7 ms·

> 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 b

by 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.
    - dtgriscom 2y ago
      When a random techie comes up with a completely novel hypothesis that contradicts a broad range of theories accepted by the vast majority of practicing physicists, the proper response is not to stop and say "Hmmm. I wonder if he's right. Let's talk about it."
      - JasonSage 2y ago
        Why not? Seems perfectly normal to just talk about it. 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.
        layer8 2y ago
        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, mirroring obvious thoughts that actual physicists have of course already thought of decades ago, and in much more detail. It is really hard and quite unlikely to come up with novel ideas that haven't already been discussed and played out ad nauseum in that field.
        JasonSage 2y ago
        I’m not suggesting the techie is correct, I just don’t think the right answer is complete dismissal instead of communication. Ok, so you know it’s obviously wrong, but there’s no obligation to then go and stifle their curiosity or imagination. Just don’t say anything or let them talk to somebody who has the time and care to indulge. 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.
        layer8 2y ago
  - quotemstr 2y ago
    > If you think there are others, please exhibit one. 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.
    - MaxikCZ 2y ago
      Thats like saying cars run because they want to, and only make us perfect the engine, and processes that happen inside it, to fool us into thinking we have a say in whether a car will run. 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.
      - shiroiushi 2y ago
        The funny thing is, though, you can easily dismiss a crazy idea like "omnitech space squid", but a majority of humans on Earth today have entire worldviews based on equally silly ideas, and it's considered wrong somehow to mock these belief systems. In fact, many scientists subscribe to these silly belief systems, but then get offended if you make up an equally silly idea about space squid or flying spaghetti monsters.
      - quotemstr 2y ago
        > 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.
      - 2y ago
  - deleted 2y ago
    [deleted]
  - alexey-salmin 2y ago
    > If you think there are others, please exhibit one. 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.
    - fpoling 2y ago
      A big problem of the modern cosmology is not only that we have observations that do not fit models but that we do not know if the observed discrepancies are the real problems with the models or are artifacts of calculations. 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.
  - raattgift 2y ago
    There are a fair number of extensions to GR that can reproduce the standard cosmology, typically avoiding or recasting DM, DE, or both. Examples include generalized teleparallel gravity and Cotton gravity. In such theories, any solution of the EFEs are solutions of the (sometimes very different) field equations of these families of theories, although the field content may have a somewhat different physical interpretation from GR. 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).
  - khafra 2y ago
    > > Surely there are infinite other possible explanations that fit the finite number of data points available > If you think there are others, please exhibit one. 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.
  - krisoft 2y ago
    > If you think there are others, please exhibit one. 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.
stoperaticless 2y ago
> 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. Well..? What are those other observations that point to expansion?
- pdonis 2y ago
  > 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.
  - handsclean 2y ago
    That’s just redshift. Redshift alone wouldn’t be evidence of expansion, just relative speed, when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle. 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.
    - pdonis 2y ago
      > That’s just redshift. 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.
handsclean 2y ago
It’s not just phlogiston, it’s the lifecycle of all scientific theories that they’re used for as long as they make accurate predictions, then we start seeing things they mis-predict, then they’re revised or replaced. You seem to think the expanding universe theory can still be saved by some data artifact or parameter tweaking, but that’s been hunted for years and we’re still at “we just can’t make it match everything we’re seeing”. Historically, that’s what precedes significant revision or replacement. > Redshift is not the only observation we have. What else is there?
- pdonis 2y ago
  > it’s the lifecycle of all scientific theories that they’re used for as long as they make accurate predictions, then we start seeing things they mis-predict, then they’re revised or replaced. 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.
  - Vecr 2y ago
    > 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.
  - nilkn 2y ago
    Galileo’s principle of relativity is used all the time.
- sandworm101 2y ago
peoplefromibiza 2y ago
> Not possible 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
sandworm101 2y ago
>> The totality of all the observations we have cannot be explained in any other way than an expanding universe. 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.
lumost 2y ago
I agree with you on the overall point, but this statement. > 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.
- pdonis 2y ago
  > Cosmology rests on the principal that physics is the same in all directions, over all translations, and over time translation. 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?

by pdonis 2y ago

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.
  - dtgriscom 2y ago
    When a random techie comes up with a completely novel hypothesis that contradicts a broad range of theories accepted by the vast majority of practicing physicists, the proper response is not to stop and say "Hmmm. I wonder if he's right. Let's talk about it."
    - JasonSage 2y ago
      Why not? Seems perfectly normal to just talk about it. 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.
      - layer8 2y ago
        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, mirroring obvious thoughts that actual physicists have of course already thought of decades ago, and in much more detail. It is really hard and quite unlikely to come up with novel ideas that haven't already been discussed and played out ad nauseum in that field.
        JasonSage 2y ago
        I’m not suggesting the techie is correct, I just don’t think the right answer is complete dismissal instead of communication. Ok, so you know it’s obviously wrong, but there’s no obligation to then go and stifle their curiosity or imagination. Just don’t say anything or let them talk to somebody who has the time and care to indulge. 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.
        layer8 2y ago
- quotemstr 2y ago
  > If you think there are others, please exhibit one. 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.
  - MaxikCZ 2y ago
    Thats like saying cars run because they want to, and only make us perfect the engine, and processes that happen inside it, to fool us into thinking we have a say in whether a car will run. 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.
    - shiroiushi 2y ago
      The funny thing is, though, you can easily dismiss a crazy idea like "omnitech space squid", but a majority of humans on Earth today have entire worldviews based on equally silly ideas, and it's considered wrong somehow to mock these belief systems. In fact, many scientists subscribe to these silly belief systems, but then get offended if you make up an equally silly idea about space squid or flying spaghetti monsters.
    - quotemstr 2y ago
      > 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.
    - 2y ago
- deleted 2y ago
  [deleted]
- alexey-salmin 2y ago
  > If you think there are others, please exhibit one. 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.
  - fpoling 2y ago
    A big problem of the modern cosmology is not only that we have observations that do not fit models but that we do not know if the observed discrepancies are the real problems with the models or are artifacts of calculations. 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.
- raattgift 2y ago
  There are a fair number of extensions to GR that can reproduce the standard cosmology, typically avoiding or recasting DM, DE, or both. Examples include generalized teleparallel gravity and Cotton gravity. In such theories, any solution of the EFEs are solutions of the (sometimes very different) field equations of these families of theories, although the field content may have a somewhat different physical interpretation from GR. 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).
- khafra 2y ago
  > > Surely there are infinite other possible explanations that fit the finite number of data points available > If you think there are others, please exhibit one. 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.
- krisoft 2y ago
  > If you think there are others, please exhibit one. 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.

stoperaticless 2y ago

> 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. Well..? What are those other observations that point to expansion?

pdonis 2y ago
> 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.
- handsclean 2y ago
  That’s just redshift. Redshift alone wouldn’t be evidence of expansion, just relative speed, when people say redshift evidence they mean the relationship between redshift and brightness of a standard candle. 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.
  - pdonis 2y ago
    > That’s just redshift. 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.

handsclean 2y ago

It’s not just phlogiston, it’s the lifecycle of all scientific theories that they’re used for as long as they make accurate predictions, then we start seeing things they mis-predict, then they’re revised or replaced. You seem to think the expanding universe theory can still be saved by some data artifact or parameter tweaking, but that’s been hunted for years and we’re still at “we just can’t make it match everything we’re seeing”. Historically, that’s what precedes significant revision or replacement. > Redshift is not the only observation we have. What else is there?

pdonis 2y ago
> it’s the lifecycle of all scientific theories that they’re used for as long as they make accurate predictions, then we start seeing things they mis-predict, then they’re revised or replaced. 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.
- Vecr 2y ago
  > 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.
- nilkn 2y ago
  Galileo’s principle of relativity is used all the time.
sandworm101 2y ago

peoplefromibiza 2y ago

> Not possible 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

sandworm101 2y ago

>> The totality of all the observations we have cannot be explained in any other way than an expanding universe. 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.

lumost 2y ago

I agree with you on the overall point, but this statement. > 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.

pdonis 2y ago
> Cosmology rests on the principal that physics is the same in all directions, over all translations, and over time translation. 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?