Dark Energy/Matter: Why Does It Make Sense?

[kindlin]

Why does it make more sense to imagine so much dark energy and dark matter to make things work (cosmologically speaking). Why can't gravity change? It just seems to make a lot more sense to alter one theory, than to start imagining all of this extra none-interacting material, which, oh , btw, is affected by gravity, and oh, btw, space itself is full of dark energy that's flinging everything away! muahaha

 

[Dale]

This is a pretty common thing in the history of science. Whenever you have a model which has been experimentally confirmed to work well in a wide variety of known circumstances then when you find a deviation you first look for unknown sources in the existing model before looking for a new model.

For example, both Neptune and Pluto were discovered because of deviations from the predictions of Newtonian gravity. Similarly, the neutrino was discovered because of deviations from the predictions of conservation laws.

For the specific case of GR, we know that it works well in a wide variety of circumstances, and we also know that we don't have an independent way to measure the total energy and matter content of the universe. Therefore it makes much more sense to assume that our experimentally validated model works and use that model to estimate the unknown portions of the matter and energy content of the universe than it would make to assume that the unknown portions are exactly 0 and make a new model to fit that assumption.

The difference between dark matter/energy and the previous examples is simply that we have not yet discovered the corresponding Neptune and neutrino.

 

[shahbaznihal]

Also, alterations to our understanding of gravity on cosmological scales hasn't been very promising. It is not sufficient to explain all the discrepancies.

 

[Chalnoth]

Why does it make more sense to imagine so much dark energy and dark matter to make things work (cosmologically speaking). Why can't gravity change? It just seems to make a lot more sense to alter one theory, than to start imagining all of this extra none-interacting material, which, oh , btw, is affected by gravity, and oh, btw, space itself is full of dark energy that's flinging everything away! muahaha

Lots and lots of physicists have tried to modify gravity in such a way that it can explain our observations. So far, all such attempts have failed. Here is one example of a rather visceral observation which is quite a strong demonstration of the existence of dark matter:
http://blogs.discovermagazine.com/cosmicvariance/2006/08/21/dark-matter-exists/

To be fair, some people who have been working with modified gravity models have also been able to fit their model to the above cluster. But they could only do so by adding a fourth type of neutrino (i.e., a different kind of dark matter).

 

[sardar]

I understand the skepticism towards the concept of dark energy and dark matter. It does seem counterintuitive to imagine the existence of these mysterious substances in order to explain the workings of the universe. However, let me offer some insights into why it makes more sense to incorporate these concepts into our understanding of the cosmos.

Firstly, let's consider the evidence for dark energy and dark matter. The existence of dark matter has been supported by observations of the rotation of galaxies, gravitational lensing, and the large-scale structure of the universe. Similarly, dark energy has been proposed to explain the observed accelerated expansion of the universe. These are not just theoretical concepts, but rather they are based on empirical data and observations.

Now, let's address the idea of altering gravity instead of introducing dark matter and dark energy. While it may seem more intuitive to modify our understanding of gravity, the problem lies in the fact that the current theory of gravity, Einstein's general theory of relativity, has been extensively tested and has been found to be incredibly accurate in describing the behavior of objects on a large scale. Any attempt to modify this theory would need to be consistent with all the observations and experiments that have been done so far, which is a daunting task.

Moreover, altering gravity would not be able to explain all the observations that point towards the existence of dark matter and dark energy. For example, the behavior of galactic clusters and the large-scale structure of the universe cannot be explained by just modifying gravity. Additionally, the effects of dark matter and dark energy are observed at scales much larger than what can be explained by gravity alone.

In essence, incorporating dark matter and dark energy into our understanding of the universe is not just a matter of convenience, but rather it is necessary to explain the vast amount of observational data that we have. It is important to keep an open mind and continue to explore and test these concepts in order to further our understanding of the universe. Science is all about constantly questioning and refining our theories, and the concept of dark matter and dark energy is a prime example of this process.