>like having the cosmic microwave background blue shifted into gamma rays This is patently false. It is indeed true that a relativistic spacecraft would see a

>like having the cosmic microwave background blue shifted into gamma rays This is patently false. It is indeed true that a relativistic spacecraft would see a highly anisotropic microwave background: a strong blueshift in the direction of travel, a strong redshift in the opposite direction. But at 99.5% of the speed of light, the blueshift factor is only about 20. This would shift the 2.7 K microwave background to a temperature of about 54 K; that is still pretty darn cold.