Big Bang: Space & Time Explained

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Discussion Overview

The discussion revolves around the concept of the Big Bang, particularly focusing on the nature of space and time in relation to the event, the methods used to estimate the age of the universe, and the implications of cosmic expansion. Participants explore theoretical and observational aspects, as well as speculative ideas about the universe's future.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that the Big Bang was an explosion of space and time, suggesting that it is impossible to define "when" or "where" it occurred since space and time did not exist prior to the event.
  • There is a question about the validity of stating an exact age for the Big Bang (e.g., 13.7 billion years ago), with some arguing that while we can measure how long ago it was, we cannot discuss time before the Big Bang.
  • Participants discuss the methods used to estimate the age of the universe, including the observation of galaxies and their recessional velocities, leading to the application of Hubble's law and calculations involving Hubble's constant.
  • One participant challenges the simplicity of a previous explanation regarding Hubble's measurements, noting that the redshift-distance law is only approximately true and diverges at larger distances.
  • Speculative questions are raised about whether the universe will eventually contract back to a singularity, akin to the life cycle of a star, and what forces might drive such a process.
  • There are references to models and observations that inform our understanding of cosmic expansion, with mentions of the FLRW metric and the Lambda-CDM model as currently favored cosmological models.
  • Some participants express uncertainty about the factors that could reverse cosmic expansion, suggesting concepts like reverse inertia or entropy without reaching a consensus.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of the Big Bang and the implications of cosmic expansion. There is no consensus on the speculative aspects of the universe's future or the interpretation of observational data related to Hubble's law.

Contextual Notes

Limitations include the dependence on specific cosmological models, the unresolved nature of certain mathematical relationships, and the varying interpretations of observational data.

robsharp14
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The big bang was an explosion of space and time and becouse space and time was not inexistance until after the big bang it is impossible to ask when or where the big bang happened... right.
 
Space news on Phys.org
correct
 
robsharp14 said:
The big bang was an explosion of space and time and becouse space and time was not inexistance until after the big bang it is impossible to ask when or where the big bang happened... right.

mgb_phys said:
correct

So what's with people saying exactly when it happened (13.7 bly ago)?
 
TrickyDicky said:
So what's with people saying exactly when it happened (13.7 bly ago)?

No problem measuirng how long ago it was, you simply can't say anything about time before then
 
mgb_phys said:
No problem measuirng how long ago it was, you simply can't say anything about time before then

Does mathematical model predict BB's age? Or is it all observational?

what about http://www.physorg.com/news198135631.html
"-since a singularity cannot be mathematically defined."
 
Age relative to what?
 
Modeling and observation both were used. Basically galaxies were observed and there recessional velocities were measured (not at all easy to do) and this was graphed on the y-axis of a graph and on the x-axis the distance of the galaxies was plotted. Then a linear regression was plotted and the slope is equal to Hubble's constant (Ho) and was used in the equation V=HoD (V=recessional velocity, D = distance) The value is around 72 or so (km/s)/Mpc I believe.
From here you take the equation V=D/t and solve for t

Vt=D
t=D/V
----and then take the equation V=HoD and rearrange the variables so that one side is D/V

1=(Ho)/V
1/Ho=D/V
----and then substitue the vaules to get the equation: t=1/Ho
Taking the value you get from this you multiply it by 1/(# of seconds in a year) and by 1/(number of kilometers in a megaparsec(mpc)) in order to remove the km and mpc units on the value and you are left with the age of the universe.
 
travwg33 said:
Modeling and observation both were used. Basically galaxies were observed and there recessional velocities were measured (not at all easy to do) and this was graphed on the y-axis of a graph and on the x-axis the distance of the galaxies was plotted. Then a linear regression was plotted and the slope is equal to Hubble's constant (Ho) and was used in the equation V=HoD (V=recessional velocity, D = distance) The value is around 72 or so (km/s)/Mpc I believe.
From here you take the equation V=D/t and solve for t

Vt=D
t=D/V
----and then take the equation V=HoD and rearrange the variables so that one side is D/V

1=(Ho)/V
1/Ho=D/V
----and then substitue the vaules to get the equation: t=1/Ho
Taking the value you get from this you multiply it by 1/(# of seconds in a year) and by 1/(number of kilometers in a megaparsec(mpc)) in order to remove the km and mpc units on the value and you are left with the age of the universe.


Thank you!...This appears to be what i have been asking for, a concise explanation...

can i assume then that since the age of the universe has changed some during my lifetime that the observation part of this procedure was what they were correcting with?..thanks
 
A new question.
I know when a sun is large enough when it dies it expands and then retracts into a black hole. is the same thing true of the big bang? i mean will there be a point of time where everything comes back to the the singularty. Moreover what is the force that brings it back to the begging. gravity?
 
  • #10
When a cube of sugar dissolves completely into a glass of water and all the molecules are even dispersed that would represent a universe that has stopped expanding. so what is the factor that brings it back together?
 
  • #12
travwg33 said:
Modeling and observation both were used. Basically galaxies were observed and there recessional velocities were measured (not at all easy to do) and this was graphed on the y-axis of a graph and on the x-axis the distance of the galaxies was plotted. Then a linear regression was plotted and the slope is equal to Hubble's constant (Ho) and was used in the equation V=HoD (V=recessional velocity, D = distance) The value is around 72 or so (km/s)/Mpc I believe.
From here you take the equation V=D/t and solve for t

Vt=D
t=D/V
----and then take the equation V=HoD and rearrange the variables so that one side is D/V

1=(Ho)/V
1/Ho=D/V
----and then substitue the vaules to get the equation: t=1/Ho
Taking the value you get from this you multiply it by 1/(# of seconds in a year) and by 1/(number of kilometers in a megaparsec(mpc)) in order to remove the km and mpc units on the value and you are left with the age of the universe.

travwg33, your explanation is not entirely correct. Or perhaps you left out a few things in order to keep it simple. What Hubble measured was in actuality the redshift-distance law, which is: zc = constant x distance = HL. However, this realationship is only approximately true, and is only valid for "small" distances, i.e small redshifts. The larger the redshift, the greater divergence in the validity of the Hubble Law (redshift-distance law).

At distances of comological significance, the Velocity-Distance Law must be used:
V = H0L, where "V" is a true recession velocity caused by the expansion of space. And as such, V (recession velocity) can exceed the speed of light. Recession velocity is not a "normal" velocity, and is not constrained by the rules of Newton or Special Relativity

In order to determine H0 at the present time, one must apply a particular cosmological model giving the global geometry and rate of change of the scaling factor (R). Observations are made in order to determine which cosmological model best fits the observational evidence. Currently, the best cosmological model consistent with observational data is the FLRW metric combined with the Lamda-CDM model.
 
  • #13
Kylebrad98 said:
When a cube of sugar dissolves completely into a glass of water and all the molecules are even dispersed that would represent a universe that has stopped expanding. so what is the factor that brings it back together?

some say that its reverse inertia, others say its entropy I am not sure i have a lot more digging and recording to do before I am able to answer this question anywho. your about to take a dive into the topsy turvy and all kinds of curvy world of quantum physics, have fun.
 
  • #14
Dmitry67 said:
Age relative to what?
Relative to the big bang, taken to have occurred at t = 0 in the rest frame of the CMB.
 

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