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The question is "how long has it been since the big bang." It's an important and relevant question for cosmology and physics. It isn't really a stance on the "b

The question is "how long has it been since the big bang." It's an important and relevant question for cosmology and physics. It isn't really a stance on the "beginning of time," which may have started long before this moment, but it is the start of the universe as far as physics is concerned.

davorak 3y ago
> but it is the start of the universe as far as physics is concerned At least what we currently spend most of time studying/researching in physics right now. We can hope to expand beyond that given enough time.
- philipov 3y ago
  > ...given enough time. There might literally not be enough time to expand beyond that, given how cosmological horizons work. Being part of the system we're trying to observe puts some nasty limits on what we can know, even in principle.
  - outworlder 3y ago
    There are even (ever shrinking) limits on how much of the universe we can observe.
  - kulahan 3y ago
    Pull the levers and see what happens, and then write it down. That's really all we can do.
  - davorak 3y ago
    I agree we practically may never know and fundamentally the rules of the universe might end up making it impossible to know somethings, but as far as I know the ultimate limits are currently unknown so 'We can hope ...'.
  - mensetmanusman 3y ago
    It's kind of cool to think that some idea that someone has at some point in the timeline of consciousness might be true; but impossible to prove.
malux85 3y ago
One thing I have always wondered, since gravity is proportional to the mass of the two objects and inversely proportional to the square of the distance between them, if the universe was smaller with the same mass, wouldn’t gravity have been more “dense” in an earlier universe? And since we know that gravity affects the rate of flow of time, wouldn’t the rate of time be enormously distorted earlier universe? I’m not trained in any of this, so hopefully there are greater minds here who can help me understand
- candiodari 3y ago
  We know that the force carrying particles of all forces have a frequency, just like any other particle. That means that if particles on average move faster than, say, double that frequency, they can't exist. So there must have been a time when electromagnetism, the weak and even the strong force just didn't exist. They couldn't. So particles would just have totally ignored those forces. We don't know if gravity is the same, but ... why wouldn't it. Though of course according to relativity gravity just wouldn't care, but that just raises a lot more questions than it answers.
  - addaon 3y ago
    > particles on average move faster than, say, double that frequency What does it mean to compare ("faster") a velocity and a frequency (inverse time)?
    - candiodari 3y ago
      I don't think there's a good answer to this question, at least not when it comes to the nature of particles and light, because we don't have a good answer to what movement and time are. We already know both light and particles are you moving relative to fields. Light is you moving relative to an electromagnetic field. If you move towards a magnetic field you would find it starts "glowing", in fact, that is what light is. But it's not like a magnetic field reacts to you because you start moving. The issue is that movement and time are fundamental to the universe, yes, in the way relativity describes but also in a totally different unknown way. In some ways particles are "just" things moving relative to one another. Which, for one thing, brings the perspective question (if you accelerated to a "real" speed, would you see a different universe? Because you would disagree with us slowpokes here on earth on what particles exist at least in some cases. But would you see an entirely different universe?)
deleted 3y ago
[deleted]
fnordpiglet 3y ago
Maybe I guess. Many models stipulate that time began with the Big Bang. Many propose the Big Bang was a local event that obliterated our ability to observe time before it. We have models where the universe rips apart, collapses, or just evolves forever and always has and always will. I think what’s crucial to understand is we have a lot of different possible explanations for what we see, some of them discuss beginnings and ends, some do not. Perhaps as a mathematician with a relatively closed set of possibilities for explanations that’s unsettling. But, I’ve always found the various paradoxes in math to illustrate similar problems in formulating a closed and coherent anything, including the universe.
ajross 3y ago
> It isn't really a stance on the "beginning of time," which may have started long before Well... yes it is, in the rigorous sense of "time" defined by general relativity. There's no "before" for a singularity. It may not be the whole story, but whatever metaphysical notion defines the "before/beyond/outside/why" that drives the big bang, it's not a place on the "time" axis of spacetime.
- mathematicaster 3y ago
  IMHO this conflates model with reality. GR is a model.
  - lvncelot 3y ago
    Specifically, GR is a model that breaks down at singularities. That time "begins" at the Big Bang is a prediction of GR, but until we have a model of quantum gravity there's no telling whether that's actually true or whether the conditions at the big bang are something GR can't fully describe. Similar to the singularities in black holes - everything up to a stone's throw of the event horizon is pretty well explained by GR, but as far as the horizon itself or the region beyond are concerned, there might be dragons as far as we know.
    - skissane 3y ago
      > That time "begins" at the Big Bang is a prediction of GR I don’t think that’s right. If we interpret Big Bang theory as claiming that there is a singularity at a finite distance into the past history of every present event, then GR can’t predict what happened at or prior to that singularity. Whether time “began” then or whether there was “more time on the other side” is a question GR alone cannot answer, not a prediction of GR
    - Beldin 3y ago
      Black hole singularities do not start right after their event horizon. The event horizon only demarcates where the black hole singularity becomes an inevitable (inescapable) point in all possible futures.
chinabot 3y ago
How I work it out in my head that time effectively did not exist before the big bang is that; If everyone agrees that time slows as the gravity increases, and we assume at the time of the big bang that all the mass of the universe was in an infinitely small space, the conclusion is we had an infinitely large gravity and time would be effectively be stopped. Take it with a grain of salt.
- Angostura 3y ago
  But that could have been a pause, rather than a start, perhaps?
  - MobiusHorizons 3y ago
    It is a singularity, which just means we don’t have a way of answering any questions about what was before
- 31337Logic 3y ago
  I like this. But you still have a Prime Mover problem. If time effectively halts at T0, then what possible event could occur (outside of time?) to nudge that infinitely large glob off mass into the motion we observe today?
  - Ygg2 3y ago
    There is an Anthropic Principle solution. If the events occured differently, we wouldn't be here to observe them.
    - canadianfella 3y ago
      [dead]
    - guerrilla 3y ago
      That explains nothing in this context.
moomin 3y ago
There’s an alternative take that says that, as the universe contracts, it eventually hits a point where other effects (quantum, but also possibly unknown effects) predominate and that this kicks off another stage of expansion. Which is to say that there exist respected papers that outline this scenario in great detail, but there’s precious little observable evidence of a previous universal cycle.

davorak 3y ago

> but it is the start of the universe as far as physics is concerned At least what we currently spend most of time studying/researching in physics right now. We can hope to expand beyond that given enough time.

philipov 3y ago
> ...given enough time. There might literally not be enough time to expand beyond that, given how cosmological horizons work. Being part of the system we're trying to observe puts some nasty limits on what we can know, even in principle.
- outworlder 3y ago
  There are even (ever shrinking) limits on how much of the universe we can observe.
- kulahan 3y ago
  Pull the levers and see what happens, and then write it down. That's really all we can do.
- davorak 3y ago
  I agree we practically may never know and fundamentally the rules of the universe might end up making it impossible to know somethings, but as far as I know the ultimate limits are currently unknown so 'We can hope ...'.
- mensetmanusman 3y ago
  It's kind of cool to think that some idea that someone has at some point in the timeline of consciousness might be true; but impossible to prove.

malux85 3y ago

One thing I have always wondered, since gravity is proportional to the mass of the two objects and inversely proportional to the square of the distance between them, if the universe was smaller with the same mass, wouldn’t gravity have been more “dense” in an earlier universe? And since we know that gravity affects the rate of flow of time, wouldn’t the rate of time be enormously distorted earlier universe? I’m not trained in any of this, so hopefully there are greater minds here who can help me understand

candiodari 3y ago
We know that the force carrying particles of all forces have a frequency, just like any other particle. That means that if particles on average move faster than, say, double that frequency, they can't exist. So there must have been a time when electromagnetism, the weak and even the strong force just didn't exist. They couldn't. So particles would just have totally ignored those forces. We don't know if gravity is the same, but ... why wouldn't it. Though of course according to relativity gravity just wouldn't care, but that just raises a lot more questions than it answers.
- addaon 3y ago
  > particles on average move faster than, say, double that frequency What does it mean to compare ("faster") a velocity and a frequency (inverse time)?
  - candiodari 3y ago
    I don't think there's a good answer to this question, at least not when it comes to the nature of particles and light, because we don't have a good answer to what movement and time are. We already know both light and particles are you moving relative to fields. Light is you moving relative to an electromagnetic field. If you move towards a magnetic field you would find it starts "glowing", in fact, that is what light is. But it's not like a magnetic field reacts to you because you start moving. The issue is that movement and time are fundamental to the universe, yes, in the way relativity describes but also in a totally different unknown way. In some ways particles are "just" things moving relative to one another. Which, for one thing, brings the perspective question (if you accelerated to a "real" speed, would you see a different universe? Because you would disagree with us slowpokes here on earth on what particles exist at least in some cases. But would you see an entirely different universe?)

deleted 3y ago

[deleted]

fnordpiglet 3y ago

Maybe I guess. Many models stipulate that time began with the Big Bang. Many propose the Big Bang was a local event that obliterated our ability to observe time before it. We have models where the universe rips apart, collapses, or just evolves forever and always has and always will. I think what’s crucial to understand is we have a lot of different possible explanations for what we see, some of them discuss beginnings and ends, some do not. Perhaps as a mathematician with a relatively closed set of possibilities for explanations that’s unsettling. But, I’ve always found the various paradoxes in math to illustrate similar problems in formulating a closed and coherent anything, including the universe.

ajross 3y ago

> It isn't really a stance on the "beginning of time," which may have started long before Well... yes it is, in the rigorous sense of "time" defined by general relativity. There's no "before" for a singularity. It may not be the whole story, but whatever metaphysical notion defines the "before/beyond/outside/why" that drives the big bang, it's not a place on the "time" axis of spacetime.

mathematicaster 3y ago
IMHO this conflates model with reality. GR is a model.
- lvncelot 3y ago
  Specifically, GR is a model that breaks down at singularities. That time "begins" at the Big Bang is a prediction of GR, but until we have a model of quantum gravity there's no telling whether that's actually true or whether the conditions at the big bang are something GR can't fully describe. Similar to the singularities in black holes - everything up to a stone's throw of the event horizon is pretty well explained by GR, but as far as the horizon itself or the region beyond are concerned, there might be dragons as far as we know.
  - skissane 3y ago
    > That time "begins" at the Big Bang is a prediction of GR I don’t think that’s right. If we interpret Big Bang theory as claiming that there is a singularity at a finite distance into the past history of every present event, then GR can’t predict what happened at or prior to that singularity. Whether time “began” then or whether there was “more time on the other side” is a question GR alone cannot answer, not a prediction of GR
  - Beldin 3y ago
    Black hole singularities do not start right after their event horizon. The event horizon only demarcates where the black hole singularity becomes an inevitable (inescapable) point in all possible futures.

chinabot 3y ago

How I work it out in my head that time effectively did not exist before the big bang is that; If everyone agrees that time slows as the gravity increases, and we assume at the time of the big bang that all the mass of the universe was in an infinitely small space, the conclusion is we had an infinitely large gravity and time would be effectively be stopped. Take it with a grain of salt.

Angostura 3y ago
But that could have been a pause, rather than a start, perhaps?
- MobiusHorizons 3y ago
  It is a singularity, which just means we don’t have a way of answering any questions about what was before
31337Logic 3y ago
I like this. But you still have a Prime Mover problem. If time effectively halts at T0, then what possible event could occur (outside of time?) to nudge that infinitely large glob off mass into the motion we observe today?
- Ygg2 3y ago
  There is an Anthropic Principle solution. If the events occured differently, we wouldn't be here to observe them.
  - canadianfella 3y ago
    [dead]
  - guerrilla 3y ago
    That explains nothing in this context.

moomin 3y ago

There’s an alternative take that says that, as the universe contracts, it eventually hits a point where other effects (quantum, but also possibly unknown effects) predominate and that this kicks off another stage of expansion. Which is to say that there exist respected papers that outline this scenario in great detail, but there’s precious little observable evidence of a previous universal cycle.