This was excellent. Mr. Barbour was very easy to understand and did something that few bloggingheads do: cut a paragraph short after a few minutes, out of a desire not to monopolize the conversation.

Yes, they were both very good listeners (respectful, attentive, non-competitive).

I had no idea that Captain Jean-Luc Picard was an expert on time!

I'm confident that this was Science Saturday for it discussed science in a way that Science Saturday has lately been sort of shy about doing. I hope we will see more like this in the future.

I am not sure I completely follow how one gets to time is an illusion.
He seemed to be implying that if there was no movement of bodies in the universe by which to measure a change of position of some sort, there would be no time... Is that the argument?
It seems strange because I do not conceptualize time as linked explicitly to whether objects move or not. I suppose if everything was completely static in the universe, then the concept of time would be meaningless, as there would be no such thing as past or future, only the present, only that snapshot of existence and reality.
But the universe we observe is not static... so how then does one get to the idea that time does not exist? In what way does it not exist? As a concept? As .. ?
Or is it he thinks time simply emerges from the movement of objects? Even if this is the case, how does that negate its existence in a universe where objects move?
And the examples of the form if you moved the entire universe to the right 6 feet, you couldn't tell anything.. this

i have to watch it again but i think what barbour's taking einstein's concept of relative time (earth's time and mars' are both correct/the faster you're traveling through space the less you age due to light waves' peaks and valleys spreading out/entropy increases forward and backward through "time" and creates an illusion of aging, etc.) one step further by saying that even this "scientific" use of time, which acknowledges that there is no "time" but that the idea of it can serve a purpose such as elapsed time of the universe measured by bodies traveling with the expansion of space, is merely an illusion. i think he's saying that if you think of the universe as nothing but force fields/particles interacting then you get as series of "now" moments, similar to a movie projector, that our brain interprets as change (because it's happening faster than our brain can sample the information) but it's really just entropy/random interactions. some newer theories postulate that if the smallest "piece" of the universe is the Planck length then there must be Planck "time" - that being the amount of time light takes

This discussion was WAY over my head, but it got me thinking about a very elementary question of spacial mechanics that never occurred to me before: Why do all the planets in our solar system orbit the Sun on a single plane? What's to stop them from orbiting on intersecting planes and colliding? I'm sure there must be a very elementary explanation for this, but I have no idea what it is. If you can stop rolling on the floor laughing at my ignorance, can anyone explain this to me? I got a "C" in high school physics--and the question clearly shows why...

Quoting rfrobison: This discussion was WAY over my head, but it got me thinking about a very elementary question of spacial mechanics that never occurred to me before:

Why do all the planets in our solar system orbit the Sun on a single plane? What's to stop them from orbiting on intersecting planes and colliding? I'm sure there must be a very elementary explanation for this, but I have no idea what it is.

If you can stop rolling on the floor laughing at my ignorance, can anyone explain this to me? I got a "C" in high school physics--and the question clearly shows why...

I'm not an expert in this, but here are a couple of basic points. First, the planets do not all orbit in exactly the same plane. Pluto's plane is tilted 17° with respect to Earth's. (OMG PLUTO IS NOT A PLANET.) Second-most different: Mercury at 7°. I think the most widely accepted explanation for why most of the planets are in pretty much the same plane, though, is that the solar system formed out of an accretion disk ; i.e., a bunch of gas and dust spinning around a gravitational center -- which was or became a star, our Sun. As the

Thanks, BJ. That helped a bit. I seem to recall seeing on of those astronomy shows on the "Discovery Channel" or someplace using the illustration about how the water in a tub with the plug pulled out swirling around the drain. Same idea, I guess...

Barbour is a pretty formidable personality. I had the feeling that Callender was either overawed by the match-up, or maybe he's just not accustomed to extemporaneous dialog before a camera. Either way, much as I liked Craig, this was a pretty one-sided conversation. Thankfully, it was a pretty compelling side.

http://bloggingheads.tv/diavlogs/194...2:20&out=62:32 Sorry I couldn't resist

From his paper, it seems all Julian wants is for us to stop saying "X happened in a time interval of Y", and instead say "X happened once while Y happened Z times". I don't particularly have a problem with this, it just seems pointless. Of course our Newtonian sense of time arises from displacements in bodies that follow the same correlations (in this case, Kepler's laws). Otherwise, no one would perceive time as an one way arrow, we would all think of time as a turbulent lake. We would in effect, be living in pandemonium. I am either missing something, they are talking about a property of the universe that has no Newtonian metaphor that is sensical while still retaining the meaning it would have in general relativity, or we just spent an hour on a common sense statement.

Do they think pluto was created in the accreation disk also, or that it was captured by our solar system sometime in the past? Its been awhile, but I think I remember Pluto's eccentricity was way greater then the other planets, and was in fact alot closer to a non periodic comet. This would suggest to me it was not formed in the acreation disk, but I am no expert on this, or even an educated laymen really.

Quoting Starwatcher162536: Do they think pluto was created in the accreation disk also, or that it was captured by our solar system sometime in the past?

Its been awhile, but I think I remember Pluto's eccentricity was way greater then the other planets, and was in fact alot closer to a non periodic comet. This would suggest to me it was not formed in the acreation disk, but I am no expert on this, or even an educated laymen really.

You're right about the eccentricity, which combines with its rather more severe orbital tilt to make one wonder about it. I don't know what the latest thinking is on whether Pluto was part of the accretion disk or later captured; certainly, I have heard both arguments. P.S. I usually refer to myself as "an interested layman," since that's easier to defend than "educated." ;^)

Quoting Starwatcher162536: Do they think pluto was created in the accreation disk also, or that it was captured by our solar system sometime in the past?

Its been awhile, but I think I remember Pluto's eccentricity was way greater then the other planets, and was in fact alot closer to a non periodic comet. This would suggest to me it was not formed in the acreation disk, but I am no expert on this, or even an educated laymen really.

Pluto is a Kuiper Belt object, and as such is currently believed to have been part of the mass of the accretion disk. The eccentricity is, I would guess, is possibly explained by the fact that there aren't any shepherding masses like Jupiter (so far as we know) at those distances to have corralled the smaller objects into a more orderly arrangement.

The Kuiper belt is believed to consist of planetesimals; fragments from the original protoplanetary disc around the Sun that failed to fully coalesce into planets and instead formed into smaller bodies, the largest less than 3000 km in diameter.

Time is presence of motion and forces. Time is slow where expansion of space is slow. Time is caused by expansion of space. Gravity is nothing but time differential. For more on this line of thinking go to timephysics.com