The Webb Telescope further deepens the Hubble tension controversy in cosmology
quantamagazine.org
quantamagazine.org
The slides are delightfully visual and comprehensive yet terse, walking you up the rungs of the cosmic ladder from the Earth through the moon, sun, and beyond. I can almost guarantee you’ll learn something new and fascinating.
In the process of writing this, I thought "Surely we have launched a satellite pair that can take parallax measurements at similar times in different places!" They could range off of each other with Time of Flight, be positioned much further apart than a few AU, and take parallax star measurements at more or less the same time without atmospheric distortion, but it doesn't seem like we have. Both Hipparcos and Gaia were satellites that were deployed to measure parallax, but not as a pair. My reading suggests they used multi-epoch astrometric observations (speed ladder dependent) to generate their parallax measurements and it seems our current parallax and star catalogues are based on the measurements taken by these two satellites. New Horizons got the most distant parallax measurements by comparing simultaneous* earth observations, but it was limited to Proxima Centauri and Wolf 359, far from a full star catalogue.
I would love if someone more knowledgeable can steer me towards a paper or technique that has been used to mitigate the cosmic distance ladder's dependency on this cosmic speed ladder. Regardless of how certain we think we are of our velocity through the universe, it seems to me that sidestepping that dependency through simultaneous* observations would be worthwhile considering how dependency laden the cosmic distance ladder already is.
[1] https://en.wikipedia.org/wiki/Milky_Way
[2] https://arxiv.org/pdf/astro-ph/9312056
* Insert relativity caveat here for the use of "simultaneous". What I mean in this context is more simultaneous than waiting months between measurements.
The more I read about this, the more it feels like phlogiston theory[1]. Works great for describing observations at first, but as more observations are made, some contradict the theory, so exceptions are made for these cases (phlogiston must have negative mass sometimes/there must be extra matter or energy for galaxies to spin as fast as they do), and then finally someone discovers something (oxygen/???) that explains all observations much simpler and requires no weird exceptions.
Not possible. Redshift is not the only observation we have. The totality of all the observations we have cannot be explained in any other way than an expanding universe.
> How can we be so sure it's space that's expanding, not time?
Our best current model does not say "it's space that's expanding, not time". It says that in one particular frame (the comoving frame), the overall spacetime geometry can be described using a "time" that always corresponds to the time of comoving observers and a "space" whose scale factor increases with that time.
> The more I read about this, the more it feels like phlogiston theory
This is an extremely unjustified comparison. Phlogiston theory never accounted well for actual observations.
> as more observations are made, some contradict the theory
None of the observations being discussed contradict the general model of an expanding universe. They only pose problems for the indirect methods we use to convert our direct observations into model parameters.
> Not possible.
In all honesty, Cosmology rests on the principal that physics is the same in all directions, over all translations, and over time translation. While this is a good assumption (good luck testing alternatives!!). There are a variety of papers exploring the topic of how much these assumptions would need to be violated to mirror observations.
A good example being
what if the electron was more massive in the past?
All Redshift would then be explained away ;)
P.S.
There are very good reasons to believe that the electron was not more massive in the past.
That the laws of physics are the same. That doesn't mean the geometry of spacetime is the same or that the configuration of matter and energy is the same.
> There are a variety of papers exploring the topic of how much these assumptions would need to be violated to mirror observations.
What papers? Do you have any references?
> A good example being
what if the electron was more massive in the past?
All Redshift would then be explained away ;)
What is your basis for this extraordinary claim?
> Redshift is not the only observation we have.
What else is there?
No, that's not what always happens with scientific theories. For example, Newtonian mechanics is still used, even though we now know it's not exactly correct; it's an approximation to relativity that works reasonably well for weak gravitational fields and relative speeds that are small compared to the speed of light.
The "mechanics" that Newtonian theory (and its predecessors, Galilean mechanics and Kepler's model of the solar system) replaced were indeed replaced--nobody uses Aristotelian physics or Ptolemaic cosmology any more, not even as approximations. But that does not always happen.
Yeah, about that... A not-insignificant number of people would have a hard time explaining why the moon has phases, let alone be able to do something like explain the sidereal day.
The relatively CMB, which points to a past when the universe was more homogenous than it could/should be given SoL limitations on communication between distant locations. The only answer is that those locations were at some point in the past much closer together.
Surely there are infinite other possible explanations that fit the finite number of data points available to us. Probably what you meant is that the expanding universe theory is the simplest of them all and creates less problems then others.
If you think there are others, please exhibit one.
> Probably what you meant is that the expanding universe theory is the simplest of them all and creates less problems then others.
There are no other theories that I'm aware of that account for all the data we have, even approximately.
I could easily do that (god tinkering with our measurements? we live in a simulation?) but explanations by themselves are worthless. Any set of facts can be "explained" but it doesn't really help.
The science is concerned with theories that don't just explain known facts and measurements but also predict new ones. These are also known as falsifiable theories because a theory is falsifiable IFF it predicts at least one new observation that can be actually made and tested.
Now even these can obviously be constructed ad infinitum. For your question of alternatives to expansion, take a theory from the same field (e.g. tired light), then take facts it doesn't fit and make specific ad-hoc carve-outs for these facts in the theory. Sure it makes it ugly and complex but it remains a scientific falsifiable theory. Furthermore this exact things happens very often in the scientific community because theories don't fall immediately when the first contradiction is found. They only fall when a better theory appears to supersede them and until then they just develop a "protective belt of ad-hoc assumptions" as Lakatos called it. No need to mention that the same thing will happen to the "better theory" in due time.
I write all of this not because I have a good cosmological theory sitting in my closet but rather because your statement "The totality of all the observations we have cannot be explained in any other way than an expanding universe" is outright false. As I show above it not only can be explained in an infinite number of ways, but you can also construct and infinite number of scientific theories that fit the totality of observations. Because this "totality" is alas finite.
This reminds me of my school math teacher who once told me that "the sequence 1, 2, 6, 24, 120, 720 cannot be explained other way than by n!". A pity I didn't know about Lagrange Polynomials at that age and had to spend the whole evening to construct a fitting polynomial by hand.
For example, to simulate a galaxy one should use a model based on General Relativity. But mathematics behind GR is too complex to allow simulations on the scale of the galaxy even with all that modern computation power. So instead of GR the calculations use Newtonian mechanics with minimal corrections for the light speed limit. Plus there are a lot of other simplifications like replacing star systems with hard balls that reflects when hit each other with no notion of matter transfer or ejection in the process.
Then we see that the simulation does not fit data. A typical explanation that is used is that of dark matter hypothesis. But this is unjustified.
We have no proof that numerical simplifications are mathematically valid and do not lead to a big error on a galactic scale. Moreover, there were recent papers that tried to account at least for some effect of General Relativity. Apparently it was enough to explain at least some effects previously attributed to the dark matter.
So it can be that the dark matter is just an artifact of inaccurate simulations.
However, generically, these extensions tend to have an under-determination problem frustrating attempts to arrive at a unique spacetime for a given distribution of matter or a unique distribution of matter which can exist in a given spacetime (or both problems). That makes them less attractive than GR, or even possibly outright unsuitable bases for initial-values formulations (and thus are unlikely to overthrow numerical relativity soon).
If everyone like you attempts to rail road the imaginative process at the beginning of hypothesis formation, then we'll never get to the point of being able to exhibit one, should one be possible.
The demand for rigour at this point in a discourse - which was pretty clearly signalled by the commenter to be offered at a stage prior to substantive hypotheis formation - just shuts down the imaginative process. It's not constructive.
I'm a mathematician by education, and I cannot tell you how many people insist on things like 0.999... < 1 without an understanding of (a) what the left side of that expression even means, (b) what a real number is, or (c) what basic properties the real numbers have. Going "no, you're wrong, and it would take me a couple of full lectures to explain why but trust me we're pretty sure about this" is a reasonable answer to that, provided that you have indeed established that to your own satisfaction, at least.
From Wikipedia, an intuitive explanation of an elementary proof:
> If one places 0.9, 0.99, 0.999, etc. on the number line, one sees immediately that all these points are to the left of 1, and that they get closer and closer to 1. For any number that is less than 1, the sequence 0.9, 0.99, 0.999, and so on will eventually reach a number larger than . So, it does not make sense to identify 0.999... with any number smaller than 1. Meanwhile, every number larger than 1 will be larger than any decimal of the form 0.999...9 for any finite number of nines. Therefore, 0.999... cannot be identified with any number larger than 1, either. Because 0.999... cannot be bigger than 1 or smaller than 1, it must equal 1 if it is to be any real number at all.
And then:
> The elementary argument of multiplying 0.333... = 1/3 by 3 can convince reluctant students that 0.999... = 1.
To put another way, there is a big difference between saying some specific alternative theory is wrong/unlikely/bad, and claiming there exists no alternative theories at all regardless of quality.
If we mean 9×10^-i for i from 1 to infinity, then let's just state so. Let's not blame people to interpret towards other direction when they are provided misguiding hints.
Regarding infinity, there is a constructive proof that it doesn't exists which work perfectly provided that there is an infinite amount of resources allocated to it's execution.
My point is that it's not closed-minded of me if I fail to provide a complete answer to someone making such a claim, particularly if that person hasn't done any of the research or rigor to handle what is - by the standards of an expert - a pretty easy question to answer. Outsiders can occasionally result in great insights, but they do that through very hard work, not from ten seconds of thinking about a field they haven't learned anything but the pop-science version of.
Most of the theories being speculated about in this thread are veering into "not even wrong" territory, in that they're not even necessarily well-defined. When you're talking about cosmology you'd better bring your general relativity game, which means you better bring your differential geometry game, which means you better have a graduate-level mathematics education. I have a graduate-level mathematics education and on a good day I could half explain to you what a metric tensor is and what the hell it has to do with curvature ("it's, uh, it's kinda like a Jacobian I guess, except the dx and dy are local vectors that can't be translated globally around the space").
Without those tools, you don't even have meaningful notions of what "distance" even is on a cosmological scale, much less how it changes with time! It's like speculating about biology without knowing what a protein is, or speculating about computer science without knowing what a for loop is. It's just not going to get you anywhere.
For example, we know that 1/3 = 0.333...
3 * 1/3 = 3 * 0.333...
1 = 0.999...
You can also do it with subtraction. For example, 1 - 0.999... = x. Assuming x is greater than 0, then it should evaluate to 0.000...1.
But we can't have the digit 1 after an infinite number of zeros. If there truly were a "1" after infinite zeros, it implies reaching the end of infinity, which is a logical contradiction. So x can't be greater than 0.
In this context, the notation 0.999... does not represent a process. It represents a fixed number.
Which number? Well, if you reason through it you'll find that it has to be the same number as that represented by the notation 1.
An insight that is crucial (and pretty obvious in hindsight, though many people seem not to be exposed to it) is to distinguish between a number and its representations. "1" is not a number, it is merely the representation of a number. And numbers have many different representations. As a member of this forum, you can probably appreciate that "12" and "0xC" are two different representations of the same number. In the same way, 0.999... and 1 are different representations of the same number.
0.999...[forever] is not a sequence, it is a number. Numbers have values, they don't approach things. The misleading part is that 'forever' is not something about evolution or the passage of time. It's not 'happening' or 'sequential' like the sequence. There is no 'and then another 9'. All the 9s are really there, at once. And it is closer to 1 than any term in the sequence. Since the sequence gets closer and closer to 1, converging to it asymptotically, 0.999...[forever] cannot differ from 1; if it did the sequence wouldn't converge.
.3… + .3… + .3… = .9… = 1
If not then it's logical to conclude they wind up at the same "place", that is, the same number. Or equivalently: it can't have any other value besides 1.
If you care about such things, then you're a mathematician.
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First, you're making a category error. "0.9999..." is a single value, not the sequence of values 0.9, 0.99, 0.999, 0.9999... Single values cannot "asymptotically approach" anything, any more than the value 2 or the value 7 can asymptotically approach anything. It's just a number like any other.
To show what value 0.9999... takes on, we need to do two things. First, we need to show that this notation makes sense as a description of a real number in the first place, and second, we need to show what that real number is (and it will happen to be 1).
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So, why is it a real number?
Well, remember what we mean by place value. 0.9 means "0 ones, 9 tenths[, and zero hundredths, thousandths, and so on]". 0.99 means "0 ones, 9 tenths, 9 hundredths, [and zero of everything else]". Another way to say this is that 0.9 is the value 0 * 1 + 9 * 0.1 [plus 0 times 0.01, 0.001, and so on], and that 0.99 is the value 0 * 1 + 9 * 0.1 + 9 * 0.01 + [0 of everything else].
What that means is that if 0.9999... means anything, it means 9 tenths, plus 9 hundredths, plus 9 thousandths, plus 9 ten-thousandths, plus 9 hundred-thousandths, and so on and so forth forever. In other words, 0.9999... is the value of an infinite sum: .9 + .09 + .009 + .0009 + ...
Infinite sums, in turn, are by definition the limit of a sequence. This is where that "asymptotic" thing comes back, but notice the distinction. 0.9999... is not the sequence, it is the LIMIT OF the sequence, which has a single value.
To show that it's a real number, then, we need to show that the limit of the sequence 0.9, 0.99, 0.999, 0.9999... does in fact exist. But this sequence is clearly increasing, and it is clearly not greater than 1, so we can (among other things) invoke the Monotone Convergence Theorem [1] to show that it must converge (i.e., the limit exists). Alternately, you can think back to your algebra 2 or calculus classes, and notice that this is the geometric series [2] given by sum 9 * 10^-n, and this series converges.
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Now, why is it equal to 1?
Well, there's a few ways to prove that, too. But the simplest, in my book, is this: given any two different real numbers x and y, I'm sure you would agree that there is a value z in between them (this is not a difficult thing to prove rigorously, provided you've done the hard work of defining the real numbers in the first place). The average of x and y will do. But we can flip that statement around: if there is NOT a value between two real numbers, those two real numbers MUST be equal.
In more symbolic terms, we claim that for all real numbers x and y such that x < y, there exists z such that x < z < y. So if there ISN'T such a z, then we must not have x < y in the first place. (This is the contrapositive [3], if you're not up on your formal logic.)
So consider the values of 0.9999... and 1. What value lies between them? Can you find one? As it turns out, no such value exists. If you pick any real number less than 1, your 0.99[some finite number of nines]9 sequence will eventually be bigger than it - and therefore, since the sequence is increasing, its limit must be bigger than that value too.
Since there are no numbers between 0.9999... and 1, they must be equal.
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[1] https://en.wikipedia.org/wiki/Monotone_convergence_theorem [2] https://en.wikipedia.org/wiki/Geometric_series [3] https://en.wikipedia.org/wiki/Contraposition
But the expansion of the universe has been thoroughly studied for over a century. We're past the brainstorming phase.
I generally think people should brainstorm to generate ideas and then filter them down. And it's true that filtering too early can significantly decrease the quality of ideas.
And it's also true that in a place like Hacker News there will be smart people from all sorts of backgrounds getting to experience the joy of exploring a new topic that they're not fully up to speed on yet.
The risk though is that somebody who thoroughly understands the field is reading your comment. So for that reason I think it's a good practice to always be aware that technical fields we're not expert in are usually more subtle than we initially think.
Explaining is neither hard nor useful and it's not what science is normally concerned with. The goal is to predict new observations not to explain known ones.
I learn things all the time by wondering if somebody else is right. Much better than just thinking everything is simply the way I think it is now.
Even if you know somebody is wrong, talking about it is absolutely harmless.
Part of being an expert is knowing how to filter out the noise so that you can actually get some work done.
If one wanted to deal with noise all day, they'd join SETI. Or parliment.
If someone has a novel theory, let them come up with evidence to support it, and clear identification of how the theory can be invalidated.
That's not closed-mindedness; that's pragmatism. Could they actually be right? Yes, in the same way that a baby could beat Muhammad Ali - but you won't see anyone lining up to buy tickets.
You only have so much time in your life, so no need to waste it on peoples' 10-second "theories", like "How about achieving faster-than-light communication by stuffing so many photons down the fibreoptic cable that they "push" each other faster?". Some ideas are just plain dumb and obviously not worth a trained person's time.
> If someone has a novel theory, let them come up with evidence to support it, and clear identification of how the theory can be invalidated.
Ok, sure, but you can’t really be coming to _Hacker News_ expecting the latter, or none of the former, so it’s a moot point and poor expectations.
The original commenter I’m replying to, taken at their word, is ready to dismiss anything somebody says, regardless of merit with no further discussion, just because they think there’s “no way” that person could be right. Which is hilariously close-minded way to conduct oneself.
> The issue is that these physics threads always end up the same, with commenters having only popular-level background offering suggestions they came up in five minutes
… is this really an issue?
I speculate you’ve taken something you don’t want to see personally and dressed it up as “the problem” when you could instead just find a way to be okay with it.
But maybe there’s something genuinely problematic with that behavior which I don’t know about.
On the other hand, who cares? This is a random internet forum, not the Proceedings of the National Academy of Sciences, so maybe there is no such thing as a proper response?
For now, we dont know any other way to explain than to say it expands, except maybe imaginative fantasies from amateurs on Hackernews, but does it count ?
I looked it up on the Wikipedia page for Exotic Matter and there isn't much exploration or tested theories on it.
One easy process for generating infinite explanations that fit a finite number of data points is taking the simplest theory you have, and adding extra rules that don't affect any of the existing data points.
e.g., if the standard explanation for observations like red shift, CMB, the abundance of light elements, etc. is H² = (ȧ/a)² = (8πG/3)ρ - kc²/a² + Λc²/3, One alternate explanation that fits all the data is H² = (ȧ/a)² = (8πG/3)ρ - kc²/a² + Λc²/3 + T, where T is the number of teacups in the asteroid belt. No observation has yet been made which would falsify this theory, and it fits the data just as well as the standard explanation. We reject it on the grounds of parsimony, not falsification.
One can construct such alternative theories quite easily: Everything is exactly as the "expanding universe theory" predicts except in a phone booth sized volume in a specific part of space 10 lightyears away from Earth where the universe is contracting.
Does not explain anything, and it is not testable in any practical sense. So it is not a good theory in any way, but it is a different one and it matches all the current observations.
Benevolent giant omnitech space squid manipulate EM radiation incident on the solar system to fool our primitive meat brains and sand computers into thinking we're alone in the universe so we don't go venture our and embarrass our local cluster.
See? There exist infinite theories explaining any set of data points. Parsimony, choosing the simplest theory that explains the facts, is what lets us make progress understanding and predicting the world around us. It's hard to predict space squid.
Sure, it is a hypothesis, but thanks to the Scientific Method the majority of people with knowledge in the field knows its most likely BS.
Going the same "it can be for ANY reason, guys!" in any field, will not get you much far, regardless if you feel justified in your ignorance or not.
Of course not. The point is logical correctness: as a matter of logic, infinite theories explain any set of facts. Are almost all of these theories useless? Of course. We should restrict our attention to plausible theories.
But how do we decide which theories are plausible? We look for the ones that require the fewest assumptions.
"That is like saying computers run because they want to, and only make us perfect the CPU, and secret processes inside it, to fool us into thinking we have a say in whether a computer will run."
I am going to quietly turn off my computer.
I am just thinking about Steven Wolfram's causal networks.
That's not a theory, nothing has been explained, merely further convoluted.
It’s not a scientific theory though. Which is a super important distinction in this discussion
Isn't it the case that we don't actually know if the universe is expanding, we only know that from our POV things are moving away from us and from each other, based on models and observations that are approximations at best?
In that frame an expanding universe seems to be the simplest and more elegant solution, but it's entirely possible it's not the correct one.
for example: what if, on the antipodes of the universe (assuming something like that exists), things appear to move closer to the relative POV? we'll never know
If someone has a theory that incorporates "the totality of all observations" then physics is over. Redshift explains most observations, no other concept even comes close, but there are certainly things out there that remain unknown that are not explained by redshift. Dark energy is such a monumental observation that every theory in cosmology must remain caveated.
Well..? What are those other observations that point to expansion?
The apparent brightness and apparent angular size of distant galaxies, and more importantly, the relationship between the three observables of redshift, apparent brightness, and apparent angular size. No known model other than the expanding universe predicts the actually measured relationship between those three observations.
https://en.wikipedia.org/wiki/Angular_diameter_distance
You know how distant objects appear smaller, well in an expanding universe that isn't completely true, very distant objects start looking bigger again. Roughly speaking this happens because the distance between paths different photons take to get to us gets stretched by the expansion.
Theres also the very obvious observation of the cosmic microwave background, which isn't explained by any non-expanding universe model.
The problem with that is that, if the Universe had remained the same size and has the finite age it appears to have, there would not have been time for information from the "north" side of our observable Universe to reach the "south" side. After all, the "north" side's light is only just now reaching us, at the center of our observable Universe, and would have to travel a very long way again to reach the south side. In cosmological/relativity terms, we say they're not causally connected.
The obvious explanation for this is that the early Universe expanded from a very small region that was causally connected for long enough to reach thermal equilibrium, and then expanded. So while the "north" side of the observable Universe and the "south" side of the observable Universe cannot communicate from their current positions (and in an expanding Universe will never be able to do so again), they were able to communicate in the past for long enough to establish equilibrium.
Without expansion, you need a way for two patches of sky that have never been able to communicate with one another to somehow "agree" to be the same temperature. And that's pretty hard to do.
No.
“universe appeared everywhere at once at exactly same temperature” Same level of obviousness, if not more.
For some reason a disclaimer is mandatory these days: I am not saying I know more than cosmologists, just that inflation is nowhere near the “obvious explanation” territory.
I wanted to address this in a few ways: 1. The speed of light is absolutely invariant,
however the space it travels through, can not only be varient, but it can be varient in ways that we are failing to understand In two ways, one way is that we are reaching to understand it, and the other is that we may never understand it.
Is the speed of atoms invarient? I.e.is the temperature invarient?
Occams razor is one of the most powerful tools along with the belief in the both the elegance of the universe, and it's nature to make things very tricky to uncover that elegance.
There are some very deep thinkers here.
> Because the universe is expanding, a pair of distant objects that are now distant from each other were closer to each other at earlier times. Because the speed of light is finite, the light reaching us from this pair of objects must have left them long ago when they were nearer to one another and spanned a larger angle on the sky.
No, it isn't. I explicitly described two other direct observations that are not redshift.
> when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle.
No, they don't. Redshifts of distant objects are directly observed. We don't need a "standard candle" to measure them.
Observations of apparent brightness are used to estimate distances to objects by comparing apparent brightness to the absolute brightness of a "standard candle" that is the same kind of object. However, such distance estimates are model-dependent; before they can even be made, the model parameters first have to be estimated using the observed relationship between redshift, apparent brightness, and apparent angular size.
> And regardless of whether you call it redshift or the relationship between redshift and something else, it would be impacted by a change to redshift.
I have no idea what you mean here.
How do you know the object is distant? (notion being challenged “more redshift -> more distance”)
Please answer. Thanks for the patience.
In particular it doesn't explain observed reductions in surface brightness (expansion has the effect of "defocusing" collimated light). And it doesn't explain observed time dilation effects.
Sci-fi already grants alternative physics to enable FTL and other magic. What about hard sci-fi, but wrong-hard sci-fi?
Extra credit: go back to Zeno and all motion is paradoxical, what would you even do in the game?
> Flight of Nova is a simulator based on newtonian mechanics in which you control spacecraft in the Noren star system. You fly multiple types of spacecraft doing transport and search missions in an environment with realistic aerodynamics and orbital physics.
Orbiting doesn't require power. Even a satellite in a very low orbit only needs a slight boost once in a while to counter the drag.
"According to The Original Series (TOS) writers' guide, the effective range of a transporter is 40,000 kilometers."
Not to mention contradicting the laws of conservation of energy and momentum.
Fritz Zwicky attempted to propose a mechanism of tired light that was caused by Compton scattering off of the intergalactic medium. But these kinds of scattering mechanisms produce far too much blurring in the expected images of distant galaxies and galaxy clusters.
No, what we know is that there is no invariant global concept of "energy" at all except in a special class of spacetimes (the ones with a timelike Killing vector field), to which the spacetime that describes our universe as a whole does not belong.
However, "tired light" (at least the versions of it that aren't ruled out the way the Zwicky model you describe was) violates local energy-momentum conservation, which is a valid conservation law in GR (the covariant divergence of the stress-energy tensor is zero).
I am always entertained when some nonsense I learned actually has something to do with the real world.
I have an interesting addition to it:
Time dilation could be that going very fast in the space makes you relatively faster in one direction.
The thing is, atoms also have to travel; so the atoms (and matter in general) have a slightly longer distance to travel, to achieve the same chemical reaction. Which means interactions between atoms is slower, giving illusion of a slower time due to slower inter-atoms reactions.
Though the phrasing seems a bit ambiguous. Could you put some math behind those words?
As an obvious example, doppler shift often needs to be accounted for to communicate with spacecraft.
But that is not what our best current model of the universe actually says. Our best current model of the universe says that the observed redshift of a distant object tells us by what factor the universe expanded between the time the light was emitted and now (when we see the light). Viewing it as a Doppler shift is an approximation that only works for small redshifts (much less than 1).
But without looking at the direct rules of the system, this is the best you can do.
It’s not like you can just open the source code of the universe. You observe and make a theory that explains the observations, then the theory holds at least until a new observation contradicts the theory.
Is the current theory wrong? Maybe. But everything can be wrong and the world is always welcome to hear a new theory that completely explains all current observations.
But to just say a theory is wrong without providing a completely explained new one adds nothing.
It certainly does. You don't have to know how something works to be able to know how it doesn't work. And there is value in knowing how something doesn't work, even if you don't know how it works.
For instance, our observations imply both general relativity and quantum field theory are necessary to model various aspects of the world. That’s an example of a Y. The only known X that’s ever been discovered that can encompass all aspects of that Y at all energy levels is string theory. Yet we are rightly careful to assume string theory is correct and enshrine it into the core body of scientific consensus. That does not mean we cannot or should not investigate it or even theory build on top of it, but it does mean we should refrain from assuming it must be true just because nobody can find anything better.
The vast majority of science is not disproving a theory but adding nuance to it. Newtonian physics wasn't disproven by quantum physics, but quantum physics showed that Newtonian physics has limitations as a model. It's not unreasonable to assume our best model is true until there is a reasonable amount of data to the contrary.
As others have said, your point adds little to the conversation until you bring good data to the argument.
Suggesting that we avoid possible dogma has intrinsic value. Let us step back and consider the fact that the combination of general relativity and the Standard Model already cannot explain our most basic cosmological observations. We cannot explain the stability of even our own galaxy based on current models. This situation clearly calls for some basic caution before we enshrine possible unproven explanations into humanity’s view of the universe. There’s a lot of evidence, both long established and newly growing, which shows that our models can’t consistently explain many of the basic things we see around us when we look up at the sky.
Your original point says very little. Yes, science acknowledges that you can never 100% say "X causes Y". Science is about getting closer and closer to that 100% with better models and better data while acknowledging it's impossible to get there completely. That's why people are saying your point is a nothing-burger. It's stating the obvious based on a strawman position.
He is making an epistemic argument, and epistemology is a part of proper science, though not of scientism, which is what you are bringing.
Binary is not the only form of logic available, but it is the most popular in discussions of the unknown.
> Your original point says very little.
You are literally mixing up subjective and objective.
> Yes, science acknowledges that you can never 100% say "X causes Y".
Careful though: science also does the opposite. Do you know why? Because science is composed of scientists, and scientists are Humans, and Humans are famously unable to distinguish between facts and their opinion of what is a fact. In fact, doing so is almost always inappropriate, and socially punished.
> Science is about...
It may intend to aspire to that, but what it is, is what it is. And what that is, comprehensively, is unknown, because it is unknowable. But we do know portions of what it is: there's the part you said, but there is also deceit, hyperbole, delusion, etc...again, because it is composed of Humans, and this is how Humans are. In my experience, all Humans oppose extreme correctness, I have never met a single one who does not.
What I wrote needed to be said, despite evidently containing very little interesting content, precisely because of how severely it provokes certain people who claim not to even disagree with it. The degree of the provocation proves the value of the statement.
A good scientist will tell you that we don't assume it is truth. Instead, it is the closest thing to truth we can get at this time, but we are always seek better. But like a limit, we can only ever approach closer and never arrive at truth. As the other poster mentioned, we don't have a way to open up the source code of the universe.
Some scientists get a bit too attached to theories and can move them from "closest we currently have to truth" to "truth", but I think the bigger issue is that the non-scientists involve in transmitting science too often present it as truth, instead of the best approximation we currently have. Often because fake confidence beats out measured modesty, and the one claiming to have truth is more convincing than the one saying we can't know truth and only better approximate it.
A scientist will say science is true for the sake of simplifying the philosophy of science to those unfamiliar with it, but any scientist who thinks they have captured objective truth has lost the philosophical foundations of science.
This is not correct; string theory is not the only candidate we have for a theory of quantum gravity.
I said it’s the only theory of gravity and everything else at all energy levels, and that’s true. In fact, you’ll notice I did not even use the term “quantum gravity” to avoid the exact confusion you fell into anyway.
To me it seems like you're arguing that it was a bad idea to build on the assumption of Newton's theory of gravity because eventually it would be replaced by Einstein's theories of relativity. Which is obviously not sensible, since Einstein's theories were in part the result of trying to explain inaccurate predictions made by building on Newton's theory.
If the only option for finding out better evidence for or against X is by building those models and watching them either keep matching observations or finding a contradiction that can lead to the downfall of X as the suspect, then it is if you want to progress science any further.
Maybe there is another area that will give results faster, but much of the easy and fast science has already been science. And if someone finds a better option we missed, which does happen from time to time, add some rigor to it, verify it with testing, and they'll likely have themselves a Nobel prize.
(As far as any other HN reader could ever perceive)
It’s just a fact of reality that no one else on HN can verify with certainty whether or not you are a genuine, bonafide, human being, especially online.
Everyone who is engaging with you is just assuming you are.
1. As other commenter said, X causes Y does not mean that Y implies X. There can be another cause for the Doppler.
And surprisingly, 2. There is at least one known mechanism that cause Doppler WITHOUT moving: when the observer is in a gravity well (ex: earth) and observing a stationary object outside the gravity well (ex: some fixed point in outer space)
It wouldn't surprise me if we discover someday another Doppler mechanism that occurs at those same large scales
This is gravitational redshift, not Doppler shift. Doppler shift specifically means redshift due to an object moving away--but to really be correct that definition has to be limited to flat spacetime, or to a small enough region in a curved spacetime that the curvature can be ignored.
I suppose that's possible. Does that hypothesis adequately explain our observations?
Is the model we currently have completely "correct"? Almost certainly not. But it appears to be less wrong[0] than earlier models.
If you (or anyone) can show how the above describes our observations better and more completely than our current models, then it's likely "less wrong."
But you offer no evidence or even logical argument to support your hypothesis. As such, it's not much more than idle speculation and essentially equivalent, from a scientific standpoint, as suggesting the universe is a raisin dropped into a sugar syrup solution[1] and absorbing the liquid -- hence the expansion of the universe.
In our first version, imagine all of the stars at rest. Now, we emphatically know this not to be true locally due to all kinds of measurements, but let's go with it. What happens? The moment you let these stars "go," they begin to draw toward one another due to gravity. You would have gravitational collapse. We do not see that.
Next iteration: we throw the stars, and the galaxies, and the galactic clusters away from one another. No expansion required. Here we have two options. In the first, we did not throw with enough speed, they expand out ... slow to a halt ... and the gravitational collapse again. Again, unobserved. Option two, you have thrown at escape velocity and what you would see is an asymptotically decreasing speed, never quite hitting zero, since gravity works "forever away." Also unobserved.
What you're suggesting is basically the Steady State concept, a kind of static universe. This is a very old idea. So old it was given a kind of courtesy term in general relativity, which would eventually be set to zero.
Here is a rule for any armchair astrophysicists: whatever you think of, that was most likely an idea at one point and was eventually ruled out.
The relevant XKCD is Astrophysics - https://xkcd.com/1758/ ( https://www.explainxkcd.com/wiki/index.php/1758:_Astrophysic... )
The transcript from explain:
[A sign on two posts, in the grass in front of a building with windows and double doors, a window on each door, and bars facing outwards. There is a cement walk leading to the doors. On the sign is the text:]
Department of Astrophysics
Motto:
Yes, everybody has already had the idea, "Maybe there's no dark matter—Gravity just works differently on large scales!" It sounds good but doesn't really fit the data.Don't get hung up on redshifts for evidence of the big bang. The CMB is the real smoking gun. Read up on it, it's entirely worth it. I can recommend Simon Singh's book "Big Bang".
There is also a plethora of other probes that in concordance all point to the same thing: that the universe is almost 14 billion years old and expanded from a very hot, dense state. It's settled science, really.
It's cool to say "in the first milliseconds of the existence of the universe X and Y happened", but how did time supposedly run as usual while everything else was on the fringe of our understanding of reality? There don't seem to be any answers to this (or I haven't looked thoroughly enough) but it feels like a very important question that's always overlooked by everyone talking about this.
Like, if you'd like to really dive into it then you're going to need to go through a lot of textbooks first.
If you are moderately familiar with multi-variable calc, then here is a good book to get started down the GR hole: https://www.amazon.com/Mathematical-Methods-Physicists-Compr...
Suffice to say, yes, there have been a lot of grad students that have the exact same questions and issue that you currently have. Further, once they have reached the end of the mathematical education required to understand how space time works in the first few minutes of the universe, they focus those questions into the issues we have with inflation. Those issues mostly come from our lack of understanding about how GR and QM interact, so the first 10e-43 seconds or so. At least, that is my understanding. Physicists are welcome to tell me how dumb I am right now!
https://en.wikipedia.org/wiki/Cosmic_time
https://en.wikipedia.org/wiki/Chronology_of_the_universe
If you're into podcasts at all, I'd strongly recommend Crash Course Pods: The Universe. The first (full) episode goes into detail on that first fraction of a second in our universe and it's pretty enlightening without being to thick on the math.
It did; it caused the expansion to decelerate. That was true until a few billion years ago, when the matter density became smaller than the dark energy density and dark energy started to dominate the dynamics.
I think scienceclic does a good job visualizing this, but end of the day I can't see a way to distinguish event horizons regardless if they're a black hole or the distant past/big bang.
https://youtu.be/isezfMo8kWQ?si=9wGliV-Qo1bXCTRy
Specifically look at the relativity of the vacuum section, which builds to a great insight at around 5:45
There are so many intricate dependencies between these pathways that it's pretty unrealistic to postulate anything else than a big bang + cooldown process IMHO.
So, historically, they did not go hand-in-hand.
https://en.wikipedia.org/wiki/Fred_Hoyle#Rejection_of_the_Bi...
Not that I have the background to know what else they might not have accounted for to reach this conclusion.
Part of this is the distinction between what is happening and why the model says is happening. Does any physicist believe they have the perfect model? Or is it that they use the model that best fits the observations and are open to any other model, as long as it is either simpler or produces fewer contradictions than the current model (and is just as testable).
I think too often we hear reports of "science says X is what happens" when the reality is more like "science says that the current model based on X happening is what best describes current data and observations".
The Copernican principle is, indeed, attractive to the modern mind because its neutrality. But it's not neutral. It's just as loaded as any other principle, no matter how crazy it may sound today, philosophical, religious, or merely personal.
I'll leave this comment here since I'm about to get rate limited: I read/heard a great idea recently, what if gravity is an emergent quantity like heat? Maybe dense fermions just radiate gravitons just like a hot mass radiates photons?
Gravity is the result of spacetime curvature, if I remember correctly.
Anti-mass is mass where Gravity goes Out instead of In.
The anti-mass and mass accelerated away from eachother at the start and the redshift is it's repulsion away.
The big bang was first postulated by an agent of the vatican, and scientists raised in any religious context tend to generate experiments that confirm their beliefs.
I'm likely misinterpreting the article, but it seems to frame things in a way that first assumes expansion should be constant and it's a question of what the right constant value is between the measured/theoretical discrepancies.
(*yeesh, editing all those spelling errors from typing on my phone)
This tells us that either our model of the universe is wrong (therefore the cosmic microwave background method is giving us an incorrect answer) or that something is wrong with how we're calculating the distances along the cosmic distance ladder. The latter was originally the assumption that should be proven true with more and better data from newer telescopes. This is now turning out not to be the case: our cosmic distance ladder calculations seem to have been very good, so it now seems more likely that our model of the universe is wrong.
Not according to at least one research group described in the article: the Freedman group, which is only getting the higher answer using Cepheids, but gets a lower answer, one consistent with the CMBR calculations, by two other methods. Which raises the possibility that it's the Cepheid part of the cosmic distance ladder that's the problem.
Perhaps we need some outside groups to take a look at this to see if either group is making systematic errors in their analyses.
I agree this would be a good thing.
https://youtube.com/playlist?list=PLnU8XK0C8oTDaiwe8Us_YNl4K...
He also has an alternative theory for stellar physics that might call into question the interpretation of Cepheids and SNs, tho I don't think he's done a major analysis there, at least afaik
It also sound like progress that we seem to have 2 “scales” to play with to try to develop a consistently measurable distance.
It's exciting to see how the question drives many new discoveries.
[1] https://en.wikipedia.org/wiki/Great_Attractor
I'll try to paraphrase what it meant: measuring H0 comes down to measuring the relative velocity of galaxies around us. The great attractor was a relatively recent discovery that the "closer" galaxies, the ones we can use in the distance ladder, all have a common component in their velocities which we've recently begun to understand better.
I personally wouldn't trust the CMB calculation at all until the dark matter issue is resolved.
There is an equivalent boatload of evidence for modified gravity that can't be explained by particle dark matter [1], but one set of observations is hand waved away as a minor inconvenience while the other set is taken as definitive proof.
If gravity doesn't work the way we expect, then lensing in galaxy collisions isn't necessarily telling us what we think it is.
But setting that aside, if we take even the most naive modified gravity, MOND, then lensing does require a form of particle dark matter, like sterile neutrinos, but the total amount of dark matter required to explain the evidence is only double the amount of visible matter, rather than almost 10x the amount of visible matter as in LCDM. This has significant implications for calculating the Hubble constant from the CMB [2].
[1] https://tritonstation.com/2024/06/18/rotation-curves-still-f...
[2] TeVeS is wrong, but it shows that modified gravity significantly effects the H0 calculation, https://arxiv.org/abs/1204.6359
Whenever a scientist says that it's not possible that the model is wrong, then I just roll my eyes. Of course models can be wrong - and isn't that exciting? Good on them for making sure that there are no errors in the measurements - that's incredibly valuable and absolutely necessary - but I'm really excited to see creative models being thought up that are drastically different. My personal hell is the universe being consistent and boring.
I'm sure scientists have to deal with people jumping on them about their model being wrong, but this part is clearly exaggeration.
I no longer engage with these people for sport, but about 15-10 years ago I had two scientific creationists that I kept around as virtual pets. one was Hindu and one was from the religion of peace. neither was very stable and both were prone to getting a bit emotional about it.
each time, they would pick one piece of settled science, but they didn't have the mathematical machinery to understand the model itself, so they would rely on the layman cartoon versions and misunderstand something crucial there. for example, the existence of error bars on the concordance plot of radioactive dating. from this they could throw doubt on the whole chronology of the formation of the solar system and the evolution of man. for one of them, a technological civilisation from Hindu mythology existed millions of years ago. for the other, their very peaceful god created everything personally in one go, and evolution by natural selection didn't happen.
But no one said that. Im fact, scientists are known to say things like: all models are wrong, but some are useful.
> That the three methods disagree “is not telling us about fundamental physics,” Freedman said. “That’s telling us there’s some systematic [error] in one or more of the distance methods.”
Freedman is saying that the model is not wrong.
To argue that the physics is wrong, you are likely to be arguing that very well tested theories like general relativity, special relativity or electromagnetism are off in some way. That's a much higher bar than just the measurements of either the ladder or CMB being wrong in some way.
It's easy to think up ways that your sensor could be 5-10% off. It's very difficult to come up with an entirely new theory of gravity that explains everything we observe about the world, but also makes gravity a few percent weaker in this one case.
Conversely, the hypothesis that LambdaCDM is wrong does nothing to explain why the distance ladder methods disagree.
She clearly isn't saying that any model is infallible, she's just saying that clear flaws with one set of models throw into question some specific accusations that a different model is wrong.
You actually need to pay attention to the details; the physicists certainly are. Glib contrarianism isn't very useful here.
You shouldn't really roll your eyes at that. They're ultimately doing all the work which will prove it right or wrong. They might wind up not liking the answer they get, but the conviction is necessary to get them there because human emotions are weird.
Anyone with an ounce of sense should have concluded that LCDM was wrong long ago. Hopefully this will finally cause physicists to actually try something different.
Now the Euclid satellite has been launched, which I remember being the big hope that it will give us data that will finally enable us to tell which LCDM alternative could replace LCDM as the standard model of cosmology. You won't even get funding for such a mission unless you make a case for how it can improve our understanding of the universe. "We hope it will confirm our currently accepted view" will not get you one cent.
So I'm not sure where you get the confidence that nothing different is being tried and that professional scientists wouldn't have an ounce of sense. I find it a bit disrespectful actually.
I invite you to read the introduction (and introduction of part 1) of this review paper of the science behind the Euclid mission: https://arxiv.org/abs/1606.00180
It's understandable to laymen, co-authored by reputable, leading scientists in the field (disclaimer: I'm on the author list) and I hope that after reading it you would revise your opinion.
Here is a short excerpt:
> The simplest explanation, Einstein’s famous cosmological constant, is still currently acceptable from the observational point of view, but is not the only one, nor necessarily the most satisfying, as we will argue.
> So I'm not sure where you get the confidence that nothing different is being tried and that professional scientists wouldn't have an ounce of sense. I find it a bit disrespectful actually.
Try talking to a MOND proponent and you'll get a very different picture of how open scientists are to alternate approaches and questioning LCDM.
I think you mean, "nothing could be made to fit the data as well as LCDM". See below.
> When new data came in, and it pointed yet again at LCDM, it was considered a disappointment.
This is highly revisionist, and exemplifies the kind of cherry picking that has kept LCDM alive when it has outright failed numerous predictions and had to be adjusted after the fact to fit the data:
From Galactic Bars to the Hubble Tension: Weighing Up the Astrophysical Evidence for Milgromian Gravity, https://www.mdpi.com/2073-8994/14/7/1331
LCDM is a complete mixed bag when it comes to predictions, where MOND has a very slight edge. It's absolutely clear that MOND is not correct or complete either, but it is undeniable that it has had greater predictive success than anyone anticipated and with far fewer free parameters than LCDM, mostly in areas where LCDM is weak. If LCDM can't explain why MOND has been so successful, which it currently cannot, then it is incomplete at best.
Basically, the only good, almost definitive, evidence for particle dark matter is gravitational lensing, but if we're considering modified gravity anyway, then lensing isn't necessarily telling us what we think.
On the flip side, no possible cold dark matter halo is compatible with recent observations that rotation curves are flat past a million light years [1]. I can't wait to see what epicycles they add to LCDM to save it this time.
[1] https://tritonstation.com/2024/06/18/rotation-curves-still-f...
See https://en.wikipedia.org/wiki/Cosmological_principle
Basically, if this weren't to hold true, a lot of astronomy would fall over, even physics.
Most people don't realize that science—and even everything in life—has to start from some axioms/assumptions, just like math. I first realized this fact when I was reading the Relativity book written by Einstein himself, who challenges the assumptions in classical physics.
As time goes, some of the assumptions could be proved to be unnecessary or even wrong. There must be still some assumptions left, though—because without them, we can't talk about science, or anything, really.
> A group of researchers argued in 2021 that observations of the Hubble tension may imply that only quintessence models with a nonzero coupling constant are viable.
It doesn't.
"The simplest explanation for dark energy is that it is an intrinsic, fundamental energy of space" [1]. That's the cosmological constant.
Dark energy is a thing because we don't assume that to be the case. Irrespective of your dark energy model, however, there will be a predicted global average.
Briefly, recent large scale maps of the universe suggest that the universe might not be as uniform as we thought it was. In particular we appear to be in a large region (something like a couple billion light years across) of low density.
Dark energy is needed to make the solution to Einstein's field equations for the whole universe match observations. However that solution was derived based on a universe with matter distributed uniformly. At the time it was first derived that appeared to be the case--we thought the Milky Way was the whole universe.
When we learned that the Milky Way was just a small galaxy in a vastly larger universe than had thought we were in and that there were bazillions of other galaxies, those galaxies appeared to be distributed uniformly enough the the solution to the field equations still worked.
Later we found that there is some large scale structure in the distribution of galaxies, like superclusters, but those seemed uniform enough throughout the universe that things still worked.
If that couple of billion light year low density region turns out to exist (large scale mapping of the universe is hard enough that it may just be observational error) the universe may not actually be uniform enough to for the field equations based on uniform matter distribution to actually work.
Some researchers worked out the solutions to the field equations for a universe that has such large low density bubbles big enough to invalidate the uniform universe solution, and found that such a universe would have an expansion force without the need to invoke any kind of dark energy.
There was a recent PBS Space Time episode that covered this: "Can The Crisis in Cosmology be SOLVED With Cosmic Voids" [1]. The above is my summary of what I remember from that. See the episode for a better explanation and references to the research.
It seems like if there were some error in the luminosity measurement for cepheids, it would propagate to the measurements with supernovas...
I would expect that stacking measurement techniques (as is common with cosmology, where distances are vast and certainty is rare) would also stack error, like summing the variance in gaussians...
In 50-100 years they'd get a much better angular fix on stars that are too distant for Earth-orbit-sized angular measurements.
Lower power, but a telescope like this does not need constant power, so some kind of short term power storage (capacitor I would assume, or some kind of ultra long life battery) could handle that.
I believe that work on such a project would be interesting, even if it isn't ever done. It is something that if you worked on it as a grad student, and then became a professor and your grad students worked on it ... and they became professors and their grad students worked on it - they'd be the ones seeing the results.
Not so much a "this is a way to do things..." but rather a "thinking about research that spans generations and the problems that they solve in the process of doing that great project has useful spinoffs."
A mission out to 550 AU at New Horizons speed of 2.9 AU / year (it still boggles the mind of talking about those speeds and distances) is nearly 200 years from launch to primary science objective.
It's "only" been 45 years since Mariner 2 to New Horizons.
It'd be a nice use for falcon heavy - to get them the necessary delta-v. But the constraint isn't cargo space on launch. This isn't a starlink constellation, the orbits are necessarily massively different, meaning each spacecraft needs its own large delta-v so a single-launch, multiple spacecraft option is less attractive.
The constraint is budget, fuel, and ambition.
Now what you could do is get a telescope out around a far outer planet and use the orbital parallax like we do from earth. A Starship might have a bunch of extra cargo space for this. But I just don't see how it is better than a big faring on falcon heavy.
EDIT: You know what? I am completely mistaken here. I was not thinking about the diff b/w FH and starship correctly.
Once the thing becomes reliable there are zero missions the FH can do that starship can't with a payload equipped with a third stage motor.
Why: FH + Starship w/( rocket + payload)
And not: FH + (rocket + payload)
Falcon Heavy can lift a lot of mass but unless you’re launching tungsten into orbit you can’t fit interesting things into the fairing.
A full Falcon Heavy stack can take 63,800kh to LEO. A Starship stack can take 150,000kg to LEO. The available Δv is substantially higher.
Falcon 9 has payload to Mars of 4 tons, and Falcon Heavy has 9 tons to Pluto. I bet both would work.
I am sure there are calculations for this ...
PS. Of course, the rate of technological development is the unknown variable hete, I am sure.-
For example, say your calculations say that the optimal time for the mission is 10 years from now, once a currently in-development propulsion technology matures. You publish that, and the investors, government and the public, all motivated to support you by the dream of your ambitious mission, suddenly lose interest. Your funding dries out, as you're repeatedly told to call back in 10 years. The fact that the 10 year estimate, having been dependent on existing funding, is now "literally never", escapes them.
See also: "nuclear fusion is always 30 years away". It is, because original 30 year timeframe assumed continued funding that never happened, and it's not happening because "it's always been 30 years away".
> You publish that, and the investors, government and the public, all motivated to support you
Interesting how PR/culture indeed is a factor - a tangible factor in this. Indeed optimizing for "PR Goodwill" might be a thing ...
(Knowing this field I'm sure there are some astronomers who argue that there are still some systematic uncertainties that are not fully being accounted for, but from what I understand it's pretty hard to account for it with the Gaia results at this point.)
The assumption that these observations indicated an expanding universe was delivered to us by LeMaitre; if you believe in an expanding universe with a finite age, then give credit where it is due...
I think people forget that, due to the longer wavelengths to which it's sensitive, Webb actually has a poorer angular resolution than Hubble.
"c" / "age of Universe" = Hubble constant (i.e. "c"/13.7 billions ly / 3.26 ly per pc = 71.3 km/s per mpc.)
I'm no mathematician or physicist, but this stuff just fascinates me. I interpret it something like:
The further one looks, the faster objects in the universe are expanding. However, when one looks out at the universe, they are looking backwards in time, to a time when the universe was expanding at a more rapid pace. Right? Close to the big bang? Because there was a period of rapid expansion after the big bang, so the universe had to have moved faster in the earlier universe? So the only part of space that actually appears to be static would be around our local space, the stars we can see?
Often the universe is depicted as a giant bubble, expanding outwards in all directions. It is how the human mind is built to think, a classic blunder dating back to the days of Ptolemy, where Earth was the center of everything.
At the edge of our observable universe is the beginning of it all. We can fast forward then through time to see the most modern picture of our universe, the reference frame that is our own galaxy. We are not at rest in a static galaxy, so why should the laws of relativity and dilation not apply to massive objects
Everywhere else we look is in the past, and the cosmic background is visible from every direction. So once expanded in 3D space, and accounting for time, all of space would appear to be accelerating towards the cosmic background and point of the big bang?
“[...]But in 1929 astronomer Edwin Hubble measured the speed of many galaxies and found, to his surprise, that all were moving away from us-- in fact, the further away the galaxy, the faster it was going. His measurements showed that space is expanding everywhere, and no matter where you look, it will seem as if all galaxies are receding because the distance between everything is constantly growing. Faced with this news, Einstein decided to remove the cosmological constant from his equations.” -some scientific American article
It’s not moving away from us, it’s moving towards the beginning of time at a faster and faster rate, but only because we’re looking backwards through time. In reality, due to our reference frame, and other subsequent frames of observed bodies, we are the only point in the observable universe that is in the “present”. To that effect, when everything appears to be moving away from us at a faster and faster rate, it is moving away from the origin (big bang) at a slower and slower rate.
Galaxies are not moving away, they are showing an accelerating speed due to the time difference, and the slightly higher cosmological constant several hundred million years in the past, a constant that scales with time and its relation to distance according to metric expansion and the speed of light. It is the higher constant with relation to distance that gives the illusion of a universe whose expansion is accelerating.
It can be assumed then, that as you move between vast points in space, the universe will update; showing that astronomical objects aren’t accelerating away, but are not in fact moving at all. If not moving towards each other and closer together.
So no matter where you travel, it is likely that the bubble of the observable universe travels with you, you do not accelerate away faster the closer you get to the galaxies that appear from Earth or other reference points from Earth to be expanding faster away.
If you look at the night sky from a planet in one of these far away galaxies, the overall structure of the universe would be very similar if not the same to the structure as it appears from Earth. With all galaxies appearing to be accelerating away from each other at a faster and faster rate.
Sorry im high on shrooms
So the pressure around our bubble is not uniform, there are more bubbles on one side than another, other bubbles are much larger and some are very tiny causing tiny "lumps" of pressure in various places on our bubble.
Decades ago I really liked the "big collapse" theory that has now been abandoned, it was so "simple" in comparison to a universe that keeps expanding and not uniformly at that.
I can't measure my own weight with an uncertainty that's less than 1%. I wonder what these peeps are on...
How To Measure The Tiniest Forces In The Universe https://youtu.be/pXoZQsZP2PY and World's Heaviest Weight https://youtu.be/_k9egfWvb7Y - both from Veritasium.
From the expanded description on the heaviest weight:
> Before visiting NIST in Washington DC I had no idea machines like this existed. Surely there's an accurate way to measure forces without creating such a huge known force?! Nope. This appears to be the best way, with a stack of 20 x 50,000 lb masses creating a maximum force of 4.45 MN or 1,000,000 pounds of force. I also wouldn't have thought about all the corrections that need applying - for example buoyancy subtracts about 125 pounds from the weight of the stack. Plus the local gravitational field strength must be taken into account. And, the gravitational field varies below grade. All of this must be taken into account in order to limit uncertainty to just five parts per million (.0005%)
Or approximately 3.25 million light years.
I have difficulty conceptualizing "distance over time ... over [huge] distance"
I guess it means "chunks about so [megaparsecs] large are moving [themselves] at a speed of so many Km. per second" but I could be wrong
The distances, time and speeds are indeed very hard to comprehend from our usual references :)
Thanks for taking time to break it all down
Kurzgesagt did a video on that - TRUE Limits Of Humanity – The Final Border We Will Never Cross https://youtu.be/uzkD5SeuwzM
G (the gravitational constant) is an interesting one: the value is only known to about 5 significant figures, but GM (the gravitational constant multiplied by the mass of the Earth) is known a lot more accurately, unsurprisingly, considering how well GPS works. Some of those constants seem to be known to about 12 significant figures.
One of the proximate causes around our failure to progress in this and other areas is the funding model of publish or perish. Many researchers are trying to carve out a career, but not necessarily to contribute to progress or advancement. An examination of the funding structure and incentives for universities and researchers appears to be in order.
One suggestion would be to limit grants for private universities and colleges. Another would be to cap compensation for university and college staff. Yet another would be to add funding or tax breaks for technology scale up and application development in the private sector. And another would be cutting funding to masters', PhD and post-doc levels, and increasing funding for 1-, 2- and 4- year career oriented and skill development programs. Yet another suggestion would be limiting loan eligibility to 1-, 2- and 4- year degree or lower programs. Another would be tying university and college funding to the success of attached technology scale up and application development programs. Another would be requiring undergraduate and lower grants and tuition revenue to be spent directly on those programs and facilities, and research funds to be kept and spent separately.
I would like to know some examples of how recent, publicly funded PhD, masters degree and postdoc work or research has materially advanced or will advance our world's knowledge and progress and has resulted in material benefits to society, and not just unreproducible studies on paper and unviable technologies and products.