APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

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APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by APOD Robot » Wed May 23, 2018 4:10 am

Image Spiral Galaxy NGC 4038 in Collision

Explanation: This galaxy is having a bad millennium. In fact, the past 100 million years haven't been so good, and probably the next billion or so will be quite tumultuous. Visible toward the lower right, NGC 4038 used to be a normal spiral galaxy, minding its own business, until NGC 4039, to its upper left, crashed into it. The evolving wreckage, known famously as the Antennae, is featured here. As gravity restructures each galaxy, clouds of gas slam into each other, bright blue knots of stars form, massive stars form and explode, and brown filaments of dust are strewn about. Eventually the two galaxies will converge into one larger spiral galaxy. Such collisions are not unusual, and even our own Milky Way Galaxy has undergone several in the past and is predicted to collide with our neighboring Andromeda Galaxy in a few billion years. The frames that compose this image were taken by the orbiting Hubble Space Telescope by professional astronomers to better understand galaxy collisions. These frames -- and many other deep space images from Hubble -- have since been made public, allowing interested amateurs to download and process them into, for example, this visually stunning composite.

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Ann » Wed May 23, 2018 5:18 am

Ah, the Antennae galaxies. The most iconic of all iconic colliding galaxies.

A couple of factors are the most interesting ones about NGC 4038/4039. First, while NGC 4038 and NGC 4039 appear to be almost perfectly matched in size, it is clear that one of them (NGC 4038) is gas-rich and starforming, while the other one, NGC 4039, is gas-poor and strongly dominated by old and middle-aged stars. Note that the disk of NGC 4038 is distinctly bluer than the yellowish disk of NGC 4039.

Because of all the gas in NGC 4038, there is a huge amount of star formation in this galaxy, while the star formation in NGC 4039 is anemic.

Another very interesting factor is all the thick dust in "the site of collision" between the two galaxies, where they seem to join. All this dust is a product of the collision in itself and all the star formation it has given rise to. The dust itself fuels more star formation, because I believe that there are very many young stars in the process of being born inside that deep dark dust.

Finally, today's caption said that the Antennae galaxies will eventually merge and form one large spiral galaxy. How can we be sure that the end product will not be one large elliptical galacy? Is it because there is so much gas and dust in NGC 4038?

NGC 4038 and 4039 remain a very interesting pair of galaxies.

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Boomer12k » Wed May 23, 2018 7:19 am

A Mash pit of Matter, Energy, Space, and Time....

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by NCTom » Wed May 23, 2018 11:50 am

In what appears to be such a dust rich area at the primary point of collusion, how would this affect growth rate in individual stars? Would they form faster, mature faster, and explode at an earlier age than would occur in "leaner" star forming regions? If this is the case, an internal observer would be in the midst of a real fireworks show!

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by bls0326 » Wed May 23, 2018 12:59 pm

The "crashed into it" link leads to an interesting ASOW about "Galaxies in Collision" (2012).

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by orin stepanek » Wed May 23, 2018 1:32 pm

Beautiful; and in a billion years it will be one big beautiful galaxy! 8-)
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Wed May 23, 2018 1:54 pm

NCTom wrote:
Wed May 23, 2018 11:50 am

In what appears to be such a dust rich area at the primary point of collusion, how would this affect growth rate in individual stars? Would they form faster, mature faster, and explode at an earlier age than would occur in "leaner" star forming regions?
  • Mr. McGuire: I just want to say one word to you. Just one word.

    Benjamin: Yes, sir.

    Mr. McGuire: Are you listening?

    Benjamin: Yes, I am.

    Mr. McGuire: Shockwaves.

    Benjamin: Exactly how do you mean?
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Ann » Wed May 23, 2018 2:10 pm

NCTom wrote:
Wed May 23, 2018 11:50 am
In what appears to be such a dust rich area at the primary point of collusion, how would this affect growth rate in individual stars? Would they form faster, mature faster, and explode at an earlier age than would occur in "leaner" star forming regions? If this is the case, an internal observer would be in the midst of a real fireworks show!
The huge Tarantula Nebula in the Large Magellanic Cloud.
Credit: ESO/R. Fosbury (ST-ECF)
A near infrared image of the R136 cluster, obtained at high resolution with
the MAD adaptive optics instrument at ESO’s Very Large Telescope.
R136a1 is resolved at the center with R136a2 close by, R136a3 below right,
and R136b to the left. Credit: ESO/VLT




























Well, in a rich starforming area chock full of prime starforming stuff, we might expect starbursts to take place. In a starburst, stars do form at a frenetic pace, and many very massive stars form, too. And massive stars quickly go supernova - well, in a few million years, at least.

In the picture at left, you can see the huge Tarantula Nebula in the Large Magellanic Cloud, powered by the mighty starburst cluster, R136. In the picture at right, the central massive cluster, R136a, is resolved. At the center you can see R136a1, the most massive star known.
Wikipedia wrote:

RMC 136a1 (usually abbreviated to R136a1) is a Wolf–Rayet star located at the center of R136, the central condensation of stars of the large NGC 2070 open cluster in the Tarantula Nebula. It lies at a distance of about 50 kiloparsecs (163,000 light-years) in a neighbouring galaxy known as the Large Magellanic Cloud. It has the highest mass and luminosity of any known star, at 315 M☉ and 8.7 million L☉, and is also one of the hottest at around 53,000 K.
So indeed, if there will be a starburst inside the thick dark dust at the site of collision between NGC 4038 and NGC 4039 (and my guess is that there will be, or else there is one or more starbursts going on already), then stars will indeed be born there at an incredibly rapid pace, and the most massive ones will also die young in titanic supernovas.

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Wed May 23, 2018 2:14 pm

Click to play embedded YouTube video.
https://en.wikipedia.org/wiki/LHS_2520 wrote:
<<LHS 2520, also known as Gliese 3707, is a red dwarf star in the constellation Corvus. With an apparent magnitude of 12.12. it is too faint to be seen with the unaided eye. A cool star of spectral type M3.5V, it has a surface temperature of 3024 K. The star was too faint to have had its parallax measured by the Hipparcos satellite. Earth-based measurement gives its parallax as 77.93 ± 2.41 milliarcseconds, yielding a distance of 42 ± 1 light-years. In Action Comics #14 (January 2013), which was published 7 November 2012, Neil Degrasse Tyson appears in the story, in which he determines that Superman's home planet, Krypton, orbited LHS 2520. Tyson assisted DC Comics in selecting a real-life star that would be an appropriate parent star to Krypton, and picked the star in Corvus, and which is the mascot of Superman's high school, the Smallville Crows.>>
https://en.wikipedia.org/wiki/Gaia_(spacecraft) wrote:
The Hipparcos and Tycho-1 Catalogues were used to create the Millennium Star Atlas: an all-sky atlas of one million stars to visual magnitude 11.

Gaia has these goals: Determine the position, parallax, and annual proper motion of 1 billion stars with an accuracy of about 20 microarcseconds (µas) at 15 mag.

Derive the atmospheric parameters (effective temperature, line-of-sight interstellar extinction, surface gravity, metallicity) for all stars observed, plus some more detailed chemical abundances for targets brighter than V = 15.
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by DL MARTIN » Wed May 23, 2018 6:21 pm

I continue to be troubled by the failure to account for the 60 million year old aspect of the Antennae image. The dialogue that portrays the 100 million years of activity between the two galaxies as current events denies the archeological nature of the observation. Scientific rigor is lacking.

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Chris Peterson » Wed May 23, 2018 6:26 pm

DL MARTIN wrote:
Wed May 23, 2018 6:21 pm
I continue to be troubled by the failure to account for the 60 million year old aspect of the Antennae image. The dialogue that portrays the 100 million years of activity between the two galaxies as current events denies the archeological nature of the observation. Scientific rigor is lacking.
Are you talking about some kind of compensation for the distance to these objects? That's completely irrelevant to understanding what we're seeing. When we see something is the current event.
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Wed May 23, 2018 6:41 pm

Chris Peterson wrote:
Wed May 23, 2018 6:26 pm
DL MARTIN wrote:
Wed May 23, 2018 6:21 pm

I continue to be troubled by the failure to account for the 60 million year old aspect of the Antennae image. The dialogue that portrays the 100 million years of activity between the two galaxies as current events denies the archeological nature of the observation. Scientific rigor is lacking.
Are you talking about some kind of compensation for the distance to these objects? That's completely irrelevant to understanding what we're seeing. When we see something is the current event.
  • In any event...60 million years is particularly irrelevant in this case:
https://en.wikipedia.org/wiki/Antennae_Galaxies wrote:
<<About 1.2 billion years ago, the Antennae were two separate galaxies. NGC 4038 was a barred spiral galaxy and NGC 4039 was a spiral galaxy. Before the galaxies collided, NGC 4039 was larger than NGC 4038. 900 million years ago, the Antennae began to approach one another, looking similar to NGC 2207 and IC 2163. 600 million years ago, the Antennae passed through each other, looking like the Mice Galaxies. 300 million years ago, the Antennae's stars began to be released from both galaxies. Within 400 million years, the Antennae's nuclei will collide and become a single core with stars, gas, and dust around it. Observations and simulations of colliding galaxies suggest that the Antennae Galaxies will eventually form an elliptical galaxy.>>
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by DL MARTIN » Wed May 23, 2018 6:50 pm

Perhaps Chris Peterson can enlighten me as to exactly what has happened to the Antennae during the last 60 million years. Or, can he be absolutely certain the Sun is still shining?

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Wed May 23, 2018 7:16 pm

DL MARTIN wrote:
Wed May 23, 2018 6:50 pm

Perhaps Chris Peterson can enlighten me as to exactly what has happened to the Antennae during the last 60 million years. Or, can he be absolutely certain the Sun is still shining?
No one can "enlighten you as to exactly what has happened to the Antennae during the last 60 million years" which is why we simply don't care. We don't measure absolute time as time before the present but rather as time after the big bang. (This collision took place roughly 13 billion years after the big bang.)
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Chris Peterson » Wed May 23, 2018 7:23 pm

DL MARTIN wrote:
Wed May 23, 2018 6:50 pm
Perhaps Chris Peterson can enlighten me as to exactly what has happened to the Antennae during the last 60 million years. Or, can he be absolutely certain the Sun is still shining?
It doesn't matter. Special relativity tells us that "now" is the moment when we observe something (assuming the signal is reaching us at the speed of light). We see this galactic collision at one point in its evolution. Think of it like a movie. Whatever you're seeing at a particular moment doesn't depend upon what's on the film that you haven't yet seen.
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Ann » Wed May 23, 2018 10:49 pm

DL MARTIN wrote:
Wed May 23, 2018 6:21 pm
I continue to be troubled by the failure to account for the 60 million year old aspect of the Antennae image. The dialogue that portrays the 100 million years of activity between the two galaxies as current events denies the archeological nature of the observation. Scientific rigor is lacking.
You may of course choose to be troubled by the fact that nothing can travel faster than light, and that light only travels at ~300,000 kilometers per second, and that the light from the Antennae galaxies that we can see in the sky right now displays a certain redshift, which allows us to infer that the light that we see was emitted by the Antennae galaxies some 60 million years ago.

You may, if you want to, also choose to be troubled by the fact that the Andromeda galaxy can be inferred to be two million light-years ago. It is not the redshift of the Andromeda galaxy that has led scientists to that conclusion (indeed, the Andromeda galaxy displays a blueshift), but rather it is the brightness of certain "standard candles" like Cepheid variables in the Andromeda galaxy that has told us how far away our sister galaxy is.

The fact that the light that reaches us from Andromeda is indeed some two million years old can of course be seen as troubling. What has happened to our sister galaxy in that two million year gap, between the time when the light we can see was emitted and the time that is "now"? Perhaps the Andromeda galaxy is no longer there? Perhaps it has exploded? Evaporated? Or perhaps it is already on our doorstep, but we won't know for another two million years?

And what about our own Sun? It is eight light-minutes away. It something happens to our Sun, we won't know until after eight minutes. Isn't that worrying?

No. None of this is worrying. Yes, our human lives are short, and the oldest recorded observations of the night sky are just a few thousand years old, but we do know enough about stars and galaxies to be able to say: Don't worry. The Sun is an ordinary star, it is a single star, it is not interacting with anything, and it is in the prime of its life. Yes, it is going to die, but not for a long time. It is still there, for the next eight minutes, and the next, and the next. And we do know that it has been shining on the Earth for some four and a half billion years already.

And the Andromeda galaxy is large and magnificent, and it is interacting somewhat with our own galaxy, but nothing catastrophic is about to happen to either of our galaxies for as long as humanity is likely to exist.

And the Antennae galaxies are interacting violently, and yes, if you could magically travel to them faster than light to see them up close right now - which you absolutely can't, since that is one of the most fundamental laws of physics - then you would see, indeed, that their appearance would have changed somewhat. Some of the brilliant blue stars in NGC 4038 would have exploded as supernovas, and others would have turned into red giants. And new brilliant clusters of stars may have begun to peek out of the thickest black dust of these galaxies. And the distorted shapes of the galaxies may have changed a bit more. But not by much.

We know that stars live for a long time. Most, but not all stars live longer than 60 million years. Most live for billions of years, and many - but not our own Sun - probably live for trillions of years. We also know that galaxies evolve slowly, because the Hubble Deep Field images have told us a lot about how galaxies change in size and shape over billions of years. We know that in most cases, 60 millions years is a tiny, tiny part of a galaxy's lifetime.

You may of course still worry about the fact that we don't know how the appearance of the Antennae galaxies has changed since the light that paint their faint images in the sky was emitted some 60 million years ago. It is up to you what you choose to worry about. Personally I choose to marvel at the fact that beings as tiny as brief as ourselves have managed to amass such an amazing body of knowledge about the huge, huge Universe that we are tiny, tiny part of.

Ann
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Chris Peterson » Wed May 23, 2018 11:02 pm

Ann wrote:
Wed May 23, 2018 10:49 pm
And what about our own Sun? It is eight light-minutes away. It something happens to our Sun, we won't know until after eight minutes. Isn't that worrying?
Hey, why stop there? Isn't it worrisome that when your cat gives you that look that says "Feed me!", it will have been hungry for 10 nanoseconds or more before you're aware of it? Who knows what will have changed with your cat in the time it takes to get its message!
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Thu May 24, 2018 2:48 am

Chris Peterson wrote:
Wed May 23, 2018 11:02 pm
Ann wrote:
Wed May 23, 2018 10:49 pm

And what about our own Sun? It is eight light-minutes away. It something happens to our Sun, we won't know until after eight minutes. Isn't that worrying?
Hey, why stop there? Isn't it worrisome that when your cat gives you that look that says "Feed me!", it will have been hungry for 10 nanoseconds or more before you're aware of it? Who knows what will have changed with your cat in the time it takes to get its message!
No problemo there.

Your cat is simply an entangled quantum blob that may or may not be hungry until
those 10 nanoseconds are up and that quantum blob collapses into an actual cat.
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by rlking » Thu May 24, 2018 11:33 am

Lovely picture. It looks so dramatic and cataclysmic, and the caption is very melodramatic. Looking at pictures like this, one is tempted to think that any life there is likely to be totally snuffed out in what appears to be a sort of cosmic fireball, sterilised in a bath of deadly electromagnetism.

And yet, my suspicion is that sentient beings living in the colliding galaxies would likely be just fine, and if they hadn't yet developed significant observational capabilities like ours they really wouldn't notice at all.

Consider this: a simple calculation suggests a supernova explosion (100 billion times as bright as the sun) at a distance of 5 light years from the sun would appear about the same brightness as the sun - though with presumably a far higher output of X rays, gamma rays etc. That would certainly be enough to totally destabilise, perhaps even destroy, earth's atmosphere. But what if it were 100 light years away? It would then only be one four-hundredth as bright; and at 1000 light years only one forty-thousandth: it would be several times brighter than the full moon, and a magnificent sight, but no danger to us at all.

In the colliding galaxy scenario, the rate of star formation and supernova explosions would be greatly increased. But even if it increased by 100 times, that would still only be on average about 1 per year. For a medium-sized galaxy with a diameter of 50,000 lightyears, it would take a couple of thousand years for every point to have a supernova within 1000 lightyears, and very much longer to have one dangerously close. Of course these collisions are non-uniform events, so there would probably be regions where the destructive potential is much higher than others. But overall, I suspect that a substantial proportion of life-bearing planets would be unscathed. But naked-eye astronomy would be rather more spectacular for their inhabitants than for us.

As Douglas Adams famously said, 'Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space'.

And that bigness helps enormously to keep us safe from even the most violent cosmic events. But the most magnificent thing is that gravity, an almost incomprehensibly weak force, spreads its tentacles everywhere and overcomes that vastness, to give us this wonderful universe.

NCTom

Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by NCTom » Thu May 24, 2018 11:40 am

A day late with the thanks, but thanks to all of you for your responses to my query. You get my day started right!

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Chris Peterson » Thu May 24, 2018 2:03 pm

neufer wrote:
Thu May 24, 2018 2:48 am
Chris Peterson wrote:
Wed May 23, 2018 11:02 pm
Hey, why stop there? Isn't it worrisome that when your cat gives you that look that says "Feed me!", it will have been hungry for 10 nanoseconds or more before you're aware of it? Who knows what will have changed with your cat in the time it takes to get its message!
No problemo there.

Your cat is simply an entangled quantum blob that may or may not be hungry until
those 10 nanoseconds are up and that quantum blob collapses into an actual cat.
I believe you are confusing my cat with my buddy Erwin's cat.
Chris

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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Chris Peterson » Thu May 24, 2018 2:06 pm

rlking wrote:
Thu May 24, 2018 11:33 am

Consider this: a simple calculation suggests a supernova explosion (100 billion times as bright as the sun) at a distance of 5 light years from the sun would appear about the same brightness as the sun - though with presumably a far higher output of X rays, gamma rays etc. That would certainly be enough to totally destabilise, perhaps even destroy, earth's atmosphere. But what if it were 100 light years away? It would then only be one four-hundredth as bright; and at 1000 light years only one forty-thousandth: it would be several times brighter than the full moon, and a magnificent sight, but no danger to us at all.
The biggest risk to planetary systems from a galactic collision isn't from supernovas or other high energy events, but from gravitational perturbations. When you have stars passing within a light year or less of each other, there is a significant likelihood that planetary orbits will be altered in those systems. That is likely to be devastating for any complex life on those planets.
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Thu May 24, 2018 3:03 pm

Chris Peterson wrote:
Thu May 24, 2018 2:06 pm

The biggest risk to planetary systems from a galactic collision isn't from supernovas or other high energy events, but from gravitational perturbations. When you have stars passing within a light year or less of each other, there is a significant likelihood that planetary orbits will be altered in those systems. That is likely to be devastating for any complex life on those planets.
With tidal forces dropping off inversely with the cube of the distance a solar mass star at 50 AU will have about the same tidal force on the Earth/Sun as Jupiter currently does. I have never heard of a star passing by at around a light year as having any effect other than stirring up a lot of comets from the Oort cloud (and changing the Sun's motion).
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by Chris Peterson » Thu May 24, 2018 3:16 pm

neufer wrote:
Thu May 24, 2018 3:03 pm
Chris Peterson wrote:
Thu May 24, 2018 2:06 pm

The biggest risk to planetary systems from a galactic collision isn't from supernovas or other high energy events, but from gravitational perturbations. When you have stars passing within a light year or less of each other, there is a significant likelihood that planetary orbits will be altered in those systems. That is likely to be devastating for any complex life on those planets.
With tidal forces dropping off inversely with the cube of the distance a solar mass star at 50 AU will have about the same tidal force on the Earth/Sun as Jupiter currently does. I have never heard of a star passing by at around a light year as having any effect other than stirring up a lot of comets from the Oort cloud (and changing the Sun's motion).
Models demonstrate that stellar mass objects inside a light year do modify orbits. Jupiter has a huge tidal effect. If you were to instantaneously shift Jupiter into a different position in its orbit, it might well significantly alter the orbits of the other planets. It's a chaotic system.

I've read a number of papers in recent years that posited one or more mass extinctions occurring because of small changes in Earth's orbit caused by passing stars. Far from solidly demonstrated, of course, but very possible.
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Re: APOD: Spiral Galaxy NGC 4038 in Collision (2018 May 23)

Post by neufer » Thu May 24, 2018 3:28 pm

Click to play embedded YouTube video.
Chris Peterson wrote:
Thu May 24, 2018 2:03 pm
neufer wrote:
Thu May 24, 2018 2:48 am
Chris Peterson wrote:
Wed May 23, 2018 11:02 pm

Hey, why stop there? Isn't it worrisome that when your cat gives you that look that says "Feed me!", it will have been hungry for 10 nanoseconds or more before you're aware of it? Who knows what will have changed with your cat in the time it takes to get its message!
No problemo there. Your cat is simply an entangled quantum blob that may or may not be hungry until those 10 nanoseconds are up and that quantum blob collapses into an actual cat.
I believe you are confusing my cat with my buddy Erwin's cat.
Art Neuendorffer