I recall a physics teacher claiming that if an object was to reach the speed of light its mass would be the same as the universe, and therefore the speed of light is a cosmological speed limit. Is this true? I was discussing this with a student and we came to the following conclusions; Take for example a body that has a 90kg mass (such as me!!): since K.E. = 1/2mv^2 and e = mc^2 (a) as the body undergoes some small acceleration (e.g. from 0m/s to 1m/s) its mass must increase because its (kinetic) energy is increasing. Granted this will only be very small KE = 0.5 x 90 x 1^2 = 45J this equates to an increase in mass of 45J/9E16 = 5.0E-16kg (b) Now imagine the body accelerates from 1m/s to 2m/s. The previous increase in mass should be added to the 1kg mass if the K.E. equation was reapplied to work out the change in energy of this second acceleration (from 1m/s to 2m/s). The change in energy will therefore be slightly greater even though the velocity increases by the same amount (1m/s). (c) We agreed that feeding a continually increasing mass back in the equation for kinetic energy would result in an even bigger increse in mass as the object accelerates further (perhaps an exponential increase?) Furthermore, a continually increasing v-squared term would also result in a greater increase in energy (therefore mass). Is this resoning correct? Would these effects necessarily bring my mass to the same as the universe were I to reach speed of light? This would truely be a dieters nightmare!