Speed of Light question

[glass]

No, they don't have mass, so they're not affected the same way as particles with mass. Notably, that they don't slow down when subjected to gravitational attraction. They can however still be diverted by the gravity well of large mass.

I thought light did have mass, on account of it having energy. Like moving objects gain mass, but with the mass-velocity starting at 0,0, rather than starting from the mass due to an object's matter.

Have I been barking up the wrong tree all this time?


still confused glass.

 

[Pinotage]

I thought light did have mass, on account of it having energy. Like moving objects gain mass, but with the mass-velocity starting at 0,0, rather than starting from the mass due to an object's matter.

Have I been barking up the wrong tree all this time?


still confused glass.

Here's an article that might help:

Does light have mass?

Pinotage

 

[glass]

Here's an article that might help:

Does light have mass?

Pinotage

Thanks, that makes sense (sorta). So, I was just a bit behind the times.


glass.

 

[Raven Crowking]

We know that light bends when it comes near a great mass- say a distant star's light can have its position change to our perception if that light passes by a black hole or a star between here and there.

Would it be to much to think that light can be bent, could it not be slowed by the same force that bends it? Could that same force not alter its speed to go faster? Say the light speeds towards the massive star then slows as it passes then tries to pull away from that same star. Could that be true?

Could it be true that light is just the fastest think we can perceive?

I recall hearing once that a scientist stated flat that man would never surpass the speed of sound, the laws of physics would not allow. It was on one of those history shows about breaking the speed of sound. Of course we broke the speed of sound many times over, but it proves to me that our understanding of physics is pretty much at kindergarten level while the universe is running at beyond Doctoral level.

Just a thought that has been bothering my sleep.

This is a misperception of what relativity actually says. The light is not bent by mass. Space-time is bent by the mass (compressed in its vicinity, if you like), and the light is following a straight line.

Re: Speed of light in a vacuum; when light travels through different media, it is actually travelling farther. The speed of light remains constant in all media; the media just makes it seem to slow down to the outside observer.

(more later)


RC

 

[Umbran]

This is a misperception of what relativity actually says. The light is not bent by mass. Space-time is bent by the mass (compressed in its vicinity, if you like), and the light is following a straight line.

To be even more accurate, this is true for all objects, not just light. All objects travel along straight lines in spacetime. Near massive objects, spacetime is curved.

The disconnect is that our brains are wired to assume spacetime is flat. We see bent trajectories in a flat space, when we are actually looking at straight trajectories in flat space. To a large degree, it is only a difference in perspective.

Re: Speed of light in a vacuum; when light travels through different media, it is actually travelling farther.

That's one way to say it, but note that it is not travelling farther due to curvature of spacetime...


RC[/QUOTE]

 

[Raven Crowking]

That's one way to say it, but note that it is not travelling farther due to curvature of spacetime...

....Depending upon your interpretation of quantum mechanics. In some interpretations, matter itself is essentially space-time curvature scrunched up into little knots.


RC

 

[Umbran]

....Depending upon your interpretation of quantum mechanics. In some interpretations, matter itself is essentially space-time curvature scrunched up into little knots.

Well, I was about to come back and edit my post there - it isn't curvature in spacetime due to gravitational mass.

I am a physicist, and I don't trust any model that doesn't make unique testable predictions. The models you mention here are among that class.

 

[fuindordm]

Well, I was about to come back and edit my post there - it isn't curvature in spacetime due to gravitational mass.

I am a physicist, and I don't trust any model that doesn't make unique testable predictions. The models you mention here are among that class.

Well, they may be testable one day. And it's possible that improved cosmological data (for example, from the Planck satellite mission) may provide indirect constraints. The early universe (and by extension the current universe) is the only naturally occuring laboratory for very high-energy interactions.

The key thing to realize about general relativity (GR) is that it's a differential theory.

In the same way that calculus analyzes curves by assuming they can be approximated by straight lines locally (the derivative = dy/dx is an example of this), GR is a theory that stitches together differential patches of flat space-time (described by special relativity) into a continuum. So GR can't accurately describe an environment where space-time might be cuspy (inside the event horizon of a black hole) or 'frothy' (on string theory scales, where particles are being created and destroyed by quantum fluctuations). There's no clear way of extending the theory to cover such situations, which is why most unified theories are particle/field theories (modeling the effects of gravity with gravitons rather than curved space-time).

Ben

 

[Desdichado]

This discussion is really fun! But sadly, over my head. But this is pretty heady, fascinating stuff.

 

[Raven Crowking]

Well, I was about to come back and edit my post there - it isn't curvature in spacetime due to gravitational mass.

I am a physicist, and I don't trust any model that doesn't make unique testable predictions. The models you mention here are among that class.

Actually, the models I mention here (coupled with relativity) led me to believe that, as one left an area of concentrated mass, the expansion of the universe would add apparent speed to one's motion. Of course, I am not a physicist (except in the amature theoretical sense), so I was simply doing armchair speculation and "common-sense" analysis of the theories and data that I was reading, coupled with a few insights gained from conversations while taking astrophysics at Santa Monica Community College. I suppose it would be fair to say that I came up with my own interpretation of the data, based upon elegance more than anything else. When I first read of the discovery of quintessence, I was quite pleased. I just wish I was mathematician enough to determine whether or not it fell within the range my interpretation would allow for.


RC