Speed of light and time.
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18-03-2014, 10:34 AM
RE: Speed of light and time.
(18-03-2014 10:33 AM)DeavonReye Wrote:  Thanks, itsnotmeitsyou.

No problem. Educating people about science is one of my favorite hobbies. Well, educating people who actually want to learn, that is. Thumbsup

Excuse me, I'm making perfect sense. You're just not keeping up.

"Let me give you some advice, bastard: never forget what you are. The rest of the world will not. Wear it like armor, and it can never be used to hurt you." - Tyrion Lannister
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18-03-2014, 11:01 AM
RE: Speed of light and time.
(18-03-2014 10:17 AM)itsnotmeitsyou Wrote:  This reveals an underlying misunderstanding of physics.

First, nothing that has mass is traveling at the speed of light through space. The things that do propagate at the speed of light have no mass.

Pedantic mode - nothing with rest mass!

(18-03-2014 10:17 AM)itsnotmeitsyou Wrote:  Second, that's not how relativity works. Time only slows/stops from the perspective of the object travelling. An outside observer will still experience time "normally"

Indeed. Everyone in their own reference frame sees time pass "normally" for anything else in their reference frame.

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18-03-2014, 11:08 AM
RE: Speed of light and time.
(18-03-2014 11:01 AM)cjlr Wrote:  
(18-03-2014 10:17 AM)itsnotmeitsyou Wrote:  This reveals an underlying misunderstanding of physics.

First, nothing that has mass is traveling at the speed of light through space. The things that do propagate at the speed of light have no mass.

Pedantic mode - nothing with rest mass!
aye, but when teaching the basics, I find it best not to add every technical detail. It usually leads to more questions or glazed looks. The questions can help to further educate (i.e. explaining what is meant by 'rest mass' vs 'mass'), but only if they need/want more info on the topic.

Excuse me, I'm making perfect sense. You're just not keeping up.

"Let me give you some advice, bastard: never forget what you are. The rest of the world will not. Wear it like armor, and it can never be used to hurt you." - Tyrion Lannister
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18-03-2014, 11:40 AM
RE: Speed of light and time.
And the 'objection' that inflationary expansion violates this - just no.

Space is expanding faster than the speed of light, particles with rest mass are not.

Skepticism is not a position; it is an approach to claims.
Science is not a subject, but a method.
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18-03-2014, 11:51 AM
RE: Speed of light and time.
(18-03-2014 11:40 AM)Chas Wrote:  And the 'objection' that inflationary expansion violates this - just no.

Space is expanding faster than the speed of light, particles with rest mass are not.

This is one of those awesome facts that blew my mind the first time I heard it. That eventually, the space between galaxies will be expanding so rapidly that the light will never be able to cross them. Shocking

Excuse me, I'm making perfect sense. You're just not keeping up.

"Let me give you some advice, bastard: never forget what you are. The rest of the world will not. Wear it like armor, and it can never be used to hurt you." - Tyrion Lannister
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18-03-2014, 12:13 PM
RE: Speed of light and time.
Yeah, . . . that is mind blowing to think about.
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21-03-2014, 08:41 AM
RE: Speed of light and time.
(18-03-2014 11:01 AM)cjlr Wrote:  
(18-03-2014 10:17 AM)itsnotmeitsyou Wrote:  First, nothing that has mass is traveling at the speed of light through space. The things that do propagate at the speed of light have no mass.
Pedantic mode - nothing with rest mass!

Well, if we're being pedantic:
The concept of "relativistic mass" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass - belonging to the magnitude of a 4-vector - to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself.
E. F. Taylor, J. A. Wheeler (1992), Spacetime Physics, second edition, New York: W.H. Freeman and Company, pp. 248–249, ISBN 0-7167-2327-1
via http://en.wikipedia.org/wiki/Mass_in_spe...ontroversy

Give me your argument in the form of a published paper, and then we can start to talk.
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21-03-2014, 08:48 AM
RE: Speed of light and time.
(21-03-2014 08:41 AM)Hafnof Wrote:  
(18-03-2014 11:01 AM)cjlr Wrote:  Pedantic mode - nothing with rest mass!

Well, if we're being pedantic:
The concept of "relativistic mass" is subject to misunderstanding. That's why we don't use it. First, it applies the name mass - belonging to the magnitude of a 4-vector - to a very different concept, the time component of a 4-vector. Second, it makes increase of energy of an object with velocity or momentum appear to be connected with some change in internal structure of the object. In reality, the increase of energy with velocity originates not in the object but in the geometric properties of spacetime itself.
E. F. Taylor, J. A. Wheeler (1992), Spacetime Physics, second edition, New York: W.H. Freeman and Company, pp. 248–249, ISBN 0-7167-2327-1
via http://en.wikipedia.org/wiki/Mass_in_spe...ontroversy

Nah, that's being very pedantic!

There's the tradeoff between referring to 'mass' (which is less well defined but generally intuitively understood) and 'momentum' (which is rigourously defined and not nearly as intuitive).

Most texts do just say 'mass', with the understanding that appropriate context-sensitive interpretation will follow...

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21-03-2014, 09:42 AM
RE: Speed of light and time.
I don't know if this is the same question or a different one, but I thought I'd ask.

How long does it take light to get here from the nearest star (other than the sun)? And when I ask that question, the key word is "long," because time is at issue, no?

If I'm on earth, and I see the nearest star (other than the sun), I can conclude that what I'm seeing is that star as it appeared 4.2 years ago. Everybody with me so far? Good, because that was the easy part.

Now, let's say that four years ago, I was actually AT that nearest star and began traveling to earth at the speed of light. How much time will pass for me when I arrive? It can't be 4.2 years. It would have to be much less, right? But if less than 4.2 years passes for me, would that not mean that I have not reached earth yet? I mean, it can't just be a couple of seconds or a few minutes for me, because It's going to take me 4.2 years to reach my destination, right?

My head just blew up.
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21-03-2014, 10:15 AM
RE: Speed of light and time.
(21-03-2014 09:42 AM)TwoCultSurvivor Wrote:  I don't know if this is the same question or a different one, but I thought I'd ask.

How long does it take light to get here from the nearest star (other than the sun)? And when I ask that question, the key word is "long," because time is at issue, no?

If I'm on earth, and I see the nearest star (other than the sun), I can conclude that what I'm seeing is that star as it appeared 4.2 years ago. Everybody with me so far? Good, because that was the easy part.

Now, let's say that four years ago, I was actually AT that nearest star and began traveling to earth at the speed of light. How much time will pass for me when I arrive? It can't be 4.2 years. It would have to be much less, right? But if less than 4.2 years passes for me, would that not mean that I have not reached earth yet? I mean, it can't just be a couple of seconds or a few minutes for me, because It's going to take me 4.2 years to reach my destination, right?

My head just blew up.

That's the crazy thing about relativity and speed. If you were travelling AT the speed of light, no time would pass at all from your perspective. However, from the reference point of the rest of the universe, 4.2 years would have passed. If you were travelling NEAR the speed of light, some time would pass for you, but not much. The rest of the universe would still watch your journey take 4.2 years.

Excuse me, I'm making perfect sense. You're just not keeping up.

"Let me give you some advice, bastard: never forget what you are. The rest of the world will not. Wear it like armor, and it can never be used to hurt you." - Tyrion Lannister
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