Time/Space Fabric and Relativity

[Suburbanite]

Can someone PLEASE explain this to me patiently? I am having the hardest time understanding why this is true....

[Samildanach]

What part specifically?

The basics of relativity theory are

The faster you travel the more time slows.
The speed of light is a constant whatever speed you travel

[Suburbanite]

okay cause like in my class the teacher was talking about how light bends towards matter as well as other matter via gravity. How is this possible?!

[Compugasm]

Even a photon has mass, which would be affected by gravity.

[gallo]

Originally posted by Suburbanite okay cause like in my class the teacher was talking about how light bends towards matter as well as other matter via gravity. How is this possible?!

Yep. That was one of the predictions that Einstein made about the general theory of relativity, the light would bend in the presence of a large body (and therefore a strong gravitational field). Einstein made the prediction sometime before 1920, I think and it wasn't confirmed until sometime in the 1950s. I'm not sure of those dates. Anyway, it was confirmed by the observation of a star that was very close to the sun during an eclipse. It's position appeared to chang as the light from the star was bent as it passed the sun.

Since then it has been confirmed by other observations. There are several "gravitational lenses" in space where star light is bent as it passes some large body between. There are even examples of where we see two stars on earth as the light is bent as it goes around both sides of a massive star.

Another confirmation of relativity has been the red shifting of light from massive stars. We see the light normally, but the absorption bars from various elements are shifted toward the red end of the spectrum. The more massive the star, the more the shift.

And still the speed of light is the same.

[Pooeypants]

Originally posted by Compugasm, Even a photon has mass, which would be affected by gravity.

Photon has no mass, it has momentum though.

[Compugasm]

It doesn't? Then how ... nevermind. I tried look up the answer in the wiki and "blah blah blah [wierd symbols] blah blah blah". screw it. Suburbanite, it just bends because it's a particle. And cheese is made of particles. You can bend cheese, therefore photons bend.

[Suburbanite]

hehe thanks Comp, but you're way off on that one. imagine putting a paper weight on a table cloth (without a table under it) that is something like how this works, but i still dont get it

[Vee]

I don't know

but I'd imagine it has mass

just the mass is insignificant - not measurable by us

[PatrickHenry]

Originally posted by Compugasm, It doesn't? Then how ... nevermind. I tried look up the answer in the wiki and "blah blah blah [wierd symbols] blah blah blah". screw it. Suburbanite, it just bends because it's a particle. And cheese is made of particles. You can bend cheese, therefore photons bend.

Heh.

The reason light "bends" due to gravity is that mass bends the fabric of space/time. Massive black holes aren't matter as such. They are singularities. But their intense mass creates extreme warpage in the vicinity.

Sub, try this:
[url=http://www.amazon.com/exec/obidos/tg/detail/-/0375412883/002-1916053-6497647?v=glance]

[Suburbanite]

bah i dont want to read a whole book, isnt it possible to explain how mass actually does this?!

[Samildanach]

No, I mean what is mass really? No one knows, you could say its bound up energy due to the e=mc2 etc but no one really knows what energy is either.

[Nono]

Originally posted by PH Sub, try this...

Having had an honest crack at Gribbin, Hawking and others who have the pretension of "popularizing" this stuff, I still nevertheless frequently go "Duhhh...", and therefore sympathize with Suburbanite.

Is it really possible for us unwashed masses to wrap our minds around such counter-intuitive stuff? Is it really possible, without all the background training, to read a paperback and actually gain insight into a subject that even the experts keep changing their minds about? (See Hawking's recent change of heart re singularities.)

[PatrickHenry]

If you boys won't even make the effort to read a book, pursuing your interest, how can somebody impart knowledge?
Here's the review of the book I posted:

As a boy, Brian Greene read Albert Camus' The Myth of Sisyphus and was transformed. Camus, in Greene's paraphrase, insisted that the hero triumphs "by relinquishing everything beyond immediate experience." After wrestling with this idea, however, Greene rejected Camus and realized that his true idols were physicists; scientists who struggled "to assess life and to experience the universe at all possible levels, not just those that happened to be accessible to our frail human senses." His driving question in The Fabric of the Cosmos, then, is fundamental: "What is reality?" Over sixteen chapters, he traces the evolving human understanding of the substrate of the universe, from classical physics to ten-dimensional M-Theory. Assuming an audience of non-specialists, Greene has set himself a daunting task: to explain non-intuitive, mathematical concepts like String Theory, the Heisenberg Uncertainty Principle, and Inflationary Cosmology with analogies drawn from common experience. For the most part, he succeeds. His language reflects a deep passion for science and a gift for translating concepts into poetic images. When explaining, for example, the inability to see the higher dimensions inherent in string theory, Greene writes: "We don't see them because of the way we see…like an ant walking along a lily pad…we could be floating within a grand, expansive, higher-dimensional space." For Greene, Rhodes Scholar and professor of physics and mathematics at Columbia University, speculative science is not always as thorough and successful. His discussion of teleportation, for example, introduces and then quickly tables a valuable philosophical probing of identity. The paradoxes of time travel, however, are treated with greater depth, and his vision of life in a three-brane universe is compelling and--to use his description for quantum reality--"weird." In the final pages Greene turns from science fiction back to the fringes of science fact, and he returns with rigor to frame discoveries likely to be made in the coming decades. "We are, most definitely, still wandering in the jungle," he concludes. Thanks to Greene, though, some of the underbrush has been cleared.

But maybe you'll find the magic elixir of knowledge, and imbibing it, will become knowledgeable without effort...

[Suburbanite]

is there no simple answer?

[Nono]

Lighten up, Pat. I have made an effort, but still find these things hard to grasp. Maybe I'm just 'cosmologically challenged'. :confused:
Will, however, consider this book.

[Suburbanite]

oh and is black matter what makes up black holes or what

[Nono]

Nah, them thangs is called dark holes.

[Suburbanite]

uhhh

[Samildanach]

Yes there is a simple answer, mass acts on space like a plughole acts on water.