Thread: A basic question about light and Relativity

Relativity tells us when an object reaches light speed,the time freezes.
OK,lets imagine a situation. If the time stops,how could a photon continue its movement in its own "time system"? But,the fact is we can see the photon moving in our time system.
Sorry for my lack of knowledge. This question has confused me for many years.

Originally Posted by Sandett

Relativity tells us when an object reaches light speed,the time freezes.
OK,lets imagine a situation. If the time stops,how could a photon continue its movement in its own "time system"? But,the fact is we can see the photon moving in our time system.
Sorry for my lack of knowledge. This question has confused me for many years.

Relativity says no such thing.

Your confusion is due to lack of understanding of the basics of special relativity. Read the sticky thread for this forum.

Better yet, read a good physics book that discusses special relativity.

You might try either The Feynman Lectures on Physics by Feynman, Leighton and Sands or Introduction to Special Relativity by Rindler.

There is no admissible reference frame for special reltivity attached to a photon.

Originally Posted by DrRocket

Originally Posted by Sandett

Relativity tells us when an object reaches light speed,the time freezes.
OK,lets imagine a situation. If the time stops,how could a photon continue its movement in its own "time system"? But,the fact is we can see the photon moving in our time system.
Sorry for my lack of knowledge. This question has confused me for many years.

Relativity says no such thing.

Your confusion is due to lack of understanding of the basics of special relativity. Read the sticky thread for this forum.

Better yet, read a good physics book that discusses special relativity.

You might try either The Feynman Lectures on Physics by Feynman, Leighton and Sands or Introduction to Special Relativity by Rindler.

There is no admissible reference frame for special reltivity attached to a photon.

Well, thanks for your short reply, but this question hasn't be resolved to me.
I am just a common guy having some interest on such physics questions and might not have time to learn the entire Relativity to resolve some questions I thought of. And I knew some limited knowledge long time ago such as "Faster objects has slower time flow. Gravity also slows the time".
This question is due to T=T'/√1-(v/c)².
http://upload.wikimedia.org/math/7/e...fb7c2e7e6e.png

And some books or articles ever said if an object reaches light speed,the time of the object freezes. Even faster than light speed,you can get back to the pass. Though I know to accelerate an object into light speed requires infinite energe, and there's no object faster than light atm.

By the way, why can't a photon be considered it's time frame?
Well, is it related to "The speed of light is a constant for all inertial frame"
If a photon can't be considered it's own time frame, what does this mean? No time "interacts" on it?

Downhill skiing: light speed reachable
Downhill cycling: light speed not reachable


Do you get it? No wheels vs. wheels

Originally Posted by Sandet

Well, thanks for your short reply, but this question hasn't be resolved to me.
I am just a common guy having some interest on such physics questions and might not have time to learn the entire Relativity to resolve some questions I thought of.

Too bad.

Your ignorance of the subject is apparently sufficiently profound that you cannot understand an answer to your question when it is given to you.

There is really no alternative to your learning enough about relativity to understand why what you propose is absurd.

Originally Posted by DrRocket

Originally Posted by Sandet

Well, thanks for your short reply, but this question hasn't be resolved to me.
I am just a common guy having some interest on such physics questions and might not have time to learn the entire Relativity to resolve some questions I thought of.

Too bad.

Your ignorance of the subject is apparently sufficiently profound that you cannot understand an answer to your question when it is given to you.

There is really no alternative to your learning enough about relativity to understand why what you propose is absurd.

LOL,you are trolling now.
Telling someone a thing doesn't need so many belittling words.
And ridiculing someone doesn't show how great you are.
I have a book for you,too. http://www.amazon.com/Dude-Thats-Rud...3496367&sr=1-1

And one more thing. if you wanna tell someone a thing,plz make it straightforward, don't stop halfway.

And in my second post, I have been aware of massless particles can't apply to special relativity. that's why there's another new question.

Well, if you are unwilling to tell me in friendly attitude, shut your mouth up plz.
Also, if you wanna correct my grammar to insult me, get out of this topic plz.
I don't need trolling,DrRocket.

Dr. rocket is not a great educator, but he has given some useful advice: read the sticky on relativity on this forum and see if that helps you to an understanding.

Originally Posted by Ophiolite

Dr. rocket is not a great educator, but he has given some useful advice: read the sticky on relativity on this forum and see if that helps you to an understanding.

Well, there is another similar topic below just on the first page of this forum.

Is it really impossible to travel faster than light?
http://www.thescienceforum.com/Is-it...ght-24893t.php

LOL,similiar topics but very different replies.
I haven't known DrRocket until now.
I don't know why he fxxked up with me.
And finally he made my topic in a mess.
errr, a doomed day. :/

Originally Posted by Sandett

[And finally he made my topic in a mess.

Sorry to say so, but your topic was a mess from the beginning. Dr. Rocket can be rude, but I don't think he was in this case. He simply stated the truth. You cannot understand the subject by going about it in the manner that you are.

Originally Posted by Harold14370

Originally Posted by Sandett

[And finally he made my topic in a mess.

Sorry to say so, but your topic was a mess from the beginning. Dr. Rocket can be rude, but I don't think he was in this case. He simply stated the truth. You cannot understand the subject by going about it in the manner that you are.

are you sure you read the new question of my second post?
And does the sticky topic Special relativity Primer mention photons or massless particles can't apply to Special relativity?
Well, too sad, I get the above understanding from another science forum later.

Do you think special relativity is very easy for the public? do you ask a rookie to act like a well-trained soldier?
Or this forum belongs to the ones who well know relativity and forbids discussing basic questions? Or this forum doesn't welcome the public like me? OK, if this forum doesn't welcome the public, i quit.

A doomed day. :/

Originally Posted by Sandett

And does the sticky topic Special relativity Primer mention photons or massless particles can't apply to Special relativity?

Not directly, but it hopefully will give you enough basics to understand the answer.


But put quite simply: Time does not "freeze" at the speed of light, it becomes undefined, (and likewise it does it run backward at speeds greater than c.)

You can see this by looking at the time dilation formula.




What happen's when v=c?

you get



Divison by 0 is undefined.

And if you increase v to greater than c, you get an answer which contains the square root of a negative number, also undefined.

Thus, the speed of light is not a valid reference frame from which to view the outside universe. Massless particles have no "view of the outside world" to consider.

Originally Posted by Janus

Originally Posted by Sandett

And does the sticky topic Special relativity Primer mention photons or massless particles can't apply to Special relativity?

Not directly, but it hopefully will give you enough basics to understand the answer.


But put quite simply: Time does not "freeze" at the speed of light, it becomes undefined, (and likewise it does it run backward at speeds greater than c.)

You can see this by looking at the time dilation formula.




What happen's when v=c?

you get



Divison by 0 is undefined.

And if you increase v to greater than c, you get an answer which contains the square root of a negative number, also undefined.

Thus, the speed of light is not a valid reference frame from which to view the outside universe. Massless particles have no "view of the outside world" to consider.

Thank you so much. :-D
I should throw out some popular science books that have misleading knowledge now.