[spanner34.5]

Speed of light is not always 'c'.

Interesting development into the theory of all sorts.

http://www.bbc.co.uk/news/uk-scotland-30949979

http://www.bbc.co.uk/news/uk-scotland-glasgow-west-30944584

http://www.thejournal.ie/speed-of-light-slow-1900175-Jan2015/

[Thork]

I told everybody this 2 months ago. But now the BBC says so ...

http://forum.tfes.org/index.php?topic=2142.0

I am better than all the scientists. 

[Rama Set]

Slowing down a photon is not news, but I am interested to know why it remained at that speed.  I tweeted NDT for insight.

[Thork]

Slowing down a photon is not news, but I am interested to know why it remained at that speed.

Would acceleration not require additional energy that is not present in the system?

[Rama Set]

Slowing down a photon is not news, but I am interested to know why it remained at that speed.

Would acceleration not require additional energy that is not present in the system?

The theory says that photons are massless and are required to travel at c.  I am pretty sure, but will double check now, that a photon, upon exiting a refractive medium, goes back up to c_v.

[Ghost of V]

This is very interesting. The repercussions of this could be profound.

[Rama Set]

Slowing down a photon is not news, but I am interested to know why it remained at that speed.

Would acceleration not require additional energy that is not present in the system?

The theory says that photons are massless and are required to travel at c.  I am pretty sure, but will double check now, that a photon, upon exiting a refractive medium, goes back up to c_v.

So the apparent change in velocity of a photon through a refractive medium is due to a delay created by a photon being absorbed and re-emitted by a particle in the medium.

Apparently this news story is not the entire story and in fact there is no ground-shaking discovery here:

http://www.reddit.com/r/science/comments/2tdgts/scientist_slow_the_speed_of_light_in_free_space/

http://www.sciencemag.org/content/early/2015/01/21/science.aaa3035

I will keep an eye on this, but we have to wait a little longer for ftl travel I guess.

[Pete Svarrior]

I mean, I had to check. its c, right? Its a constant. 299,792,457m/s

Why would you remind us of your blatant displays of ignorance?

[Rama Set]

I feel like your post is the one doing the reminding.

[Pete Svarrior]

I feel like your post is the one doing the reminding.

Well, he did deliberately link to the thread. Of course, I amplified the effect, but that stikes me as much less counter-intuitive.

I would argue that it makes more sense for me to maliciously mock others than it does for Thork to link to stuff that makes him look like an idiot and yet claim that it somehow helps his case.

[Rama Set]

I would argue that it makes more sense for me to maliciously mock others than it does for Thork to link to stuff that makes him look like an idiot and yet claim that it somehow helps his case.

You make a good point, but then again... Thork.

[Fortuna]

If photons are massless, then why are they affected by gravity?

[Rushy]

If photons are massless, then why are they affected by gravity?

Mass has nothing to do with gravity. It just so happens that mass correlates with energy and the energy itself spurs gravity. Photons have energy, therefore they have gravity. Newton's gravity equation is still useful for most gravity calculations, but the equation itself is not theoretically sound and it falls apart when relativistic or quantum physics comes into play.

Most high school curriculums still deem Newton's equation as "good enough" but using it for precise calculations is a Very Bad Idea.

[Lord Dave]

If photons are massless, then why are they affected by gravity?

Mass has nothing to do with gravity. It just so happens that mass correlates with energy and the energy itself spurs gravity. Photons have energy, therefore they have gravity. Newton's gravity equation is still useful for most gravity calculations, but the equation itself is not theoretically sound and it falls apart when relativistic or quantum physics comes into play.

Most high school curriculums still deem Newton's equation as "good enough" but using it for precise calculations is a Very Bad Idea.

I thought photons weren't affected by gravity so much as they followed the curve of space, which is distorted in strong gravity.

[Rushy]

I thought photons weren't affected by gravity so much as they followed the curve of space, which is distorted in strong gravity.

That's one way to think about it, but there isn't a functional difference between saying it is gravity or space distortion, since gravity is literally interpreted as space distortion.