Cosmology Has Some Big Problems(blogs.scientificamerican.com)
blogs.scientificamerican.com
Cosmology Has Some Big Problems
https://blogs.scientificamerican.com/observations/cosmology-has-some-big-problems/
75 comments
The fact that SOME galaxies are inconsistent with the theory of Dark Matter actually strengthens that theory.
If the difference in rotation curves, the usual signature of dark matter at the galaxy level, from what GR predicts based on the mass of luminous objects was due to a modification in the way gravity works, then that should apply to ALL galaxies. Modified Newtowian Dynamics (MOND) (or the relativistic TeVeS models) should work the same for all galaxies, at least all of roughly same mass and same depth of the gravitational potential.
The fact that we can find similar sized and aged galaxies that behave like they have different amounts of dark matter is therefore NOT caused by the way gravity works. The next best explanation is that most galaxies contain dark matter, but some loose it through their evolution history, e.g. due to interaction with other galaxies.
If the difference in rotation curves, the usual signature of dark matter at the galaxy level, from what GR predicts based on the mass of luminous objects was due to a modification in the way gravity works, then that should apply to ALL galaxies. Modified Newtowian Dynamics (MOND) (or the relativistic TeVeS models) should work the same for all galaxies, at least all of roughly same mass and same depth of the gravitational potential.
The fact that we can find similar sized and aged galaxies that behave like they have different amounts of dark matter is therefore NOT caused by the way gravity works. The next best explanation is that most galaxies contain dark matter, but some loose it through their evolution history, e.g. due to interaction with other galaxies.
To be clear, they're not inconsistent with the theory of dark matter, they're inconsistent with those galaxies specifically having dark matter. The author was wording that in a confusing way.
That's right they are inconsistent with the combination of
1.) dark matter is the correct theory and
2.) they have the usual amount of dark matter for a galaxy of that size.
Surprisingly this is does not make the theory of dark matter (#1) less likely, but actually makes it more likely. Because the alternative is #1b "gravity works differently than we think". But that would have to hold for all galaxies.
Surprisingly this is does not make the theory of dark matter (#1) less likely, but actually makes it more likely. Because the alternative is #1b "gravity works differently than we think". But that would have to hold for all galaxies.
To be even more clear, "dark matter" isn't a theory. It is a name for something we need theories about.
I wish the article had made that apparent.
I wish the article had made that apparent.
Dark matter is a hypothesis, and one that makes pretty strong predictions, several of which have come true, so it's not inappropriate to call it theory.
The phenomenon of galaxies demonstrating significanty more mass than their sum of normal matter is the observation that is explained by dark matter.
The phenomenon of galaxies demonstrating significanty more mass than their sum of normal matter is the observation that is explained by dark matter.
Sorry but that’s an intellectual dodge. A verbal fiddle. Saying it is a “name for something” doesn’t make the fact that it’s a hypothesis disappear. One is simply positing the need for more “Russian dolls” inside the Russian doll one has hypothesised to begin with.
The way I understood it, they are not inconsistent with anything, they just happen to have no DM in them.
I found the authors' points about reports from the past several months disingenuous, since he's advertising a book that was clearly written and edited well before those announcements. It's valid to talk about those points in the context of arguments from the book, but leading with those points implies those arguments are a result of those points.
For some reason edits are silently failing, but an addendum to
> Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.
Admittedly the DE from Einstein is for very different reasons than the DE today, but we again had the big bang and no DE from the 60s until the 90s (observations from https://en.wikipedia.org/wiki/Supernova_Cosmology_Project) so they don't go hand in hand.
> Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.
Admittedly the DE from Einstein is for very different reasons than the DE today, but we again had the big bang and no DE from the 60s until the 90s (observations from https://en.wikipedia.org/wiki/Supernova_Cosmology_Project) so they don't go hand in hand.
I've rarely seen more spectacular agreements with a theory than those of a Lambda-CDM fit of Planck's 2015 data. That can't be wrong (but as I've never worked on it, this statement is just some guy's personal impression based on his physics instinct). What's your take on those results?
> > Today's space telescopes provide no direct view of anything
> I have no idea what that means. They literally observe the sky...
Seriously! At this point they're just spitballing.
> I have no idea what that means. They literally observe the sky...
Seriously! At this point they're just spitballing.
I was maybe a bit too cavalier here. I think I understand what the author means - the data that they gather is understood in the context of the model that we think is best.
But, it isn't as if cosmologists are rigidly holding to the model. Here's a paper looking at extensions to lambda CDM https://arxiv.org/abs/1512.05356. As I mentioned, changing GR is being looked at as an alternative to DE http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen...
People aren't challenging some things though - I don't think anyone is seriously working on cosmologies that don't include a big bang, because without one I can't imagine how you explain the CMB.
But, it isn't as if cosmologists are rigidly holding to the model. Here's a paper looking at extensions to lambda CDM https://arxiv.org/abs/1512.05356. As I mentioned, changing GR is being looked at as an alternative to DE http://www.resceu.s.u-tokyo.ac.jp/workshops/resceu08s/presen...
People aren't challenging some things though - I don't think anyone is seriously working on cosmologies that don't include a big bang, because without one I can't imagine how you explain the CMB.
Sorry but I’d have to disagree: There are plenty of people working on cosmologies that don’t include the Big Bang, or that do include it but only as one facet of a larger theoretical framework.
As for not being able to imagine how you explain the CMB without the Big Bang, well, there are plenty of good arguments being made here that put to paid that “limitation.” As well, think of the Michelson-Morley experiment. In that era, no one could imagine how light could propagate through space without the presence of a medium permeating that space.
I’ll venture one step further. Dark Matter is to current cosmology what the aether was to 19th century cosmology.
As for not being able to imagine how you explain the CMB without the Big Bang, well, there are plenty of good arguments being made here that put to paid that “limitation.” As well, think of the Michelson-Morley experiment. In that era, no one could imagine how light could propagate through space without the presence of a medium permeating that space.
I’ll venture one step further. Dark Matter is to current cosmology what the aether was to 19th century cosmology.
>It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe?
>To explain observations of galaxies inconsistent with general relativity, the existence of dark matter was posited as an unknown and invisible form of matter calculated to make up more than a quarter of all mass-energy content in the universe
Food for thought: the best current evidence of dark matter is the Bullet Cluster[0]. In particular, look at this picture: https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_s...
At first, these were two blobs of dark matter and gas. They collided. That resulted in what we see now: the dark matter portions (purple, measured by gravity lensing) magically went through each other (because dark matter is weird like that) while the gas portions (pink) actually collided and formed a shockwave (like normal matter behaves), with much of the gas remaining in the middle.
The tone in the article quotes there makes it seem like dark matter is some esoteric rounding error, but that seems like pretty "solid" evidence for... the anomalous mass readings we call dark matter.
0: https://en.wikipedia.org/wiki/Bullet_Cluster
>To explain observations of galaxies inconsistent with general relativity, the existence of dark matter was posited as an unknown and invisible form of matter calculated to make up more than a quarter of all mass-energy content in the universe
Food for thought: the best current evidence of dark matter is the Bullet Cluster[0]. In particular, look at this picture: https://upload.wikimedia.org/wikipedia/commons/a/a8/1e0657_s...
At first, these were two blobs of dark matter and gas. They collided. That resulted in what we see now: the dark matter portions (purple, measured by gravity lensing) magically went through each other (because dark matter is weird like that) while the gas portions (pink) actually collided and formed a shockwave (like normal matter behaves), with much of the gas remaining in the middle.
The tone in the article quotes there makes it seem like dark matter is some esoteric rounding error, but that seems like pretty "solid" evidence for... the anomalous mass readings we call dark matter.
0: https://en.wikipedia.org/wiki/Bullet_Cluster
[deleted]
I've never been a fan of Dark Matter. Not all galaxies have dark matter, but only incredibly diffuse galaxies don't have it[0]. Doesn't that mean that the density of matter in a galaxy is what gives rise to "faster rotations/more gravity", and not just the total matter irrespective of its galactic density?
Furthermore, the "Bullet Cluster" example is telling. Apparently, the extra mass stuck around the more dense part of the galaxy, and not in the less dense gas cloud that resulted from the collision. Again, only the dense parts of this cluster exhibit "faster rotations/more gravity".
So to me, this is terribly un-compelling. So there's a magic invisible matter that just so happens to only coalesce around dense galaxies/galactic areas and never around sparse ones.
[0] http://www.astronomy.com/news/2019/03/ghostly-galaxy-without...
edit: s/no matter/irrespective of (poor use of the homonym "matter")
Furthermore, the "Bullet Cluster" example is telling. Apparently, the extra mass stuck around the more dense part of the galaxy, and not in the less dense gas cloud that resulted from the collision. Again, only the dense parts of this cluster exhibit "faster rotations/more gravity".
So to me, this is terribly un-compelling. So there's a magic invisible matter that just so happens to only coalesce around dense galaxies/galactic areas and never around sparse ones.
[0] http://www.astronomy.com/news/2019/03/ghostly-galaxy-without...
edit: s/no matter/irrespective of (poor use of the homonym "matter")
Ethan Siegel write up on this problem: https://www.forbes.com/sites/startswithabang/2018/06/22/why-...
But also about other claims from the Ekeberg's article (who, as I see, is a "a philosopher of science"):
https://www.forbes.com/sites/startswithabang/2018/07/26/ther...
"There's A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating"
Careful reader of Ekeberg's article can both recognize that the article claims are inspired by the claims of the "cheating" side but also that where he writes his own he completely fails on physics. I.e. if one side is cheating, he'd be a third side, the one that's completely unscientific: even the physicists that develop theories that compete with dark matter would not write what Ekeberg wrote: "Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. But according to the latest measurements, it is not, suggesting the theory needs to be reexamined." It's plain nonsense. The reason:
https://www.forbes.com/sites/startswithabang/2019/01/16/myst...
"Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible."
We even have the pictures where the galaxies and dark matter aren't at the same place, totally the opposite of Ekeberg's "everywhere" strawman claim, and exactly that opposite was always treated as the biggest support for dark matter:
https://www.forbes.com/sites/startswithabang/2017/11/09/the-...
Once I've reached that strawman claim, I've checked what the profession of Ekeberg is. I openly admit his uncritical bias just confirmed my own bias about that profession.
https://www.forbes.com/sites/startswithabang/2018/07/26/ther...
"There's A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating"
Careful reader of Ekeberg's article can both recognize that the article claims are inspired by the claims of the "cheating" side but also that where he writes his own he completely fails on physics. I.e. if one side is cheating, he'd be a third side, the one that's completely unscientific: even the physicists that develop theories that compete with dark matter would not write what Ekeberg wrote: "Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. But according to the latest measurements, it is not, suggesting the theory needs to be reexamined." It's plain nonsense. The reason:
https://www.forbes.com/sites/startswithabang/2019/01/16/myst...
"Ironically, the discovery of a galaxy without dark matter — amidst a sea of galaxies that require huge amounts of it — helps prove the validity of the dark matter-rich picture of the Universe. Only if normal matter can be separated out from the dark matter and left to form its own structures would such a galaxy be possible."
We even have the pictures where the galaxies and dark matter aren't at the same place, totally the opposite of Ekeberg's "everywhere" strawman claim, and exactly that opposite was always treated as the biggest support for dark matter:
https://www.forbes.com/sites/startswithabang/2017/11/09/the-...
Once I've reached that strawman claim, I've checked what the profession of Ekeberg is. I openly admit his uncritical bias just confirmed my own bias about that profession.
@astro123
There’s a tautology in your critique. You’re attempting to suggest that there is evidence for dark matter. There isn’t. Dark matter is a theory, one that has not yet produced empirical evidence to support it (& perhaps cannot ever do so.)
There’s a tautology in your critique. You’re attempting to suggest that there is evidence for dark matter. There isn’t. Dark matter is a theory, one that has not yet produced empirical evidence to support it (& perhaps cannot ever do so.)
@astro123
The following excerpt is the crux of the author’s argument regarding DM, & it points to the dark elephant in the room that a lot of physicists are bothered by but don’t want to discuss:
“It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? The answer lies in a peculiar feature of cosmological physics that is not often remarked. For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm, is not to describe known empirical phenomena but rather to maintain the mathematical coherence of the framework itself while accounting for discrepant observations. Fundamentally, they are names for something that must exist insofar as the framework is assumed to be universally valid.”
The following excerpt is the crux of the author’s argument regarding DM, & it points to the dark elephant in the room that a lot of physicists are bothered by but don’t want to discuss:
“It's perhaps worth stopping to ask why astrophysicists hypothesize dark matter to be everywhere in the universe? The answer lies in a peculiar feature of cosmological physics that is not often remarked. For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm, is not to describe known empirical phenomena but rather to maintain the mathematical coherence of the framework itself while accounting for discrepant observations. Fundamentally, they are names for something that must exist insofar as the framework is assumed to be universally valid.”
Biggest takeaway from this is how many underlying presuppositions appear to be assumptions.
Yes.
To be fair, I bet most, if not all, cosmologists would agree that they know far less than they don't know. The title of the article is a bit sensationalistic from that point of view, but then I guess "Cosmology has some big details to work on" isn't nearly as catchy.
Interesting view. Near the end, it says:
“The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.”
Empiricism is based on sense observations. And a lot of science has been confined to human senses. I’m curious if tapping into more basic science research by analyzing different types of senses, for instance, available to animals, may offer breakthroughs down the line. For instance, fish employ the lateral line system to detect pressure gradients in the environment.
“The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.”
Empiricism is based on sense observations. And a lot of science has been confined to human senses. I’m curious if tapping into more basic science research by analyzing different types of senses, for instance, available to animals, may offer breakthroughs down the line. For instance, fish employ the lateral line system to detect pressure gradients in the environment.
When it comes to cosmology, our observations have been using light, because that's what has traveled in space. It is pretty obviously not that useful to ask a dog to sniff the sky or a homing pidgeon to navigate to Alpha Centauri, or something. We've obviously long since passed using only the visible spectrum.
We also recently added gravitational wave detection to our repertoire. I seriously doubt any animals out there are detecting gravitational waves.
I'm not sure how a science based on observing every wavelength of light we can get our hands on, the vast majority of which no animal on Earth can detect or use, and also gravitational waves, is "confined to human senses".
We also recently added gravitational wave detection to our repertoire. I seriously doubt any animals out there are detecting gravitational waves.
I'm not sure how a science based on observing every wavelength of light we can get our hands on, the vast majority of which no animal on Earth can detect or use, and also gravitational waves, is "confined to human senses".
Yes and no. Yes, we're seeing gravity waves and radio waves and gamma rays and near infrared and millimeter wave and neutrinos, and maybe a few others that I forget. We're way past human senses, or any animals.
And yet I keep thinking of a deaf species that runs across Beethoven's Ninth Symphony. They can put an oscilloscope on the pressure waves in the air, so they can "see" what's going on. They can study the different frequencies of vibrations, and they can find patters in the time variation of those frequencies.
But they can't hear it. Hearing Beethoven's Ninth is really different from studying the frequencies with an oscilloscope. They could even hook up a brain scanner to a human listening to it, watch the brain start lighting up, and they still wouldn't understand.
We can gather data via all these different frequencies and modes. And yet I wonder how much we're not getting, not because we don't have the data, but because we don't have the right... something. (I can't even figure out what words to use for that something. The music analogy is the best I can do.)
And yet I keep thinking of a deaf species that runs across Beethoven's Ninth Symphony. They can put an oscilloscope on the pressure waves in the air, so they can "see" what's going on. They can study the different frequencies of vibrations, and they can find patters in the time variation of those frequencies.
But they can't hear it. Hearing Beethoven's Ninth is really different from studying the frequencies with an oscilloscope. They could even hook up a brain scanner to a human listening to it, watch the brain start lighting up, and they still wouldn't understand.
We can gather data via all these different frequencies and modes. And yet I wonder how much we're not getting, not because we don't have the data, but because we don't have the right... something. (I can't even figure out what words to use for that something. The music analogy is the best I can do.)
I actually think there's a bit of an answer to that, in the No Free Lunch theorem. To "experience" Beethoven's 9th Symphony, you need cognitive biases that it can tickle in the way that Beethoven intended. An alien missing those biases won't "get it", but then they'll get things we won't. But there's no solution to having the right biases for everything. All we can do is throw a lot of things at it and hope for the best, and what's more, that's the best we or any alien in the physical universe could do.
(Heck, you don't even need a deaf species. There's a lot of reason to believe that birds don't experience music the way we do, and they're not even strictly speaking "aliens".)
So there's no particular gain to worrying about being limited to "human" senses, because there is no actionable way to "transcend" them in that sense other than by being something other than what you are. It's certain to be true, there's nothing to be done about it that we aren't already doing, and thus, it isn't really an interesting criticism to vaguely suggest that we should somehow be something other than ourselves.
(Heck, you don't even need a deaf species. There's a lot of reason to believe that birds don't experience music the way we do, and they're not even strictly speaking "aliens".)
So there's no particular gain to worrying about being limited to "human" senses, because there is no actionable way to "transcend" them in that sense other than by being something other than what you are. It's certain to be true, there's nothing to be done about it that we aren't already doing, and thus, it isn't really an interesting criticism to vaguely suggest that we should somehow be something other than ourselves.
I wasn't suggesting that we should be other than ourselves - just that, by being ourselves, there are things that we don't "get", even when we can see the data.
> Hearing Beethoven's Ninth is really different from studying the frequencies with an oscilloscope.
I'm not sure that's a good analogy. When you hear Beethoven's Ninth, you're not understanding it any more than someone who drives a car is understanding the car. You can enjoy it. Which is to say, you have an appreciation for its acoustic beauty but that doesn't really have anything to do with understanding it.
Perhaps there is some intelligence that set up the cosmos and they get some aesthetic pleasure from it. And perhaps our experience is too foreign from those being's to get the same pleasure from it but that does not mean that minus that experience we can't understand entirely how it works.
I'm not sure that's a good analogy. When you hear Beethoven's Ninth, you're not understanding it any more than someone who drives a car is understanding the car. You can enjoy it. Which is to say, you have an appreciation for its acoustic beauty but that doesn't really have anything to do with understanding it.
Perhaps there is some intelligence that set up the cosmos and they get some aesthetic pleasure from it. And perhaps our experience is too foreign from those being's to get the same pleasure from it but that does not mean that minus that experience we can't understand entirely how it works.
> Which is to say, you have an appreciation for its acoustic beauty but that doesn't really have anything to do with understanding it.
Beethoven's Ninth has words (at least, the third movement does). If you speak German, you can understand them.
Beethoven's Ninth has words (at least, the third movement does). If you speak German, you can understand them.
Access to higher dimensions? Aliens shaking their heads as we waste enormous amounts of energy to travel through R3 in a straight line instead of taking a short walk in R7.
This makes me think of a quote on humans and science.
Italo Calvino said, "science interests me precisely because of my efforts to escape anthropomorphic knowledge; at the same time, however, I'm convinced that our imagination can only be anthropomorphic".
I'm not sure how to take in this quote - I wonder where humans stand in the progression of science.
Italo Calvino said, "science interests me precisely because of my efforts to escape anthropomorphic knowledge; at the same time, however, I'm convinced that our imagination can only be anthropomorphic".
I'm not sure how to take in this quote - I wonder where humans stand in the progression of science.
Useful note, I get this thought sometimes, too. And you write, “We can gather data via all these different frequencies and modes. And yet I wonder how much we're not getting, not because we don't have the data, but because we don't have the right... something.”
Do you mean some type of “receptor” that we might be unaware of? For instance, data is flowing by but we can’t recognize/capture it?
Do you mean some type of “receptor” that we might be unaware of? For instance, data is flowing by but we can’t recognize/capture it?
We also cavalierly assume that our brains are universal understanding machines. While we have no problem knowing that there are sounds we cannot hear, and light we cannot see, we're reluctant to admit that there are thoughts we cannot think. Concepts which may be true and universal, but which are literally inconceivable to us.
But if you believe the theory of evolution, there is no reason why you should assume that. Our brains evolved to give us a good enough answer, fast enough, enough of the time to give us an edge at surviving. Any ability to truly understand what's truly going on would be purely by accident.
It's a good analogy, although I feel compelled to point out that Beethoven never heard Beethoven's Ninth either, since he was profoundly deaf when he wrote it.
Would the idea of a flatlander being incapable of comprehending 3-space be similar to what you're thinking?
Probably. The flatlander may be able to create a 3-dimensional vector space as a mathematical construct, but still has no clue what it's like to walk around in 3D.
About this:
"It is pretty obviously not that useful to ask a dog to sniff the sky or a homing pidgeon to navigate to Alpha Centauri, or something."
That example might be bad, but there are others that are valid. For instance, in healthy human women, the menstruation cycle seems to be the exact length of the moon's orbit. Is that a coincidence, or do human bodies have a way of gaining data from the moon? If so, what is that data? Maybe the mechanism is as simple as a springy protein that can absorb tidal forces and convert it to an information signal. Or perhaps something novel is going on.
There are potentially a lot we can learn about the universe by making simple observations here on Earth.
"It is pretty obviously not that useful to ask a dog to sniff the sky or a homing pidgeon to navigate to Alpha Centauri, or something."
That example might be bad, but there are others that are valid. For instance, in healthy human women, the menstruation cycle seems to be the exact length of the moon's orbit. Is that a coincidence, or do human bodies have a way of gaining data from the moon? If so, what is that data? Maybe the mechanism is as simple as a springy protein that can absorb tidal forces and convert it to an information signal. Or perhaps something novel is going on.
There are potentially a lot we can learn about the universe by making simple observations here on Earth.
> For instance, in healthy human women, the menstruation cycle seems to be the exact length of the moon's orbit.
That seems to be absolute coincidence. If there was a value in syncing to the lunar cycle it would stand to reason there would be a synchronization with the characteristics of the lunar cycle - ie ovulation on the 14th day or something. As it is, there is no link between when a woman's cycle and the lunar cycle begin, they just happen to occur with the same (ugh) period. I don't know what tidal forces women could be keying into that would result in totally seperate start and end dates.
It's also important to note the 28 days falls on the average, but the range is anywhere from 21 to 35 days for normal women. It's in no way the exact length of the moon's orbit.
That seems to be absolute coincidence. If there was a value in syncing to the lunar cycle it would stand to reason there would be a synchronization with the characteristics of the lunar cycle - ie ovulation on the 14th day or something. As it is, there is no link between when a woman's cycle and the lunar cycle begin, they just happen to occur with the same (ugh) period. I don't know what tidal forces women could be keying into that would result in totally seperate start and end dates.
It's also important to note the 28 days falls on the average, but the range is anywhere from 21 to 35 days for normal women. It's in no way the exact length of the moon's orbit.
When there is any kind of weak forcing function, they synchronize. Artificial light is a new phenomenon. Before, moonlight was extremely important to everyone.
> Maybe the mechanism is as simple as a springy protein that can absorb tidal forces and convert it to an information signal.
Tidal forces don't have periodicity of a month, but change twice a day:
https://oceanservice.noaa.gov/education/tutorial_tides/tides...
"High tides occur 12 hours and 25 minutes apart. It takes six hours and 12.5 minutes for the water at the shore to go from high to low, or from low to high."
To detect the tidal forces in some organism that can't sample the sea level you'd need an organism of an immense size, not something of the size of any animal on the plant today.
> There are potentially a lot we can learn about the universe by making simple observations here on Earth.
We are making observations, but they aren't simple anymore.
It started with simpler methods than today's: there were ancient Greeks (more than 2000 years ago!) who correctly estimated the diameter of Earth and then also quite correctly calculated the distance of Earth to the moon, who haven't had too precise instruments. E.g. Hipparchus:
https://en.wikipedia.org/wiki/Hipparchus#Orbit_of_the_Moon
"According to Pappus, he found a least distance of 62, a mean of 67 1⁄3, and consequently a greatest distance of 72 2⁄3 Earth radii. With this method, as the parallax of the Sun decreases (i.e., its distance increases), the minimum limit for the mean distance is 59 Earth radii – exactly the mean distance that Ptolemy later derived."
We today precisely measure that distance to be 60.32 Earth radii.
Think about that it was more than 100 years before that famous "birth", that is, at least 120 years BC!
Still the bigger advances started when we used the instruments that enabled us to capture more signal than what just our senses without the instruments, or with the most primitive instruments, would. The first was Galileo's use of telescope to discover:
https://en.wikipedia.org/wiki/Galilean_moons
Tidal forces don't have periodicity of a month, but change twice a day:
https://oceanservice.noaa.gov/education/tutorial_tides/tides...
"High tides occur 12 hours and 25 minutes apart. It takes six hours and 12.5 minutes for the water at the shore to go from high to low, or from low to high."
To detect the tidal forces in some organism that can't sample the sea level you'd need an organism of an immense size, not something of the size of any animal on the plant today.
> There are potentially a lot we can learn about the universe by making simple observations here on Earth.
We are making observations, but they aren't simple anymore.
It started with simpler methods than today's: there were ancient Greeks (more than 2000 years ago!) who correctly estimated the diameter of Earth and then also quite correctly calculated the distance of Earth to the moon, who haven't had too precise instruments. E.g. Hipparchus:
https://en.wikipedia.org/wiki/Hipparchus#Orbit_of_the_Moon
"According to Pappus, he found a least distance of 62, a mean of 67 1⁄3, and consequently a greatest distance of 72 2⁄3 Earth radii. With this method, as the parallax of the Sun decreases (i.e., its distance increases), the minimum limit for the mean distance is 59 Earth radii – exactly the mean distance that Ptolemy later derived."
We today precisely measure that distance to be 60.32 Earth radii.
Think about that it was more than 100 years before that famous "birth", that is, at least 120 years BC!
Still the bigger advances started when we used the instruments that enabled us to capture more signal than what just our senses without the instruments, or with the most primitive instruments, would. The first was Galileo's use of telescope to discover:
https://en.wikipedia.org/wiki/Galilean_moons
Some people have noticed that the amount of light at night, absent artificial lighting, varies markedly by the month.
I know that my cats notice. Indeed corals worldwide notice, despite lacking eyes.
I know that my cats notice. Indeed corals worldwide notice, despite lacking eyes.
Makes sense, and agree with the last point, “I'm not sure how a science based on observing every wavelength of light we can get our hands on, the vast majority of which no animal on Earth can detect or use, and also gravitational waves, is "confined to human senses"”. Thanks for the explanation.
What aren’t we using from the animal kingdom? We create sensors that are extra human. Infrared etc...
Maybe this is an unknown unknown problem. We can’t develop technology for senses we do not know about and so on.
Maybe this is an unknown unknown problem. We can’t develop technology for senses we do not know about and so on.
What kind of senses available to animals are there that we should be using for science?
Also I'm not entirely sure what you mean that we're confined to "the 5 senses". First, humans have way more senses. Second, I don't think it's confining ourself to build technology that converts something we can't sense (like gravitational waves) into something we can (like a spreadsheet).
Also I'm not entirely sure what you mean that we're confined to "the 5 senses". First, humans have way more senses. Second, I don't think it's confining ourself to build technology that converts something we can't sense (like gravitational waves) into something we can (like a spreadsheet).
One way to think of scientific instruments: like telescopes, microscopes, voltmeters is that they are extensions of our senses.
But the reality of them is that they are not extensions of our senses, so much as compressors of experience. That is they map a broader reality into our limited sensate experience. When we use them we have to remember that the map is not the territory, and we have to be especially careful about artifacts they may introduce.
I agree, thanks for the note.
We have no better access to the sense data of the Ampullae of Lorenzini in a shark than we do to the signals recorded by a radio telescope. Arguably, our access is worse for the shark than for the telescope.
Ultimately, no matter what we use to record the data (animal or instrument), we can only access the results through our 5 senses.
Ultimately, no matter what we use to record the data (animal or instrument), we can only access the results through our 5 senses.
All said and done, the current state of cosmology (whether one falls in with mainstream theories or not) is a mess. It has so many addendums, codicils & caveats that one has to be almost a type of lawyer of physics to be able to navigate it.
We await our new Einstein. Our new Heisenberg. Our elegant theory of everything; or as one science writer put it: The universe on a T-shirt.
Here’s an article from Rob Sheldon, who worked on ROSETTA. He is less timid than Ekeberg:
https://uncommondescent.com/intelligent-design/rob-sheldon-t...
https://uncommondescent.com/intelligent-design/rob-sheldon-t...
@astro123
Sorry my comment uploaded before I was done. It is an error to state that there is evidence for dark matter. There is no evidence for it other than that as a hypothesis it adds support to a larger cosmological theory; that of the so-called Big Bang. But that is basically a circle in the proof. A tautology.
What about the Bullet Cluster?
If the Bullet Cluster had offered not hypothetical but empirical, incontrovertible evidence for Dark Matter, at this juncture we wouldn’t even be calling it Dark Matter anymore.
It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe.
Is it really? Have people formulated specific break downs, then gone to look for evidence?
Is it really? Have people formulated specific break downs, then gone to look for evidence?
A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248). That does indeed refute the assumpion that dark matter is everywhere, but that is not an assumption anyone makes and is not part of any relevant theory of dark matter. On the contrary, the existence of galaxies like that is generally seen as one of the strongest arguments for the existence of dark matter as an independent, if elusive physical entity.
Couldn't it just as easily mean that our predictions based on general relativity are wrong?
Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or
2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out.
It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're still allowing yourself to think that the theory is correct. How is this scientific?
Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or
2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out.
It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're still allowing yourself to think that the theory is correct. How is this scientific?
No, the only consistent explanation for both the overwhelming majority of galaxies as well as the few outliers is general relativity and independent dark mater. All other theories that make testable predictions (modified newtonian dynamics or MOND seems to be the only class that is not completely add odds with almost all observations) cannot explain the behaviour of those galacies that are as big as other galaxies but rotate wih a different speed. But the difference is easily explained with different amounts of dark matter in the galaxies, and the bullet cluster cited elsewhere in this thread give a plausible explanation of how these galaxies might form.
It's not that simple. It's not like a) Some galaxies fit predictions, b) Some do not, and we add unknown dark matter.
It's that when they do not fit predictions, there is a single parameter (the mass of dark matter) that does explain its behavior, whose model is that of a weakly interacting gas halo. So dark matter tries to fix things in a very precise way, it's not an arbitrary curve fitting exercise.
Now whether there is really weakly interacting matter out there or some other explanation is valid is still an open question afaik; but the evidence is quite strong so far.
It's that when they do not fit predictions, there is a single parameter (the mass of dark matter) that does explain its behavior, whose model is that of a weakly interacting gas halo. So dark matter tries to fix things in a very precise way, it's not an arbitrary curve fitting exercise.
Now whether there is really weakly interacting matter out there or some other explanation is valid is still an open question afaik; but the evidence is quite strong so far.
> Now whether there is really weakly interacting matter out there
Not "out there". It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day.
Not "out there". It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day.
> It's supposed to be >80% of the matter of the universe. We supposedly are eating some every day.
It's >80% of the average density of the matter in the universe. But that's an average over all of the universe. On the scale of our planet, or of the solar system, that density is negligible--as in "30 orders of magnitude smaller than the density of the stuff you eat" negligible.
It's >80% of the average density of the matter in the universe. But that's an average over all of the universe. On the scale of our planet, or of the solar system, that density is negligible--as in "30 orders of magnitude smaller than the density of the stuff you eat" negligible.
> Couldn't it just as easily mean that our predictions based on general relativity are wrong?
No, because general relativity with dark matter (and dark energy--the best current cosmological model we have) predicts a lot more than just galaxy rotation curves. And the whole point of the model is to explain all the things it makes predictions about, not just one.
No, because general relativity with dark matter (and dark energy--the best current cosmological model we have) predicts a lot more than just galaxy rotation curves. And the whole point of the model is to explain all the things it makes predictions about, not just one.
Not necessarily. This great video from PBS Spacetime is a fairly detailed, but good for a 'nearly' layman on the findings in depth. https://www.youtube.com/watch?v=5t0jaE--l0Y
A discussion on how a galaxy could be missing dark matter - or how it could be separated from a galaxy
A discussion on how a galaxy could be missing dark matter - or how it could be separated from a galaxy
Well... assuming that the local rules are the same as the rules billions of light-years away is an assumption, based on a philosophical presupposition that the rules are uniform. What probability should we assign to that assumption? 100% in the absence of evidence to the contrary? Or should we reserve some skepticism, remembering that it is an assumption?
Your question is reasonable: Have people formulated specific breakdowns, and gone looking? But it's also unreasonable. An assumption shouldn't necessarily be treated beyond plausible doubt until we can prove it wrong.
Your question is reasonable: Have people formulated specific breakdowns, and gone looking? But it's also unreasonable. An assumption shouldn't necessarily be treated beyond plausible doubt until we can prove it wrong.
"Have people formulated specific breakdowns, and goon looking?"
They have. Considerable effort has been expended trying to detect changes in various constants related to light, including speed but also some other things. It is expected that if constants were changing, spectra would change as well. So far as I know, all those results have been negative, but it's not for lack of trying. Similar arguments can be deployed for the nuclear forces as well w.r.t. spectrum, rates of fusion, various things you'd be able to observe in certain types of supernovae, etc.
One of the things I don't like about this genre of articles is that it's typically quite mistaken, if not outright disingenuous, about the current state of cosmology. From what I could see, the idea that cosmologists are all stodgy old fogies brought up in a paradigm of the Big Bang and who won't entertain any other thoughts is diametrically opposed to the truth. To my eyes, the field is a bubbling cauldron of various exotic ideas and attempts to resolve all these issues. There's no lack of theories in cosmology and attempts to resolve these issues, including many quite radical ones (the holographic principle, changing constants over time, heck even "Dark Energy" is quite radical in many ways even if it is also the accepted theory at the moment).
What we lack are theories that explain all the observations. Dark matter is favored not because it's the only idea that anyone has come up with, but because it's still the one that best fits the facts. (As PBS Space Time pointed out last week, ironically, the galaxies recently discovered to not contain dark matter are themselves quite strong evidence dark matter must exist: https://www.youtube.com/watch?v=5t0jaE--l0Y , because almost all other theories to explain galactic rotations are based on characteristics that can not vary by galaxy like matter distributions can. "MOND", for instance, is not "MOND, except in these two galaxies".)
If you can solve all these problems, as near as I can tell, you'll be celebrated, not shut down by the old fogerati. But be prepared for your theory to need to cover a lot of existing observations; we're centuries past "Well, what if gravity just worked differently?" or "What if the constants aren't constant?" You're going to need a great deal more detail than that.
They have. Considerable effort has been expended trying to detect changes in various constants related to light, including speed but also some other things. It is expected that if constants were changing, spectra would change as well. So far as I know, all those results have been negative, but it's not for lack of trying. Similar arguments can be deployed for the nuclear forces as well w.r.t. spectrum, rates of fusion, various things you'd be able to observe in certain types of supernovae, etc.
One of the things I don't like about this genre of articles is that it's typically quite mistaken, if not outright disingenuous, about the current state of cosmology. From what I could see, the idea that cosmologists are all stodgy old fogies brought up in a paradigm of the Big Bang and who won't entertain any other thoughts is diametrically opposed to the truth. To my eyes, the field is a bubbling cauldron of various exotic ideas and attempts to resolve all these issues. There's no lack of theories in cosmology and attempts to resolve these issues, including many quite radical ones (the holographic principle, changing constants over time, heck even "Dark Energy" is quite radical in many ways even if it is also the accepted theory at the moment).
What we lack are theories that explain all the observations. Dark matter is favored not because it's the only idea that anyone has come up with, but because it's still the one that best fits the facts. (As PBS Space Time pointed out last week, ironically, the galaxies recently discovered to not contain dark matter are themselves quite strong evidence dark matter must exist: https://www.youtube.com/watch?v=5t0jaE--l0Y , because almost all other theories to explain galactic rotations are based on characteristics that can not vary by galaxy like matter distributions can. "MOND", for instance, is not "MOND, except in these two galaxies".)
If you can solve all these problems, as near as I can tell, you'll be celebrated, not shut down by the old fogerati. But be prepared for your theory to need to cover a lot of existing observations; we're centuries past "Well, what if gravity just worked differently?" or "What if the constants aren't constant?" You're going to need a great deal more detail than that.
> Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere.
We have found evidence of a few galaxies without DM. But most galaxies provide strong evidence for DM - https://en.wikipedia.org/wiki/Galaxy_rotation_curve
> For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm
Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.
> Historically, Newton's physical laws made up a theoretical framework that worked for our own solar system with remarkable precision. Both Uranus and Neptune, for example, were discovered through predictions based on Newton's model. But as the scales grew larger, its validity proved limited.
Actually some of the earliest evidence for GR came from the orbit of mercury https://en.wikipedia.org/wiki/Tests_of_general_relativity
> It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. And if that were the case, today's multilayered theoretical edifice of the big bang paradigm would turn out to be a confusing mix of fictional beasts invented to uphold the model
This is something that people are working on! This is a hypothesized source of DE. However, disproving GR does nothing to disprove the big bang.
> Today's space telescopes provide no direct view of anything
I have no idea what that means. They literally observe the sky...
There is a ton of work to do: finding what DM is, finding what DE is, finding whether GR is correct. But I'm not sold that the author knows what he is talking about...