How does faster than light information break causality?

[J.C.MacSwell]

1 hour ago, Janus said:

If everthing else was the the same, then c would still be the invariant speed of this universe.  If light traveled at c/2, then its speed would not be invariant.  In this case, the speed of light would not be special in any way, and light would be like anything else that does not travel at c.   Light itself is not important to Relativity, and your continued belief that it is, is totally misguided.

 

Hi Janus

I took the first par as c/2 being the invariant and everything that had to adjust would be based on that...essentially the same universe on a different scale (wrt what? I have no idea...but my responses were based on that)

More particularly can you give me context to the bold? That line of thinking is foreign to me. I realize it is not just about light, and the rest of electromagnetism is tied to it as well.

Edited June 16, 2018 by J.C.MacSwell

[Janus]

7 minutes ago, J.C.MacSwell said:

Hi Janus

I took the first par as c/2 being the invariant and everything that had to adjust would be based on that...essentially the same universe on a different scale (wrt what? I have no idea...but my responses were based on that)

More particularly can you give me context to the bold? That line of thinking is foreign to me.

If you take this in context along with the second part using sound waves, it is apparent he is trying to make the same basic argument in both cases.  Later he claims that if you use sound to make your measurements you would measure relativistic effects based on the speed of sound rather than c.   He is assuming that it is light that causes Relativistic effects.

As to the phrased in bold.   Relativity rests on the concept that there is an invariant finite speed, c.   If such a invariant speed exists, then anything massless is required to travel at this speed.  Put another way, light travels at c because it is has no rest mass, and thus is required to by the rules of Relativity.  The speed at which light travels is a consequence of Relativity. The fact that light travels at c is not the [/i]cause[/i] of Relativity.

Now it just so happens that we are constituted of matter that interacts with light and this makes light a useful tool for measuring the universe around us.  This, along with the fact that light travels at the invariant speed of the universe, makes its a good choice when framing examples dealing with Relativity.  But this not mean if we were to remove light from a scenario that Relativistic effects would not manifest themselves.   You don't need light or even electromagnetic interaction for Relativistic effects to occur.  They are built into the very reality of the universe.  The invariant speed of light highlights and helped us discover the rules governing space and time, but is not responsible for them.

[J.C.MacSwell]

Thanks Janus. Understood.

[geordief]

52 minutes ago, Janus said:

If you take this in context along with the second part using sound waves, it is apparent he is trying to make the same basic argument in both cases.  Later he claims that if you use sound to make your measurements you would measure relativistic effects based on the speed of sound rather than c.   He is assuming that it is light that causes Relativistic effects.

As to the phrased in bold.   Relativity rests on the concept that there is an invariant finite speed, c.   If such a invariant speed exists, then anything massless is required to travel at this speed.  Put another way, light travels at c because it is has no rest mass, and thus is required to by the rules of Relativity.  The speed at which light travels is a consequence of Relativity. The fact that light travels at c is not the [/i]cause[/i] of Relativity.

Now it just so happens that we are constituted of matter that interacts with light and this makes light a useful tool for measuring the universe around us.  This, along with the fact that light travels at the invariant speed of the universe, makes its a good choice when framing examples dealing with Relativity.  But this not mean if we were to remove light from a scenario that Relativistic effects would not manifest themselves.   You don't need light or even electromagnetic interaction for Relativistic effects to occur.  They are built into the very reality of the universe.  The invariant speed of light highlights and helped us discover the rules governing space and time, but is not responsible for them.

Would it be possible to give an example of how relativistic effects would be evident without having recourse to  the properties of em radiation?

 

Can  the gamma factor be arrived at through other means? 

 

 

[Janus]

1 hour ago, geordief said:

Would it be possible to give an example of how relativistic effects would be evident without having recourse to  the properties of em radiation?

 

Can  the gamma factor be arrived at through other means? 

 

 

Consider the standard light clock example.  You could do the same experiment with a ball bouncing between floor and ceiling of a box.  For someone in the box, the velocity of the ball is v' and the period for a round trip would be t'. 

But for someone for which the box is moving at w, the ball is subject to the rules of Relativistic velocity addition. So unlike Newtonian Physics where the resultant speed of the ball would be sqrt(v²+w²), he would measure a lower speed than this.  one that would result in the vertical component of the ball's velocity as being equal to sqrt(1-w²/c²) with a corresponding change in the period of its round trip between floor and ceiling.  Here c is the invariant speed of the universe.  You don't need something to actually travel at the invariant speed for it to exist. 

Look at it this way. 1/0 is undefined, and thus has no answer, but that does not mean that 1/x doesn't tend towards infinity as x approaches 0.  In the same way, you can have an invariant limiting speed of the universe without there being anything that actually moved at that speed.

[swansont]

4 hours ago, geordief said:

Would it be possible to give an example of how relativistic effects would be evident without having recourse to  the properties of em radiation?

 

Can  the gamma factor be arrived at through other means? 

 

 

Muon decay. It is a weak, rather than EM, interaction.

[Mordred]

8 hours ago, Janus said:

If you take this in context along with the second part using sound waves, it is apparent he is trying to make the same basic argument in both cases.  Later he claims that if you use sound to make your measurements you would measure relativistic effects based on the speed of sound rather than c.   He is assuming that it is light that causes Relativistic effects.

As to the phrased in bold.   Relativity rests on the concept that there is an invariant finite speed, c.   If such a invariant speed exists, then anything massless is required to travel at this speed.  Put another way, light travels at c because it is has no rest mass, and thus is required to by the rules of Relativity.  The speed at which light travels is a consequence of Relativity. The fact that light travels at c is not the [/i]cause[/i] of Relativity.

Now it just so happens that we are constituted of matter that interacts with light and this makes light a useful tool for measuring the universe around us.  This, along with the fact that light travels at the invariant speed of the universe, makes its a good choice when framing examples dealing with Relativity.  But this not mean if we were to remove light from a scenario that Relativistic effects would not manifest themselves.   You don't need light or even electromagnetic interaction for Relativistic effects to occur.  They are built into the very reality of the universe.  The invariant speed of light highlights and helped us discover the rules governing space and time, but is not responsible for them.

Despite my skills good or bad lol,,,,,

 I always enjoy reading any of your posts on the topic of relativity. Another excellent post. I particularly like to highlight relativity relies upon an invariant finite speed,c then anything massless is required to travel at this speed"

I am often seen defending understanding terminology in physics. So for readers, under physics mass is resistance to inertia change the massless feature shows no resistance to inertia change ie no restrictions to reaching a maximal in information exchange. c being that maximal via any experimental observation being the limit. Light simply matches

[Eise]

Hi geordief,

I think in Why does E=mc2 (Brian Cox and Jeff Forshaw) does a very good job in explaining this. It first argues that because of causality only a Minkowski-space works, i.e. there is an 'absolute universal speed-limit'. Only afterwards it identifies that this speed limit is the same as the speed of light, with two arguments:

• the formula for time dilation previously derived with the 'light clock' is the same as the formula derived from the Minkowski-space, which means that c must be the light speed.
• After showing that E=mc², it shows that massless particles must move at exactly this speed limit.

It is a good read for lay people, with Pythagoras as one of the most advanced mathematics you need.

I made a quick reread of the book specially to be able to react on your thread, so better read it! 

 

[geordief]

On 6/18/2018 at 10:39 AM, Eise said:

Hi geordief,

I think in Why does E=mc2 (Brian Cox and Jeff Forshaw) does a very good job in explaining this. It first argues that because of causality only a Minkowski-space works, i.e. there is an 'absolute universal speed-limit'. Only afterwards it identifies that this speed limit is the same as the speed of light, with two arguments:

• the formula for time dilation previously derived with the 'light clock' is the same as the formula derived from the Minkowski-space, which means that c must be the light speed.
• After showing that E=mc², it shows that massless particles must move at exactly this speed limit.

It is a good read for lay people, with Pythagoras as one of the most advanced mathematics you need.

I made a quick reread of the book specially to be able to react on your thread, so better read it! 

 

Thanks (I missed your post at the time)

 

What chapter did they discussion the relationship between causality and c in? Chapter 2: The speed of Light?

 

I can get some of  the book online and may be able to find the relevant pages in Google Books

 

https://books.google.ie/books?id=XChKDgAAQBAJ&pg=PT42&dq=Why+Does+E%3Dmc2+causality&hl=en&sa=X&ved=0ahUKEwiYuoD0jv7bAhWICsAKHW6uBiIQ6AEIKTAA#v=onepage&q=Why Does E%3Dmc2 causality&f=false

 

although it would not be expensive to buy the book itself...

Edited July 1, 2018 by geordief