How dogmatic do you sound? and what does gravity have to do with proving the big bang?
There is much data ignored by the mainstream that shows that it is incorrect. Ever heard of Halton Arp? He showed that the doppler interpretation of the red-shift is erroneous. Also it is well known that planck radiation of every atom in the ubiquitous interstellar medium can and should emit a ambient radiation temperature of about 3K. see http://www.newtonphysics.on.ca/COSMIC/Cosmic.html
for more information