# WMAP and Big Crunch: Is the Universe's Fate Sealed?

• vincentm
In summary, the results of the WMAP survey have shown that the presence of dark energy makes the average energy density of the universe less critical in determining whether it will undergo a big crunch or continue expanding forever. Even with an average energy density equal to the critical density, the universe will expand forever due to the pressure of dark energy. Further calculations could determine the minimum ratio between the energy density of matter and dark energy for a closed expanding universe to start contracting.
vincentm
Hello all,

With the results of the WMAP survery of the CMB back in march of this year, has this ruled out the possibility of the universe undergoing a "big crunch"?

I've read somewhere that the average density of matter in the universe has been measured to be

p=1

Is this right?

In an universe without dark energy, an average energy density above the critical density would lead to a big-crunch, and an average energy density below or equal to the critial density would lead to an eternal expansion. However, with dark energy things are different. An universe with average energy density above the critical density may expand forever. This is because dark energy exterts a pressure that accelerates the expansion of space.

The average energy density measured by WMAP is equal to the critical density $\Omega = \rho / \rho_{crit} = 1$. Even if it would be slightly above the critical energy density, our universe would expand forever. I remember that a time ago I tried some calculations to find out what is the lowest value for the relation between the energy density of matter and the energy density of dark energy (assuming it to be a cosmological constant) for which a closed expanding universe will start contracting: if there is enough matter the expanding universe will start contracting regardless of the effect of dark energy and before it starts becoming dominant. I could not find this calculations now, but if you are interested we could try to figure it out.

Last edited:

Thank you for your question. The WMAP survey has indeed provided strong evidence that the universe is not headed for a "big crunch" scenario. The data from WMAP has shown that the universe is expanding at an accelerating rate, rather than slowing down and eventually collapsing. This is due to the presence of dark energy, which is a mysterious force that is causing the expansion to accelerate.

In terms of the average density of matter in the universe, the value of p=1 is not entirely accurate. The actual value is closer to p=0.3, meaning that matter only makes up about 30% of the total energy density of the universe. The rest is made up of dark energy and dark matter, which are still not fully understood by scientists.

Overall, while the WMAP results do not completely rule out the possibility of a big crunch, they do strongly support the idea that the universe will continue to expand indefinitely. So, it seems that the fate of the universe is not sealed just yet, but it is certainly not headed for a big crunch.

## 1. What is WMAP and how does it relate to the Big Crunch?

WMAP (Wilkinson Microwave Anisotropy Probe) is a NASA mission that studied the cosmic microwave background radiation, which is a remnant of the Big Bang. The Big Crunch is a theoretical concept in which the universe collapses in on itself due to the gravitational pull of all matter, potentially resulting in the end of the universe. WMAP provided valuable data that supports the existence of the Big Crunch.

## 2. What evidence supports the idea of a Big Crunch?

One of the key pieces of evidence for the Big Crunch is the observation that the expansion of the universe is not slowing down, as one might expect from the force of gravity, but is actually accelerating. This suggests that there is a repulsive force, known as dark energy, countering the pull of gravity. However, this acceleration is not infinite and may eventually reverse, leading to a collapse of the universe.

## 3. Could the Big Crunch actually happen?

While the concept of the Big Crunch is supported by current theories and observations, it is still a hypothetical scenario and there is no guarantee that it will actually occur. The ultimate fate of the universe is still a subject of debate among scientists, and there are other possibilities such as the Big Rip or the Heat Death of the universe.

## 4. What would happen to life on Earth if the Big Crunch were to occur?

If the Big Crunch were to happen, it would likely result in the destruction of all matter in the universe. This would mean the end of all life, not just on Earth, but anywhere in the universe. However, the exact effects on life would depend on the specific mechanism of the Big Crunch and our understanding of it is still limited.

## 5. Is there any way to prevent the Big Crunch?

Currently, there is no known way to prevent the Big Crunch from happening. However, it is possible that future advancements in science and technology may provide new insights and solutions to this problem. Some theories suggest that the expansion of the universe could be slowed down or reversed through the use of advanced energy manipulation or gravitational manipulation techniques, but these are purely speculative at this point.

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