Big Bang happened 13.7 billion years ago.

So it's not 'infinite' in terms of time.

   multiple big bangs, and multiple orgasims, not much difference .... infinately fascinating

As far as I understand, the big bang is supposed to have created space and time. So I guess there isn't any 'before' the big bang. Can anyone elaborate?

What "force" are you referring to LadyMadonna?

   umm, a little bit more to it?, don't worry said buddha .... be nice to yourself ....

I have always thought it acceptable to say "I don't know and no one does for sure, at least I don't make up fairy tales to comfort myself about it".

Well the force to which I am referring is the universe in its entirety. It is where all of this began.

Tao Te Ching: Chapter 1
translated by Stephen Mitchell

"The Tao [god shit] that can be told
is not the eternal Tao.
The name that can be named
is not the eternal Name."

Why do you need to give them an answer?  In my lifetime we didn't know HPV was linked to cervical cancer.  I'm sure if I listened to ministers they were probably blaiming it on the sin of promiscuity.  Humans used to believe in a solar deity - Apollo - but most people agree why the sun actually does keep showing up everyday.  Just because you don't have an answer for "where it all began" doesn't mean "God" needs to fill the gap.  Next time these people tell you how the origins of the universe are evidence of God tell them how intellectually lazy that answer is.

No. That is completely absurd. All the Big Bang theory states is that the universe expanded outwards 13.7 billion years ago from a very dense, extremely low entropy prior state. Many theists miscontrue the Big Bang as ex nihilo, "out of nothing". It is not the case. There are certain models postulating pre-Big Bang occurances, the boundary condition in Hartele-Hawking, brane cosmology, etc. But the BB itself says nothing about the creation of the universe. It simply describes an expansion occurance 13.7 billion years ago from a prior state, and the model describes occrances from the Planck time onwards from this prior state, that we can describe events from the Planck Time until the end of BB nucleosynthesis. It can be calculated like thus:

What all the stellar methods of determining astronomical distance such as gravitational lensing, spectroscopy, Cepheid variables etc are for is attempting to determine Hubble's constant. The universe is expanding in size, which means, Hubble realized, that it had a beginning expansion, which cosmologists called the Big Bang. Hubble's constant is called H, and we determine it by examining redshift. The color of light depends on its wavelength, and red has a longer wavelength than white light. Since the universe is expanding, all the galaxies are moving away from each other, which means that when we observe them, they should have a longer wavelength of emitted photons, since the acceleration away from us causes the wavelength of the light to expand (like an accordian). Measuring the redshift by measuring the distance of astronomical objects allows us to determine the rate of acceleration of expansion of the universe, and that allows us to determine precisely when the universe began expanding.

That is one way how we know the universe is 13.7 billion years old. Given the rate of expansion of the universe, if we wind the clock back to the Big Bang, it occurred 13,700,000,000 years ago give or take a couple hundred thousand years.

Now, we will be delving into some mathematics which are conceptually simple but may appear frightening. We need to understand the following concepts:

Hubble’s Law: The universe is expanding. This means that all cosmological bodies are moving away from each other. As a result of this recessional velocity, the wavelengths as observed from other bodies from which the ones being measured are receding from will shift, and become greater. Hubble’s Law states that the amount of redshift is directly proportional to distance

At small distances, the acceleration of the universe is cancelled out by gravity (Newton’s inverse square law), which means that they will be moving towards each other. As a result, observers of these bodies should see blueshift, which is the opposite of redshift. Since the body is moving closer to the observer, the wavelength will compress, not expand. However, for the purpose of this exercise, this is immaterial, since we will not be looking at short distance cosmology.

Hubble’s Constant:

Omega: That the universe is expanding depends on the density of the universe, and the two constants associated, Omega (Ω) and Lambda (λ). This is not to be confused with Lambda in physics, which represents wavelength. In cosmology it has another meaning. At any rate, Newton’s equations, which work perfectly until they disintegrate at the quantum level, dictate that all material bodies have a force of attraction between them which is precisely proportional to the square of the distance between them and the size of the body in question. This is Newton’s Inverse Square Law. Since Einsten’s General Relativity, we have understood that this works because gravity is caused by the distorting effect of material on spacetime, However, surely this means that all material bodies should quickly rush towards each other and crush into a fiery pinprick? No. The reason for this is because the universe, as in space-time itself, is expanding. As we have discovered, the universe is expanding due to Dark matter. Now, this is where Omega comes into play. The density of matter in the universe will determine Omega. Since all material bodies attract, and the expansion of space time forces them apart, there is a fight between Dark Energy and matter, and the density of matter over the universe will determine its ultimate fate.

Now, if Omega is precisely zero, then the acceleration of the universe and the gravity of matter will be in precise equilibrium and thus the universe will expand at a precise constant rate. If Omega is smaller than one then the expansion of the universe will wind down, and if it is precisely one, the universe will simply wind down and stop expanding, and if Omega is greater than one, then the density of matter will be overpowering and the universe will accelerate and then crush back into a fiery pinprick, as the universe rushes backwards into a fiery pinprick by parabolic expansion and then contraction.

We have discovered by means of measuring the redshift of supernovae, that none of these things are happening. The universe is not constantly expanding, decelerating, or contracting. In fact, it is accelerating in expansion, which is given by the dotted line on the graph marked accelerating.

The Metric Expansion of Space: this is the most accurate and current model of the universe to date. The expansion of space-time overpowers gravity and hence accelerates in expansion. We can determine the rate at which space-time accelerates using Hubble’s constant. Then, by extrapolating backwards, we can determine the precise time at which the universe began to expand, in other words, if we have the value of acceleration of the universe, we can work backwards and determine the moment of creation, that will be the origin or the singularity on that graph, when the distance between all material beings was negligible, in other words, we can work out when the Big Bang occurred.

Cosmological Redshift: There are many different types of redshift. There is the Relativistic Doppler Effect, where redshift is caused by the relative velocity of two bodies from each other (this is the effect of Special Relativity), there is gravitational redshift, caused by the distortion of space time by material bodies, but these do not matter at cosmological distances. What we need to look at is cosmological redshift, that is, the redshift caused by the expansion of space-time, this is the only form of redshift which has measurable consequences at cosmological distances.

When we examine distant galaxies, we discover they are moving away from us at a calculable rate. Based on the distance they are from us, the wavelength of light from them which we are observing also changes by a calculable amount. The recessional velocity (the speed at which other galaxies are moving away from us), the distance which galaxies are from us, the redshift, or change in wavelength as a result of this recession and distance, and lastly, the acceleration or the rate at which the velocity is increasing, are all linked by several simple equations, and from this we can easily determine the age of the universe, or rather, how long ago the point was that there was no distance between the two receding bodies, the moment of the Big Bang. Firstly,

v=HD

This is the simplest equation we must understand. The recessional velocity (the speed at which a body is moving from Earth) is directly proportional to the distance it is from us. What connects them is Hubble’s constant, which is exactly what we need to find out.

Now, what I am doing is unusual. It is perfectly accurate to determine the age of the universe using redshift and Hubble’s constant. But most cosmologists prefer the Friedman-Lemaitaire-Walker Metric, derived from Freidmann’s equations. However, these are mathematically vastly more complex than the simple equations which we are about to use (and they in turn are derived from Einstein’ solutions to general relativity, which are also very complex).

Anyway, v=HD can be rearranged to find Hubble’s constant based on the recessional velocity and distance of an observed galaxy, where we have: H=(v/D).

Also, the recessional velocity with respect to time (ie the time between the intervals measured) can be given by differentiation: dD/dT.

Hubble’s constant, the acceleration of the universe, is given in km/s/Mpc, as is v.

The next principle we must understand is z, z is the change in wavelength as observed due to the recession of galaxies. It is defined as( λemitted x λobserved/λemitted). There are simple equations which link v, z, and H, but they only work for close galaxies. When the galaxies measured are too distant, any model which uses z for estimation of Hubble’s parameter must detail the precise change in z, D, and H due to the fact that the light has taken so long to get to Earth. But for close galaxies, these paramaters will not have changed much, so we can estimate v using v=zc, where c is the speed of light. We will not be doing this. For one, close galaxies blueshift due to gravity, which also, obviously, totally distorts any result we may glean by cosmological redshift.

This means that I have to use the scale factor of the LRMW metric in order to derive an accurate result. We can calculate the distance to galaxies using Cepheid variables. We can calculate their recessional velocity using the amount by which the light has shifted. The problem is that the measurements the Cepheids give us will not account for the present position of the galaxy since the light from the Cepheids set out to Earth many millions of years ago for distant galaxies. However, if Hubble’s Law holds, this does not matter, because the acceleration of the universe is expressed as a constant, and we should still be able to use this data to extrapolate back into the Big Bang.

Now, for cosmological redshift, the formula given is:

1+z= (a_now/a_then).

a is the universe scale factor. The physical distance between commoving objects is given by L=λa(t), which is rearranged to give a(t)= L/λ

This can be expressed via Hubble’s Law (distance proportional to redshift) using this formula:

H=a₂(t)/a₁(t), where t is the time derivative of the equation

We are beginning to see how the expansion of the universe, redshift, wavelength, the distance and recessional velocities of galaxies and the time taken for this to occur all tie together and all converge to give us the age of the universe. a or the scale factor is a simple ratio of wavelength emitted: wavelength received, which allows us to account for the change over large times. If the wavelength of light which we receive from a star is twice its original wavelength, that means that the universe in terms of space-time has doubled in size since that photon left the body which emitted it. This is because cosmological redshift is caused by the expansion of space-time itself, which stretches the wavelength of light being emitted over long distances.

We will be examining standard candles later, ie Cepheid variables, but the best way to determine the absolute magnitude of an object, the very best standard candles are Type Ia supernovae. It was using observations from these from the Chiandri telescope that we first realized the universe is accelerating. The output of light from a Type 1a is always the same, and so we can use it to determine absolute magnitude and distance, and by taking pictures over several days and weeks of massive type 1a supernovae, we realized first that the universe is accelerating.

Recall that redshift is just received λ /emitted λ. This ratio is called z. Multiplying z by light speed gives us distance, however this is not as accurate as the directly proportional relationship of distance given by Hubble’s constant.

I ought to be calculating the age of the universe using the Friedmann equations, and the integration of H with the three Omega constants. I can do this, but it is ridiculously complex, and there is no need to put it in this paper. Once we have H, we can determine age as a function of acceleration of the universe, but we do not need to do that either, we can just extrapolate backwards once we have distance and acceleration, it is H that we are looking for

Hubble’s constant is hotly debated, but based on the present data, the COBE estimates place it around 71km/s/Mpc. Note that we determined this by observing Type 1a supernovae using exactly the simple formula I outlined after calculating the redshift:

v=HD, 1+z=(a_now/a_then), zc=Ho, and a(t)= L/λ, and H=a₂(t)/a₁(t). There are multiple ways, as we have seen, to express Hubble’s constant: As functions of velocity, distance, the FLRW metric, and z. As of 2007, all expressive functions of H are in concurrence. It is definitely between 50-90, and the best data indicates it is 71.

We need to find q, that is the parameter of acceleration, and in terms of Hubble’s constant, it is:

Q=-H^-2((dH/dt)+H^2)

Now, we have known since 1998 that q is a negative value, and this value must be integrated (not figuratively, as in literally integrated mathematically by means of the ∫ operator), and extrapolate from when the commoving horizon was zero, the moment of the Big Bang.

It is useful to know the 71km/s/Mpc value because it allows us our extrapolation. It allows us to calculate useful values like the Hubble length and the Hubble time. The Hubble lengths is a good value to work with, and is simply the c/Hubble Time, where the Hubble Time is 1/H0. These are crude ways to measure the age of the universe, but are helpful if you want to demonstrate the age of the universe using a calculator and a pen and a data table as opposed to a satellite. If Hubble length is c/H(t), where H(t)=1/H, then H(l)=Htc, which is 300,000/71=approximately 4220 Mpc, since we are working in km/s/Mpc. 4220Mpc is converted into light years by the fact that 1 Megaparsec is 3,262,000 light years, from which we derive: 1.37x10^10 light years or 13.7 billion ly.

Hubble Time is also useful as a rough estimate of the universe's age. The Hubble Time is a useful function of the recessional velocity, where if v=HD, then 1/H=d/v. Since it is a reciprocal, we have to reverse all of the units, and so (converting 71km/s/Mpc to 20km/s/Mly makes it easier), we have to reverse everything, so we end up with 10^6 light years per megalight year, and 9.5x10^12 km per light year, which can be demonstrated like this:

1 Light Second= 300,000km, one light year=3x10^5 x 60 x 60x 24 x 365=9.5x10^12km

The reason we need to add the 10^6 is because the second reciprocal has been changed to km/ly as opposed to km/Mly. This just makes it a lot easier. And since the H constant is in seconds, we need to express the function in seconds. One year contains 3.15x10^7 seconds  Now:

1/20x10^6x9.5x10^12x 1/3.15x10^7, which becomes roughly 1.45x10^10 years, or 14.5 billion years. As you can see, this is a crude method, but is good for quick calculation.

However, this function is only a rought estimate of the age of the universe, since H is not actually constant. However, this is not really any sort of concern regarding the scale of the length of time. A significantly lower H constant yields a higher value of 16 billion, while a much higher H constant of 90 (50-90 are generally considered as the lower and upper bounds on the constant), then we derive 9 billion. 

Wow, you really know how to educate! Thank you for the enlightenment. What a stupid assumption I had all this time.

If you're looking for an easy(er) to grasp origin of the universe, there's a decent video of Hawking on YT. 

http://youtube.com/watch?v=nFjwXe-pXvM

Thank you. Did you shut down that "aura" photography fraud with the information provided? 

+1 for the good Captain for the answer in the first post, and +1 for DG for the explaining WHY Cap'n is right.

The explanation was a bit long-winded, so I'll provide a brief review/summary:

It was his sled. There, I just saved you two boobless hours

That the one where Brian goes to TX? 

Not yet. I doubt I could shut him down, unless there is someone around here that's savvy with Australian law in these matters. But I do plan to at least confront him in some manner, to provide him with some facts.