# The Big Bang

1. Jul 12, 2010

### robsharp14

The big bang was an explosion of space and time and becouse space and time was not inexistance untill after the big bang it is impossible to ask when or where the big bang happend..... right.

2. Jul 12, 2010

### mgb_phys

correct

3. Jul 13, 2010

### TrickyDicky

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

4. Jul 13, 2010

### mgb_phys

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

5. Jul 13, 2010

### Quantum-lept

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

"-since a singularity cannot be mathematically defined."

6. Jul 13, 2010

### Dmitry67

Age relative to what?

7. Jul 15, 2010

### travwg33

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.

8. Jul 25, 2010

### Quantum-lept

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

9. Jul 28, 2010

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. Jul 28, 2010

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?

11. Jul 28, 2010

### Chronos

12. Jul 28, 2010

### Deuterium2H

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. Aug 9, 2010

### robsharp14

some say that its reverse inertia, others say its entropy im not sure i have alot more digging and recording to do before im 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. Aug 10, 2010

### bapowell

Relative to the big bang, taken to have occurred at t = 0 in the rest frame of the CMB.