we begin with syria and a conversation with steffan de mistura from munichy he is u.n.yria. we talk about the secession in hostilities and the providing of aid to the victims of aleppo. >> we are in an incredibly fragile environment. we're talking about hundreds of different groups of rebels, of people who are fighting the government. we are talking about militias fighting with the government plus warlords, so it's going to be quite a challenge, but the fact that the countries who do have an influence and should be using their influence in stopping the conflict have committed themselves gives me the feeling that they are serious. >> rose: and then a major scientific discovery, the detection of gravitational waves. we talked to

we begin with syria and a conversation with steffan de mistura from munichy he is u.n. special envoy for syria. we talk about the secession in hostilities and the providing of aid to the victims of aleppo. >> we are in an incredibly fragile environment. we're talking about hundreds of different groups of rebels, of people who are fighting the government. we are talking about militias fighting with the government plus warlords, so it's going to be quite a challenge, but the fact that the countries who do have an influence and should be using their influence in stopping the conflict have committed themselves gives me the feeling that they are serious. >> rose: and then a major scientific discovery, the detection of gravitational waves. we talked to brian greene, dennis overbye, janna levin and walter isaacson. >> everything we do gets us a tiny step closer to the origin, the big bang. i don't know if we'll ever figure it out, i don't know if we'll ever have a unified theory, the way einstein was hoping that would tie together all the forces of the universe, but everything

. >> rose: joining me from munich, germany, steffan de mistura, the u.n. special envoy for syria.ated in yesterday's meetings. i am pleased to have him on this program. tell me what you believe we have achieved at these meetings. >> well, first of all, let's look at what happened yesterday. it was not a declaration. it was not a statement. it was a commitment. secondly, it was not a commitment about something generic. it was about concrete things-- humanitarian aid to reach those besieged areas, stopping the bombing, in other words, stopping the conflict. basically a cessation of hostilities. three air, deadline, seven days. and all that to take place based on a clear commitment. now, that is something that we can call an achievement. but as you know very well, you need to test it. >> rose: gifs us a sense of the atmosphere, of the developments, the give and take, and what finally led them all to come to this agreement. >> well, yeah, you will understand, and i know you are-- you understand. i cannot reveal too much at all about what happened inside a very closed and delicate meet