》This “total” temperature can also be described as a sum of temperatures on coarse (large) scales, temperatures on finer scales, even finer scales, etc. On large scales we see the well-known climate changes. Albert Sneppen’s study documents that the temperature differences become stronger on small scales (credit: Albert Sneppen).
》In other words, climate change makes the differences in temperature grow locally — and with large temperature differences come even more extreme weather patterns.
I don't think he discovered the conclusion per se. I think he discovered an analytical path to an already known/suspected conclusion via a novel application of cosmology math to planetary climate.
It’s been common knowledge in
atmospheric science for the past 20 years (based on personal knowledge, it’s probably decades longer). Not only does it shake out of climate models, but it’s intuitive that more heat to redistribute will increase the amplitude of all the wave-like properties of the atmosphere.
Let's not downplay the astronomical math involved and the contribution made by Albert here! Just because we "know" the solution doesn't mean it's not worth valuing putting in the work to prove the conclusion. Thanks Albert!
Assuming the universe is mainly uniform, why would distant galaxies have different starts than nearby ones? Is it related to time (the light from those farther away that reaches us being from the distant past)?
> why would distant galaxies have different starts than nearby ones?
I know one reason: metallicity.
The very early universe didn’t have clumps of heavy elements to create nucleation points of sort for fusion. So big clouds of hydrogen had to very slowly draw together via “molecular…cooling in the gas phase,” which meant more massive stars that burned furiously for a short while [1].
They are older, so they had less time to produce heavier elements. Additionally lighter stars live longer, so it may be that the heavy stars just burned out in nearby galaxies.
Why wouldn't that have already been the assumption? When we look at distant galaxies we are looking billions of years in the past; so it would seem natural to find more heavy stars there that haven't burned out like they have more locally.
I expect this effect is not ignored. But please note that heavy stars do not burn in billions of years but in millions. Not seeing them locally suggests that we have slower starformation, not that we had more of them (heavy stars) billions of years ago.
I’ve always had trouble understanding this; if everything is the same age, how did they get billions of light years away from the Big Bang?
How do we know where the Big Bang occurred?
Unles it means that our galaxy is on the spherical plane(?) directly projected out in all directions from the bang, and it’s the diameter of this sphere that is billions across?
Nothing stayed where the big bang was, but everything flew away at the same speed. There is a flaw in your imagination, because as a being in 3D you probably cannot imagine how a 3D thing explodes (I certainly can't). Don't think of the universe as sphere-shaped -- it is not a 3D sphere. Think of it as the 3D surface of a 4D sphere.
Why? Let's reduce by one dimension to be able to imagine this: imagine a small thing (a grain of sand) explodes in our 3D world and all the tiny pieces are flying away at equal speed, then the structure that is created by the explosion is not a 3D sphere, but the surface of a sphere, a 2D structure, because where the explosion started, there is nothing left of the original thing, as every particle of it has moved away from that point, so at any point in time after the start of the explosion, the particles are on the surface of a sphere. That surface is a 2D structure embedded into our 3D world, much like the surface of an expanding balloon. In the same way, our universe is a 3D structure, so looked at from the outside (which we obviously cannot do), it is not a 3D sphere, but probably more like the surface of a 4D sphere.
Now imagine us as a dot on a balloon that is expanding, and other stars are also dots on the surface of the balloon. In whichever direction you look, all the stars are moving away from you (the balloon is expanding). You do not need a center of this structure to observe this moving away -- nothing is in the center -- there is no center.
Your argument and examples actually don’t imply that there is no center. The Big Bang wasnt an explosion per se, but in so far as there is a 3D spatial distribution that is not infinite, there will be parts with empty skies—-that is, edges, last stars, ends of the universe.
As far as I understand, if the “empty skies” regions even exist, we physically will _never_ be able to observe them, because due to cosmic expansion they are moving away from us faster than speed of light.
So from our point of view, we can never know if universe is actually infinitely distributed or not.
Isn't that the whole thing about the fact that when we look at any patch of sky, we don't see it just lit up with stars filling all of it ? Like if it was infinite and we had infinite stars randomly distributed, there's be a patch of sky where we'd have an infinite amount of stars in front of eachother. The fact that we do see darkness between stars indicates that there is some portion of the universe that has an edge.
Then again, there's the matter of looking so far back that you can't see stars because it's so old and thus it's not that there is an edge but just that we can't observe one.
But we _do_ see a uniform glow from every single point in the sky, it’s called Cosmic Microwave Background. We don’t see it with a naked eye because the light’s frequency has been red-shifted, the light is coming from so far away in space and time, that universe grew so much since then and stretched its wave length. There’s no “darkness between stars”, we see there an image of universe so old that stars didn’t even form yet, and it’s uniform and infinite where it’s physically possible for us to see due to speed of light limit.
> Isn't that the whole thing about the fact that when we look at any patch of sky, we don't see it just lit up with stars filling all of it ? Like if it was infinite and we had infinite stars randomly distributed, there's be a patch of sky where we'd have an infinite amount of stars in front of eachother.
That would require stars to be outputting infinite energy in the form of light we can see. They are not, so we do get enough of their light to see them with the naked eye. The farther away they are, the less and less photons make it to our eyes. So, yes, you can look up in the night sky and see infinite galaxies, but your eyes are not sensitive enough to pick out the one or two photons every few seconds and tell you there is something there.
You and I both see that the surface area of a sand grain, distributed by explosion to a different surface area with the diameter of a beach ball, has a center in 3D space.
But from the perspective of a Flatlander on the expanding surface, looking at the distance to an adjacent microbe, the universe is growing, and there is no meaningful point on that 2D surface from which the expansion emanates, it's expanding everywhere.
There's no reason to believe our universe is not infinite. It's certainly effectively so.
Here's how I understand it (but I may be totally wrong so please correct me if this is wrong).
Common knowledge is that there was an initial event called the Big Bang but there's no observational or theoretic evidence that there was such an initial event or explosion. Observations are limited by cosmological horizon, and our theories are unable to describe the state of the universe in its "early on" stage.
What we do know however is that the universe is expanding and getting less dense and colder as a result. By going backward, we interpolate the state of the universe far in the past up to a stage where it was very dense and very hot "soon after" an hypothetical instant zero that we don't know happened.
Also at that stage, the universe may have been infinite already (provided it's infinite now). Maybe it's better to think of the Big Bang has a past state of the universe rather than an "explosion" that happened at given time and place.
The theory of the Big Bang is based on the observation of inflation: spacetime itself is constantly expanding - that is, the distance between galaxies that are at rest relative to each other is increasing (more precisely, the galaxies are not at rest, but the distance between them is increasing faster than their relative speed).
So, extrapolating this in the past, at some point the universe must have been really tiny, and then grew much larger. But this growth happened essentially everywhere: spacetime itself expanded and pushed things apart at speeds greater than the speed of light (which is allowed if the coordinate system itself is what's changing), leading to objects which were once microns apart now being tens of billions of lightyears away in just a few billion years.
This kind of brings up another point that is interesting about our universe. We're under the impression that every point in the universe is experiencing the same amount of distance from the beginning of the universe from that individual point's frame of reference. But this kind of makes time so fundamentally weird compared to the spacial dimensions. We assume no point in the universe is the center, for instance. And the topology of the universe would look fundamentally different if there were some spacial coordinate (of the three) upon which every point was "pinned." But isn't saying from every individual point's frame of reference the universe is the same age equivalent to making a central point within time at the beginning? aka the big bang, of course, but that also seems to imply something about the topology of the universe for eternity after the big bang, as well. It's got one complicated topology for sure.
Yeah, the time dimension is different from the space dimensions.
To mention the obvious: everything is constantly moving through the time dimension together, for unknown reasons. Nothing like that happens with space.
This is a bit of a tangent, but the idea of "moving through time" always struck me as a little weird, because the concept of motion is dependent on time already. I like to think of things having a shape that exists along the time axis in addition to the spacial ones. The 4D shape of a thing is fixed, but captures within itself what we perceive as motion in 3D space.
But how would we know if all spatial dimensions were moving along a constant vector? We can't rely on redshit/blueshift if the medium of transmission itself is moving like everything else. The next question might be "moving in what, then?" but then why not abstractly ask the same about time.
There was some ancient religion where their god or satan figure was responsible for time - literally the god/satan beings way of destroying the universe.
Wish we could figure out some better ways to experiment with time. Seems like it's very telling of what's really going on that it's so different.
Nice try, I'd also like to know. But I am afraid no-one here will be able to answer you. But maybe we're lucky -- I'll monitor this thread.
We can never know the answer, because any possible cause was outside of our observable universe. Inside of our universe, time started at the big bang, so there was no 'before' and thus there was no cause, because the cause needs the time to be before the effect.
Well, if it's true the universe will start contracting at some point (which, some speculate, could happen sooner than we had thought[0]), and if a big crunch leads to a big bang, it is not impossible that this very moment - in the sense of these actual circumstances we're in - already happened an infinite number of times. (Still doesn't really answer the 'why?')
Good question, my understanding is that we frankly just don't know, it may be one of those things that we can't know, but that is getting awfully close to the realm of philosophy
> it may be one of those things that we can't know
This is true for anything we don’t know.
For the Big Bang, we know the intermediate problem: black holes. Gravity and quantum mechanics interacting at the same scale. The singularities there are accessible in a way the singularity of the Big Bang is not.
Someone outside the universe hit "build" on their "universe sandbox generator". The sandbox is still loading from our perspective, although from their perspective perhaps it loads instantaneously.
I mean, obviously this is nonsense, but... I can't exactly disprove it.
There's a book I read that specified that the universe could be "stateless" to an outside observer, yet the simple act of computing it allows us to exist.
It looks each epoch speaks about the universe in its own terms: as gods' creation, as a machine, as a computer, AI... So while there is no way to disprove the sandbox theory you presented, we can be 100% sure that at some point in time people will see it in a different way, and then it will change again and again. Sometimes I feel sad that there are so many mysteries of the universe and so few of them will be discovered during my lifetime.
I think one reason we want to discover more about the universe is because it gives us a sense of awe and a sense of powers greater than us. One useful trick if you're missing that is to take some mushrooms while you watch some space documentaries. Sure you don't really discover anything groundbreaking but it does open up the mind and you will definitely experience awe.
The big bang happened everywhere. Space is not a fixed size nor infinite emptiness into which the big bang poured matter. Space itself expanded from near nothing to the universe we have today. The big bang wasn't a matter grenade it was the expansion of everything including space itself from nearly infinitely small to current state.
This means that the tip of your nose, a distant mountaintop, Olympus Mons on Mars and indeed a distant galaxy were all the same space.
Imagine a balloon blowing up with an ant on it. The ant can only walk so fast but the balloon can blow up expanding the space between ants in a way that is in no way limited by ant walking speed.
Now that we are so separated it takes so long for light to get to us that we can only see the light that left billions of years ago from our frame of reference
This doesn't help with understanding, but I think it's true:
Our intuitions about physical reality come from evolving as primates on Earth. We're pretty great at intuitively understanding the world at that scale.
But at vastly different scales of size and time, those intuitions just don't apply much. So quantum physics events on nano -meter and -second scale seems completely bizarre, as do cosmological event on giga -lightyear and -year scale.
Some heretical thoughts. How do we measure distance to galaxies? By measuring redshift of the light from those galaxies and making an assumption that the only cause of redshift is spacetime expansion? What if photons slowly lose energy, and those very far galaxies are in fact much closer?
That is the "tired light" hypothesis. It is not favored lately because if it were the principal cause of redshift, certain observed details would differ.
I don't think it is entirely ruled out, but two causes of redshift are considered less likely than one.
That's an interesting one to think about; every galaxy moves away from every one, so (if I got this right) from every other galaxy's point of view, all the other galaxies are younger... or older, either / or I don't know anymore.
Light and thus causality and information travel at a constant speed of "c." As far as we know, nothing can travel faster than "c" - other than the universe itself as in during the inflationary epoch. So the further out any observer would look the longer that light would have had to travel relative to that observer. Seeing something 3 billion light years away would mean the light took 3 billion years to arrive at the observer.
> As far as we know, nothing can travel faster than "c"
What Relativity forbids is anything traveling as fast as c, as the increase in mass as c is approached would require infinite energy to reach. Relativity says absolutely nothing about faster than c, i.e. it does not forbid things such as the theoretical tachyon.
It's more like every point of view looks at the past. Which is also true if you look at your screen right now, it's just that you're looking at your screen some nanoseconds ago.
You are the oldest thing in the universe you can observe. Even the person next to you, as you observe her or him, is younger, because the speed of light is finite.
In this respect, you are the centre of your universe. But objectively speaking, there is no centre.
Reading the responses, I think I need to explain a little more fully what I meant.
My remark was intented as an explanation of one of the parents' statement: "distant means younger" when observing astronomical objects. We are not talking here about the age of the object per se (how old is the star I see, etc.), but about the age of the observation (how long ago did that happen, what I see just now). Every look into the sky is a look into the past. But also every look around you is a look into the past.
With "the oldest thing in the universe", I did mean the particles that form you (not you as a specific formation of such particles). If we say that everything of the universe started at the same time, then the atoms closest to you are the oldest things in the universe you can observe. Objectively, of course, every particle has the same age, even though it might be beyond the event horizon and never be observable. (I am simplifying somewhat here, leaving the spontanous coming and going of particles in the vaccum out of the picture.)
> You are the oldest thing in the universe you can observe.
The moon is older than we are, due to gravitational time dilation. So is Mars. Even if you account for the time it takes for light to travel to here from there.
It's similar to how every sound you hear is of an event in the near past. Every thunderclap is caused by a past and distant lightning event. As a child, we'd see lightning and then count seconds waiting to hear the thunder (sound travels slower and takes longer to arrive than the light- about 2 seconds per mile).
If you're hearing thunder now, in a way, you're hearing an event in the past. The farther the thunder traveled, the farther into the past you are experiencing.
Across the expanse of space, you are not just hearing, but seeing into the past. The farther the light traveled, the farther into the past you are experiencing now.
I re-read the parent comment and I see why you're confused. It was awkwardly worded. "Older" and "younger" are confusing ways to put it.
The fact is, simultaneous observations don't necessarily mean simultaneous events. If you hear 2 people shouting at the same time, but one person is very far away and one person is near, you can assume the person farther away actually shouted first. The reason this happens is the different delay across different distances.
The distances have to be much greater to notice the difference with light compared to sound. But compared to the expanse of the universe, light actually travels quite slowly. If the sun disappeared, we wouldn't see it disappear on Earth for 8 minutes (that's how long it takes light to reach Earth). Essentially, we are seeing the Sun as it was 8 minutes in the past.
The effect is even greater outside our solar system and even greater beyond our galaxy. We see stars and galaxies as they were, not just minutes but years and years in the past. Some stars that we see now have certainly already reached the end of their life, exploded into a supernova and collapsed. We just haven't seen it yet. The light from those events haven't reached us yet.
Everything we see is of something as it was in the past. Even though we are seeing all the stars and galaxies simultaneously, the farther away it is, the farther into the past we are observing.
The statement: "You are the oldest thing in the universe you can observe" has a very clear meaning - it literally means I am the oldest thing in the universe - out of all the things I can observe. This is obviously false - I'm less than 50 years old, and I can observe many much older things around me. Therefore, the statement is false, and no context or explanation can make it true, unless we start assigning completely new meanings to words like "oldest", "thing", "you" or "are". I was merely pointing this out. If the OP meant something else, they should have said something else. Those who try to explain how things work should use, demand and appreciate clear and logical language.
We are not talking about the age of photons. We are talking about the age of the thing that emits/reflects photons.
The confusion arose because the OP said "you are the oldest thing in the universe you can observe". They should have said "you are the most recent thing in the universe you can observe".
When you see someone standing 3m away from you, the light took 10 nanoseconds to reach your eye, so you see them as they were a very short time ago. Of course, they're only younger when measuring their age not from their birth but from the big bang.
Not according to the classical definition of age which is the time since birth. I was born a few decade ago. My grandparents are decades older then me. The earth in millions of year older than me. And the galaxies billions of lightyears away are still billions of year older than me.
Maybe the Milkyway is older than the other galaxies we observe, assuming they were all born at the same time.
The universe is not isotropic in the time dimension. However, across space the prevailing thinking is that the universe is isotropic on a large scale in the spatial dimensions.
As far as I understand (I'm not a physicist), to be able to say that the universe is isotropic across space, you need a point of view that just doesn't exist. You cannot speak about an absolute synchronicity among events happening in locations scattered among an arbitrary subset of the set of all visible galaxies, and without that, you cannot abstract time out of the picture, which you'd need to do to speak about isotropicity across space.
I don't think that, in this regard, you can say much more than "the universe is not isotropic across space-time".
You cannot speak about an absolute synchronicity among events happening in locations scattered among an arbitrary subset of the set of all visible galaxies
The cosmic microwave background gives you a physical realization of just that (but of course only approximately so), at least as far as cosmologists are concerned. The rules of relativity of course still apply, making this particular synchronicity convention just one of many others...
But the cosmic microwave background refers to one single event, that has echoes everywhere, right? If I understand correctly, you don't need to synchronize anything to have echoes everywhere.
But the cosmic microwave background refers to one single event, that has echoes everywhere, right?
An event is a single point in spacetime, whereas photon decoupling happens everywhere, defining a spacelike hypersurface we use for synchronization (in the idealized scenario).
Subsequently, the CMB allows us to single out a particular reference frame (the one where it looks isotropic) and provides a measure of expansion via its redshift/temperature which we can then translate to cosmological time (ie time since the big bang as measured by an observer following the Hubble flow) via our cosmological models.
It doesn’t. Galaxies studied were very far from Milky Way and hence much older. This discovery shows that era of massive stars ended later in evolution of universe than we’ve assumed, not that we got mass of stars wrong.
We still see younger galaxies with less massive stars not rotating as expected.
Weird English quirk when you have relativistic distances: They are older in a sense that they aren't recent. They aren't older in a sense that they've existed for a longer time. (At least in the radiation we're seeing.)
The research is about the distribution of stars in a galaxy, not mass that is missing or extra. Distant galaxies apparently have more massive stars than whatever widely used model says. From the article:
Stars in distant galaxies are typically more massive than those in our "local neighborhood"
I don't think so because many of the observations of the galaxys that make folks think that dark matter must be present (because the visible matter is not sufficient to make the galaxy stick together) are in the local group.
Funny thing about the missing mass. Papers will say "this could be explained by a dark matter Halo with this distibution". They assume it gravitationally affects regular matter the same way regular matter does. What is usually missing is 1) how dark matter interacts with dark matter 2) why it should have this particular distribution - dynamic model. Without those things, the explanation is IMHO worse than MOND because it doesnt make sense that some matter would end up with a completely different distribution. Oh and we cant actually detect it directly either, but trust us it must be there.
There is no reason for matter with very different interaction properties from the familiar stuff to have the same distribution.
In particular, familiar stuff has ways to dispose of kinetic energy, allowing it to clump into our stars and planets, that might be unavailable to putative dark matter, making any dark matter more diffuse.
Generally, you can start with the assumption that people working on dark matter hypotheses are not idiots. They might still be wrong, but if they are, they will be wrong in interesting and subtle ways, not obvious ones.
>> There is no reason for matter with very different interaction properties from the familiar stuff to have the same distribution.
Sure there is. It has similar interaction with regular matter. Any other properties need to be defined and shown to produce this claimed distribution as a result of a dynamic process. Anything less and we can just say dark matter is fairy dust.
Larger [More massive] stars are typically more luminous. Could be that there is a selection bias towards them. since they are the only ones that can be detected from that far away.
Why does “heavier” mean something when talking about a mass suspended in the vacuum of space?
Does the mass and resultant gravitational force attenuate the same ratio for small vs big stars?
Also, how do super dense neutron stars work - in the sense that atoms (and neutrons) are “mostly empty space” — are the particles in the atoms compressed closer together? Or does an atom of one substance at the center of a star have the same mass/volume as an atom of the same, either floating by itself or say, on earths surface?
"Weight" words and "mass" words get used interchangeably because it usually becomes obvious which one is meant based on context.
Here, obviously we're talking about stellar mass.
You can't really talk about the "volume" of an atom because the distance between one atom and the next closest atom really depends on the bulk material and isn't just atoms sorted into their one fixed size but is a balance of various forces.
A neutron star isn't made of atoms, but is, in a sense, one enormous atom or just a nucleus (but it's more complex than that). Mostly neutrons with some electrons and protons mixed in not separated into atoms which repel each other but in a super dense fluid of particles packed about as closely as particles in the nucleus of a normal atom.
It's a power law. Increased mass more than proportionally decreases the lifetime of a star. (A star with 100 X the mass of our sun would last about a million years).
That sort of sounds like a "sorting" process or something like survivor bias. The conditions were more likely to produce pockets of material dense and large enough to produce the larger, shorter living stars the earlier back in the universe. i.e. as Time progresses forward the stars which remain are those with more burn time and thus less mass. Otherwise would require some forces to exist which pull mass back together to counter the overall expansion of the universe.
The sun is estimated to have formed less than 5B years ago. The universe is roughly 13B and change years old, and the first stars started forming only 100M years after the beginning. There's absolutely no way it could be a first generation star.
The first-generation stars are imagined to have lasted only a few million years before going supernova and (because of their size) becoming black holes.
We can never be certain, of course, because they are all long gone. Like, 13 billion years gone. The James Webb telescope is hoped to see back nearly that far back, but not likely near enough to catch any of them.
The entire solar system precipitated out of the same interstellar dust, which has to contain the remnants of previous generations of stars, including collided neutron stars, in order for there to be heavy elements beyond iron.
Not all heavier elements are from supernovae. This is known as nucleosynthesis ( https://en.wikipedia.org/wiki/Nucleosynthesis ) and there are a number of different origins of elements. Exploding massive stars really only get you up to Rb (atomic number 37).
Edit: and this from last year https://nbi.ku.dk/english/news/news21/danish-student-solves-...