# How does gravity effects both time and light if they have no mass [duplicate]

I've been reading about how black holes can effect both time and light with gravity. So I was wondering, doesn't something have to have mass to be effected by gravity? And if so, does this mean both light and time have mass? And if not, how can gravity effect something that has no mass?

• Hi Tom. Welcome to Physics.SE. Before asking questions, it's always good to search for them or atleast have a look at the Related list. For now, your question has already been solved by many answers. A possible duplicate: physics.stackexchange.com/q/22876/11062 – Waffle's Crazy Peanut May 21 '13 at 13:39
• Gravity is the curvature of space-time and it affects energy, not only mass. There must be some post explaining this. – jinawee May 21 '13 at 13:41
• @ϚѓăʑɏβµԂԃϔ: IMO the question also mentions time, so it's not a dupe. – Manishearth May 21 '13 at 13:52
• @Manishearth: Hi Manish. I told that there are many questions that can cover that. OP has asked 2 in 1. For example, here's the question covering time..! Actually, I sped up and so, I was unable to insert more posts. In fact, the tags have almost all related posts I hope so ;-) – Waffle's Crazy Peanut May 21 '13 at 13:55
• @ϚѓăʑɏβµԂԃϔ: Good point, closed :) – Manishearth May 21 '13 at 13:57