5 ms·

> Of course, all the results have error bars. Not to mention the underlying philosophical assumptions, such that the "rate of time" has been constant across al

> Of course, all the results have error bars. Not to mention the underlying philosophical assumptions, such that the "rate of time" has been constant across all of... time. Aka: How do we know a "year" 13 Billion "years" ago bears any resemblance to one now? What would it mean for it not to?

fooker 3y ago
Philosophical indeed, as it's impossible to define the idea of a rate of time, when the idea of rate is defined in terms on time itself.
- explaininjs 3y ago
  Yes, an external reference clock is needed. If a computer chugs along doing { counter++; } at 1 clock cycle per clock cycle for 13.7 billion clock cycles, it will think 13.7 billion clock cycles have passed when counter is 13.7 billion. On the other hand, if a computer chugs along at one clock cycle per clock cycle for 1 clock cycle, and reads &counter and sees 13.7 billion, it will think 13.7 billion clock cycles have passed. Either way it's perfectly capable of introspecting it's source code and logically stepping back until the memory location was 0 to see how many clock cycles would have been required to reach it's current state, but that sort of reasoning is completely devoid of meaning without both perfect knowledge of what the true start state was, and a guarantee that no external influences have occurred. Here in reality, we know neither the our start state nor our isolation level, but the hubris of many is too string to not at least try finding some logical step-back functions and iterating them until they don't know how to go any further, then proudly proclaiming that "The Start". (after all - how could it not be The Start, look, I can iterate the inverse of my step-backward function from then to now and it matches! QED!)
  - jMyles 3y ago
    I agree with you 100% on your assessment of what can be known, but I think I disagree nearly as strongly on your assessment of the humanity that springs from attempting to know it. To exist in the state you describe - with neither start state nor isolation level measurable in any tamper-proof way - and to yet still dedicate one's life to observing and pondering the complexity of the resulting cosmos is, to my eye, laudable and beautiful. Where you see hubris, I see humility. Everyone who attempts to expand the corpus of human understanding of cosmology knows that the endgame is somewhere short of perfection. And yet they are inspired to carry on. It seems to me that matters of state, economics, medicine, technology, and many other fields will benefit from a similar disposition.
    - explaininjs 3y ago
      I think the hubris comes in when folks assume that because that answer is presented by Science/Observation rather than Religion/Philosophy, it's somehow guaranteed to be "more accurate", when in reality both are guesses with equally unknowable error bars.
  - fooker 3y ago
    This reminds me of old computer games that started to run faster on newer computers, because of strong assumptions about clock speeds! For a hypothetical entity inside the game, nothing would have changed. https://www.vogonswiki.com/index.php/List_of_CPU_speed_sensitive_games https://www.vogonswiki.com/index.php/List_of_CPU_speed_sensi...
dartos 3y ago
I’d assume that we have some notion of how the laws of physics have changed, if at all, since the Big Bang. We measure time in vibrations of a cesium isotope IIRC
- db48x 3y ago
  No, we measure the frequency of vibrations of _light_, not of a type of atom. Specifically, it is light emitted by cesium atoms that are transitioning from one specific energy state to another specific energy state. Although this is arbitrary, it is highly reproducible and would give precisely the same measured lengths of time at any point since the big bang.
  - elashri 3y ago
    That assumes that fundamental laws of physics did not change (will not change). This is what we believe and have no evidence otherwise. This is important since we rely on measuring atomic transitions of cesium atoms which itself were formed/forming billions of years after the big bang itself. The laws of physics invariance under time is a core to our understanding. It would be very disrupting if we found otherwise.
    - not2b 3y ago
      Right, but most deviations one can think of (like, changes over time to physical "constants") would have an observable effect, so ancient galaxies would look much more different from modern galaxies and spectra wouldn't look the same other than a red shift, which moves all the lines in a uniform way.
- yongjik 3y ago
  Fun fact: the Oklo reactor, a naturally occurring nuclear reactor that was active more than a billion years ago, was used to test if physical constants were the same in ancient times. https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor#Relation_to_the_atomic_fine-structure_constant https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...
speak_plainly 3y ago
Time in this context is just an arbitrary measurement. Like extrapolating the calendar back to the Big Bang which is when space/time began, another way to think about time.
dwattttt 3y ago
How do we know <anything>? Observations we can make plus models that relate those to the things we can't observe directly.
- vlovich123 3y ago
  Unfortunately we can’t observe fundamental things like “what are the rules of physics and time at the beginning of the universe?”. We look for clues and make large assumptions, but given that the universe experienced a 10^78 factor expansion during the Big Bang, assuming that actually happened, then why would it make sense to assume that the rules of the universe today are the rules for the very early beginning of the universe? A strand of DNA would become 10 light years. Given that relativity redefined our understanding of basic physics but only applies as we approach the speed of light, it would stand to reason that the rules of physics would be different from our current models based on today’s observations when the matter of the universe is packed much more tightly together.
  - itishappy 3y ago
    Entirely reasonable assumptions! Our models match surprisingly well though... The CMB has a blackbody spectrum that aligns with predictions, we see galaxies more or less when and where we'd expect them, stellar populations look like what we'd expect for a universe made of hot hydrogen, and more! It's not quite perfect, but modern physics explains stuff really quite well even billions of years ago!
    - explaininjs 3y ago
      Modern physics is guided by those observations, they can't be then used as an argument for its veracity. Let's say I walk into a room and observe someone writing a tally mark on a chalk board once every second. I count 4x10^17 tally marks. I might assume that 4x10^17 seconds ago that same person entered the room and started tallying. I might even observe for the next 4x10^17 seconds they continue to tally. Heck I might even see a recorder going that when I play back at what I assume to be 1x speed, has chalk scratches at regular intervals for 4x10^17 seconds. I still don't have any actual evidence that they started those 8x10^17 seconds ago.
Veserv 3y ago
Well for one, if the laws of physics are not time invariant (i.e. the laws of physics are not the same at all points in time) then energy can be created or destroyed [1]. So that would be quite a shocker. [1] https://en.m.wikipedia.org/wiki/Noether%27s_theorem https://en.m.wikipedia.org/wiki/Noether%27s_theorem
- itishappy 3y ago
  Doesn't dark energy do exactly that? 70% of the energy of the universe doesn't seem to want to play by our rules!
  - digging 3y ago
    Yes, but my understanding is that dark energy doesn't play by the same rules, it's an exception. I certainly can't explain why but also it may not be known exactly why, given dark energy is an unexplained phenomenon.
    - cygx 3y ago
      The party line is that energy is not conserved at cosmological scales. However, it's more of a semantic question: We can tell you exactly by how much it gets violated (that's basically the first Friedmann equation), and if you prefer, you can attribute the missing energy to the gravitational field. A lot of physicists don't like that approach as it isn't possible to write down a corresponding stress-energy tensor, ie gravitational energy cannot be properly localized.
- explaininjs 3y ago
  Do you think the current amount of energy in the universe is 0? If not, how was it created?
  - baq 3y ago
    That's a completely different question, to which the answer is 'we don't know'.
wavefunction 3y ago
I have had the same thought that primordial reality had the same timestream as us but it was much longer, like the first "year" of reality was far longer than one year today, just the thinking "could time have been shorter or longer, why not"
- denton-scratch 3y ago
  > the first "year" of reality was far longer than one year today This talk about the "rate of time" doesn't make any sense to me. A second takes one second, and always has. Isn't this like asking whether the length of a metre might have changed over time? Or the mass of a kilogramme? It looks to me like a category error.
  - explaininjs 3y ago
    `This talk about the "rate of execution" doesn't make any sense to me. A cycle takes one cycle, and always has.` The root of the question is whether there exists an external "system clock", and what that would even mean.
    - denton-scratch 3y ago
      > whether there exists an external "system clock" I'll ignore your analogy with a CPU, which I don't think is apposite. Whether there's a 'system clock', a sort of reference clock that can tell you how fast time is passing, so you can calibrate other clocks against it, seems to be the same category error. As far as I can see, either time is all there, all at once; or one second lasts exactly one second. (I've perpetrated the same category error there, because a second doesn't 'last' for some period of time; it just is). [Edit] That's not very clear. I mean: if you are measuring a distance, you use a calibrated ruler. If you doubt the calibration of your ruler, you might recalibrate for precision. But you don't have a clear idea of what one foot is, it doesn't make any sense to ask whether your one-foot ruler has grown or shrunk; how would you tell if the purported 'fact' is true or false? And if some fact about the Universe means that it has grown or shrunk, how would you tell? If you can't in principle tell whether a 'fact' is true or false, it follows that the 'fact' isn't a fact, because it has no effect on anything. See Russells Teapot.
mr_toad 3y ago
Rates are measured with time as the divisor. What does rate of time even mean?
codethief 3y ago
Could you elaborate on your questions? As it stands right now, they don't sound well-defined/answerable. ("rate of time" etc.)

fooker 3y ago

Philosophical indeed, as it's impossible to define the idea of a rate of time, when the idea of rate is defined in terms on time itself.

explaininjs 3y ago
Yes, an external reference clock is needed. If a computer chugs along doing { counter++; } at 1 clock cycle per clock cycle for 13.7 billion clock cycles, it will think 13.7 billion clock cycles have passed when counter is 13.7 billion. On the other hand, if a computer chugs along at one clock cycle per clock cycle for 1 clock cycle, and reads &counter and sees 13.7 billion, it will think 13.7 billion clock cycles have passed. Either way it's perfectly capable of introspecting it's source code and logically stepping back until the memory location was 0 to see how many clock cycles would have been required to reach it's current state, but that sort of reasoning is completely devoid of meaning without both perfect knowledge of what the true start state was, and a guarantee that no external influences have occurred. Here in reality, we know neither the our start state nor our isolation level, but the hubris of many is too string to not at least try finding some logical step-back functions and iterating them until they don't know how to go any further, then proudly proclaiming that "The Start". (after all - how could it not be The Start, look, I can iterate the inverse of my step-backward function from then to now and it matches! QED!)
- jMyles 3y ago
  I agree with you 100% on your assessment of what can be known, but I think I disagree nearly as strongly on your assessment of the humanity that springs from attempting to know it. To exist in the state you describe - with neither start state nor isolation level measurable in any tamper-proof way - and to yet still dedicate one's life to observing and pondering the complexity of the resulting cosmos is, to my eye, laudable and beautiful. Where you see hubris, I see humility. Everyone who attempts to expand the corpus of human understanding of cosmology knows that the endgame is somewhere short of perfection. And yet they are inspired to carry on. It seems to me that matters of state, economics, medicine, technology, and many other fields will benefit from a similar disposition.
  - explaininjs 3y ago
    I think the hubris comes in when folks assume that because that answer is presented by Science/Observation rather than Religion/Philosophy, it's somehow guaranteed to be "more accurate", when in reality both are guesses with equally unknowable error bars.
- fooker 3y ago
  This reminds me of old computer games that started to run faster on newer computers, because of strong assumptions about clock speeds! For a hypothetical entity inside the game, nothing would have changed. https://www.vogonswiki.com/index.php/List_of_CPU_speed_sensitive_games https://www.vogonswiki.com/index.php/List_of_CPU_speed_sensi...

dartos 3y ago

I’d assume that we have some notion of how the laws of physics have changed, if at all, since the Big Bang. We measure time in vibrations of a cesium isotope IIRC

db48x 3y ago
No, we measure the frequency of vibrations of _light_, not of a type of atom. Specifically, it is light emitted by cesium atoms that are transitioning from one specific energy state to another specific energy state. Although this is arbitrary, it is highly reproducible and would give precisely the same measured lengths of time at any point since the big bang.
- elashri 3y ago
  That assumes that fundamental laws of physics did not change (will not change). This is what we believe and have no evidence otherwise. This is important since we rely on measuring atomic transitions of cesium atoms which itself were formed/forming billions of years after the big bang itself. The laws of physics invariance under time is a core to our understanding. It would be very disrupting if we found otherwise.
  - not2b 3y ago
    Right, but most deviations one can think of (like, changes over time to physical "constants") would have an observable effect, so ancient galaxies would look much more different from modern galaxies and spectra wouldn't look the same other than a red shift, which moves all the lines in a uniform way.
yongjik 3y ago
Fun fact: the Oklo reactor, a naturally occurring nuclear reactor that was active more than a billion years ago, was used to test if physical constants were the same in ancient times. https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor#Relation_to_the_atomic_fine-structure_constant https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto...

speak_plainly 3y ago

Time in this context is just an arbitrary measurement. Like extrapolating the calendar back to the Big Bang which is when space/time began, another way to think about time.

dwattttt 3y ago

How do we know <anything>? Observations we can make plus models that relate those to the things we can't observe directly.

vlovich123 3y ago
Unfortunately we can’t observe fundamental things like “what are the rules of physics and time at the beginning of the universe?”. We look for clues and make large assumptions, but given that the universe experienced a 10^78 factor expansion during the Big Bang, assuming that actually happened, then why would it make sense to assume that the rules of the universe today are the rules for the very early beginning of the universe? A strand of DNA would become 10 light years. Given that relativity redefined our understanding of basic physics but only applies as we approach the speed of light, it would stand to reason that the rules of physics would be different from our current models based on today’s observations when the matter of the universe is packed much more tightly together.
- itishappy 3y ago
  Entirely reasonable assumptions! Our models match surprisingly well though... The CMB has a blackbody spectrum that aligns with predictions, we see galaxies more or less when and where we'd expect them, stellar populations look like what we'd expect for a universe made of hot hydrogen, and more! It's not quite perfect, but modern physics explains stuff really quite well even billions of years ago!
  - explaininjs 3y ago
    Modern physics is guided by those observations, they can't be then used as an argument for its veracity. Let's say I walk into a room and observe someone writing a tally mark on a chalk board once every second. I count 4x10^17 tally marks. I might assume that 4x10^17 seconds ago that same person entered the room and started tallying. I might even observe for the next 4x10^17 seconds they continue to tally. Heck I might even see a recorder going that when I play back at what I assume to be 1x speed, has chalk scratches at regular intervals for 4x10^17 seconds. I still don't have any actual evidence that they started those 8x10^17 seconds ago.

Veserv 3y ago

Well for one, if the laws of physics are not time invariant (i.e. the laws of physics are not the same at all points in time) then energy can be created or destroyed [1]. So that would be quite a shocker. [1] https://en.m.wikipedia.org/wiki/Noether%27s_theorem https://en.m.wikipedia.org/wiki/Noether%27s_theorem

itishappy 3y ago
Doesn't dark energy do exactly that? 70% of the energy of the universe doesn't seem to want to play by our rules!
- digging 3y ago
  Yes, but my understanding is that dark energy doesn't play by the same rules, it's an exception. I certainly can't explain why but also it may not be known exactly why, given dark energy is an unexplained phenomenon.
  - cygx 3y ago
    The party line is that energy is not conserved at cosmological scales. However, it's more of a semantic question: We can tell you exactly by how much it gets violated (that's basically the first Friedmann equation), and if you prefer, you can attribute the missing energy to the gravitational field. A lot of physicists don't like that approach as it isn't possible to write down a corresponding stress-energy tensor, ie gravitational energy cannot be properly localized.
explaininjs 3y ago
Do you think the current amount of energy in the universe is 0? If not, how was it created?
- baq 3y ago
  That's a completely different question, to which the answer is 'we don't know'.

wavefunction 3y ago

I have had the same thought that primordial reality had the same timestream as us but it was much longer, like the first "year" of reality was far longer than one year today, just the thinking "could time have been shorter or longer, why not"

denton-scratch 3y ago
> the first "year" of reality was far longer than one year today This talk about the "rate of time" doesn't make any sense to me. A second takes one second, and always has. Isn't this like asking whether the length of a metre might have changed over time? Or the mass of a kilogramme? It looks to me like a category error.
- explaininjs 3y ago
  `This talk about the "rate of execution" doesn't make any sense to me. A cycle takes one cycle, and always has.` The root of the question is whether there exists an external "system clock", and what that would even mean.
  - denton-scratch 3y ago
    > whether there exists an external "system clock" I'll ignore your analogy with a CPU, which I don't think is apposite. Whether there's a 'system clock', a sort of reference clock that can tell you how fast time is passing, so you can calibrate other clocks against it, seems to be the same category error. As far as I can see, either time is all there, all at once; or one second lasts exactly one second. (I've perpetrated the same category error there, because a second doesn't 'last' for some period of time; it just is). [Edit] That's not very clear. I mean: if you are measuring a distance, you use a calibrated ruler. If you doubt the calibration of your ruler, you might recalibrate for precision. But you don't have a clear idea of what one foot is, it doesn't make any sense to ask whether your one-foot ruler has grown or shrunk; how would you tell if the purported 'fact' is true or false? And if some fact about the Universe means that it has grown or shrunk, how would you tell? If you can't in principle tell whether a 'fact' is true or false, it follows that the 'fact' isn't a fact, because it has no effect on anything. See Russells Teapot.

mr_toad 3y ago

Rates are measured with time as the divisor. What does rate of time even mean?

codethief 3y ago

Could you elaborate on your questions? As it stands right now, they don't sound well-defined/answerable. ("rate of time" etc.)