11 ms·

What if the universe doesn't expand at all? What if we're completely wrong and redshift is caused by something else entirely, like some yet-undiscovered phenome

What if the universe doesn't expand at all? What if we're completely wrong and redshift is caused by something else entirely, like some yet-undiscovered phenomenon that occurs to spacetime or electromagnetic waves? How can we be so sure it's space that's expanding, not time? 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. [1] https://en.wikipedia.org/wiki/Phlogiston_theory https://en.wikipedia.org/wiki/Phlogiston_theory

dotnet00 2y ago
We can create and observe doppler shift by making things move towards/away from us. Thus it is proven that if something is moving away from us, it will produce a redshift. In the absence of evidence that something else is causing the redshift, the assumption should be that it is a result of things moving away from us. As an obvious example, doppler shift often needs to be accounted for to communicate with spacecraft.
- nilkn 2y ago
  X causes Y does not mean that Y implies X. It’s reasonable to suspect X given Y and an absence of other such causal relations, but it’s not necessarily reasonable to spend decades building layers and layers of models that assume X at the most basic level.
  - deleted 2y ago
    [deleted]
  - ko27 2y ago
    You are not a making insightful point at all. Nothing in the world can guarantee you that "Y implies X", after all, we can be living in a simulation. Does that mean we should shutdown all scientific discussions by repeating what you stated? Of course not.
    - nilkn 2y ago
      Point out where I said we should “shutdown all scientific discussions.” You won’t be able to, and you will then realize how incredibly absurd what you just wrote is.
      - MichaelZuo 2y ago
        The parent is pointing out that the prior comment is literally meaningless, and self defeating too, since the same logic would apply to your own existence, or simulated existence. Including any possible words you could ever write. (As far as any other HN reader could ever perceive)
        nilkn 2y ago
        Don’t you think jumping to a complete existential crisis over such a simple comment is a little extreme? That alone is a red flag that maybe dogma has taken over. No, nothing I wrote suggests one must shut down all scientific discussion or inquiry. No, it does not mean you cannot investigate X and its implications. No, it does not mean you cannot build speculative models on top of X. Yes, it does mean it’s important to be careful with language and avoid enshrining what is only an assumption as an unassailable fact of reality for generations.
        deleted 2y ago
        [deleted]
        MichaelZuo 2y ago
        Who said it’s a ‘complete existential crisis’? 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.
        nilkn 2y ago
        I said that. If you thought I was wrong in that assertion, then all you had to do was stop questioning your entire existence here. The fact that you continued to do so lends credence to my assertion rather than refuting it.
  - treflop 2y ago
    Everyone knows this. 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.
    - nilkn 2y ago
      Everybody knows it, but the principle is selectively applied. 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.
      - bumby 2y ago
        >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.
        nilkn 2y ago
        I don’t accept that I owe anyone any kind of additional data on any of this. Just like I don’t have to have a proven solution to the problem of finding a theory of everything to suggest that string theory may not be the truth of the universe while still acknowledging that it can be a worthwhile thread of inquiry and study. 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.
  - exe34 2y ago
    I think everybody would be happy if you came up with a different explanation! what's happened so far is that we have a known mechanism, and no alternative explanations have worked yet.
  - dotnet00 2y ago
    If we can suspect X given Y, but we shouldn't build models on top of the assumption of X, then what are we supposed to do with Y? 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.
  - SkyBelow 2y ago
    >but it’s not necessarily reasonable to spend decades building layers and layers of models that assume X at the most basic level. 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.
- narfay 2y ago
  This is wrong on several levels: 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)
  - dotnet00 2y ago
    As I've mentioned in another post, that leads to questioning one of the most well tested theories in physics, so you need extraordinary evidence to prove it over something as elementary as doppler shift. Like, if it's Earth's gravity well causing us to see things differently, then things that are further from Earth should observe things differently.
    - narfay 2y ago
      There is already extraordinary evidence that something in physics is behaving differently at larger scales: the behavior of galaxies (spin, gravity pull) doesn't match their mass. Any mass. There is no single mass value that predicts their entire behavior correctly. Thus dark matter, dark energy etc competing theories, which are so far untestable. It wouldn't surprise me if we discover someday another Doppler mechanism that occurs at those same large scales
  - pdonis 2y ago
    > There is at least one known mechanism that cause Doppler WITHOUT moving: when the observer is in a gravity well 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.
- pdonis 2y ago
  > In the absence of evidence that something else is causing the redshift, the assumption should be that it is a result of things moving away from us. 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).
mr_mitm 2y ago
How would you explain the CMB? We can literally see that the universe used to be much denser.
- grishka 2y ago
  And if the universe was much denser, doesn't that imply that all that matter affected its surroundings gravitationally? And as we know, time runs slower near large masses. And when something falls into a black hole, according to our very own theories, it would also red-shift because of the black hole's gravitational pull without anything having to expand.
  - mr_mitm 2y ago
    No, it implies it expanded in the meantime. We can see that it was a hot plasma up until 300k years after the big bang. This isn't some redshifted illusion, the matter was literally packed so densely and thus so hot that it was in another aggregate state. 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.
    - grishka 2y ago
      Speaking of the big bang, how did time work back then? :) 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.
      - Balgair 2y ago
        Yeah, it is overlooked because the real answers are 'hidden' behind a lot of graduate level math. And most people don't really want to learn a bookcase worth of math first to talk about it, but they talk all the same. 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-Comprehensive-Guide/dp/0123846544 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!
mwbajor 2y ago
The observation of the Hubble constant requires us to measure distance to an object in space. This is very hard to do at the extreme distances required (https://en.wikipedia.org/wiki/Parallax https://en.wikipedia.org/wiki/Parallax). In the end, the variation in the Hubble constant might be only due to our limited accuracy in measurement.
antognini 2y ago
There is a very old theory called the "Tired Light Hypothesis" which supposes that for some unknown reason light loses energy as it travels over cosmological distances. This would reproduce the observed redshifts, but it has issues predicting pretty much every other cosmological observation. 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.
- rvnx 2y ago
  I like your theory more than the current setup. 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.
  - drdeca 2y ago
    I don’t think this would match the observations that can be made from earth of things on earth? Though the phrasing seems a bit ambiguous. Could you put some math behind those words?
  - boxed 2y ago
    I think you just described relativity from the perspective of atoms. It's still the same old relativity though.
- pdonis 2y ago
  > This would reproduce the observed redshifts, but it has issues predicting pretty much every other cosmological observation. Not to mention contradicting the laws of conservation of energy and momentum.
  - antognini 2y ago
    To be fair we do already know that energy is not globally conserved over cosmological timescales. (Energy conservation is a consequence of time invariance, but cosmological expansion breaks that symmetry.) 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.
nobody9999 2y ago
>What if the universe doesn't expand at all? What if we're completely wrong and redshift is caused by something else entirely, like some yet-undiscovered phenomenon that occurs to spacetime or electromagnetic waves? How can we be so sure it's space that's expanding, not time? 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. [0] https://en.wikipedia.org/wiki/The_Relativity_of_Wrong https://en.wikipedia.org/wiki/The_Relativity_of_Wrong [1] https://en.wikipedia.org/wiki/Compote https://en.wikipedia.org/wiki/Compote
lieks 2y ago
I remember reading, a long, long time ago, a paper where the authors suggested if the universe was slightly hyperbolic, it would also cause a redshift effect. I can't seem to find it (and as far as I remember it was purely theoretical), but at the time I thought it was an neat idea. Not that I have the background to know what else they might not have accounted for to reach this conclusion.
pdonis 2y ago
> What if the universe doesn't expand at all? 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.
- alexey-salmin 2y ago
  > The totality of all the observations we have cannot be explained in any other way than an expanding universe. 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.
  - pdonis 2y ago
    > Surely there are infinite other possible explanations 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.
    - oraphalous 2y ago
      > If you think there are others, please exhibit one. 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.
cristianpascu 2y ago
The _conclusion_ that the Universe is expanding is based on the long accepted premise that the Universe is _flat_. And this premise can not be proven or disproved unless we travel great distances to actually _observe_ if the Universe does, in fact, look the same from any point you look. 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.
- deleted 2y ago
  [deleted]
SkyBelow 2y ago
My guess is that scientists are considering this, but until now no better theory has been presented. 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".
while_true_ 2y ago
Expanding universe and Big Bang Theory go hand-in-hand. There are multiple independent observations besides the red shift that make it nearly certain there had to be a BBT event to explain what we see. The universe is too hot, chaotic and clumpy for there not to have been a massive explosion to kick it all into motion. Since there is good confidence BBT happened, transitioning from that event to a steady-state non-expanding universe would require some sort of mechanism to slow then freeze the expansion. Not aware of any support for that model.
- fanf2 2y ago
  The name “big bang” was a pejorative epithet coined by Fred Hoyle, who believed in a steady-state universe that was expanding (as Hubble had argued convincingly) but had some hypothetical mechanism for creating galaxies, such that the universe could have an unbounded past and future. So, historically, they did not go hand-in-hand. https://en.wikipedia.org/wiki/Fred_Hoyle#Rejection_of_the_Big_Bang https://en.wikipedia.org/wiki/Fred_Hoyle#Rejection_of_the_Bi...
  - while_true_ 2y ago
    True, but with the BBT-affirming discovery of the cosmic microwave background in 1965 they've been hand-in-hand ever since.
deleted 2y ago
[deleted]
eisvogel 2y ago
I suspect, in a few decades, when the smoke clears and the very latest sub-infrared, stadium-sized space telescope finds fully formed galaxies several billion years "before" the alleged moment of creation, then the astronomical community will finally start to question the logic of prevailing cosmological theory, from the ground up. 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.
blindriver 2y ago
The universe is a 4 dimensional sphere, so everything could be moving away without increasing 3 dimensional space. Eventually in trillion or quadrillions of years everything would start to blue shift as things move towards us on the other side of the sphere.
- gosub100 2y ago
  So how do I travel backwards in the 4th dimension? Or conversely, where's the source of the force that propels us through the 4th dimension? 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?
  - nabakin 2y ago
    > 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.
    - gosub100 2y ago
      Yes, but it's irreconcilable with quantum mechanics. So what I described was one of many attempts to do so.
      - nabakin 2y ago
        In that case, wouldn't it have to be more complex than just a particle which creates gravity? Something which is compatible with the finding of spacetime curvature?
koolala 2y ago
I got an idea! Anti-mass! 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.
bugbuddy 2y ago
Whispers: Halton Arp
DaoVeles 2y ago
While I don't necessarily think at lot of alternative ideas proposed are correct, I always love seeing alternative concepts being considered. Very cool to see ideas that could solve standing issues even if they themselves could have issues.
at_a_remove 2y ago
Easiest method is to simply take your idea at face value. 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.
- shagie 2y ago
  > 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://xkcd.com/1758/ ( https://www.explainxkcd.com/wiki/index.php/1758:_Astrophysics 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.
l33tman 2y ago
For example the entire atomic composition of the stars in the observable universe depends exquisitely on the expansion parameters at the big bang. The ratios can be traced back through the expansion to the quark-gluon soup stage. Changing the expansion rates changes the delicate balance between the particles that form at that stage, and when the various particle fractions "freeze out" during expansion when the temperature cools (btw we're talking about seconds from the big bang here :) which can be subsequently observed in stars all over the universe by spectroscopy. It's pretty beautiful. 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.
deleted 2y ago
[deleted]
jjk166 2y ago
This is the equivalent of finding your keys an inch off from where you remember setting them down and concluding that someone broke into your home, stole your keys, took your car for a joyride, and broke back in to place them there.

dotnet00 2y ago

We can create and observe doppler shift by making things move towards/away from us. Thus it is proven that if something is moving away from us, it will produce a redshift. In the absence of evidence that something else is causing the redshift, the assumption should be that it is a result of things moving away from us. As an obvious example, doppler shift often needs to be accounted for to communicate with spacecraft.

nilkn 2y ago
X causes Y does not mean that Y implies X. It’s reasonable to suspect X given Y and an absence of other such causal relations, but it’s not necessarily reasonable to spend decades building layers and layers of models that assume X at the most basic level.
- deleted 2y ago
  [deleted]
- ko27 2y ago
  You are not a making insightful point at all. Nothing in the world can guarantee you that "Y implies X", after all, we can be living in a simulation. Does that mean we should shutdown all scientific discussions by repeating what you stated? Of course not.
  - nilkn 2y ago
    Point out where I said we should “shutdown all scientific discussions.” You won’t be able to, and you will then realize how incredibly absurd what you just wrote is.
    - MichaelZuo 2y ago
      The parent is pointing out that the prior comment is literally meaningless, and self defeating too, since the same logic would apply to your own existence, or simulated existence. Including any possible words you could ever write. (As far as any other HN reader could ever perceive)
      - nilkn 2y ago
        Don’t you think jumping to a complete existential crisis over such a simple comment is a little extreme? That alone is a red flag that maybe dogma has taken over. No, nothing I wrote suggests one must shut down all scientific discussion or inquiry. No, it does not mean you cannot investigate X and its implications. No, it does not mean you cannot build speculative models on top of X. Yes, it does mean it’s important to be careful with language and avoid enshrining what is only an assumption as an unassailable fact of reality for generations.
        deleted 2y ago
        [deleted]
        MichaelZuo 2y ago
        Who said it’s a ‘complete existential crisis’? 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.
        nilkn 2y ago
        I said that. If you thought I was wrong in that assertion, then all you had to do was stop questioning your entire existence here. The fact that you continued to do so lends credence to my assertion rather than refuting it.
- treflop 2y ago
  Everyone knows this. 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.
  - nilkn 2y ago
    Everybody knows it, but the principle is selectively applied. 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.
    - bumby 2y ago
      >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.
      - nilkn 2y ago
        I don’t accept that I owe anyone any kind of additional data on any of this. Just like I don’t have to have a proven solution to the problem of finding a theory of everything to suggest that string theory may not be the truth of the universe while still acknowledging that it can be a worthwhile thread of inquiry and study. 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.
- exe34 2y ago
  I think everybody would be happy if you came up with a different explanation! what's happened so far is that we have a known mechanism, and no alternative explanations have worked yet.
- dotnet00 2y ago
  If we can suspect X given Y, but we shouldn't build models on top of the assumption of X, then what are we supposed to do with Y? 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.
- SkyBelow 2y ago
  >but it’s not necessarily reasonable to spend decades building layers and layers of models that assume X at the most basic level. 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.
narfay 2y ago
This is wrong on several levels: 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)
- dotnet00 2y ago
  As I've mentioned in another post, that leads to questioning one of the most well tested theories in physics, so you need extraordinary evidence to prove it over something as elementary as doppler shift. Like, if it's Earth's gravity well causing us to see things differently, then things that are further from Earth should observe things differently.
  - narfay 2y ago
    There is already extraordinary evidence that something in physics is behaving differently at larger scales: the behavior of galaxies (spin, gravity pull) doesn't match their mass. Any mass. There is no single mass value that predicts their entire behavior correctly. Thus dark matter, dark energy etc competing theories, which are so far untestable. It wouldn't surprise me if we discover someday another Doppler mechanism that occurs at those same large scales
- pdonis 2y ago
  > There is at least one known mechanism that cause Doppler WITHOUT moving: when the observer is in a gravity well 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.
pdonis 2y ago
> In the absence of evidence that something else is causing the redshift, the assumption should be that it is a result of things moving away from us. 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).

mr_mitm 2y ago

How would you explain the CMB? We can literally see that the universe used to be much denser.

grishka 2y ago
And if the universe was much denser, doesn't that imply that all that matter affected its surroundings gravitationally? And as we know, time runs slower near large masses. And when something falls into a black hole, according to our very own theories, it would also red-shift because of the black hole's gravitational pull without anything having to expand.
- mr_mitm 2y ago
  No, it implies it expanded in the meantime. We can see that it was a hot plasma up until 300k years after the big bang. This isn't some redshifted illusion, the matter was literally packed so densely and thus so hot that it was in another aggregate state. 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.
  - grishka 2y ago
    Speaking of the big bang, how did time work back then? :) 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.
    - Balgair 2y ago
      Yeah, it is overlooked because the real answers are 'hidden' behind a lot of graduate level math. And most people don't really want to learn a bookcase worth of math first to talk about it, but they talk all the same. 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-Comprehensive-Guide/dp/0123846544 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!

mwbajor 2y ago

The observation of the Hubble constant requires us to measure distance to an object in space. This is very hard to do at the extreme distances required (https://en.wikipedia.org/wiki/Parallax https://en.wikipedia.org/wiki/Parallax). In the end, the variation in the Hubble constant might be only due to our limited accuracy in measurement.

antognini 2y ago

There is a very old theory called the "Tired Light Hypothesis" which supposes that for some unknown reason light loses energy as it travels over cosmological distances. This would reproduce the observed redshifts, but it has issues predicting pretty much every other cosmological observation. 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.

rvnx 2y ago
I like your theory more than the current setup. 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.
- drdeca 2y ago
  I don’t think this would match the observations that can be made from earth of things on earth? Though the phrasing seems a bit ambiguous. Could you put some math behind those words?
- boxed 2y ago
  I think you just described relativity from the perspective of atoms. It's still the same old relativity though.
pdonis 2y ago
> This would reproduce the observed redshifts, but it has issues predicting pretty much every other cosmological observation. Not to mention contradicting the laws of conservation of energy and momentum.
- antognini 2y ago
  To be fair we do already know that energy is not globally conserved over cosmological timescales. (Energy conservation is a consequence of time invariance, but cosmological expansion breaks that symmetry.) 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.

nobody9999 2y ago

>What if the universe doesn't expand at all? What if we're completely wrong and redshift is caused by something else entirely, like some yet-undiscovered phenomenon that occurs to spacetime or electromagnetic waves? How can we be so sure it's space that's expanding, not time? 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. [0] https://en.wikipedia.org/wiki/The_Relativity_of_Wrong https://en.wikipedia.org/wiki/The_Relativity_of_Wrong [1] https://en.wikipedia.org/wiki/Compote https://en.wikipedia.org/wiki/Compote

lieks 2y ago

I remember reading, a long, long time ago, a paper where the authors suggested if the universe was slightly hyperbolic, it would also cause a redshift effect. I can't seem to find it (and as far as I remember it was purely theoretical), but at the time I thought it was an neat idea. Not that I have the background to know what else they might not have accounted for to reach this conclusion.

pdonis 2y ago

> What if the universe doesn't expand at all? 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.

alexey-salmin 2y ago
> The totality of all the observations we have cannot be explained in any other way than an expanding universe. 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.
- pdonis 2y ago
  > Surely there are infinite other possible explanations 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.
  - oraphalous 2y ago
    > If you think there are others, please exhibit one. 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.

cristianpascu 2y ago

The _conclusion_ that the Universe is expanding is based on the long accepted premise that the Universe is _flat_. And this premise can not be proven or disproved unless we travel great distances to actually _observe_ if the Universe does, in fact, look the same from any point you look. 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.

deleted 2y ago
[deleted]

SkyBelow 2y ago

My guess is that scientists are considering this, but until now no better theory has been presented. 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".

while_true_ 2y ago

Expanding universe and Big Bang Theory go hand-in-hand. There are multiple independent observations besides the red shift that make it nearly certain there had to be a BBT event to explain what we see. The universe is too hot, chaotic and clumpy for there not to have been a massive explosion to kick it all into motion. Since there is good confidence BBT happened, transitioning from that event to a steady-state non-expanding universe would require some sort of mechanism to slow then freeze the expansion. Not aware of any support for that model.

fanf2 2y ago
The name “big bang” was a pejorative epithet coined by Fred Hoyle, who believed in a steady-state universe that was expanding (as Hubble had argued convincingly) but had some hypothetical mechanism for creating galaxies, such that the universe could have an unbounded past and future. So, historically, they did not go hand-in-hand. https://en.wikipedia.org/wiki/Fred_Hoyle#Rejection_of_the_Big_Bang https://en.wikipedia.org/wiki/Fred_Hoyle#Rejection_of_the_Bi...
- while_true_ 2y ago
  True, but with the BBT-affirming discovery of the cosmic microwave background in 1965 they've been hand-in-hand ever since.

deleted 2y ago

[deleted]

eisvogel 2y ago

I suspect, in a few decades, when the smoke clears and the very latest sub-infrared, stadium-sized space telescope finds fully formed galaxies several billion years "before" the alleged moment of creation, then the astronomical community will finally start to question the logic of prevailing cosmological theory, from the ground up. 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.

blindriver 2y ago

The universe is a 4 dimensional sphere, so everything could be moving away without increasing 3 dimensional space. Eventually in trillion or quadrillions of years everything would start to blue shift as things move towards us on the other side of the sphere.

gosub100 2y ago
So how do I travel backwards in the 4th dimension? Or conversely, where's the source of the force that propels us through the 4th dimension? 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?
- nabakin 2y ago
  > 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.
  - gosub100 2y ago
    Yes, but it's irreconcilable with quantum mechanics. So what I described was one of many attempts to do so.
    - nabakin 2y ago
      In that case, wouldn't it have to be more complex than just a particle which creates gravity? Something which is compatible with the finding of spacetime curvature?

koolala 2y ago

I got an idea! Anti-mass! 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.

bugbuddy 2y ago

Whispers: Halton Arp

DaoVeles 2y ago

While I don't necessarily think at lot of alternative ideas proposed are correct, I always love seeing alternative concepts being considered. Very cool to see ideas that could solve standing issues even if they themselves could have issues.

at_a_remove 2y ago

Easiest method is to simply take your idea at face value. 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.

shagie 2y ago
> 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://xkcd.com/1758/ ( https://www.explainxkcd.com/wiki/index.php/1758:_Astrophysics 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.

l33tman 2y ago

For example the entire atomic composition of the stars in the observable universe depends exquisitely on the expansion parameters at the big bang. The ratios can be traced back through the expansion to the quark-gluon soup stage. Changing the expansion rates changes the delicate balance between the particles that form at that stage, and when the various particle fractions "freeze out" during expansion when the temperature cools (btw we're talking about seconds from the big bang here :) which can be subsequently observed in stars all over the universe by spectroscopy. It's pretty beautiful. 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.

deleted 2y ago

[deleted]

jjk166 2y ago

This is the equivalent of finding your keys an inch off from where you remember setting them down and concluding that someone broke into your home, stole your keys, took your car for a joyride, and broke back in to place them there.