don't necessarily get redder with distance. They are often quite bright in the ultraviolet, which then shifts to blue wavelengths at high redshifts. The actual reason that these extremely distant galaxies appear red is because there is so much intervening Hydrogen between them and us that it absorbs all of their UV light.

That infrared image is NOT from Herschel. It's also from Hubble, using its new infrared camera (WFC3) installed by astronauts during the latest servicing mission.

And strictly speaking, galaxies don't necessarily get redder with distance. They are often quite bright in the ultraviolet, which then shifts to blue wavelengths at high redshifts. The actual reason that these extremely distant galaxies appear red is because there is so much intervening Hydrogen between them and us that it absorbs all of their UV light.



"Is the universe 13.7 billion years old from any point in the visible universe or is 13.7 billion years the age of the universe as viewed from Earth?"

I would rephrase to say;
Is the Apparent Observable Universe(AOU) 13.7 billion years old from any point in(our red sphere)/our AOU? or is 13.7 billion years the age of the AOU as viewed from Earth?

Then I would answer yes to both inquiries.

I realise that the blue sphere/ red sphere is not to scale, yet if you place another same sized red sphere (alternate viewing point) anywhere within the existing red sphere (our viewing point)you are still embedded within the blue sphere (known expansion area).

Still not sure what you are asking with 1a, but what the hell (coffee is kicking in)


In particular, consider that galaxy "1.4 billion light years away from us... (when) the Universe is only about 500 million years old. I assume at the center of that galaxy, there was a black hole and that black hole or its (merged) descendant black hole still exists. Now from the point of view of the event horizon of such a black hole (since infinite time dilation at an event horizon of a black hole); it would seem that the universe is now at most only 1.4 billion years old (i.e. a cosmic twin paradox). Hence my question 1). Or am I misthinking something basic or complex? Can you point me in the right direction?"

First, primordial Black Hole are still debatable but we will assume logical for this question and we will disregard any Black hole functions and assume I am locked in the event horizon for infinity.

Ethan please correct me if I am not as concise as I should be...
The delivery of information, to me immersed and locked in the event horizon will be no different to me when viewed by me (still 13.7 billion).

It is only an abstraction when you on Earth attempt to view my info from your reference frame that this abstraction occurs or vica versa. What I am getting at is due to the density of the opposing environments, we both see and experience the same phenomena exactly the same while we are immersed in our own density/environment.

If we could communicate without any interference from our environments (we can't)we would report that a minute is still 60 seconds within each others reference frame, but if YOU look at MY watch from your vantage point it is slow and vica versa.

So in a sense all event horizons seem the same to the observer when immersed in the same horizons/environments as the information that you experience but not when compared to each other.

It is a matter of view, it is difficult to view ones own whole environment when immersed within same environment, especially if the is no disturbance, the nature of disturbance leads to the coupling of views and an overall understanding of a connected Universe.

Think of an event horizon immersion(in this respect only) as a bottleneck of density compression, yet carry this analogy no further.
The question could be better resolved if we could use another medium to confer with each other from differing environments, such as a WIMP, but the conversation that transpired (from different environments) would still be offset due to the imperfect nature of the WIMP used.

Does that ans? Not sure.

By Sphere Coupler (not verified) on 14 May 2011 #permalink

There are at least four views to consider for density;
From within event horizon to same event horizon (my view)even time
From within event horizon to earth/you (my view)faster time
can't see

From Earth/you to Earth/you (your view)even time
From Earth/you to without event horizon (your view) slower time
can't see

For the can't see perspectives, once immersion has taken place, you are either in or out of a particular density, now acceleration effects you can see as you approach the boundary/event horizon.

See you have asked a very tricky question, am I on this side or that side of the event horizon? I have responded assuming I am on the other side.(the inside)

From my reality since I am locked within my event horizon environment My input has slowed to correspond with my environment and I don't recognise any change and I can't see your reality!

It's all relative, picture the red sphere as black hole, some info will never reach you.

From your reality as I approach the boundary I am still drinking my first cup of coffee and always will be.

So perhaps I can live for infinity (drinking my first cup of coffee)approaching my black hole,kinda jealous?

(In my reality I'm on my third and it's getting cold :?)

By Sphere Coupler (not verified) on 14 May 2011 #permalink


From Earth/you to without within event horizon (your view) slower time
can't see

By Sphere coupler (not verified) on 14 May 2011 #permalink

Now since you can see me approaching the event horizon.
#1)I see no change because input is accelerated along with me.
#2)You see me slow down because I am accelerating through a denser environment, and with your relevant decreasing perception of time, that you experience, standing on Normal Matter Earth, I am viewed slower.

Although you can't recognise this, I am traveling through more matter, faster than you, because I'm moving through a denser baryonic environment.

Your slower density perception sees me slow down, that's your fault.

Now since you can't see me on the inside of the event horizon I'll tell you what is happening to me, adding an increasing acceleration and density as I travel towards the singularity.
#1) I see no change,info reaches me at an consistent rate according to my new found environment.
#2) You (expanding space countered by matter coalescence)an environment that I like to call (mass tempered space) can't see me, you are denied.

And from a totally different new view;
Universal view=(standing on the outside of Universe or taking into account every variable possible and at rest)

a)As my distance to blackhole barycenter/singularity decreases, the density will increase and my acceleration will increase,I am viewed as increasing density accelerating within an increasing (dark energy/space) depletion.

b)You (normal matter)are viewed as a transition point between expanding space and coalescing matter.

c)Space is viewed as accelerating and expanding, with increasing baryonic depletion.

So for a reality on the non-local and highest scale,
The Universal view sees itself as a tug o war and we, normal matter are stuck in the middle.

By Sphere Coupler (not verified) on 14 May 2011 #permalink

Sphere Coupler
You are helping but I am miscommunicating my question 1) and 1a) (which in my mind are 2 versions of the same question.)

Let me try again totally different way without a black hole.
a) the universe is observed to be 13.7 Billion years old.
b) thus no matter how we determine the age of the universe and the age of objects in the universe, various ages should be consistently explanable. (e.g. a 15 billion year old star would be a problem.)

Now let me describe another possible age problem:
Consider the twin paradox. Suppose ten years ago, your twin left Earth and came back. 1 year passed for him while 10 years elapsed for him. So for him is the universe now 13.7 billion years plus 1 year and for you the universe 13.7 billion years plus 10 years.

You laugh, but you assure me that the twin paradox is a real phenomenon. Time has elapsed differently for you and your twin. Isn't the age of the universe a cumulation of local temporal events; hence my question. Or what am I misunderstanding.

Now suppose that you are 3 Billion years old; you A-EarthTwin and your twin B-TravellingTwin were here on Earth soon after it was formed. But B travelled the universe at near light speed and just returned. The universe was only 10.7 billion years old when B-TravellingTwin left While you A-EarthTwin have experienced 3 billion years of Earth life. But now B-TravellingTwin has returned and only aged 1 billion years. And the two of you now stand together on Earth.

Now, my question again. How does the current standard big bang model of cosmology reconcile that A observed the universe at 10.7 billion years and experienced the passage of 3 billion years; thus A sees total agreement between current astronomical measure of the universe's age with A's personal time experience. But B tells a different story. He and you both astronomically measured the age of the universe when it was 10.7 billion years old. But when he returned to Earth just now his atomic clock shows that only 1 billion years have elapsed. So he concludes that the universe is 11.7 billion years old.

This is my cosmic twin paradox. Both A and B twins agree the universe was 10.7 billion years old when they parted. Both twins agree that 3 billion years have passed for twin A-EarthTwin and 1 billion years have passed for twin B-TravellingTwin. Thus the experience of the two twins gives two different ages of the universe. 10.7 + 3 billion years for the A-EarthTwin and 10.7 + 1 billion years for the B-TravellingTwin. Then both twins now make astronomical measures and both observe that the universe is 13.7 billion years old.

So, my question 1)& 1a) and now is: how does the current standard big bang cosmological model reconcile itself with relativity time dilation as in the twin paradox and the apparent cumulative age of the universe?

I can speculate about answers; but I am curious how current big bang theory addresses my question. Maybe my question is misconcieved; or maybe I'm misapplying some idea.

Any thoughts will be appreciated. But, the apparent absolute time 13.7 billion years seems to contradict the cumulative relative time when that time involves relativitistic time dilation of one twin as in the twin paradox. Hence my questions.

Thanks. Any thoughts to clear up my confusion will be appreciated.

The twin paradox is a misnomer, it is not a true paradox, it is a thought experiment, that has been resolved.

A paradox is a seemingly true statement that lead to a contradiction or situation which seems to defy logic or intuition⦠More accurately described as the twin paradox thought experiment in Special Relativity.

The whole different measurement thing goes away when taken to the extreme with exact measurements.

Special relativity does not allow me to travel at or above the speed of light but Iâm going to do it anyway because Einstein was ignorant about cosmic inflation and an accelerating cosmological constant.

Wiki quote;
"While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding."

So this is a thought experiment to show that inconsistency in the two directions will cause an error.

Bob travels 10 minutes with the accelerating expansion of space at the *speed of light* (not allowed in SR), and time for him stops, he does not age, he then turns around to return exactly the way he came, in all respects and ages normally, his age is increased to X of his total outward travel time. Lets say he traveled 10 minutes out and he aged X coming back, Alice of Earth *at rest* (also not allowed in SR) seems to see him disappear, and simultaneously a signal for X years as he returns from his journey. In the end he actually ages the same X and so does Alice.

Any inconsistencies in age are due to the inconsistencies of entropy derived between his outward journey and his return journey.

Einstein is not here so I think Iâm safe.
Universal view of time dilation is directional.

A Muon at 98% light speed experiences time dilation when observed in one direction only,

.From Wiki;
Muon lifetime
A comparison of muon lifetimes at different speeds is possible. In the laboratory, slow muons are produced, and in the atmosphere very fast moving muons are introduced by cosmic rays. Taking the muon lifetime at rest as the laboratory value of 2.22 μs, the lifetime of a cosmic ray produced muon traveling at 98% of the speed of light is about five times longer, in agreement with observations.[19] In this experiment the "clock" is the time taken by processes leading to muon decay, and these processes take place in the moving muon at its own "clock rate", which is much slower than the laboratory clock.

Changing directions after traveling close to but not at or above the speed of light is not allowed by natures entropy.

Metric expansion is a key feature of Big Bang cosmology and an accelerating cosmological constant is the only accurate explanation.

Probably does not answer your question but it was fun to do and I hope fun to read.
That's how I see it.

By Sphere Coupler (not verified) on 14 May 2011 #permalink

simultaneously after ten minutes

What? I like to use the HTML tag.

By Sphere Coupler (not verified) on 14 May 2011 #permalink

Screwed that up too.

Changing directions (180 deg.) after traveling close to, but not ,at or above the speed of light is not allowed (without Degradation) by natures entropy.

By Sphere Coupler (not verified) on 14 May 2011 #permalink

Hello, nice article!

I have a small question about one paragraph:
"Back when the light from this galaxy -- the light we are seeing now -- was emitted, it was "only" about 1.4 billion light years away from us. This is still a tremendous distance, and it's made all the more impressive by the fact that the Universe is only about 500 million years old at the time!"

How can we have been 1.4 billion light years away from the galaxy, if the Universe was 500 million years old? Surely two photons, travelling in 180 degrees directions, would have been 1 billion light years away from each other when the universe was 500 million years old... and stars travel way slower than light. So I am afraid that paragraph is wrong... or can you correct me?


OKThen, I am not completly convinced that there is enough modern evidance to conclude that the Twin *paradox* thought experiment will not go away when a greater understanding is acheived.

Your question is a good one, and the answer undoubtably is wrapped up in understanding the relationships between SR GR QG the cosmological constant...

I do not know if the HafeleâKeating experiment (which claims supported evidence for the Twin *paradox*) incorporates the Sagnac effect and other such investigations.

The theory of relitivity will no doubt continue to help in our understanding, yet I do not think that it will survive without some changes, however slight, even Einstien sensed the incompleteness of his greatest thought.There is a link but I'll have to wait to avoid the spam catcher.

By Sphere Coupler (not verified) on 15 May 2011 #permalink

OK, on further review the Sagnac effect DOES confirm SR.

Still not sure if the Sagnac effect was applied to the HafeleâKeating experiment.

Heres that link that shows some historical info by Albert...

By Sphere Coupler (not verified) on 15 May 2011 #permalink

SR makes assumptions like; "the consistency of light speed in these systems is independent of the movement of the light source"

Gravitational lensing was predicted by GR, so from our perspective as Normal Matter (which is baryonic yet different than the severely compressed Blackhole baryonic matter) we can look in two directions towards a baryonic depleting Dark Energy driven space and a baryonic coalescent lack of Dark Energy driven Blackhole.

This is our view, Special Relativity, if and when we retrieve enough data as a species to look at the situation from a perspective of "outside looking in"...A Universal view we might very well view Dark matter as the fuel that keeps the system running, Dark Energy entropy and baryonic density increased enthalpy as the cause that instigates the normal matter system.
Normal Baryonic Matter continued existence based on the supply of Dark Matter.
(It's a conjecture of mine and probably others that dark matter can decay to normal matter on a universal time scale and that conversion somehow effects dark energy.)

13.7 billion years ago we apparently had
63%dark matter
0% dark energy

23%dark matter
72%dark energy

So the decay of dark matter effect slightly faster than the decay of normal matter (if a constant), gives billions more years for normal matter to survive.If dark matter and dark energy are connected, will the depletion/decay of dark matter stop the exspansion of space?
Billions of years from now will normal matter(forced to comply to a vastly exspanded space by dark energy) decay to dark matter or will it decay to blackhole matter?

I guess it reverts back to the old realty addage location, location, location.any thoughts?

By Sphere Coupler (not verified) on 15 May 2011 #permalink

Sphere Coupler
Thank you for addressing my question.
You given me some new insight and ideas to track down. I wasn't looking for a perfect answer, only a direction of thinking; you gave me that. Much appreciated. I'll reread your answers more carefully.

Sphere Coupler
On your dark matter, dark energy comments and question "any thoughts?"

"(It's a conjecture of mine and probably others that dark matter can decay to normal matter on a universal time scale and that conversion somehow effects dark energy.)" Yes this makes perfect sense; regardless of what dark matter and dark energy turn out to be or not.

I am trying to resist my own speculation here and focus on learning what current theory says (note I am not a professional). But I'm not convinced of the remainder of your thoughts on dark energy and dark matter.

My personal speculation starts with my own ignorance about frame dragging and the gravitomagnetic field of GR as it all relates to the recent Gravity Probe B experiments. My simple question is: When a photon experiences frame dragging, is it's frequency redshifted as well as it's path changed? My speculation is that yes it is redshifted; but I need to learn a lot more GR to be satisfy myself. Such a speculation if true would cascade into a number of interesting cosmological conclusions. But since, no one answered my first question in Ethan's Einstein's Last Mystery post; I never got to this question. As to how this relates to dark matter and dark energy; well that's my coffee kicking in again.

When a photon experiences frame dragging, is it's frequency red shifted as well as it's path changed?

The way I understand this is as a photon makes it's journey past a massive body, not only is it's path changed by Gravitational Lensing which "Since light always moves at a constant speed, lensing changes the direction of the velocity of the light, but not the magnitude"

it's energy level can also be altered but very slightly and the Gravity B probe has published their result with 19% error (not what they had hoped to acheive).

Have you read this?…

See the Wiki,
The LenseâThirring precession) is a gravitomagnetic frame-dragging effect is a slight phenomena depending on mass and rotation.

PoundâRebka experiment) gravitational redshift experiment.

When the photon travels through a gravitational field, its frequency and therefore its energy will change due to the gravitational redshift.

By Sphere Coupler (not verified) on 16 May 2011 #permalink

Sphere Coupler
Thank you. I had recently read the Pound-Rebka work, very nice, amazing acutally. And I've searched the Lense-Thirring precession stuff.

But no I haven't read the link that you suggest but I will.

The Pound-Rebka gravitation redshift or blueshifting is due to motion parallel to the lines of a gravitational filed.

Now my net question goes like this. But general relativity gravitomagnetism suggests an analogue to the magnetic field. And the magnetic field acts perpendicular to the direction of motion for an electrically charged particle. So my question is: does the gravitomagnetism also produce a force perpendicular to the direction of motion? And I think the answer is yes. And the example is frame fragging (i.e. the Lense-Thirring precession stuff). But what I can't find is a formula that can be interpreted as a redshift or blueshift associated with frame dragging. Geometrically, frame dragging can be viewed as the spiralling of gravitational lines of force (i.e. the curving of space); but does such curving of space equal red or blueshifting of a photon that is travelling perpendicular to the lines of gravitational force? My intuition is yes; just as magnetism produces a force perpendicular to the electric field and motion of an electric charge.

Thus here…
the 4th paragraph describes the two photon spheres of a Kerr black hole and also discusses frame dragging; but no mention of red or blueshifting. So does frame dragging equal red or blue shifting; or is frame dragging associated with red or blue shifting; or is does frame dragging have nothing to do with red or blue shifting?
Now in the above link there is one reference a pdf file that on page 14 says, "the LenseâThirring effect: the dragging of inertial frames is strongest at the equator, and in this case, it precisely cancels out the retrograde motion of the photon." I interpret this to mean that the redshifting due to motion in opposite direction to frame-dragging (which blue shifts) cancels out; thus the Kerr photon sphere has stable photon orbits provided the direction of orbit is specified. Hence the answer to my question is "yes frame-dragging equals red or blue shift of a photon depending on whether photon is moving in opposite direction to rotation (redshift) or in same direction as rotation (blueshift). But I might just be misinterpreting. And I don't see any equation for such blue or red shifts.

OK Sphere Coupler, I'm at the end of my ability to state my question and my interpretation (or my misinterpretation).

Thanks, so much for your help.

Sphere Coupler
I think the answer to my question may be found in the time dilation of the gravitomagnetic clock effect. I've downloaded some information which I'm trying to understand. If you'd rather discuss off line then simpatico29x dot gmail dot com Thanks.

Almost ununderstandable but doable.Thanks anyway.

By Sammy Makau (not verified) on 25 Feb 2012 #permalink

If what your saying is true the apparent rate of rotation of distant galaxies should be MUCH slower than the apparent rate of rotation of nearby galaxies, a Doppler downshifted ice cream truck song is not just LOWER in pitch, it is also SLOWER in tempo, yet we do NOT observe this confirmation that the red shift is a Doppler shift. Mass consensus has never ensured correct belief in the past, most human beliefs requiring theory are in error exactly to the degree there is mass consensus because mass consensus limits questions to only those that support the orthodox answers. Dark matter and dark energy constitute a lack of evidence for the big bang somehow twisted into evidence that supports it. Not one person of renown admits this constitutes a colossal failure of the orthodoxy because as throughout all history it would constitute heresy to have doubts, no one wishes to be cast out as a heretic. I purpose "dark space" as an answer, dark space downshifts light as a factor of the distance light has traveled, it looks like a Doppler shift but is not a Doppler shift, this explains why with every improvement in telescopic power we discover fully formed galactic structures that push back the time schedules for "order in the universe" over and over against all theory. It should be setting off the red warning lights when one is asked to believe that space expanded to infinity in finite time, this makes physics a religion instead of a science because In order to prove a thesis its necessary to attempt to disprove it yet no such attempt is ever made against the big bang. No comment is expected, or at best a blithe insult, the most a heretic can expect at any time in human history,

By William C Wesley (not verified) on 26 Feb 2014 #permalink

@Mr. Wesley #50: There seems to be a lot here you don't understand correctly. That misunderstanding seems to have led you to interpretations which are inconsistent with modern astrophysics. I'm not talking about your conclusions, I'm talking about your terminology and your description of the current consensus model. It is that description which is simply wrong.

You're correct that the Doppler effect changes both pitch and tempo. In the context of astrophysical observations, Doppler shifts affect things like pulsar timing rates (tempo) as well as their spectra ("pitch"). If we could observe them in far enough away galaxies where the effect is large, the observed periods of Cepheids would have to be corrected based on Doppler measurements of spectra.

However, none of that affects our measurements of galactic rotation curves. Why not? Because we don't ever actually observe the rotation! It takes the Milky Way, for example, roughly 200 *million* years to complete one rotation.

What we measure, basically by using a pinole mask and a spectrometer, is the _difference_ between the Doppler shifts on opposite edges of a given galaxy.
If the whole galaxy is moving away from us, then it's overall (average) spectrum will show a redshift, with some value 'z'. If the galaxy is rotating then one side, the side rotating toward us, will have a slightly _lower_ redshift, z-dz, while the opposite side will have a very slightly _hgher_ redshift, z+dz. We don't even, technically, need to know the average 'z' itself: measure the two sides as 'z1' and 'z2', and the difference will be 2dz, where dz is the Doppler shift due purely to the rotation.

Now we can do the same to get a whole rotation curve, from the center outward: take spectra in narrow slices across the visible disk (and out into the gas and dust outside that visible disk), and plot the deviations from the average of all the slices.

You also don't seem to understand where the hypotheses of dark matter and dark energy originated, or what evidentiary support they have from observational astronomy. "Dark matter" is the label we give to the observation that the mass we can see directly through electromagnetic effects -- stars, hot gas, cold gas, and dust -- is not enough to explain MOST of the dynamcial effects we can measure in large-scale objects. Not just galaxy rotation curves, but the motions of whole galaxies in clusters and superclusters, and the lensing (bending) of light from very distant objects as it passes through massive ensembles (like galaxy clusters).

Your final hypothesis is nothing more than the well-known and well-tested hypothesis of "tired light" (please feel free to look it up). That hypothesis makes very specific predictions for observations, as a good scientific hypothesis should, and those predictions have been demonstrated to be wrong. Therefore, the hypothesis is wrong.

By Michael Kelsey (not verified) on 26 Feb 2014 #permalink

Aye, Michael, something a lot of internet readers of fringe science don't seem to get is that not only should the scientific method include a hypothesis that can be falsified, but ALSO that if it IS falsified, that hypothesis is dropped or modified to a different hypothesis (where the falsification tests will then apply in a continuous loop).

"How can we have been 1.4 billion light years away from the galaxy, if the Universe was 500 million years old?"

It can't.

However, this isn't a problem since that isn't what you quote is saying.

Light left that galaxy nearly 13.2 billion years ago. Since the universe is 13.7 billion years old, that means that at the time the light left that galaxy, the universe was 13.7-13.2 = 0.5billion years.