Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: realmswalker on 13/10/2006 03:50:05
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its such a basic tenet of modern physics...but i dont get why it is this way...???!?!
why cant any thing go faster than light? why did einstein set that as the constant and what not?
i mean its illogical to think that if you have an engine with infinite output and you kept pushing on something, that it couldnt overcome the speed of light eventually....
idk
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An old friend answered this for me a long time ago. He nailed it using just a few words. It made me laugh too. He said; "You can't go faster then the speed of light. If you could, you'd get where you're going before you left where you were. And thats against the rules."
Pretty elegant piece of logic, I think.
On the other hand, isn't the influence of gravity immediate? Immediate is faster then 299 792 458 m / s. (I'm only assuming that immediacy of influence is a property of gravity. It can't really be measured directly can it?)
Mike
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quote:
Originally posted by lightarrow
(see the thread:http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=2010&whichpage=2)
The fact is that in practice the speed of light is infinite. What I mean: when a body's speed is not much, our definition of speed: v = space/time is a good definition, but when the body's speed is very high (that is, near the speed of light) our definition is not good anylonger, because space and time are not (enough) independent each other anylonger.
If you were inside a space-ship moving faster and faster, you would see planets, stars, approaching you in greater and greater amount, without any limit, that is, the number of stars you would see passing by you in one second, e.g., would approach infinity.
Of course we are assuming the average number of stars in a volume of space is constant, but this doesn't change the essence of the concept.
If we defined the speed of a body in a more appropriate way, that is exactly in the way we define lenght, mass, time: using a sample of it and adding n equal samples to make a sample n-times bigger, it's possible to show, mathematically, that the speed of light would become infinite.
This is the concept: you take a train, which holds railtracks attached on top of it. You can impose a certain speed v1 = v to this first train (measured in the usual way, for example);
then you put another train on the first, and impose this second train's speed is still v respect the first one. You can define a new concept of speed, saying that this second train has speed 2*v relative to the ground.
But, using Lorentz rule of speed addition, you have, according to the usual definition of speed, that the second train moves at a speed:
v2 = (v+v1)/(1+v*v1/c^2) = 2v/(1+beta^2). beta is v/c. Repeating the same for a third train on the second and so on, you have v3,...vn.
At the limit for n-->infinite, the speed is:
1.infinite, according to the new definition
2. c, according to the usual definition (you have to compute the limit mathematically).
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There was research published about a year ago which claimed to measure the velocity of gravitational waves by examining an occultation at radio frequencies and found it was in fact 'c'.
I will hunt thru the literature and see if I can find it
syhprum
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quote:
Originally posted by realmswalker
its such a basic tenet of modern physics...but i dont get why it is this way...???!?!
why cant any thing go faster than light? why did einstein set that as the constant and what not?
i mean its illogical to think that if you have an engine with infinite output and you kept pushing on something, that it couldnt overcome the speed of light eventually....
idk
There are three [theoretical] classes of objects.
There are massless objects that can only travel at the speed of light, no slower, and no faster. The photon is such.
There is ordinary matter, than can only ever travel at a speed slower than the speed of light (it is not a matter of increasing speed until you get to the speed of light, and then pushing a little harder; because you will never reach the speed of light in the first place – you will get ever closer, but the closer you get to it, the harder you have to work to get closer yet, so you never quite reach it).
Then there is a theoretical class of objects known as tachyons that can only ever travel faster than the speed of light, and can never slow down to being as slow as the speed of light (if such objects exist, then they will be very strange objects indeed, and whereas with ordinary matter, you need to add energy to make it go faster, with tachyons you need to add energy to slow it down, and you could never add enough energy to get it to slow down to the speed of light).
George
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cause light is ...ummm..fast?
NEVER! underestimate youth
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because photons have no mass.
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quote:
Then there is a theoretical class of objects known as tachyons that can only ever travel faster than the speed of light, and can never slow down to being as slow as the speed of light (if such objects exist, then they will be very strange objects indeed, and whereas with ordinary matter, you need to add energy to make it go faster, with tachyons you need to add energy to slow it down, and you could never add enough energy to get it to slow down to the speed of light).
could a tachyon possibly be an antiphoton?
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If you could, you'd get where you're going before you left where you were. And thats against the rules.
thats not entirely true. you are always where you are, and when you are. The only thing that arrives before, is your image. If light was not a barriar, than the next milestone would be instantanious. Even if you take no time at all to move from point a to point b, the image would appear at point b slightly after the image at point a dissappears. if you were to travel faster than instantanous, than you would meet up with yourself at the point, and there cannot be two of you in existance.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
thats not entirely true. you are always where you are, and when you are. The only thing that arrives before, is your image. If light was not a barriar, than the next milestone would be instantanious. Even if you take no time at all to move from point a to point b, the image would appear at point b slightly after the image at point a dissappears. if you were to travel faster than instantanous, than you would meet up with yourself at the point, and there cannot be two of you in existance.
But if your image arrived before you it would still go againts the rules as that image would contain information which is basically the same thing as you arriving before you left.
Michael
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quote:
Originally posted by science_guy
could a tachyon possibly be an antiphoton?
no. photons are like their own anti-particles, but i don't think anything should be a photon's anti-particle, because if you annihilate photons, what do you get as a result?
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I have now located the article concerning the measurement of the velocity of gravitational waves
http://arxiv.org/PS_cache/gr-qc/pdf/0206/0206022.pdf
syhprum
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quote:
But if your image arrived before you it would still go againts the rules as that image would contain information which is basically the same thing as you arriving before you left.
I already explained that arriving before you left is impossible, since man cannot achieve time travel. Going faster than light does not mean going faster than time, although the faster you go, the slower time gets. Your image is the local light being bounced off your ship. If you were going faster than light, than you would arrive at your destination before the light that bounced off you at the starting point did, but you would only be invisible for as long as it takes for light from your ship to reach the observer at the location. Your image is not somthing that contains important information about you, but how the observer sees the light bouncing off your ship.
Another reason that Going as fast as light might be impossible, is that when you are going as fast as light, than time essentialy stops, therefore the signals to stop would never reach the engines in the ship and you would be trapped in hyperspace.
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no. photons are like their own anti-particles, but i don't think anything should be a photon's anti-particle, because if you annihilate photons, what do you get as a result?
if light is considered energy, than maybe the annihilation of an anti-photon and a photon is the reverse effect of the annihilation of any other matter/antimatter reaction: Maybe it would create mass.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
Originally posted by science_guy
if light is considered energy, than maybe the annihilation of an anti-photon and a photon is the reverse effect of the annihilation of any other matter/antimatter reaction: Maybe it would create mass.
A gamma photon with high enough energy colliding with a nucleus can already create mass generating a pair electron-antielectron. Where is the anti-photon, in that case?
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A photon as its alto ego a wave packet can either annihilate or reinforce a similar one but of course they cannot be described as photons and anti-photons
syhprum
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The concept of tachyons has been thrown out. That was only a stop-gap theory to plug a hole in an existing theory; but the theory that needed it has been modified so the need for the existence of tachyons became void.
Brand new forum at
http://beaverland.forumup.us
More than just science
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wow, our topic has been graced with DoctorBeaver's presence![^][^]
What was the theory that concerned this?
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
Originally posted by science_guy
wow, our topic has been graced with DoctorBeaver's presence![^][^]
What was the theory that concerned this?
I'm not sure offhand. There was something about it a book I was readng a while back.
Brand new forum at
http://beaverland.forumup.us
More than just science
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quote:
Originally posted by realmswalker
its such a basic tenet of modern physics...but i dont get why it is this way...???!?!
why cant any thing go faster than light? why did einstein set that as the constant and what not?
i mean its illogical to think that if you have an engine with infinite output and you kept pushing on something, that it couldnt overcome the speed of light eventually....
idk
Ok, I'll try and outline this briefly, but keep in mind that this explanation will be rather simplified and therefor probably imprecise in certain details. Ok? Here goes:
The basic idea that we're starting with here, is that the speed of light is apparently always the same, no matter from where you are observing it, or how fast you as an observer are moving. This may be hard to accept, but so far, all experiments done to test this idea seem to confirm it. So let's just accept that as fact for the moment (if this is actually true, and the implications of it not being true might be an interesting topic in another thread).
So now, imagine two lamps, of identical build, fastened to the roofs of two identical rooms. On the floor, opposite from the lamps, there are two light detectors. One of the rooms is stationary from the observers point of view. So now, in the stationary room, the lamp shines a beam of light to the detector on the floor below it. If the observer measurs how long it took the beam to reach the detector, he'll see that it is obviously the height of the room, divided by the speed of light.
Now the same experiment is conducted in the second room, while it is moving sideways at a constant speed relative to the observer. The beam of light now travels a longer distance, namely the diagonal of a rectangle with the height of the room, and the width being the distance travelled during the time it takes. So now, if we accept that the speed of the light was the same, and the distance was larger, and the time from our point of view was the same, the only way to explain it is if the time in the room was running slower that for the observer. Clear so far?
Now we'll keep imagining that experiment, while speeding up the moving room. You'll see that the angle at which the beam of light is travelling gets flatter and flatter, the closer we get to the speed of light. The distance the beam travels gets longer and longer, so the local time in the room gets slower and slower. If we continue this up until the room is moving at the speed of light, time will stop completely in the room. If you've followed this far, you've understood a major part of relativity.
Now, analogue to time slowing down, things moving at high speeds also tend to get heavier (actually, more massive. There are similar thought experiments that show why this is so, but they're quite a bit more complex that the time slowing one we did above). This increase of mass doesn't happen linearly. At first up to about half the speed of light, the gain in mass is very small, after that, it keeps getting quicker. For the last percent of lightspeed, the increase in mass is very very large. Now along with an increase in mass, comes an increase in inertia. You'll notice this if you try pushing a cart. The more mass is on the cart, the harder you have to push. Now if our object would actually reach the speed of light, it's mass would increase to infinite. This means that the closer we get to the speed of light, the more energy we'd need to keep speeding things up. The actually get to lightspeed, we'd need an infinite amount of energy, which in a finite universe is more than can ever be available. The conclusion of all this, is that objects without mass can move at the speed of light, because their mass stays at zero. Anything with a non-zero mass cannot, because it would take an infinite amount of energy to get it to those speeds.
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Very interesting.
Can you explain why mass gets larger when you get closer to the speed of light? I would understand why time might slow down...
could going faster be an example of converting time into space? Whereas going slower is an example of converting space into time?
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
Originally posted by science_guy
Very interesting.
Can you explain why mass gets larger when you get closer to the speed of light? I would understand why time might slow down...
could going faster be an example of converting time into space? Whereas going slower is an example of converting space into time?
[xx(]
Brand new forum at
http://beaverland.forumup.us
More than just science
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quote:
Originally posted by science_guy
Can you explain why mass gets larger when you get closer to the speed of light? I would understand why time might slow down...
I suppose the starting point should be whether someone can explain what mass is.
Mass seems to be nothing but a number that tells you how responsive or unresponsive something is to external force, which is just another way of saying that the closer an object is to travelling at the speed of light, the more unresponsive it becomes to external forces that may try and alter its velocity.
George
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quote:
Originally posted by DoctorBeaver
quote:
Originally posted by science_guy
Very interesting.
Can you explain why mass gets larger when you get closer to the speed of light? I would understand why time might slow down...
could going faster be an example of converting time into space? Whereas going slower is an example of converting space into time?
[xx(]
Oops! did we confuse you? [^][^]
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I suppose the starting point should be whether someone can explain what mass is.
Mass seems to be nothing but a number that tells you how responsive or unresponsive something is to external force, which is just another way of saying that the closer an object is to travelling at the speed of light, the more unresponsive it becomes to external forces that may try and alter its velocity.
so, because we are getting closer to the velocity of light, the measure of mass vs. external forces increases, and therefore the amount of external forces has to increase in order to go faster?
If you were observing a ship going closer to the velocity of light, would it actually appear to increase in mass, or would it just require more force to move, and therefore appear to increase in mass because of greater resistance to movement?
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
Originally posted by science_guy
Can you explain why mass gets larger when you get closer to the speed of light? I would understand why time might slow down...
If the equation m = E/c^2 it's not a mystery for you, then the answer to your question is:
E = m(0)*c^2/SQRT[1-(v/c)^2]
where m(0) is the "rest mass" = "invariant mass" = the mass of the body when it's at rest. Sometimes it's called just "mass", while the one we are talking now it's called "relativistic mass".
So, from those equations you can see that m = m(0)/SQRT[1-(v/c)^2] and this means that the more v approaches c, the more v/c approaches 1 and the greater is the (relativistic) mass m, approaching infinity.
Said in another way: if we want to preserve the law of momentum conservation, then the momentum p must be defined in this way:
p = m(0)*v/SQRT[1-(v/c)^2]. This comes from Lorentz transforms.
So, the term multipling v can be seen as our "mass".
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quote:
Originally posted by science_guy
If you were observing a ship going closer to the velocity of light, would it actually appear to increase in mass, or would it just require more force to move, and therefore appear to increase in mass because of greater resistance to movement?
Both. The increase in mass is effective in any sense, even for what concerns gravitational mass.
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and thats why we can never reach the speed of light, becuase we cant reach infinite engine output! Makes perfect sense.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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Exactly.
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I've always liked Italian Stuff. [:D][:D]
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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quote:
Originally posted by science_guy
I've always liked Italian Stuff.
Thank you.
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I'm curious as to the explanation for why gravitational force can move not only faster than light, but instantly. If the sun stopped emitting light, we would still see light for about eight minutes as the last photons traveled from it to us, but if it's gravity suddenly disappeared, we would not continue in our orbit for eight minutes. We would immediately commence a fairly straight line divergence effected only by the gravity fields of the moon and the other planets and debris of our rapidly scattering planetary system. [?]
D.G.Davis,Jr.
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I believe that gravity is not really a force, but a bend in space. This can be illustrated by looking at an eclipse of the sun. Becuase the sun's gravity bends space, what we would interperate as a curved line becomes a straight line, and therefore light must follow that path, and in doing so, you can see stars behind the sun during an eclipse. Becuase gravity is a bend in space, we also must follow this curve in space, and settle in it, which pulls our body towards the center of the "hole" in space. Because of this, the force does not need time to reach us, because we are already in it, and it would affect us immediatly after appearance/disappearance.
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I would engage you in a battle of wits, but it is against my moral code to attack the unarmed.
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Sorry, but where did you read that gravitational force moves instantly?
http://en.wikipedia.org/wiki/Speed_of_gravity
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General relativity predicts that gravitational radiation should exist and propagate as a wave at the speed of light.
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There IS one question in this sequence that I have not yet found a clear answer to and that is does the gravitational attractive force force between two bodies only depend on the rest mass of the bodies or does it increase with the increasing velocity? I think that it may only apply to the rest mass. In which case materials orbiting black holes will actually find it very difficult to get into the hole because one definition of a black hole event horizon is that it is the point where the escape velocity reaches the speed of light. The orbital velocity is a little bit lower than this but is still quite close to the velocity of light and so the relativistic mass ingrease is very noticable requiring a lot of extra enegy input to get an orbit that low.
Learn, create, test and tell
evolution rules in all things
God says so!
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quote:
Originally posted by Soul Surfer
There IS one question in this sequence that I have not yet found a clear answer to and that is does the gravitational attractive force force between two bodies only depend on the rest mass of the bodies or does it increase with the increasing velocity? I think that it may only apply to the rest mass. In which case materials orbiting black holes will actually find it very difficult to get into the hole because one definition of a black hole event horizon is that it is the point where the escape velocity reaches the speed of light. The orbital velocity is a little bit lower than this but is still quite close to the velocity of light and so the relativistic mass ingrease is very noticable requiring a lot of extra enegy input to get an orbit that low.
1.The gravitational force depends on the space-time curvature, wich depends on the stress-energy tensor (G_mu_nu = 8(pi)T_mu_nu) which depends on every form of energy, not rest mass only; so it depends on relativistic mass, not simply rest mass.
2.Orbiting near a black hole, a body probably loose energy as gravitational waves, so loosing velocity and hence going in an inner orbit.
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I causiously suggested that the influence of gravity was instantanious in a post earlier in this thread. I carefully choose the word "influence" rather then the word "speed". I might be the only guy here who thinks there is a difference. Syhprum hunted down and shared an artical that addressed the speed of gravity. Thank you for that Syhprum.
That paper concluded that the speed of gravity = C(g)
The mathmatic support they offered is a bit over my head so I won't even try to misinterprate it (lol), but the logic by which they built the model seemed damned to result in a number which is about equal to the speed of light.
Mike
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quote:
Originally posted by jysk
I causiously suggested that the influence of gravity was instantanious in a post earlier in this thread. I carefully choose the word "influence" rather then the word "speed". I might be the only guy here who thinks there is a difference.
When you will study physics more deeper at school, you will understand that there is no difference between "influence" and "speed", in the sense that the "influence" must have a "speed of influence". You will learn that physics treats very well defined things, otherwise it's not physics, but literature, instead.
Anyway, I hope you don't take these as critics on you; your interest in physics is a positive thing in itself, ok?
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so light arrow, does that mean that if I were traveling very fast, all the time in circles on earth, that I would measure the strength of gravity as greater than 9.81 ms^2?
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quote:
Originally posted by thebrain13
so light arrow, does that mean that if I were traveling very fast, all the time in circles on earth, that I would measure the strength of gravity as greater than 9.81 ms^2?
Soul Surfer talked about "gravitational attractive force force between two bodies" and not about "gravitational acceleration". Since the acceleration, in the first approximation, is given by force/mass, if force and mass increases of the same amount, the acceleration doesn't varies.
I said "in the first approximation" because, relativistically, F = m*a it's not true anylonger.
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The plot thickens! sorry I probably was a bit loose in my expression a was really talking about the way a body accelerates under gravity as its velocity beomes relatavistic
I have been trying to understand how strongly relatavistic motion affects the orbits of objects close to (or even inside) a black hole.
So you are saying that the acceleration of a body under gravity towards the centre of gravity as it approaches the event horizon of a black hole does not change as its mass increases as a result of its velocity increase. How then does angular momentum fit into this?
so you are saying that the acceleration on a body as its mass increases in a relatavistic orbit around a black hole
This is the best information I have found so far
http://www.fourmilab.ch/gravitation/orbits/
as you will see the orbits are extremely peculiar
This of course only applies to non rotating black holes the important thing is what happens when the hole is rotating?
Learn, create, test and tell
evolution rules in all things
God says so!
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quote:
Originally posted by Soul Surfer
I have been trying to understand how strongly relativistic motion affects the orbits of objects close to (or even inside) a black hole.
It's a good question! By the way, the document you pointed to is very nice!quote:
So you are saying that the acceleration of a body under gravity towards the centre of gravity as it approaches the event horizon of a black hole does not change as its mass increases as a result of its velocity increase.
I was talking about gravitational acceleration, not about the total resultant acceleration.
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I believe I made myself unclear through the usage of the word "moves". My point, however, remains. The influence of the sun's gravitation (or sudden loss thereof) would be instantly apparent to us even if we were on Pluto, while it would be some time before we realised that it had been removed due to light speed lag.
D.G.Davis,Jr.
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The influence of the sun's gravitation (or sudden loss thereof) would be instantly apparent to us even if we were on Pluto, while it would be some time before we realised that it had been removed due to light speed lag.
What does, physically mean "influence"?
What does, physically mean "realise"?
If you don't give a precise physical meaning to these words, you are not talking about physics, but about something else.
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"thats not entirely true. you are always where you are, and when you are. The only thing that arrives before, is your image. If light was not a barriar, than the next milestone would be instantanious. Even if you take no time at all to move from point a to point b, the image would appear at point b slightly after the image at point a dissappears. if you were to travel faster than instantanous, than you would meet up with yourself at the point, and there cannot be two of you in existance."
But the questions is why can't "anything" travel faster than light, and so, it seems, that conceiving of the question in terms of you or me, or man, misses the point of the question. Nature changes when observed at different scales. The "facts of nature" described by classical physics and "the facts of nature" described at the quantum scale of accuracy are radically different.
The theoretical physicist, David Bohm, speculated that there is another domain that is existent at a scale smaller than Planck's Constant - Man just has not developed the technology to explore that domain. ( more accurately Bohm speculated infinite domains). The speed of light is a limitation that defines the domain of the human experience. If something travelled faster than light, that something would have a radically different expereience of "reality" than our own.
"Never express yourself more clearly than you think." (Niels Bohr)