The idea that we live in a Universe undergoing a period of acceleration is a new , yet strongly held , notion in cosmology .
As this can , potentially , be explained with a modification to General Relativity we look at current cosmological data with the purpose of testing aspects of gravity .
Firstly we constrain a phenomenological model ( mDGP ) motivated by a possible extra dimension .
This is characterised by a parameter \alpha which interpolates between \alpha = 0 ( LCDM ) and \alpha = 1 ( the Dvali Gabadadze Porrati ( DGP ) model ) .
In addition , we analyse general signatures of modified gravity given by the growth parameter \gamma and power spectrum parameter \Sigma .
We utilise large angular scale ( \theta > 30 arcminutes ) Weak Lensing data ( CFHTLS-wide ) in order to work in the more linear regime and then add , in combination , Baryon Acoustic Oscillations ( BAOs ) and Supernovae .
We subsequently show that current weak lensing data is not yet capable of constraining either model in isolation .
However we demonstrate that even at present this probe is highly beneficial , for in combination with BAOs and Supernovae we obtain \alpha < 0.58 and \alpha < 0.91 at 1 \sigma and 2 \sigma , respectively .
Without the lensing data no constraint is possible .
Inclusion of all angular scales ( 1 \leq \theta \leq 230 arcminutes ) allows a noticeable but not significant increase in the constraining power of the joint probes with \alpha < 0.56 and \alpha < 0.86 also at 1 \sigma and 2 \sigma , respectively .
Both analyses correspond to a disfavouring of the flat DGP braneworld model ( \alpha = 1 ) at over 2 \sigma .
We highlight these are insensitive to potential systematics in the lensing data such as an underestimation of the shear at high redshift .
For the growth signature \gamma we show that , in combination , these probes do not yet have sufficient constraining power .
Finally , we look beyond these present capabilities and demonstrate that Euclid , a future weak lensing survey , will deeply probe the nature of gravity .
A 1 \sigma error of 0.104 is found for \alpha ( l _ { \mathrm { max } } = 500 ) whereas for the general modified signatures we forecast 1 \sigma errors of 0.045 for \gamma and 0.25 for \Sigma _ { 0 } ( l _ { \mathrm { max } } = 500 ) , which is further tightened to 0.038 for \gamma and 0.069 for \Sigma _ { 0 } ( l _ { \mathrm { max } } = 10000 ) .