Wallace

Science Advisor

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## Main Question or Discussion Point

Since the WMAP 5 year data is now out and contains no nasty new surprises, what does everyone think about the current and future status of gravity? Please read these more detailed descriptions of the poll options before you vote! Note that these options are all basically beyond what we can know with any kind of confidence at present, but what is your gut feeling? It might be interesting to compare the poll results to what we know in 5 years (or more) time!

1) GR is the true theory of gravity and is correct for every situation where it gives a sensible results (i.e. away from singularities). Any future quantum gravity theory might explain in more detail the nature of the centre of black holes and the very very very early Universe but will leave all other GR predictions unchanged. In this case dark matter is real and dark energy is either really some energy source or a true cosmological constant.

2) As above but dark matter and/or dark energy will be shown to be a result of spurious errors either in observation (i.e. for some reason distant SN are intrinsically dimmer for some reason other than acceleration) or a result of the FRW model for GR being a poor approximation and an improved model, using GR only, explains the data without dark energy and/or dark matter.

3) GR turns out to be a poor model for gravity on large scales and a new theory is developed that explains away dark matter and/or dark energy as simply the result of wrongly interpreting the data with GR as the gravity model. This new theory may or may not be a full quantum gravity theory that also explains the centres of black holes and the very very very early Universe without producing singularities.

4) The pessimistic option. We are inherently constrained in terms of what we can ever be able to measure from Earth and therefore we will never be truly able to know whether GR+dark stuff or a new theory of gravity is a better option. Both may be able to explain the data to some degree and we won't be able to say for sure which one is correct.

5) Fence sitter option. At this stage it is impossible to have any gut feeling about the eventual outcome, all or a few of the above options are equally likely.

Note that none of the options mention any direct laboratory detection of dark matter and/or dark energy. If this was to occur that information would feed back into cosmology to support some and reject other options, so if you think this will or won't occur that can guide your choice as well.

Lets not get overly speculative, but what is your leaning at the moment?

1) GR is the true theory of gravity and is correct for every situation where it gives a sensible results (i.e. away from singularities). Any future quantum gravity theory might explain in more detail the nature of the centre of black holes and the very very very early Universe but will leave all other GR predictions unchanged. In this case dark matter is real and dark energy is either really some energy source or a true cosmological constant.

2) As above but dark matter and/or dark energy will be shown to be a result of spurious errors either in observation (i.e. for some reason distant SN are intrinsically dimmer for some reason other than acceleration) or a result of the FRW model for GR being a poor approximation and an improved model, using GR only, explains the data without dark energy and/or dark matter.

3) GR turns out to be a poor model for gravity on large scales and a new theory is developed that explains away dark matter and/or dark energy as simply the result of wrongly interpreting the data with GR as the gravity model. This new theory may or may not be a full quantum gravity theory that also explains the centres of black holes and the very very very early Universe without producing singularities.

4) The pessimistic option. We are inherently constrained in terms of what we can ever be able to measure from Earth and therefore we will never be truly able to know whether GR+dark stuff or a new theory of gravity is a better option. Both may be able to explain the data to some degree and we won't be able to say for sure which one is correct.

5) Fence sitter option. At this stage it is impossible to have any gut feeling about the eventual outcome, all or a few of the above options are equally likely.

Note that none of the options mention any direct laboratory detection of dark matter and/or dark energy. If this was to occur that information would feed back into cosmology to support some and reject other options, so if you think this will or won't occur that can guide your choice as well.

Lets not get overly speculative, but what is your leaning at the moment?