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Author Topic:   Speed of Light Barrier
onifre
Member (Idle past 2950 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 121 of 178 (504054)
03-24-2009 10:12 AM
Reply to: Message 120 by DevilsAdvocate
03-23-2009 9:57 PM


Hi DA,
Just to add...
There is speculation of faster than light zero-mass particles/energy called tachyons (yes, Star Trek borrowed this idea from main stream science). However, this idea is purely hypothetical with no evidence yet supporting it.
Tachyons would still not be able to send information at faster-than-light speeds.
From wiki:
quote:
Even if tachyons were conventional, localisable particles, they would still preserve the basic tenets of causality in special relativity and not allow transmission of information faster than light, contrary to conventional scientific thought and what has been written in many works of science fiction.
Today, in the framework of quantum field theory, tachyons are best understood as signifying an instability of the system and treated using tachyon condensation, rather than as real faster-than-light particles, and such instabilities are described by tachyonic fields. According to the contemporary and widely accepted understanding of the concept of a particle, tachyon particles are too unstable to be treated as existing. By that theory, faster than light information transmission and causality violation with tachyons are impossible on both grounds: they are non-existent in the first place (by tachyon condensation) and even if they existed (by Feinberg's analysis) they wouldn't be able to transmit information (also by Feinberg's analysis).

"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks
"I never knew there was another option other than to question everything"--Noam Chomsky

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shalamabobbi
Member (Idle past 2848 days)
Posts: 397
Joined: 01-10-2009


Message 122 of 178 (504687)
04-01-2009 3:26 PM
Reply to: Message 92 by DevilsAdvocate
03-04-2009 5:28 AM


Re: FTL
DA writes:
In essense, a spaceship would be stationary and would bend the space around itself using massive quantities of energy. This is similar to the effect that gravity has on the fabric of spacetime. Thus it is not really that you are travelling faster than the speed of light to get to the stars/galaxies/etc but rather you are shortening the space in between you and your destination.
Of course this is all hypothetical and the energy required would be enormous. However, possibly by harnessing the energy from antimatter and matter collisions this energy could be tapped. Also, the implications of how this effects the 'fabric' of spacetime and matter in between these two locations is unknown.
I am not very knowledgeable about cosmology. I haven't finished Greene's book yet, the fabric of the cosmos.
My question is about this idea of warping spacetime using energy. What advantage does energy have over matter to warp spacetime? Since gravity causes light paths to bend, energy must affect spacetime as well, but would an equivalent amount of energy affect spacetime any different than the original mass?
The only idea I can think of is if the energy were confined to a smaller volume than the original mass then maybe it might have a greater effect on the spacetime.
Please someone elaborate on this.
Thanks.

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Perdition
Member (Idle past 3237 days)
Posts: 1593
From: Wisconsin
Joined: 05-15-2003


Message 123 of 178 (504693)
04-01-2009 5:40 PM
Reply to: Message 118 by Taq
03-23-2009 6:03 PM


I've heard of the tachyon before. I'm more interested in what is it that sets this limit. Why can't tachyons go slower and why can't photons go faster. Is there something about space itself that imposes a limit?

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 124 of 178 (504694)
04-01-2009 5:40 PM
Reply to: Message 122 by shalamabobbi
04-01-2009 3:26 PM


Re: FTL
would an equivalent amount of energy affect spacetime any different than the original mass?
Not in the sense you are thinking, but this needs mildly caveating - if the energy content of a volume is not in the form of a solid mass, then the energy distribution will be different, which will cause a different effect upon the local space-time.
Please someone elaborate on this.
To create any "anti-gravity" effect (wormhole, Alcubierre warp drive, etc) you need a -ve energy density or "exotic" matter. Examples of this are Casimir energy, dark energy, and the inflaton field.

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 125 of 178 (504696)
04-01-2009 6:20 PM
Reply to: Message 123 by Perdition
04-01-2009 5:40 PM


Why can't tachyons go slower and why can't photons go faster. Is there something about space itself that imposes a limit?
When you get close to c, you are no longer dealing with something that you would recognise as "speed". Speed is a concept that only makes sense somewhat *below* c. Tachyons do not "travel" in any obvious sense. c itself simply reveals our own length/time-scale within the geometry of space-time.

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Replies to this message:
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Perdition
Member (Idle past 3237 days)
Posts: 1593
From: Wisconsin
Joined: 05-15-2003


Message 126 of 178 (504754)
04-02-2009 12:56 PM
Reply to: Message 125 by cavediver
04-01-2009 6:20 PM


See, this is why I dropped out of physics. Well, mostly it was calculus that kicked my ass, but the general relativity and quantum mechanics, while very interesting, relied too heavily on that type of math.

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Michamus
Member (Idle past 5157 days)
Posts: 230
From: Ft Hood, TX
Joined: 03-16-2009


Message 127 of 178 (505169)
04-08-2009 11:15 AM
Reply to: Message 125 by cavediver
04-01-2009 6:20 PM


Hi cavediver,
I am a bit ignorant when it comes to physics.
Speed is a concept that only makes sense somewhat *below* c.
So is the statement "The speed of light" a misrepresentation as LS is a constant?

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onifre
Member (Idle past 2950 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 128 of 178 (505196)
04-08-2009 6:17 PM
Reply to: Message 127 by Michamus
04-08-2009 11:15 AM


Hi Michamus,
So is the statement "The speed of light" a misrepresentation
The "speed of light" does represent an actual number see here:speed of light
So, when physicist use a tool to measure a photon in a vacuum it does render an actual, measurable speed.
as LS is a constant?
Yes it is. When measured, using an istrument to measure with, in a vacuum, the speed of a photon is constant (c).
In an effort to make sense of it a bit more for you, I would say that "speed", also, only makes sense to the person observing the object in motion.
A photon heading toward Earth at (c) is said to be traveling at light speed toward us, from our frame of reference. But, from the frame of reference of the photon, it is the Earth that is traveling toward it at (c). In other words, to the photon, it is not moving at all. Yet, when we, on Earth, look at the photon in our frame of reference we are stationary and it is moving at a defined speed.
I hope this helps a bit. Just a student myself in this subject.

"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks
"I never knew there was another option other than to question everything"--Noam Chomsky

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Replies to this message:
 Message 129 by Taq, posted 04-09-2009 6:49 PM onifre has replied
 Message 130 by shalamabobbi, posted 04-09-2009 7:08 PM onifre has replied

  
Taq
Member
Posts: 9970
Joined: 03-06-2009
Member Rating: 5.6


Message 129 of 178 (505281)
04-09-2009 6:49 PM
Reply to: Message 128 by onifre
04-08-2009 6:17 PM


In an effort to make sense of it a bit more for you, I would say that "speed", also, only makes sense to the person observing the object in motion.
A photon heading toward Earth at (c) is said to be traveling at light speed toward us, from our frame of reference. But, from the frame of reference of the photon, it is the Earth that is traveling toward it at (c). In other words, to the photon, it is not moving at all. Yet, when we, on Earth, look at the photon in our frame of reference we are stationary and it is moving at a defined speed.
[uber-nerd nit pick]It is actually stranger than this. We don't actually observe a photon moving. We simply measure the time it takes to get from point A to point B. In between point A and point B it can be in any number of places. It is only whe a photon interacts with matter does it appear in just one place.
So might it be more accurate to describe the speed of light as the speed of the propogation of light?
[/uber-nerd nit pick]

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Replies to this message:
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shalamabobbi
Member (Idle past 2848 days)
Posts: 397
Joined: 01-10-2009


Message 130 of 178 (505283)
04-09-2009 7:08 PM
Reply to: Message 128 by onifre
04-08-2009 6:17 PM


photon frame?
onifire writes:
But, from the frame of reference of the photon, it is the Earth that is traveling toward it at (c).
I remember asking the professor about the frame of reference from the photon's POV and he remarked that special relativity doesn't work for that frame. But since in the limit distance would shrink to nothing, I would think that for the photon the universe is a pancake and it travels 'along' its axis no distance at all, it departs and arrives instantly from the same point(s) that overlap. There is separation of the point of departure and point of arrival in our frame, but I wouldn't think there would be in the photon's frame, if such a frame can even be discussed.
Maybe cave diver or son goku will chime in..

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onifre
Member (Idle past 2950 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 131 of 178 (505289)
04-09-2009 8:33 PM
Reply to: Message 130 by shalamabobbi
04-09-2009 7:08 PM


Re: photon frame?
There is separation of the point of departure and point of arrival in our frame, but I wouldn't think there would be in the photon's frame, if such a frame can even be discussed.
The example of the frame of reference of the photon was meerly analogous.
However, even when there are no observers and no measurement taking place, the photon is not alone. Other particle exist, even in a vaccum, virtual particles for example. These make up a frame of reference too, so the photon is always locked in to (c).

"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks
"I never knew there was another option other than to question everything"--Noam Chomsky

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onifre
Member (Idle past 2950 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 132 of 178 (505290)
04-09-2009 8:52 PM
Reply to: Message 129 by Taq
04-09-2009 6:49 PM


My photon example was only an analogy.
We don't actually observe a photon moving.
From the observer’s point of view, the photon moves with measurable velocity, measurable frequency, measurable energy. The time experienced by the photon is still zero from start to finish of its journey, but the observer still knows it is moving at a particular pace and also vibrating as it goes. When it is said that a photon is "observed" I don't mean visually followed, I mean measured.
We simply measure the time it takes to get from point A to point B.
Well, it's a bit more defined than that. See: Cartesian coordinate systems
In between point A and point B it can be in any number of places...
...within a vector.
So might it be more accurate to describe the speed of light as the speed of the propogation of light?
Sure, or the speed of propagation of electromagnetic waves in a vacuum. - (electromagnetic constant)

"I smoke pot. If this bothers anyone, I suggest you look around at the world in which we live and shut your mouth."--Bill Hicks
"I never knew there was another option other than to question everything"--Noam Chomsky

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 Message 129 by Taq, posted 04-09-2009 6:49 PM Taq has replied

Replies to this message:
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Taq
Member
Posts: 9970
Joined: 03-06-2009
Member Rating: 5.6


Message 133 of 178 (505303)
04-10-2009 12:37 AM
Reply to: Message 132 by onifre
04-09-2009 8:52 PM


From the observer’s point of view, the photon moves with measurable velocity, measurable frequency, measurable energy. The time experienced by the photon is still zero from start to finish of its journey, but the observer still knows it is moving at a particular pace and also vibrating as it goes. When it is said that a photon is "observed" I don't mean visually followed, I mean measured.
It was a minor and very tedious nit pick. I just happen to really enjoy these types of discussions.
I find the differences between our macroscopic experience of the world and the microscopic world of quantum mechanics to be a very exciting difference. It's not as if we measure the speed of light like we would a car going down the freeway. It is more like measuring the velocity of a bullet by measuring the time it takes between the bullet being fired and the bullet striking a target 200 yds down range. We don't see the bullet in between with our naked eye, but we do hear the bang and then see the strike. Light is somewhat like this, but even stranger.

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 134 of 178 (505345)
04-10-2009 12:32 PM
Reply to: Message 132 by onifre
04-09-2009 8:52 PM


From the observer’s point of view, the photon moves with measurable velocity, measurable frequency, measurable energy.
Not really. You can only determine the photon's properties by its effect when it interacts with something. By that time it no longer exists. You cannot observe/measure/experiment-on photons in transit.

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 135 of 178 (505346)
04-10-2009 12:35 PM
Reply to: Message 130 by shalamabobbi
04-09-2009 7:08 PM


Re: photon frame?
I would think that for the photon the universe is a pancake and it travels 'along' its axis no distance at all, it departs and arrives instantly from the same point(s) that overlap. There is separation of the point of departure and point of arrival in our frame, but I wouldn't think there would be in the photon's frame
Yes, this is essentially correct.

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