# Is the colour of a wave from a far galaxy the same for us as for a galaxy which lies between?

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Because of the expansion of the universe, light from a far galaxy is redshifted. The expansion of the universe will make the wavelength of light longer. But is the colour of such light the same for us, as for an galaxy which is between us and the far galaxy.

I first thought that a further galaxy's speed was higher than ours, but I don't think that's right it is relative. But is the speed of the far galaxy from a view of the further galaxy higher than from our view? I don't think so because the universe is expanding faster the further you look. So for the further galaxy the speed of the far galaxy is less high than from our view because the far galaxy is further away from us.

So is the conclusion right that the colour of the same wave is more red for us on earth than from the further galaxy?

If I understand you right, you're asking whether or not the redshift of the photons emitted from a far-away galaxy happens the instant it leaves the galaxy.

If so, the answer is no. The redshifting of photons happen gradually as they travel through the expanding Universe. You can find the derivation here where you'll see that every infinitesimally small increase $da$ of the scale factor $a$ of the Universe (its "size") increases the photon's redshift by an amount $dz$, or, in terms of wavelength, by an amount $dlambda$.

If galaxy $B$ lies at redshift $z_mathrm{B}$, then an observer in galaxy $A$ at redshift $z_mathrm{A}$ lying between us and $B$ (so that \$z_mathrm{A}

## … at least in our Universe

The redshifting is not due to the source moving away from us. If the expansion hadn't been gradual, but we instead lived in a crazy universe that were static when the distant galaxy emitted the light, and static when we observe, but somehow expanded suddenly by some factor in the meantime, then we would still observe a redshift, even though the galaxy were static both when it emitted the light and when we observed it.

The light from distant galaxies is redshifted because they are moving away from us and the more distant the galaxy is the faster it moves, and so the more the light is redshifted.

A galaxy between us and a very distant galaxy is also moving away from us, but less fast. From the point of view of that galaxy the light of the distant galaxy is redshifted less than from our position, because the distant galaxy is not moving away from it as fast.

The light would appear less red in "a galaxy which lies between".

## Galaxy 5 billion light-years away shows we live in a magnetic universe

With the help of a gigantic cosmic lens, astronomers have measured the magnetic field of a galaxy nearly five billion light-years away. The achievement is giving them important new clues about a problem at the frontiers of cosmology -- the nature and origin of the magnetic fields that play an important role in how galaxies develop over time.

The scientists used the National Science Foundation's Karl G. Jansky Very Large Array (VLA) to study a star-forming galaxy that lies directly between a more-distant quasar and Earth. The galaxy's gravity serves as a giant lens, splitting the quasar's image into two separate images as seen from Earth. Importantly, the radio waves coming from this quasar, nearly 8 billion light-years away, are preferentially aligned, or polarized.

"The polarization of the waves coming from the background quasar, combined with the fact that the waves producing the two lensed images traveled through different parts of the intervening galaxy, allowed us to learn some important facts about the galaxy's magnetic field," said Sui Ann Mao, Minerva Research Group Leader for the Max Planck Institute for Radio Astronomy in Bonn, Germany.

Magnetic fields affect radio waves that travel through them. Analysis of the VLA images showed a significant difference between the two gravitationally-lensed images in how the waves' polarization was changed. That means, the scientists said, that the different regions in the intervening galaxy affected the waves differently.

"The difference tells us that this galaxy has a large-scale, coherent magnetic field, similar to those we see in nearby galaxies in the present-day universe," Mao said. The similarity is both in the strength of the field and in its arrangement, with magnetic field lines twisted in spirals around the galaxy's rotation axis.

Since this galaxy is seen as it was almost five billion years ago, when the universe was about two-thirds of its current age, this discovery provides an important clue about how galactic magnetic fields are formed and evolve over time.

"The results of our study support the idea that galaxy magnetic fields are generated by a rotating dynamo effect, similar to the process that produces the Sun's magnetic field," Mao said. "However, there are other processes that might be producing the magnetic fields. To determine which process is at work, we need to go still farther back in time -- to more distant galaxies -- and make similar measurements of their magnetic fields," she added.

"This measurement provided the most stringent tests to date of how dynamos operate in galaxies," said Ellen Zweibel from the University of Wisconsin-Madison.

Magnetic fields play a pivotal role in the physics of the tenuous gas that permeates the space between stars in a galaxy. Understanding how those fields originate and develop over time can provide astronomers with important clues about the evolution of the galaxies themselves.

## Contents

The Balmer series is characterized by the electron transitioning from n ≥ 3 to n = 2, where n refers to the radial quantum number or principal quantum number of the electron. The transitions are named sequentially by Greek letter: n = 3 to n = 2 is called H-α, 4 to 2 is H-β, 5 to 2 is H-γ, and 6 to 2 is H-δ. As the first spectral lines associated with this series are located in the visible part of the electromagnetic spectrum, these lines are historically referred to as "H-alpha", "H-beta", "H-gamma", and so on, where H is the element hydrogen.

 Transition of n Name Wavelength (nm, air) Energy difference (eV) Color 3→2 4→2 5→2 6→2 7→2 8→2 9→2 ∞→2 H-α / Ba-α H-β / Ba-β H-γ / Ba-γ H-δ / Ba-δ H-ε / Ba-ε H-ζ / Ba-ζ H-η / Ba-η Balmer break 656.279 [2] 486.135 [2] 434.0472 [2] 410.1734 [2] 397.0075 [2] 388.9064 [2] 383.5397 [2] 364.6 1.89 2.55 2.86 3.03 3.13 3.19 3.23 3.40 Red Aqua Blue Violet (Ultraviolet) (Ultraviolet) (Ultraviolet) (Ultraviolet)

Although physicists were aware of atomic emissions before 1885, they lacked a tool to accurately predict where the spectral lines should appear. The Balmer equation predicts the four visible spectral lines of hydrogen with high accuracy. Balmer's equation inspired the Rydberg equation as a generalization of it, and this in turn led physicists to find the Lyman, Paschen, and Brackett series, which predicted other spectral lines of hydrogen found outside the visible spectrum.

The red H-alpha spectral line of the Balmer series of atomic hydrogen, which is the transition from the shell n = 3 to the shell n = 2, is one of the conspicuous colours of the universe. It contributes a bright red line to the spectra of emission or ionisation nebula, like the Orion Nebula, which are often H II regions found in star forming regions. In true-colour pictures, these nebula have a reddish-pink colour from the combination of visible Balmer lines that hydrogen emits.

Later, it was discovered that when the Balmer series lines of the hydrogen spectrum were examined at very high resolution, they were closely spaced doublets. This splitting is called fine structure. It was also found that excited electrons from shells with n greater than 6 could jump to the n = 2 shell, emitting shades of ultraviolet when doing so.

Balmer noticed that a single wavelength had a relation to every line in the hydrogen spectrum that was in the visible light region. That wavelength was 364.506 82 nm . When any integer higher than 2 was squared and then divided by itself squared minus 4, then that number multiplied by 364.506 82 nm (see equation below) gave the wavelength of another line in the hydrogen spectrum. By this formula, he was able to show that some measurements of lines made in his time by spectroscopy were slightly inaccurate and his formula predicted lines that were later found although had not yet been observed. His number also proved to be the limit of the series. The Balmer equation could be used to find the wavelength of the absorption/emission lines and was originally presented as follows (save for a notation change to give Balmer's constant as B):

λ is the wavelength. B is a constant with the value of 3.645 0682 × 10 −7 m or 364.506 82 nm . m is equal to 2 n is an integer such that n > m.

In 1888 the physicist Johannes Rydberg generalized the Balmer equation for all transitions of hydrogen. The equation commonly used to calculate the Balmer series is a specific example of the Rydberg formula and follows as a simple reciprocal mathematical rearrangement of the formula above (conventionally using a notation of m for n as the single integral constant needed):

The Balmer series is particularly useful in astronomy because the Balmer lines appear in numerous stellar objects due to the abundance of hydrogen in the universe, and therefore are commonly seen and relatively strong compared to lines from other elements.

The spectral classification of stars, which is primarily a determination of surface temperature, is based on the relative strength of spectral lines, and the Balmer series in particular is very important. Other characteristics of a star that can be determined by close analysis of its spectrum include surface gravity (related to physical size) and composition.

Because the Balmer lines are commonly seen in the spectra of various objects, they are often used to determine radial velocities due to doppler shifting of the Balmer lines. This has important uses all over astronomy, from detecting binary stars, exoplanets, compact objects such as neutron stars and black holes (by the motion of hydrogen in accretion disks around them), identifying groups of objects with similar motions and presumably origins (moving groups, star clusters, galaxy clusters, and debris from collisions), determining distances (actually redshifts) of galaxies or quasars, and identifying unfamiliar objects by analysis of their spectrum.

Balmer lines can appear as absorption or emission lines in a spectrum, depending on the nature of the object observed. In stars, the Balmer lines are usually seen in absorption, and they are "strongest" in stars with a surface temperature of about 10,000 kelvins (spectral type A). In the spectra of most spiral and irregular galaxies, active galactic nuclei, H II regions and planetary nebulae, the Balmer lines are emission lines.

In stellar spectra, the H-epsilon line (transition 7→2, 397.007 nm) is often mixed in with another absorption line caused by ionized calcium known as "H" (the original designation given by Joseph von Fraunhofer). H-epsilon is separated by 0.16 nm from Ca II H at 396.847 nm, and cannot be resolved in low-resolution spectra. The H-zeta line (transition 8→2) is similarly mixed in with a neutral helium line seen in hot stars.

## “Galactic Motherload” –Gigantic Kilonova Eruptions Seed the Universe With Silver, Gold and Platinum

On October 16, 2017, an international group of astronomers and physicists excitedly reported the first simultaneous detection of light and gravitational waves from the same source–a merger of two neutron stars. Now, a team that includes several University of Maryland astronomers has identified a direct relative of that historic event.

The newly described object, named GRB150101B, was reported as a gamma-ray burst localized by NASA’s Neil Gehrels Swift Observatory in 2015. Follow-up observations by NASA’s Chandra X-ray Observatory, the Hubble Space Telescope (HST) and the Discovery Channel Telescope (DCT) suggest that GRB150101B shares remarkable similarities with the neutron star merger, named GW170817, discovered by the Laser Interferometer Gravitational-wave Observatory (LIGO) and observed by multiple light-gathering telescopes in 2017.

A new study suggests that these two separate objects may, in fact, be directly related. The results were published on October 16, 2018 in the journal Nature Communications.

“It’s a big step to go from one detected object to two,” said study lead author Eleonora Troja, an associate research scientist in the UMD Department of Astronomy with a joint appointment at NASA’s Goddard Space Flight Center. “Our discovery tells us that events like GW170817 and GRB150101B could represent a whole new class of erupting objects that turn on and off–and might actually be relatively common.”

Troja and her colleagues suspect that both GRB150101B and GW170817 were produced by the same type of event: a merger of two neutron stars. These catastrophic coalescences each generated a narrow jet, or beam, of high-energy particles. The jets each produced a short, intense gamma-ray burst (GRB)–a powerful flash that lasts only a few seconds. GW170817 also created ripples in space-time called gravitational waves, suggesting that this might be a common feature of neutron star mergers.

The apparent match between GRB150101B and GW170817 is striking: both produced an unusually faint and short-lived gamma ray burst and both were a source of bright, blue optical light and long-lasting X-ray emission. The host galaxies are also remarkably similar, based on HST and DCT observations. Both are bright elliptical galaxies with a population of stars a few billion years old that display no evidence of new star formation.

“We have a case of cosmic look-alikes,” said study co-author Geoffrey Ryan, a postdoctoral researcher in the UMD Department of Astronomy and a fellow of the Joint Space-Science Institute. “They look the same, act the same and come from similar neighborhoods, so the simplest explanation is that they are from the same family of objects.”

In the cases of both GRB150101B and GW170817, the explosion was likely viewed “off-axis,” that is, with the jet not pointing directly towards Earth. So far, these events are the only two off-axis short GRBs that astronomers have identified.

The optical emission from GRB150101B is largely in the blue portion of the spectrum, providing an important clue that this event is another kilonova, as seen in GW170817. A kilonova is a luminous flash of radioactive light that produces large quantities of important elements like silver, gold, platinum and uranium.

While there are many commonalities between GRB150101B and GW170817, there are two very important differences. One is their location: GW170817 is relatively close, at about 130 million light years from Earth, while GRB150101B lies about 1.7 billion light years away.

The second important difference is that, unlike GW170817, gravitational wave data does not exist for GRB150101B. Without this information, the team cannot calculate the masses of the two objects that merged. It is possible that the event resulted from the merger of a black hole and a neutron star, rather than two neutron stars.

“Surely it’s only a matter of time before another event like GW170817 will provide both gravitational wave data and electromagnetic imagery. If the next such observation reveals a merger between a neutron star and a black hole, that would be truly groundbreaking,” said study co-author Alexander Kutyrev, an associate research scientist in the UMD Department of Astronomy with a joint appointment at NASA’s Goddard Space Flight Center. “Our latest observations give us renewed hope that we’ll see such an event before too long.”

It is possible that a few mergers like the ones seen in GW170817 and GRB150101B have been detected previously, but were not properly identified using complementary observations in different wavelengths of light, according to the researchers. Without such detections–in particular, at longer wavelengths such as X-rays or optical light–it is very difficult to determine the precise location of events that produce gamma-ray bursts.

In the case of GRB150101B, astronomers first thought that the event might coincide with an X-ray source detected by Swift in the center of the galaxy. The most likely explanation for such a source would be a supermassive black hole devouring gas and dust. However, follow-up observations with Chandra placed the event further away from the center of the host galaxy.

According to the researchers, even if LIGO had been operational in early 2015, it would very likely not have detected gravitational waves from GRB150101B because of the event’s greater distance from Earth. All the same, every new event observed with both LIGO and multiple light-gathering telescopes will add important new pieces to the puzzle.

“Every new observation helps us learn better how to identify kilonovae with spectral fingerprints: silver creates a blue color, whereas gold and platinum add a shade of red, for example,” Troja added. “We’ve been able identify this kilonova without gravitational wave data, so maybe in the future, we’ll even be able to do this without directly observing a gamma-ray burst.”

Image at top of page: An artist’s illustration of two merging neutron stars. University of Warwick/Mark Garlick

## Can we build Star Trek: Voyager's Displacement Wave? The Science Behind the Fiction

Star Trek: Voyager, the first series to spend the majority of its time outside the Alpha Quadrant, ran for 172 episodes, airing its final episode 20 years ago this week. It began in a familiar way, a Starfleet mission to locate a missing ship. But the crew of Voyager quickly encounters an unusual phenomenon.

A displacement wave, traveling at incredible speed, makes contact with the ship, killing several members of the crew. When the dust settles, Voyager finds itself in the Delta Quadrant, having traveled more than 70,000 light-years from Earth. Even by Trek standards, the Voyager was going really, really fast. But is there any real-life counterpart to this futuristic faster-than-light travel?

#### More Science Behind the Fiction

DISPLACEMENT

Star Trek couldn't exist as a franchise without displacement. The warp drives utilized on Federation ships depend on displacement of space-time in order to circumvent relativity and the light-speed barrier. The displacement wave seen in the first episode of Voyager takes this process to an extreme via the Caretaker, an entity tasked with the protection of the Ocampa people. The Caretaker, noting his own imminent demise, uses displacement arrays to gather various species from around the galaxy in the hope of finding a compatible species to take over his task.

The exact nature of the wave is never clearly explained, what is clear is the wave's ability to rapidly transport craft and crew across vast distances without violating relativity.

The Milky Way has a diameter of 100,000 light-years and the crews of Voyager and the Maquis ship cover most of that distance in moments. Making that distance through ordinary acceleration would require speeds tens of thousands of times that of light-speed (C), or a really, really long time. Traveling at that speed would result in incredible time dilation, such that when the crew did eventually return home, they would return to a world entirely unrecognizable — if there was a world to return to at all. The only workable explanation is the creation of a space-time bubble that moved the ships without violating C inside localized space-time.

RELATIVISTIC LIMITS OF SPEED

The first thing to understand is that the speed of light actually has nothing to do with light, it's just the most apparent way of measuring the cosmic speed limit. The speed of light (186,282 miles per second) is more accurately thought of as the speed of causality.

Gravity waves, photons, and gluons all travel at C. The common characteristic they all share is they are massless. The cosmic speed limit is the maximum speed at which any two particles can communicate or interact with one another.

There's a common thought experiment involving a very long stick which helps to illustrate this point. It goes as follows. Imagine a button one light-minute away, capable of being triggered in two ways. The first is by interaction with light, the second is by being pressed with a stick. Now imagine you have a stick one light-minute across resting against the button. You shine a light at the button and push the stick at the same time. What happens?

The intuitive answer is the stick would press the button instantly, while the light would take a full minute to reach its destination. But that isn't what would happen. When you move a stick in your backyard, it appears to move together all at once, but force is being communicated and it's happening at the cosmic speed limit or slower. It seems instant because the distances involved are very small, cosmically speaking.

A stick one light-minute across would need to transmit the force of motion along its length before interacting with the button. The fastest this could happen is C. In actuality, it would happen more slowly because the force is moving through a medium — the stick — not through a vacuum.

Whether or not any light is present is irrelevant. The cosmic speed limit is the speed of causality and matter slows things down.

The key takeaway is that the maximum speed limit within any localized area of space is C. There's no going any faster. But that doesn't necessarily hold true between two non-local areas of space.

We all know the universe is expanding and more distant objects are receding from us at faster rates. If you look far enough into the distance, you'll find galaxies traveling away from us faster than the cosmic speed limit. This is because of the nature of expansion. Every part of the universe is expanding at the same rate, as a result, the farther you look, the more that expansion adds up. It seems counterintuitive but it's true. And, it tells us something really important about rates of travel.

The cosmic speed limit cannot be exceeded within a local area of space-time, but you can manipulate space-time in such a way that space-time itself exceeds the limit. Therein lies the key to potential faster-than-light travel.

BREAKING THE LIMIT

Exceeding the light-speed barrier has been a long-time staple of science fiction, but Star Trek holds the honor of its most well-known incarnation with the iconic Warp Drive. It makes for good fiction but seems to fly in the face of general relativity.

Enter Miguel Alcubierre, a physicist and Star Trek fan. In fact, Alcubierre was inspired by Star Trek when thinking about his hypothetical model. What's become known as the Alcubierre drive describes a way to encapsulate a craft inside a localized bubble of space-time while manipulating the space around it.

The space in front of the craft would be compressed while the space behind it expands. The craft inside the bubble never exceeds the light-speed barrier through its own local space-time. Instead, it travels by riding a sort of space-time wave. It would be like shrinking a ten-mile commute down to a quarter-mile and just putting the rest of the commute behind you. Suddenly, you can make the trip in just a couple of minutes without ever breaking the speed limit.

The idea was exciting in that it allows for possible FTL travel without violating relativity. There were just a few hang-ups, it requires either negative mass or a ring of negative energy to operate. And, the amount of matter needed to create the energy required exceeds the mass of the observable universe. That's a pretty big problem to have.

Subsequent work by other scientists has refined Alcubierre's idea such that the mass needed is closer to that of the Sun. To be sure, that's a huge improvement over the whole of the universe, but it's still a lot. Considering our current technological capabilities, they might as well be the same thing.

Even if we could get the mass required down to a manageable amount, there's yet another hurdle. Once inside this warped bubble of space-time, there would be no way to escape from the inside. The ship would effectively be in a locked room with no doors or windows.

A warp drive, or displacement wave, remains well within the confines of science fiction for now. But we've crossed seemingly uncrossable horizons before, and we've got a couple of centuries before the Vulcans come looking for us. There's still time.

## HFLS3 – a record-breaking galaxy

The galaxy HFLS3 as seen by Herschel, along with subsequent observations. Click for a larger version. Image credit: ESA/Herschel/HerMES/IRAM/GTC/W.M. Keck Observatory

Astronomers using Herschel have discovered a distant galaxy that challenges the current theories of galaxy evolution. Seen when the Universe was less than a billion years old, it is forming stars at a much faster rate than should be possible according to existing predictions.

This particular galaxy, known only as “HFLS3”, is so distant that the light we see has taken 13 billion years to get to Earth. We see it as it was when the Universe was only 880 million years old, long before current theories of galaxy evolution predict that such a galaxy should have existed. In the infant Universe, galaxies should have been forming stars at a much slower rate than is observed in HFLS3.

Herschel has been surveying the distant cosmos, finding hundreds of thousands of distant galaxies. By looking at sub-millimetre light, Herschel is revealing how fast these distant galaxies are forming stars, and by determining the ages of the galaxies, astronomers are building up a cosmic timeline of star formation, searching for when the first massive galaxies started churning out stars.

“Looking for the first examples of these massive star factories is like searching for a needle in the haystack, and the Herschel data is extremely rich,” says Dominik Riechers, Cornell University, who led the investigation. “We were hoping to find a galaxy at such vast distances, but we could not expect that they even existed that early on in the Universe.”

The galaxy “HFLS3” was seen as a small red dot in the Herschel images, and its colour is what first intrigued the team. “This galaxy gained our attention because it was bright, yet very red, compared to others like it,” says Dave Clements, Imperial College London. “But while Herschel is great at highlighting these galaxies, we need to use other telescope to investigate further,” he adds.

The first step was to rule out any other effects that could cause the galaxy to look so bright. Using optical and near-infrared telescope, such as the Gran Telescopio Canarias in the Canary Islands and the Keck Telescope in Hawaii, the faint light from a much closer galaxy was seen. Although it lies in almost the same place in the sky, this relatively nearby imposter could not account for the brightness of HFLS3 in the Herschel images.

Artist’s impression of a starburst galaxy. Image credit: ESA/C.Carreau

It was observations with radio and millimetre-wave telescopes, such as the Plateau de Bure Interferometer in the French Alps, which determined that this tiny galaxy, only around one twentieth the size of our Milky Way, is seen at such an immense distance. These additional observations also showed that HFLS3 is incredibly rich in carbon, nitrogen and oxygen, forming compounds such as carbon monoxide, water and ammonia.

“The stars being born in HFLS3 heat up the surrounding material within the galaxy.”, explained Peter Hurley, University of Sussex. “This material contains gas molecules such as carbon monoxide and water, which emit their own unique signatures when heated. By comparing the observations with models, we can gain a better understanding of the conditions within this extreme object.”

Combined with the Herschel observations, these measurements allow the astronomers to deduce that this tiny star factory is producing stars around two thousand times faster than our own Milky Way, making it a type of galaxy known as a “starburst”. Environments like this do not exist on galaxy-wide scales in the Universe today.

“This galaxy is just one spectacular example, but it’s telling us that early star formation like this is possible,” explains Jamie Bock, Caltech, and one of the leaders of HerMES survey which originally found this galaxy.

“We’ve shown that Herschel data can find these extreme examples,” says Seb Oliver, University of Sussex, and the other leader HerMES. “The next step is to sift through the Herschel data more carefully, and try to deduce just how common such galaxies were in the early Universe”, he concludes.

• Full field as seen by Herschel.
• Zoom-in on Herschel image of HFLS3
• Optical image of HFLS3 (GTC)
• Near-IR (orange) and millimetre-wave (blue) image of HFLS3 (seen in mm-wave) and a much closer galaxy, which is seen better in near-infrared light (Keck Observatory/IRAM)

## ‘Where there’s a great conjunction, there’s a geek with a tripod’

The great conjunction of Jupiter and Saturn on 26 December 2020, in Dietisberg. Photograph: Ross Bennie

This photo, taken on 26 December 2020, in Dietisberg, shows the recent great conjunction of Jupiter and Saturn. I had to wait five days after the planets were closest before the sky was clear enough for a photo. But where there’s a great conjunction, there’s bound to be a geek with a camera tripod. Always a bit of a downer when you find the perfect spot and someone else has got there first. It was on top of a very small hill, so I’d have to either talk to them or go somewhere else. As an unsociable introvert, I found a third option and sneakily made him a part of the photo.

I’m most interested in transient events like eclipses, conjunctions, and comets. I have very fond memories of standing in an hours-long and freezing-cold queue when a student in the 80s, waiting to glimpse Halley’s comet through an old telescope at the Royal Observatory. Everyone who’d seen it came past and said it wasn’t worth standing in line for, but we’d all waited so long already that we stuck around and did eventually catch a fuzzy glimpse of the comet through the telescope. They were right – it wasn’t worth waiting for. But the camaraderie in the queue is what I remember now. Ross Bennie, 54, college lecturer, Wünnewil, Switzerland

## What does the Universe really look like?

Ask anyone who's looked up at a dark sky on a clear, moonless night, and you'll immediately hear tales about how incomprehensibly vast the Universe is.

But what you're looking at isn't much of the Universe at all. In fact, practically every point of light you see, including the vast swath of stars too dim to individually resolve, comes from within our own Milky Way galaxy. As we know from generations of telescopes, observatories, observations, as well as physicists and astronomers, the Universe goes far beyond that.

Image credit: NASA, ESA, R. Windhorst, S. Cohen, and M. Mechtley (ASU), R. O'Connell (UVa), P. McCarthy (Carnegie Obs), N. Hathi (UC Riverside), R. Ryan (UC Davis), & H. Yan (tOSU).

There are hundreds of billions of galaxies (at least) out there in our observable Universe, spread out, from our vantage point, over a sphere some 46 billion light-years in radius.

If we were to look at it, as human beings, we'd be limited by the biology of our eyes. Very well adapted for seeing in well-illuminated conditions, we'd do somewhat less well in intergalactic space we'd only be able to see the closest and brightest of all light sources, which would most likely limit us to only a few dozen galaxies if we were plunked down in a random location.

As it is, we're within our own galaxy, and so have thousands upon thousands of foreground stars that we have to ignore when we look deep into the Universe. We also are familiar with using tools like telescopes and/or cameras -- required to see even nearby, bright galaxies like Messier 109, above -- to help enhance our understanding of what's out there.

No wonder so many of us have dreams of voyaging across the Universe, seeing what's out there, of all the galaxies and how they clump and cluster together, of the different forms they take, and of what such an adventure would look like.

Recently, the Cosmic Flows Project has put together a stunning video (narrated in French) that's a 17-minute tour through the local Universe within 300,000,000 light-years. It's a remarkable look at not only our Milky Way, our local group, our nearest supercluster (the Virgo supercluster, of which we're on the outskirts, and which contains about 100,000 galaxies), and the largest superclusters and voids found nearby! When you've got the time, you definitely want to watch the whole thing.

Video credit: Hélène Courtois, Daniel Pomarède, R. Brent Tully, Yehuda Hoffman, and Denis Courtois.

But you might look at this and wonder just how we figure this out. From our vantage point here on Earth -- or even in space from someplace within our Solar System -- there's a lot of information to filter through and figure out. The simplest thing you can do actually gets you very far: remember Hubble's Law, or the fact that not only is the Universe expanding, but the distance a galaxy is from us is directly proportional to its recession speed.

It turns out that redshift is actually a somewhat easy property of a galaxy to measure, so if you know Hubble's law, you can infer how far away that galaxy is.

Well, kind of. Hubble's Law gives a very good approximation for distances on average, on large scales. But Hubble's law doesn't account for all of an object's redshift. There's also the very minor issue (that's sarcasm) of all the other matter in the Universe, and the gravitational effects it's had over the past 13.8 billion years.

Matter has this annoying property that it clumps and clusters together, and that's because gravitational attraction causes it to move. Don't get me wrong, this is great for lots of things, but it's not great when you're trying to figure out how distant an object is based on its motion!

It creates distortions along the line-of-sight, known as redshift-space distortions.

As you can see, on the left, these distortions create apparent lines or streaks that point radially towards you. We call these features Fingers of God. These happen because galaxies that are clustered together move more rapidly, both towards and away from the center of the cluster, which spreads them out in redshift.

There's also a less noticeable effect, where clusters move relative to one another and fall into superclusters and filaments these actually have the reverse effect on larger scales, creating flatter features on very large scales. There are some who call this the Kaiser effect (after Nick Kaiser), but I've always called them Pancakes of God.

So, how do we overcome these redshift space distortions? Believe it or not, this is one of the times where simulations have helped us tremendously! Thanks to the way that structure forms over the history of the Universe, from its gravitational evolution, we can figure out exactly how, on all distance scales, clustered objects translate from redshift space, which is easy to measure, into real space, which is the Universe we actually live in.

At this point, we understand clustering in our Universe -- as well as the dark matter and dark energy that it's dependent on -- to make this transformation with incredibly high degrees of confidence. So sure, we start in the same place: we measure the redshift of galaxies and plot them out accordingly.

But then we use all the things we know about mass and matter and gravity to understand how these galaxies have clustered together, and to map out -- to the best of our abilities -- their peculiar velocities, or their velocity with respect to the Hubble flow. By subtracting those peculiar velocities out, we can get estimates for their real-space positions, and hence, for how far away in each direction each galaxy is.

So what would flying through the Universe -- the real space Universe -- actually look like? Not to human eyes, but to our eyes as they'd be if we had pupils the size of giant telescopes? Well enjoy this brilliant video by Miguel Aragon, Mark Subbarao and Alex Szalay of the Sloan Digital Sky Survey that puts it all together!

And this is "only" about 400,000 galaxies in their actual positions, or just 0.0003% of the galaxies in the Universe, at most.

And that's just a tiny glimpse into what the Universe really looks like!

### More like this

The Cosmic Flows video (which I've seen before) is fascinating, but that SDSS fly-through is stunningly beautiful! I started to get the same feeling I get when I stare at the Hubble Deep Field.

Good blog. I watched videos. Wow. Great stuff. Thanks to all.

The narrator is speaking English, she just has a French accent.

Thank you Ethan, I understand the Cosmic Flows video much better now!

I've read that if you picked a random spot in the Universe, the odds are you wouldn't be able to see a single galaxy or star with the naked eye. (David Deutsch said it, I think.)

" if you picked a random spot in the Universe, the odds are you wouldn’t be able to see. "

well.. if it's truly random then that spot could be in some other galaxy and you would see more or less the same thing you see from earth. If you happen to find yourself in intergalactic space, again depends where. If you're in some galaxy cluster, you would see some galaxies as point sources like stars. If you happen to land in a particularly big intergalactic void, then yes.. all you would see is nothing.

But such a big generalization, that the chances are you won't see anything, is wrong IMO.

"Hubble’s Law, or the fact that not only is the Universe expanding, but the distance a galaxy is from us is directly proportional to its recession speed."

I have a question that may make no sense whatsoever since my astrophysics degree got lost in the mail.

As I understand it: Galaxy A is receding from us at a certain rate. Galaxy B, which is twice as far away as Galaxy A, is receding from us at twice the rate of Galaxy A. Is the space between Galaxy B and Galaxy A expanding at a faster speed than the space between us and Galaxy A? Or does it seem like it's going faster because there's twice as much expanding space between us and Galaxy B, and it just looks faster from our perspective? Or is it all the same thing because of Relativity?

the second one. there is twice as much. and vice versa. to someone in galaxy B we would appear to be moving away faster than galaxy A which is nearer to it. Basically every unit of space is expanding. everything appears to be moving away from everything else.

I've heard that before, too.

It's quite wrong. It's true that the Universe is highly clustered into clumps and filaments, but -- if you removed our entire galaxy -- we'd be able to see a large number of galaxies. Andromeda and Triangulum would be the brightest, and other local group galaxies would be prominent as well, but there would also be many galaxies from beyond the local group, including at least two I can think of (including one of our Messier Mondays) more than 10 million light years distant.

So, there are plenty of locations from where not a single galaxy would be visible, but if you plunked yourself down at a random location, far fewer than 50% of those places would have that property.

So there you have it. The universe looks like--a mammogram!

This is why I believe in a Supreme Being

re #13 is it because you don't understand and do not wish to know your knowledge is limited and work to reduce the limitations. Hence will decide to dump the idea "I have no idea" into "Goddidit" and therefore drop the idea that maybe you could find out about things if you spent a little effort?

This is why I believe in a Supreme Being

What an of thing to say, when nothing here presents evidence for such a being.

And thank you to my tablet for changing 'odd' to 'of'. I should have caught that.

Thanks! That's what I was thinking but as I said, my astrophysics degree got lost in the mail. )

Has the science of cosmology and astrophysics become absolutely positively 100% accurate were the theories are concrete undeniable evidence? While Classical Physics and Quantum Mechanics still duke it out? Which to give super detailed reports about measurements would be required. Personally, I think not, and don't buy the hype! Scientists want to pretend they have all the answers. I seriously doubt they understand the question!

It would be more than advisable to get acquainted with the Electromagnetic theory "Electric Universe" for short. It answers more questions than the gravitational model and will ultimately replace Newtonian physics as well as much of Einstein's assumptions on how our universe operates. Just Google "Electric Universe Theory" and be prepared to be amazed.

Re #19: How are classical physics and quantum mechanics "duking it out"? If you mean that our two main theories in physics, general relativity and the standard model are incompatible, then yeah, we know that. However, they are hardly "duking it out". They are both right, just there are domains in which they give different answers.

It's a similar situation as Newtonian physics. Newtonian physics is perfectly right as long as you stay within its domain. We've launched interplanetary probes and made moon landings using only Newtonian physics. It works well within its proscribed domain. Similarly, GR and SM both work well within their domains, which in the case of GR includes just about any cosmological observation.

Obviously, both GR and SM cannot be absolutely complete. However, any new theory to replace them must yield predictions in line with them for observations within their domains. That is, we can explain the observations of cosmology with GR, and even when it's replaced, the new theory must give the same predictions. So yes, we are pretty confident in our cosmological models, at least unless new data becomes available. If so, then we would change the model.

Joe, that crock has been peddled here before.

Just not in the way you'd hoped.

If you think scientists pretend to know all the answers, then you're only listening to pretend scientists.

EU proposes that the sun is powered not by fusion, but by an interstellar DC current. Test this hypothesis. Calculate the minimum current strength required to explain the observed output of the sun, assuming a perfect conversion of input energy to output energy. Then calculate the strength of the induced magnetic field of such a current at 1 AU. Hint: It will be much stronger than the earth's magnetic field.

Then step outside with a compass and prove the theory false.

I've heard of Electric Boogaloo and Electric Avenue, but Electric Universe is new. How large a surge protector is needed?

I'm gonna take you to Electric Avenue.

Cool article and interesting to think about. It might seem bizarre now, but with quantum processors we will eventually accomplish some incredible things, like run computer simulated universes (as modeled above) that are indistinguishable from our own “real” universe, even complete with simulated minds. There is even a new book out that discusses the implications of all this (i.e., “On Computer Simulated Universes”) and introduces concepts such as the 'Computer Simulated Universes Evolutionary Hypothesis'. With many active simulations, there would be a wide range of physical properties differing from universe to universe. Universes with more positive physical traits to support life would produce better environments for more advanced civilizations to evolve to the point where they themselves would create their own computer simulated universes. And this process would continue. So over a long period of time, universes would evolve with the physics more favorable for life. The book argues that universes, over time, might have been naturally selected for particular physical properties, with an end result of creating more and more habitable and longer-lived universes. This line of reasoning explains how the laws of physics might actually evolve relying on a process somewhat similar to human or species evolution.

i love this article because it has a lot of diagrams that show us what the universe is like for real and i especially like the graph aswell i think people should use this article more often because the universe is an interesting thing to know. i i find it interesting because everything on here is what i am looking for

## Experience

Galaxy Watch Active2 tracks your movements so you can just slip it on and get working out. With swimming added to automatic tracking you now get seven exercises, while manual tracking works for all activities for dozens you can track. Running coach function gives you actionable advice in real time. 5 , 6

• Walking
• Running
• Cycling
• Rowing
• Elliptical
trainer
• Dynamic
Workout
• Swimming

### Show some competitive spirit

Exercise is more rewarding when everyone joins in. Discover who can take the most steps in a Group Challenge.
Train with friends or join a public competition to stay motivated and achieve your fitness goals. 7

### Healthy living starts with a clear mind

Be sound in body and mind with a watch that cares for both. Use the stress tracker to watch your stress levels when you're feeling tense, and follow the suggested guided breathing exercises to get some peace of mind. 5 , 8 , 9

### See how well you sleep

Sleep Score analyzes your time spent in awake, REM, light, and deep sleeping cycles, then tells you the quality of your rest. Improve your score with helpful tips and insights from the National Sleep Foundation right on your wrist. 5 , 9 , 10

### A friendly reminder to wash your hands

Stay on top of your personal hygiene with handwashing reminders. Set them up to alert you at regular intervals. The app automatically detects when you're washing your hands and gives you a handy countdown to make sure you do a great job. Just a friendly reminder that helps you keep yourself healthy. 11

### Measure blood pressure on the move

Check your blood pressure via the Samsung Health Monitor App without regularly needing a cuff. Before first use simply
calibrate with a cuff, then smart sensors measure your blood pressure through pulse wave analysis as you wear it. Check
it daily to track trends and get reports right on your phone. 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20

### Track your heart's rhythm with ECG

Touch the watch's back button for up to 30 seconds
to have its built-in electrode sensor measure
This ECG on the go tests for
at a glance. See results over time from
your
phone, and share the report for even more
insights. 21 , 22 , 23 , 24 , 25 , 26 , 27

### Heart rate tracking for peace of mind

Monitoring your health is at the core of Galaxy Watch Active2 with a full eight photodiodes on the rear side of a new curved design that moulds to your wrist. Health monitoring keeps an eye on your heart rate and sends you an alert when it goes above or below normal levels. 5 , 28

### Give your life an assist

Get a jump on life with a smart assistant on your wrist. Control your camera to enrich the shooting experience, view and like on social media, and translate on the go. Newly added On-going Icon displays running apps on the watch face for easy access, and you can even catch incoming calls with Wi-Fi. 29 , 30 , 31 , 32

### Stay connected without your phone

Take your contacts, messages and music with you on an LTE-powered life assistant that lets you leave your phone behind. Go on a run with the peace of mind of being connected and not weighed down. Keep your music streaming as you go or download ahead of time for areas with low connectivity.

## Verdict

Samsung Galaxy A12 is a decent smartphone. The company has worked on its form factor while providing better cameras and enhanced battery life. Though it is not a perfect budget phone considering its display and gaming performance as its competitor, it is very close. To sum it up, it comes with good cameras, it is perfect for day to day usage and we would recommend Galaxy A12 who want something in the price range of Rs 10,000 – 15,000.