Why we can never travel faster than the speed of light

[Neogaia777]

You seem to be talking about natural conclusions drawn from what we see. My question is more theoretical --not why we don't see such things, and not even to speculate as to why we see (or don't see) what we do (or don't), but rather, why it would not be possible for faster-than-light travel within a galaxy?

I'm still working on that one myself. And I think I need more knowledge, etc. So, I'm probably going to try and get more knowledge at some point about it, etc. I used to think it was because of infinite mass, or if not that, then the time dilation effect on those particles in motion as they approached c, which is still a factor, but the answer I seemed to get from others when I was asking it is because it takes an infinite amount of work, etc. So, I think I need more knowledge, and need to study it a lot more, etc

You didn't address, for example, why @sjastro keeps referring to 0.88c, instead of the intuitive 1.2c relative to each other, when two light sources depart each other in exactly opposite directions at a speed of 0.6c each.

Again, I don't completely understand why that is yet either, and I think I need more knowledge, which I'm probably going to try and get at some point, etc.

God Bless.

 

[sjastro]

Thanks. Close enough. It did not pick up on (not at all to say that it should have picked up on) what it demonstrated, that I have had no explanation that I can understand or even to identify that it does explain, HOW what it calls Global and I call between galactic [clusters] has a [real] difference of spacetime compared to local spacetime within a galaxy. Maybe the same question asked differently is why metric expansion is a property of spacetime itself, and not mere motion within a 3-d metric. Is spacetime a medium? a force? or just a mental grid expanding to represent the receding distances?

As before, I just don't get it. So. I don't mean to tax anyone further. Thanks for your patience.

This is a science forum which should be educational and feel free to ask questions which is far better than the science bashing rubbish served up by a few individuals.

I gave a simple explanation of metric expansion which explains why the recession velocity of a galaxy increases with increasing distance from the observer and the velocity is proportional to the distance.

The James Webb telescope has broken cosmology. Can it be fixed?

@Bradskii The universe on a supergalactic scale is kind of arranged like a hexagonal grid, kind of anyway, etc. And the growth/expansion is being caused by those very, very empty hexagonal centre's inside each hexagonal cell, pushing out on everything else, etc, (whatever constitutes the walls...

www.christianforums.com

Even without gravity, the expansion of the universe is insignificant at local scales, using the Hubble constant value of 70 km/s/Mpc, if we use the Earth's diameter as our local scale the recession velocity at a distance of 12,740 km is 0.000000000029 m/s which is beyond measurement with the most sensitive instruments available today.

In classical physics space was simply a coordinate system to define the position of objects, today spacetime in the form of a vacuum is a quantum field in the lowest energy state from which virtual particles pop into and out of existence which has been indirectly observed in laboratory experiments.
Dark energy which has caused the expansion of the universe to accelerate is a property of spacetime.

 

[SelfSim]

Maybe the same question asked differently is why metric expansion is a property of spacetime itself, and not mere motion within a 3-d metric. Is spacetime a medium? a force? or just a mental grid expanding to represent the receding distances?

I'm not sure about this, but I get the sense that you may be trying to visualise spacetime like what many around here call a 'physical', or a 'material' object? If so, it very clearly isn't either of those.

Its a model (which differs from a tangible material thing) and it has changed over time. @sjastro has pointed out, it has changed 3 times: '(i) classical physics space, (ii) spacetime in the form of a vacuum is a quantum field in the lowest energy state from which virtual particles pop into and out of existence which has been indirectly observed in laboratory experiments' and (iii) Dark energy was included as a parameter of GR's spacetime in order to account for the observed the expansion (acceleration) of the universe.

I'm unclear on whether that may help a little(?) I'm just trying to assist with the visualisation here .. (its not easy to bridge the conceptual gap).

 

[SelfSim]

Meh .. I'll probably get flak from this, but Brian Greene's What is Space Youtube lays out the history of how scientists have visualised what space is. The first 10 minutes are foundational. The last plug about the Holographic Principle is not accepted as mainstream .. (if anyone makes it that far). The video is a little out of date, as the Higgs (for eg) was finally discovered a couple of years ago at CERN LHC.

 

[Neogaia777]

Meh .. I'll probably get flak from this, but Brian Greene's What is Space Youtube lays out the history of how scientists have visualised what space is. The first 10 minutes are foundational. The last plug about the Holographic Principle is not accepted as mainstream .. (if anyone makes it that far). The video is a little out of date, as the Higgs (for eg) was finally discovered a couple of years ago at CERN LHC.

I watched the whole video, some of it was new to me, and some of it wasn't, but for anyone who cares to watch it at about beginning at the 10 minute mark, up to about the 15 minute mark, I'm still struggling and still do have some questions about some of that?

For example, of course if you are taking any kind of measurements from outside of the cab, about the light emitted from it's headlights, it is still going to be the same no matter what, etc. But aren't you also catching up to that light if you are the one that is inside the cab, and is in motion, headed in the same direction as that light, etc? Aren't you going to eventually catch up to the light emitted from your own headlights if you could get up to the speed of light, etc? Or does this idea that the speed of light is always the same for everybody mean you would not catch up to that light? But if that is the case, and you were traveling at the speed of that light, and you could not catch up to the light emitted from your own headlights, then wouldn't the light that was being emitted from your own headlights have to be traveling at a greater speed than the speed of light? And if you could take a measurement of that light from inside of your own cab, that would be you moving toward that light, wouldn't that measurement measure the speed of that light as being slower than the speed of light if that light were measured from inside the cab traveling in the same direction as that light?

Or how can both be true? How can the measument of the speed of that light from outside of the cab, or the ground, be the same as the measurement that would be taking place of that same light, but from inside the cab as it went, how can they be the same, etc? It would seem that the one from inside the cab would have to measure it a little bit slower as it was headed in the same direction as it, etc, otherwise it's like you are saying that that light is traveling at two different speeds, and yet also is not, etc, but is also traveling at the same speed at the same time, etc?

Take Care/God Bless.

 

[Neogaia777]

The reason we come to the conclusion the speed of light is invariant is because it is exactly 350 years since its speed was first measured and no one over the centuries has found the speed to change irrespective if the observer or the light source move towards or away from each other.

I hope you don't mind me bothering you again, but I've just been sitting around doing some thinking, so...?

So, the speed of light through space (space-time) never changes, and with that I would 100% agree. But, if you were headed the in the same direction as a light source/beam at a pretty good speed, then both you and the light source/photons/beam were like, side by side, etc, then wouldn't it be from your point of view traveling along with it, wouldn't it appear to be traveling slower beside you as both you and it went? Because if it would not appear to be moving any slower beside you as you both went, then the speed of light light beam would have to be the speed of light plus however fast you were traveling, correct? Which can't be right because that would mean it would be being measured as traveling beyond the speed of light, right?

Another reason is that if the speed can be exceeded in an observer's frame of reference causality is violated and events are no longer ordered, you could die before being born.

Why could or would you die? I don't think anybody for sure knows that, etc?

If infinite mass is not a factor, then then the only other factor is time slowing down to a crawl, and maybe even a halt, as you got to the speed of light, etc. Only "for you" does it do this though, and only because your getting very close to (or at) the speed of light, etc. So what would happen if you could go beyond it? I guess nobody knows or can say for sure, etc. I don't know if you could say for sure that you would die though, etc.

But if that were not ever a factor at all, because it also slows down all the processes for all of those atoms/particles, which would probably prevent you from being able to get them up close to the speed of light, etc. Anyway, if that were not a factor at all, then I don't see why you couldn't theoretically get up to, or even exceed the speed of light theoretically or in theory, etc?

And as far as the speed of light not ever changing, which is doesn't actually, but your speed can or does, etc. Anyway, take a look at post #57 (and #59) again, about traveling in a straight line from Earth to Mars, and what you would see as you went if you could put cameras both in front of and behind your, well, let's say "ship" in this case, etc. What you would record ahead of you would be in fast-forward mode a little bit, depending upon how fast you were traveling, etc, and in slow motion mode a little bit for what was behind you or what you were leaving as you went, depending on how fast (or slow) you were going, etc, but would go back to normal mode when you stopped traveling or moving, etc, but would repeat again when you started your trek back, etc, only this time it would be Earth ahead of you and Mars behind you on the way back, instead of the other way around that it was originally before that when you originally left, etc.

But, if you could theoretically exceed the speed of light, it would be no different, it's just that ahead of you, it would be/record a longer period of time/images in a very short amount of time, or would be in super fast forward mode, etc, until you stopped at it that is, etc, and then behind you, the images would even go temporarily back in time for a temporary period of time, or would rewind for a temporary amount of time, if you could exceed the speed of light, etc, and then if you turned around and went back, then it would happen again, or super fast forward mode for what was ahead of you again up to the time you left, plus whatever total amount of time you spent traveling and/or stopped for a little while before you originally left, etc. And behind you would go back to whatever it was before you left plus the total time it took you to travel or you spent stopped for a little while before you originally left or decided to go back, etc. No time ever actually changes, etc. It just that you would see what was distant from you a certain amount of time in it's past for a temporary amount of time, but that would return to normal with no actual change in the passage of time when you went and got back, etc. (I'm thinking of something much farther away than Mars in this case or for this example, etc) (light years away in this case, and with the ability to travel at many multiple times the speed of light preferably in these cases, etc)

Anyway, my original point was about light, and the speed of it, etc. In the fabric of space-time, it never changes, etc, but your speed can or does, etc, and if your headed in the same direction of some light at a decent speed, etc, then from your perspective or point of view measuring the speed of light traveling with you or beside you, etc, then you would see that light going slower beside you than someone on the ground, right? Yes? No?

Take Care/God Bless.

 

[Neogaia777]

@sjastro

Another curious question I have? For those particle accelerators where they can get a particle up to 99.9999% of the speed of light, or whatever, can they show or prove that the processes for that or those particles, do they slow down or not, etc? (Yes or No would suffice for this one, etc)

Or do they have to apply an almost infinite amount of work or thrust to get them up to those speeds? Yes or No maybe? Or just how do they get them up to those speeds exactly, etc?

Much thanks.

Take Care/God Bless.

 

[Neogaia777]

But, if you could theoretically exceed the speed of light, it would be no different, it's just that ahead of you, it would be/record a longer period of time/images in a very short amount of time, or would be in super fast forward mode, etc, until you stopped at it that is, etc, and then behind you, the images would even go temporarily back in time for a temporary period of time, or would rewind for a temporary amount of time, if you could exceed the speed of light, etc, and then if you turned around and went back, then it would happen again, or super fast forward mode for what was ahead of you again up to the time you left, plus whatever total amount of time you spent traveling and/or stopped for a little while before you originally left, etc. And behind you would go back to whatever it was before you left plus the total time it took you to travel or you spent stopped for a little while before you originally left or decided to go back, etc. No time ever actually changes, etc. It just that you would see what was distant from you a certain amount of time in it's past for a temporary amount of time, but that would return to normal with no actual change in the passage of time when you went and got back, etc. (I'm thinking of something much farther away than Mars in this case or for this example, etc) (light years away in this case, and with the ability to travel at many multiple times the speed of light preferably in these cases, etc)

This might be clearer if I included some numbers.

Ok, Alpha Centauri is 4 ly away, right? Well, let's say you had the ability to get to it in 10 minutes. On your way there or ahead of you during the whole 10 minute trip, you'd see or record 4 years plus 10 minutes worth of images in the space of the 10 minutes it took you to get there, or to Alpha Centauri, etc, and if you looked back at Earth from there, you'd see Earth 4 years plus 10 minutes in it's past since you left there 10 minutes ago, etc, and you would also have saw Earth rewind that much in the space of 10 minutes on your way to Alpha Centauri also, etc. And then let's say you spent another 10 minutes at Alpha Centauri before deciding to head back to Earth, and it took you another 10 minutes to get back there, etc. Well, on your way back to Earth, you'd see Earth fast forward 4 years plus 30 minutes, or would see 4 years plus 30 minutes worth of images or footage in the space of 10 minutes, etc (actually 4 years plus 10 minutes, but let's not confuse the issue anymore than it needs to be here, etc) But, anyway, you see 4 years plus 10-30 minutes worth of images or so on your way back to Earth in the space of 10 minutes, etc. And you'd arrive back at Earth precisely 30 minutes later from the time you originally left which was the same amount of time as your whole trip, etc, the 20 minutes you spent traveling, plus the 10 minutes you spent stopped at Alpha Centauri, etc. And behind you as you traveled back to Earth from Alpha Centauri, you'd see it rewind back 4 years plus 30 minutes or so ahead in the space of 10 minutes, etc, and Alpha Centauri would go back to the same image it was when you originally left Earth for it, but plus the 30 minutes of your trip, etc. No time ever changed or changes for anything ever anywhere even if you could do this, etc. It's just that when your 4 light years or so away, those images are, or do become, that old regardless, but go back to normal or catch up when you get there or go there regardless, etc. But this would also mean that you might have to account for that maybe when you decide to go there in the first place to say, in order to maybe not collide with anything or something, etc, especially if it's a lot farther away than Alpha Centauri and you could get there very, very quickly, etc, because what we are seeing from here (Earth) is always that much or amount "old", etc, so you might have to make a few adjustments for what it is like quote/unquote "now", etc. Because the universe is also the same "age" equally everywhere, etc, and what we are seeing of it is not how it is "now", but is a lot "older" than that, etc, and I tend to wonder if our modern day pictures of the universe account for that or not, etc? Because none of them ever seems to stipulate that, or say anything about it, etc?

Anyway,

God Bless.

 

[Hans Blaster]

@sjastro

Another curious question I have? For those particle accelerators where they can get a particle up to 99.9999% of the speed of light, or whatever, can they show or prove that the processes for that or those particles, do they slow down or not, etc? (Yes or No would suffice for this one, etc)

Or do they have to apply an almost infinite amount of work or thrust to get them up to those speeds? Yes or No maybe? Or just how do they get them up to those speeds exactly, etc?

Much thanks.

Take Care/God Bless.

Muons provide a really clear example of very fast particles being "slowed down" by relativity.

Muons are particles similar to electrons, but the only have a lifetime of 2.2 microseconds (1/500,000th of a second). Even at the speed of light they only travel less than 1 km before they decay. (Decay to an electron and two neutrinos)

Muons from space are formed by collision of high energy cosmic rays with the atmosphere and they reach the surface of the Earth. They wouldn't reach the surface of the earth before decaying without time dilation which slows the clock many fold and allows them to travel tens of km. (This is described in paragraph 2 of the link below.)

DOE Explains...Muons

 

[Neogaia777]

Another reason is that if the speed can be exceeded in an observer's frame of reference causality is violated and events are no longer ordered, you could die before being born.

@sjastro

Another curious question I have? For those particle accelerators where they can get a particle up to 99.9999% of the speed of light, or whatever, can they show or prove that the processes for that or those particles, do they slow down or not, etc? (Yes or No would suffice for this one, etc)

@sjastro

Ok, now I think I understand your comment above, about dying before being born, etc. Because maybe according to the current laws of physics (causality, etc), that if you could exceed the speed of light, then time for the one in motion (you in this case) could begin flowing backwards maybe, according to the current laws of physics maybe? Or that's my assumption anyway, etc? But in all reality, no one knows for sure, correct?

And instead of my maybe asking if time slows down for that particle, maybe I should have said, can it be proven that those particles experienced time any differently, etc? Which from all of the outside observers, would be time slowing down for that particle, maybe by examining whether the processes with it experienced time any slower, or actually very much significantly slower at those speeds, and/or any differently, etc?

God Bless.

 

[Neogaia777]

Muons provide a really clear example of very fast particles being "slowed down" by relativity.

Muons are particles similar to electrons, but the only have a lifetime of 2.2 microseconds (1/500,000th of a second). Even at the speed of light they only travel less than 1 km before they decay. (Decay to an electron and two neutrinos)

Muons from space are formed by collision of high energy cosmic rays with the atmosphere and they reach the surface of the Earth. They wouldn't reach the surface of the earth before decaying without time dilation which slows the clock many fold and allows them to travel tens of km. (This is described in paragraph 2 of the link below.)

DOE Explains...Muons

Great, so it's proven then, thanks for providing that information, I appreciate it.

Does this effect (time dilation) have anything at all to do with the difficulty of having to get them (particles) (or anything) up to light speed? Or at speeds very close to light speed? Or is that a separate issue entirely?

Thanks again!

Take Care.

 

[Hans Blaster]

Great, so it's proven then, thanks for providing that information, I appreciate it.

Does this effect (time dilation) have anything at all to do with the difficulty of having to get them (particles) (or anything) up to light speed? Or at speeds very close to light speed? Or is that a separate issue entirely?

Thanks again!

Take Care.

It's all one effect, measured by that relativistic factor.

 

[Neogaia777]

It's all one effect, measured by that relativistic factor.

But did the particle traveling at very nearly the speed of light also have a massive increase in it's mass also?

 

[sjastro]

I hope you don't mind me bothering you again, but I've just been sitting around doing some thinking, so...?

So, the speed of light through space (space-time) never changes, and with that I would 100% agree. But, if you were headed the in the same direction as a light source/beam at a pretty good speed, then both you and the light source/photons/beam were like, side by side, etc, then wouldn't it be from your point of view traveling along with it, wouldn't it appear to be traveling slower beside you as both you and it went? Because if it would not appear to be moving any slower beside you as you both went, then the speed of light light beam would have to be the speed of light plus however fast you were traveling, correct? Which can't be right because that would mean it would be being measured as traveling beyond the speed of light, right?

Since the question has been asked how can two objects travelling at 0.6c have an approach velocity of 0.88c we can use this to answer your question as well.

According to Galilean relativity, a frame S’ moving relative to a ground frame S at a velocity v in the x direction the coordinates (x’,t’) in S’ are transformed to coordinates (x,t) in S by the equations,

x’ = x – vt, t’ = t

t’ = t because time is absolute in Galilean relativity.

Let’s consider the following.

The position of the object x’ in frame S’ moving at a speed u’ at some time t’ is,
x’(t’) = u’t’ + x₀ where x₀ is its initial position.

Substituting x’ = x-vt and t’= t gives,

x(t)-vt = u’t + x₀
x(t) = (u’+v)t + x₀

Differentiating x(t) with respect to t gives the velocity in the ground frame S.

u = dx/dt = u’+ v

Hence in Galilean relativity the velocities for two objects approaching each other at a speed 0.6c, the approach velocity relative to the ground frame is 0.6c + 0.6c = 1.2c.
Similarly for your example a car moving at a speed v, the velocity of the light from the headlamps relative to the ground frame is v + c.

SR however tells us nothing can exceed the speed of light in any frame of reference.
Furthermore, time is not absolute and we need to use the Lorentz transformations,

x’ = ϒ(x-vt), t’ = ϒ(t-vx/c²) where ϒ = 1/√(1-v²/c²)

We can derive the velocity equation using the Lorentz transformations.

In frame S’
x’ = u’t’

Using the Lorentz transformations substituting for x' and t',

ϒ(x-vt) = u’ ϒ(t-vx/c²)
(x-vt) = u’(t-vx/c²)
x + u’v/c² = u’t + vt
x(1 + u’v/c²) = (u’ + v)t
x = (u’ + v)t/( 1 + u’v/c²)

The velocity u in the ground frame S is,

u = dx/dt = (u’ + v)/( 1 + u’v/c²)

For two objects approaching each other at a speed of 0.6c u’ = 0.6c and v = 0.6c.
u = 1.2c/(1+ 0.36) = 0.88c.

In the case of a car travelling at a speed v with its headlights on u’ = c hence,
u = (c + v)/(1+cv/c²) = (c + v)/(1+v/c) = c(c + v)/(c + v) = c.

Irrespective of the velocity v of the car, the velocity of the light from the headlamps will never be c + v according to the Galilean transformations but always c using the Lorentz transformations.

Why could or would you die? I don't think anybody for sure knows that, etc?

If infinite mass is not a factor, then then the only other factor is time slowing down to a crawl, and maybe even a halt, as you got to the speed of light, etc. Only "for you" does it do this though, and only because your getting very close to (or at) the speed of light, etc. So what would happen if you could go beyond it? I guess nobody knows or can say for sure, etc. I don't know if you could say for sure that you would die though, etc.

But if that were not ever a factor at all, because it also slows down all the processes for all of those atoms/particles, which would probably prevent you from being able to get them up close to the speed of light, etc. Anyway, if that were not a factor at all, then I don't see why you couldn't theoretically get up to, or even exceed the speed of light theoretically or in theory, etc?

And as far as the speed of light not ever changing, which is doesn't actually, but your speed can or does, etc. Anyway, take a look at post #57 (and #59) again, about traveling in a straight line from Earth to Mars, and what you would see as you went if you could put cameras both in front of and behind your, well, let's say "ship" in this case, etc. What you would record ahead of you would be in fast-forward mode a little bit, depending upon how fast you were traveling, etc, and in slow motion mode a little bit for what was behind you or what you were leaving as you went, depending on how fast (or slow) you were going, etc, but would go back to normal mode when you stopped traveling or moving, etc, but would repeat again when you started your trek back, etc, only this time it would be Earth ahead of you and Mars behind you on the way back, instead of the other way around that it was originally before that when you originally left, etc.

But, if you could theoretically exceed the speed of light, it would be no different, it's just that ahead of you, it would be/record a longer period of time/images in a very short amount of time, or would be in super fast forward mode, etc, until you stopped at it that is, etc, and then behind you, the images would even go temporarily back in time for a temporary period of time, or would rewind for a temporary amount of time, if you could exceed the speed of light, etc, and then if you turned around and went back, then it would happen again, or super fast forward mode for what was ahead of you again up to the time you left, plus whatever total amount of time you spent traveling and/or stopped for a little while before you originally left, etc. And behind you would go back to whatever it was before you left plus the total time it took you to travel or you spent stopped for a little while before you originally left or decided to go back, etc. No time ever actually changes, etc. It just that you would see what was distant from you a certain amount of time in it's past for a temporary amount of time, but that would return to normal with no actual change in the passage of time when you went and got back, etc. (I'm thinking of something much farther away than Mars in this case or for this example, etc) (light years away in this case, and with the ability to travel at many multiple times the speed of light preferably in these cases, etc)

Anyway, my original point was about light, and the speed of it, etc. In the fabric of space-time, it never changes, etc, but your speed can or does, etc, and if your headed in the same direction of some light at a decent speed, etc, then from your perspective or point of view measuring the speed of light traveling with you or beside you, etc, then you would see that light going slower beside you than someone on the ground, right? Yes? No?

Take Care/God Bless.

If you exceed the speed of light you run into causality issues where there are no ordering of events such as dying before being born.
The explanation is not straightforward but was given in this post.

Why I think perhaps time-travel is impossible

Think about it, if you for example use a strong magnet to speed things up in sort of an attempt to travel in time, people would notice and resist the changes, so only nature would change and speed up or go backwards, but I have the suspicion that the same would happen to nature also, that it...

www.christianforums.com

In a nutshell if you exceed the speed of light you are no longer inside the light-cones.

​

Inside the light cones spacetime is time-like where causality is preserved, outside the cones spacetime is space-like where causality is not preserved.

 

[SelfSim]

Since the question has been asked how can two objects travelling at 0.6c have an approach velocity of 0.88c we can use this to answer your question as well.

According to Galilean relativity, a frame S’ moving relative to a ground frame S at a velocity v in the x direction the coordinates (x’,t’) in S’ are transformed to coordinates (x,t) in S by the equations,

x’ = x – vt, t’ = t

t’ = t because time is absolute in Galilean relativity.

Let’s consider the following.

View attachment 360532​

The position of the object x’ in frame S’ moving at a speed u’ at some time t’ is,
x’(t’) = u’t’ + x₀ where x₀ is its initial position.

Substituting x’ = x-vt and t’= t gives,

x(t)-vt = u’t + x₀
x(t) = (u’+v)t + x₀

Differentiating x(t) with respect to t gives the velocity in the ground frame S.

u = dx/dt = u’+ v

Hence in Galilean relativity the velocities for two objects approaching each other at a speed 0.6c, the approach velocity relative to the ground frame is 0.6c + 0.6c = 1.2c.
Similarly for your example a car moving at a speed v, the velocity of the light from the headlamps relative to the ground frame is v + c.

SR however tells us nothing can exceed the speed of light in any frame of reference.
Furthermore, time is not absolute and we need to use the Lorentz transformations,

x’ = ϒ(x-vt), t’ = ϒ(t-vx/c²) where ϒ = 1/√(1-v²/c²)

We can derive the velocity equation using the Lorentz transformations.

In frame S’
x’ = u’t’

Using the Lorentz transformations substituting for x' and t',

ϒ(x-vt) = u’ ϒ(t-vx/c²)
(x-vt) = u’(t-vx/c²)
x + u’v/c² = u’t + vt
x(1 + u’v/c²) = (u’ + v)t
x = (u’ + v)t/( 1 + u’v/c²)

The velocity u in the ground frame S is,

u = dx/dt = (u’ + v)/( 1 + u’v/c²)

For two objects approaching each other at a speed of 0.6c u’ = 0.6c and v = 0.6c.
u = 1.2c/(1+ 0.36) = 0.88c.

In the case of a car travelling at a speed v with its headlights on u’ = c hence,
u = (c + v)/(1+cv/c²) = (c + v)/(1+v/c) = c(c + v)/(c + v) = c.

Irrespective of the velocity v of the car, the velocity of the light from the headlamps will never be c + v according to the Galilean transformations but always c using the Lorentz transformations.

If you exceed the speed of light you run into causality issues where there are no ordering of events such as dying before being born.
The explanation is not straightforward but was given in this post.

Why I think perhaps time-travel is impossible

Think about it, if you for example use a strong magnet to speed things up in sort of an attempt to travel in time, people would notice and resist the changes, so only nature would change and speed up or go backwards, but I have the suspicion that the same would happen to nature also, that it...

www.christianforums.com

In a nutshell if you exceed the speed of light you are no longer inside the light-cones.

View attachment 360533

​

Inside the light cones spacetime is time-like where causality is preserved, outside the cones spacetime is space-like where causality is not preserved.

Man you're patient ..
This latest barrage of questions hasn't changed in content, for pages now. They're covering the exact same ground.
Its like there's a mind out there that just can't stop asking questions .. just for a moment, in order to let the imports of previous answer sink in.
For days you've been at it, now ..

 

[Hans Blaster]

But did the particle traveling at very nearly the speed of light also have a massive increase in it's mass also?

Yep. The relativistic mass goes up the same factor time goes down by. Personally I like to think of the rest mass and then KE or momentum have the "gamma" factor in them modifying the normal Newtonian formulation.

 

[sjastro]

Man you're patient ..
This latest barrage of questions hasn't changed in content, for pages now. They're covering the exact same ground.
Its like there's a mind out there that just can't stop asking questions .. just for a moment, in order to let the imports of previous answer sink in.
For days you've been at it, now ..

I have a theory @Neogaia777 is outside the light cones and is asking questions that have already been answered.

 

[Neogaia777]

Yep. The relativistic mass goes up the same factor time goes down by. Personally I like to think of the rest mass and then KE or momentum have the "gamma" factor in them modifying the normal Newtonian formulation.

Could you maybe be so kind as to very shortly and succinctly tell me with just a few words what this "gamma" factor is maybe? Or maybe a way I could look it up if you can't put it that way maybe? (I'm exposing myself to a few new to me things online right now and am trying to inform myself better about it or this/these subjects, or all of this so far in this thread, etc, as I have also been going back and re-reading some of the posts so far in this thread while I am doing this as well, etc)

Thanks.

Take Care.

 

[SelfSim]

I have a theory @Neogaia777 is outside the light cones and is asking questions that have already been answered.

More seriously though, my penchant for speaking on behalf of human minds, finds all this quite disturbing.
There's a fairly broad distribution of different types of human minds though .. This one is clearly several standard deviations from the norm .. but still human, I think(?) That latest Chinese AI you've been talking to has blown my mind and has seriously made me wonder about about my own claims about how to test for the presence of other conscious human minds .. hmm .. (?)

 

[Neogaia777]

Man you're patient ..
This latest barrage of questions hasn't changed in content, for pages now. They're covering the exact same ground.
Its like there's a mind out there that just can't stop asking questions .. just for a moment, in order to let the imports of previous answer sink in.
For days you've been at it, now ..

I have a theory @Neogaia777 is outside the light cones and is asking questions that have already been answered.

Hey now, be nice, ok. I'm a curious sort that likes to ask a lot of questions, etc.

And you guys should probably also read the reply I just now made to @Hans Blaster just now as well.

Really though, I thank you guys for putting up with me though, etc. I promise I'm going to put a lot more thought and energy and effort and time and research into this and also try not to rehash some of the same old things/questions in the meantime, ok.

Take Care/God Bless.