Coincidence/Fine Tuning Problem

Today we’re gonna talk about one of the remaining mysteries of the universe, fine tuning problem. Are we just lucky? Let me explain. So we already talked about this energy budget of the universe. So 70 percent of the energy budget of the universe is dark energy, and then 24 percent is dark matter. And then only 4.6 percent, it’s something we are familiar with. But, in this universe this dark energy and dark matter are comparable amount. It’s not like dark energy is 1,000 times more than dark matter, or dark matter is 1,000 times dark energy. And then this comparable amount of dark energy and dark matter is what we need for human to be born.

For example, if the universe is 99 percent dark energy, then everything is fly apart, and there will be no stars born, no planets born and then no human is born. So it’s a very, you know, empty universe. On the other hand, if the universe is 99 percent dark matter, then everything is going to be black hole, everything is going to be collapsed, by the gravity, and everything is going to be black hole, and then again, there’s no star, no planet, no human. That’s very, very dark universe. But, our universe is very well balanced between dark energy and dark matter, it’s about the same amount. That’s why stars can born, planets can born, and then we human was born.

And why it is so fine-tuned? Are we just lucky, or is there any physical reason? That’s an interesting question. Uh, let me explain it, how unusual this is, in this view graph. So, this plot is from Einstein’s equation, if you solve Einstein’s equation and plot and the evolution of amounts of dark matter, or amount of dark energy as a function of time. And if dark matter, omega matter, dark matter is born at the beginning of the universe, then you can follow this curve and dark matter stays at one, 100 percent, even today. Right, so this is just a black hole universe.

If dark energy, omega-lambda, is zero at the beginning of the universe, then again this flat curve, if you follow this line, the energy, dark energy, also stays zero at today, so redshift zero it’s today, this is about the time of the CMB. So, but our current value measured by the CMB radiation is here. It’s 70 percent dark energy, and 30 percent, uh, dark matter, right? To be able to do that, 70 percent dark energy, 70, 30 percent dark matter today, then, if you go back in time, dark energy must be 0.000000003, and dark matter must be 99.9999996 percent. We need this precise number to be able to reach our current state.

Isn’t that weird, so this dark energy is almost zero, right? But it cannot be zero, it has to be a little bit more than zero to be this value. And dark matter, this 0.999…, this is almost one, right? But it cannot be one, it would stay, if it’s one it’s gonna be black hole universe. It has to be little bit, one billionth times less than one, otherwise we cannot reach this state. Isn’t that weird? So this is, it looks like the universe, these parameters are fine-tuned so that we can reach here. So this is the fine-tuning problem. One famous cosmologist, Mike Turner, um, had a metaphor that called this as a Nancy Kerrigan problem. Nancy Kerrigan is a former U.S.

Olympic skater, but, uh, she was attacked, um, on her leg just before the Olympics, so, at that time she said “Why me? Why now?” it’s the same, similar problem is happening in the universe. So, what’s going (on)? It doesn’t look like coincidence, isn’t it? One out of billions? That can be too, too good to be true, to be a coincidence. So, some people argue, this may be the reason, um, to consider the multi-universe. There may be, the argument is like this. There may be multiple, multiple universe, with different cosmological parameters.

And then, um, there happened to be fine-tuned universe with dark energy 70 percent, dark matter 30 percent, and that’s where humans can born, that’s why we are born, in this universe. So in this argument there may be, there are a lot of universe, where human cannot born, cannot be born, because of dominated by dark energy or dark matter.

So this one of the arguments. But, the problem is this we cannot, uh, observe, we cannot confirm because we can only observe this universe. The theory, there’s a lot of theoretical models, maybe dark energy is oscillating, so dark energy dominated, and then come back, maybe, um,

but still this is also just a theory, 00:06:42.000 –> 00:06:45.000 so this fine-tuning problems

still remains a mystery of the universe. Very interesting.