Can mass go faster than the speed of light?

[spiffomatic64]

My original post had a bunch of theories on the matter, but I know very little about this subject.

Can matter go faster than c? if so, what changes at this point? anything?

if not, why can't it?

personally I don't think it can, and had some reasoning, but Id rather hear what we know before making a bunch of stuff up first :)

 

[Hootenanny]

My original post had a bunch of theories on the matter, but I know very little about this subject.

Am I correct to assume that you have posted here before, specifically under an different username?

Can matter go faster than c? [...] if not, why can't it?

According to Einstein's Theory of Relativity a massive body cannot travel at or faster than C, however, it may travel at a speed arbitrarily close to C. Relativity also requires than any massless particles travel at C throughout all time and space.

 

[spiffomatic64]

Am I to understand that you have posted here before, specifically under an different username?

No, I posted and it was removed because I didnt read the rules :( lol twas my own fault.

I posted this question in the form of an answer (my own uninformed theories) and I wanted to hear if it was right, partially right, wrong, partially wrong etc.

According to Einstein's Theory of Relativity a massive body cannot travel at or faster than C, however, it may have a speed arbitrarily close to C. Relativity also requires than any massless particles travel at C throughout all time and space.

ah, I guess that's a cue to read up on that right? :) or would you care to laymanize the reason why massive bodies cannot travel >=c :-D

as far as massless bodies, are there more than photons? I thought that was it. everything else is just negligible (for our uses) but still has some mass.

 

[Hootenanny]

No, I posted and it was removed because I didnt read the rules :( lol twas my own fault.

That's okay then, things can get a little confusing if people post with multiple usernames.

ah, I guess that's a cue to read up on that right? :) or would you care to laymanize the reason why massive bodies cannot travel >=c :-D

I would certainly recommend reading something about Einstein's theories, a good place to start is Einstein's own book 'Relativity', which was intended for the layman. However, a somewhat mathematical illustration of why massive particle's cannot attain C is shown https://www.physicsforums.com/showpost.php?p=1080986&postcount=7". The post is rather brief, so let me know if you need more clarification.

as far as massless bodies, are there more than photons? I thought that was it. everything else is just negligible (for our uses) but still has some mass.

Gluons and the theorized Gravitions are both also massless particles.

 

[spiffomatic64]

That's okay then, things can get a little confusing if people post with multiple usernames.

I would certainly recommend reading something about Einstein's theories, a good place to start is Einstein's own book 'Relativity', which was intended for the layman. However, a somewhat mathematical illustration of why massive particle's cannot attain C is shown https://www.physicsforums.com/showpost.php?p=1080986&postcount=7". The post is rather brief, so let me know if you need more clarification.

Gluons and the theorized Gravitions are both also massless particles.

Im definitely going to get Einstein’s book, but in the meantime, what does Mo stand for? (The extent of my formal physics info is limited to HS :D)

 

[Hootenanny]

Im definitely going to get Einstein’s book, but in the meantime, what does Mo stand for? (The extent of my formal physics info is limited to HS :D)

M₀ is the invariant or rest mass of a body and is what one would normally call an object's mass.

 

[MeJennifer]

Can matter go faster than c? if so, what changes at this point? anything?

if not, why can't it?

It actually depends a bit on how you look at it. :)

It is a fact that no two objects of mass can travel at a relative speed of c. I say relative speed since there is of course no such thing as an absolute speed! However take note that a traveler could certainly travel for one year to something 10 light years away. In fact the faster he accelerates the less time it would take him to get there, but he won't be able to get there instantly.

 

[JesseM]

However take note that a traveler could certainly travel for one year to something 10 light years away. In fact the faster he accelerates the less time it would take him to get there, but he won't be able to get there instantly.

Of course, in the frame of an inertial observer who's moving along with him once he's accelerated up to a significant velocity relative to his destination, the distance between his destination and his starting point is a lot less than 10 light years. Meanwhile, in inertial frame where the distance is 10 light years, it will always take more than 10 years for the traveler to reach his destination.

 

[MeJennifer]

Of course, in the frame of an inertial observer who's moving along with him once he's accelerated up to a significant velocity relative to his destination, the distance between his destination and his starting point is a lot less than 10 light years. Meanwhile, in inertial frame where the distance is 10 light years, it will always take more than 10 years for the traveler to reach his destination.

Yes but think about it practical terms. Sirus B is 8.6 light years away, a space colony could do the trip in one year as long they accelerate hard or long enough.

 

[spiffomatic64]

It actually depends a bit on how you look at it. :)

It is a fact that no two objects of mass can travel at a relative speed of c. I say relative speed since there is of course no such thing as an absolute speed! However take note that a traveler could certainly travel for one year to something 10 light years away. In fact the faster he accelerates the less time it would take him to get there, but he won't be able to get there instantly.

I thought c was absolute?

as far as traveling 10 lightyears in less than 10 years, that's from the point of view of a third party right?

 

[MeJennifer]

as far as traveling 10 lightyears in less than 10 years, that's from the point of view of a third party right?

Nope, it is from the point of view of the traveler.

 

[JesseM]

as far as traveling 10 lightyears in less than 10 years, that's from the point of view of a third party right?

The time is from the point of view of the traveler as MeJennifer says, but the distance is from the point of view of a third party (someone who remains at rest relative to the starting point and the destination). As I said, once the traveler is moving at a significant velocity relative to the destination, in the inertial frame where he's temporarily at rest, the distance will be much smaller.

 

[spiffomatic64]

Nope, it is from the point of view of the traveler.

so you are saying, if I am moving at .9c, and I emit photons they are going 1.9c?

I didnt think that was right.

 

[MeJennifer]

so you are saying, if I am moving at .9c, and I emit photons they are going 1.9c?

I am not saying that at all.

 

[JesseM]

Yes but think about it practical terms. Sirus B is 8.6 light years away, a space colony could do the trip in one year as long they accelerate hard or long enough.

Well, it's 8.6 light years away in our frame, all spatial distances are relative. And if a spaceship wanted to go there and then return to Earth, although the trip could be shorter from their point of view, they would always find that when they returned to Earth more than 17.2 years would have passed here.

 

[spiffomatic64]

The time is from the point of view of the traveler as MeJennifer says, but the distance is from the point of view of a third party (someone who remains at rest relative to the starting point and the destination). As I said, once the traveler is moving at a significant velocity relative to the destination, in the inertial frame where he's temporarily at rest, the distance will be much smaller.

I know time is relative to the stuff around him, but wouldn't he still "experiance" 10 years, where as the rest of the world would have only passed about 1 year or so.

 

[spiffomatic64]

I am not saying that at all.

if its from the point of view of the traveler, then to a third party the light would be going faster than light speed right?

 

[JesseM]

so you are saying, if I am moving at .9c, and I emit photons they are going 1.9c?

"Moving at 0.9c" doesn't mean anything unless you specify what it's relative to. If you're moving at 0.9c relative to Earth and you fire a photon, it will move at 1c relative to you, and also at 1c relative to the Earth, because of the way relativistic velocity addition works.

 

[matheinste]

Hello all.

Does no one want to commit themselves to say specifically that nothing can traveller at a speed greater than c ?

Matheinste.

 

[Doc Al]

as far as traveling 10 lightyears in less than 10 years, that's from the point of view of a third party right?

It just means that he can travel 10 Earth lightyears in less that 10 traveler years, so you are mixing frames a bit (but it makes an important point about high-speed space travel). If the traveler measured the distance he traveled according to his own frame, his speed would of course be less than c.

 

[MeJennifer]

As I said, once the traveler is moving at a significant velocity relative to the destination, in the inertial frame where he's temporarily at rest, the distance will be much smaller.

But the fact remains that the space colony is in principle able to go to Sirus B in less than 8.6 years. And however they accelerate, the fact remains that light takes 8.6 years to go from Earth to Sirus B, hence Sirus B is 8.6 light years away from Earth!

 

[peter0302]

If you really want to get technical, objects with imaginary mass could travel faster than 'c'. :)

And as a practical matter, you can get from point A to point B where if you measured your distance before the trip, and divided by the amount of time it took you, you'd think you traveled faster than 'c'. But of course the problem is that, from everyone else's perspective, the journey took a hell of a lot longer!

 

[JesseM]

I know time is relative to the stuff around him, but wouldn't he still "experiance" 10 years, where as the rest of the world would have only passed about 1 year or so.

No, the other way around. In the frame of the origin point (let's say this is the frame of the Earth) it will always take at least 10 years to reach a destination which is 10 light years away in the Earth's frame. But for the traveler it can be much shorter, say 1 year. From the point of view of the Earth's frame, this is because the traveler's clock is slowed down, so it hasn't ticked as much time as it "should" in the 10 years it takes to reach the destination. From the point of view of the frame where the traveler is at rest after having attained some large velocity relative to the Earth, this is because the distance from the Earth to the destination has Lorentz-contracted to 1 light year or less.

 

[JesseM]

But the fact remains that the space colony is in principle able to go to Sirus B in less than 8.6 years.

As measured by their own proper time, but not in the coordinate time of the Earth's frame.

And however they accelerate, the fact remains that light takes 8.6 years to go from Earth to Sirus B

Only in the coordinate time of the Earth's frame! In the coordinate time of the traveler's rest frame light takes a lot less than 8.6 years to get from Earth to Sirius B.

hence Sirus B is 8.6 light years away from Earth!

Only in the coordinates of one particular (arbitrary) frame, not in any physical frame-independent sense.

 

[spiffomatic64]

No, the other way around. In the frame of the origin point (let's say this is the frame of the Earth) it will always take at least 10 years to reach a destination which is 10 light years away in the Earth's frame. But for the traveler it can be much shorter, say 1 year. From the point of view of the Earth's frame, this is because the traveler's clock is slowed down, so it hasn't ticked as much time as it "should" in the 10 years it takes to reach the destination. From the point of view of the frame where the traveler is at rest after having attained some large velocity relative to the Earth, this is because the distance from the Earth to the destination has Lorentz-contracted to 1 light year or less.

ah yea sorry, :) that's what I meant.

 

[Doc Al]

But the fact remains that the space colony is in principle able to go to Sirus B in less than 8.6 years.

Good.

And however they accelerate, the fact remains that light takes 8.6 years to go from Earth to Sirus B, hence Sirus B is 8.6 light years away from Earth!

And all this time I thought distance was frame dependent! (Just teasing--but shame on you for pulling a fast one.)

The point is that the distance between Earth and Sirius depends on the frame doing the measuring. It is 8.6 light years as measured in the Earth frame--not the traveler's frame.

 

[MeJennifer]

Only in the coordinates of one particular (arbitrary) frame, not in any physical frame-independent sense.

So you are saying that the distance in light years between the Earth and Sirus B is not always 6.8 light years? If you say that you are wrong. If you place a mirror on Sirus B and point a laser from the Earth to Sirus B you will receive the light back in 2 * 6.8 = 13.6 years. You can record that with a chronometer and everybody would obviously have to agree that it took light 2 * 6.8 years to make a full roundtrip!

 

[spiffomatic64]

"Moving at 0.9c" doesn't mean anything unless you specify what it's relative to. If you're moving at 0.9c relative to Earth and you fire a photon, it will move at 1c relative to you, and also at 1c relative to the Earth, because of the way relativistic velocity addition works.

Im going to read this a bit more, as I have never heard anything like that.

but in the mean-time (if anyone wants to, obviously)

care to laymanize this? I understand that people will perceive things slower or faster based on their frame of referance, but if I am going really fast. then things I am percieving would be going slower. The light would be going light speed to me.

but the problem I have with this is that, from Earth's point of view, (the traveler is moving away from earth) the light would be moving at the same speed as the traveler, not going anywhere relative to the traveler.


sorry not trying to argue here, just trying to understand :) feel free to give up, and ill just go buy some books ;)

 

[Doc Al]

So you are saying that the distance in light years between the Earth and Sirus B is not always 6.8 light years? If you say that you are wrong. If you place a mirror on Sirus B and point a laser from the Earth to Sirus B you will receive the light back in 2 * 6.8 = 13.6 years. You can record that with a chronometer and everybody would obviously have to agree that it took light 2 * 6.8 years to make a full roundtrip!

Get a grip. You are just measuring the roundtrip time and distance according to Earth measurements. Or are you saying that the high-speed traveler will also measuring the same transit time for the light to make its round trip?

 

[MeJennifer]

Get a grip. You are just measuring the roundtrip time and distance according to Earth measurements. Or are you saying that the high-speed traveler will also measuring the same transit time for the light to make its round trip?

Get a grip?

We are talking about the time it takes for light to go from Earth to Sirus B. That is 6.8 years. This can both be measured and recorded.

 

[Doc Al]

Get a grip?

We are talking about the time it takes for light to go from Earth to Sirus B. That is 6.8 years. This can both be measured and recorded.

Seriously... get a grip! You are talking about the time it takes light to go from Earth to Sirius B as measured on Earth clocks! Distance and time are frame-dependent quantities.

 

[JesseM]

So you are saying that the distance in light years between the Earth and Sirus B is not always 6.8 light years?

Didn't you say 8.6 before? That's also what it says in the chart at the bottom of this article.

If you say that you are wrong. If you place a mirror on Sirus B and point a laser from the Earth to Sirus B you will receive the light back in 2 * 6.8 = 13.6 years. You can record that with a chronometer and everybody would obviously have to agree that it took light 2 * 6.8 years to make a full roundtrip!

If Sirius B is 8.6 ly away as you said, Earth's clock will show that 17.2 years pass between when the light is sent out and when it returns. But do you really think that other frames cannot explain this perfectly well in terms of their own coordinates? Take the frame of someone moving at 0.6c relative to Earth/Sirius B, so the Lorentz contraction and time dilation factor 1/gamma is 0.8. In their frame, the distance between Earth and Sirius B is 8.6 * 0.8 = 6.88 light-years. If they see Sirius B and Earth moving in the +x direction, with Earth at x=0 when the light is emitted and Sirius B at x=6.88 at the same moment, then you have to remember it will take longer than 6.88 years in this frame for the light to reach Sirius B, since Sirius is rushing away from it at 0.6c. To find the time, just solve for t in 1c*t = 0.6c*t + 6.88 light years (because the photon's position as a function of time is x(t) = 1c*t, while Sirius B's position as a function of time is x(t) = 0.6c*t + 6.88 ly, so setting them equal shows when they meet), which gives t = 6.88/0.4 = 17.2 years. Then when the light is reflected back, it takes less than 6.88 years for the light to return to Earth, since the Earth is rushing towards the point it was reflected; the time can be found by solving for t in 6.88 ly - 1c*t = 0.6c*t which gives t = 6.88/1.6 = 4.3 years. So, in this frame the total time for the light to go from Earth to Sirius B and back is 17.2 + 4.3 = 21.5 years. But don't forget that in this frame, Earth's clocks are slowed down by a factor of 0.8, so during this time they have only advanced forward by 21.5 * 0.8 = 17.2 years, exactly the same prediction as was made in Earth's frame.

 

[MeJennifer]

So, in this frame the total time for the light to go from Earth to Sirius B and back is 17.2 + 4.3 = 21.5 years.

That may be so by his clock but he is not directly measuring the rountrip time at all as that would be impossible. Fact remains that it takes 17.2 years for light to make a roundtrip from Earth to Sirius B.

 

[MeJennifer]

Seriously... get a grip! You are talking about the time it takes light to go from Earth to Sirius B as measured on Earth clocks! Distance and time are frame-dependent quantities.

How else do you propose to make a direct measurement on the rountrip time of light from the Earth to Sirus B?

 

[JesseM]

That may be so by his clock but he not directly measuring the rountrip time at all as that would be impossible. Fact remains that it takes 17.2 years for light to make a roundtrip from Earth to Sirus B.

OK, so imagine a clock that starts at Earth at the moment the light is emitted, accelerates to some high fraction of lightspeed, then later turns around and makes it back to Earth in time for the light's return. Here we have used a single clock to measure both departure and return too, so isn't this a "roundtrip" time? If you restrict roundtrip time to inertial clocks, what physical justification do you have for saying roundtrip time measured by inertial clocks is somehow more "real" than roundtrip time measured by non-inertial clocks?

 

[MeJennifer]

OK, so imagine a clock that starts at Earth at the moment the light is emitted, accelerates to some high fraction of lightspeed, then later turns around and makes it back to Earth in time for the light's return. Here we have used a single clock to measure both departure and return too, so isn't this a "roundtrip" time? If you restrict roundtrip time to inertial clocks, what physical justification do you have for saying roundtrip time measured by inertial clocks is somehow more "real" than roundtrip time measured by non-inertial clocks?

You are missing the point, the traveling clock will not measure the roundtrip time of light at all it will simply desynchronize from the Earth's clock due to its speed differential when it traveled and hence all it will "measure" is the time difference between the Earth's clock when it will come back to Earth.

It is not about the clock but about the time it takes light to go from A to B. For instance if Earth or Sirius B were to accelerate the roundtrip time of light, due to special relativity, would obviously change. But obviously the time it takes light to go from A to B does not depend on Jimmy going on a trip with a clock that is going to be desynchronized with a clock on Earth.

Edited to add:

We actually do not have to restrict ourselves to intertial clocks. Suppose both Earth and Sirius B are accelerating then we still can record a roundtrip time and determine how long it takes light to go from Earth to Sirius B and back, however we would have to realize that the roundtrip time may not remain constant over time if the accelerations are variable, a situation a bit like distances in non-stationary spacetimes in GR.

 

[JesseM]

You are missing the point, the traveling clock will not measure the roundtrip time of light at all

Do you call it "traveling" in contrast to the Earth clock? But of course there are countless frames where the Earth clock is traveling too. There is no physical sense in which the time between two events as measured by an inertial clock that has the two events on its worldline is any more "real" than the time between the same two events as measured by a non-inertial clock that has the events on its worldline; they are just two different proper times for two different clocks.

It is not about the clock but about the time it takes light to go from A to B.

The only physical notion of time in relativity is proper time. Again, one clock's proper time isn't any more "real" than any other clock's proper time. So although you can talk about the proper time for light to go from Earth to Sirius B and back as measured by a clock on Earth, there's no reason to think of this as "the" time for light to go from Earth to Sirius B and back.

 

[Count Iblis]

It is interesting to consider tunneling. Suppose a clock on the North Pole tunnels to the South Pole. What will be the proper time that will have elapsed?

 

[peter0302]

The universe will have imploded before that was likely to occur, so I wouldn't worry about it. :)

 

[DaveC426913]

The universe will have imploded before that was likely to occur, so I wouldn't worry about it. :)

Funny thing about probabilities is that it is exactly as likely to happen tomorrow as on the last day of the universe.

 

[Count Iblis]

The universe will have imploded before that was likely to occur, so I wouldn't worry about it. :)

Let me reformulate the question to make it better defined. Suppose a scientists at the North Pole accidentally drops his watch. But to his amazement he can't find it on the ground. Then a scientist on the South pole sees a watch appear on the ground, apperently out of thin air. The watch has tunneled through the earth. What will be the time difference between the events of the watch being dropped and the watch reappering as indicated by the watch itself?

 

[MeJennifer]

The only physical notion of time in relativity is proper time. Again, one clock's proper time isn't any more "real" than any other clock's proper time.

A strawman argument as I am not disagreeing with that at all.

So although you can talk about the proper time for light to go from Earth to Sirius B and back as measured by a clock on Earth, there's no reason to think of this as "the" time for light to go from Earth to Sirius B and back.

There is only one proper time between any sequence of events or in this case 3 events, the emission, relfection and absorbtion of light. All observers must agree on the elapsed proper time between those events. That such an amount of elapsed proper time does not agree with their clocks is either due to relative motion or spacetime curvature.

 

[JesseM]

A strawman argument as I am not disagreeing with that at all.

Really? Then why did you place so much emphasis on this statement:

And however they accelerate, the fact remains that light takes 8.6 years to go from Earth to Sirus B, hence Sirus B is 8.6 light years away from Earth!

If you agree that light only takes 2*8.6 years round trip according to one arbitrary clock, and that the time would be different according to other equally valid clocks, then why do you think Sirius B "is" 8.6 light years from Earth? Do you agree that there is absolutely nothing physically special about the measurements that give the round-trip time as 2*8.6 years as opposed to some other number?

There is only one proper time between any sequence of events

There is only one proper time on a given worldline that contains those events, but there are multiple possible worldlines that contain the events, and they measure different proper times between the events. Do you disagree?

or in this case 3 events, the emission, relfection and absorbtion of light. All observers must agree on the elapsed proper time between those events.

Do you disagree that in relativity the term "proper time" is only used in the context of particular worldlines, that there is no unique "proper time" between distinct events which can have multiple worldlines that pass through both? If you do disagree, then you are using the term "proper time" incorrectly.

That such an amount of elapsed proper time does not agree with their clocks is either due to relative motion or spacetime curvature.

"Relative motion" relative to what exactly? You certainly can't talk about motion relative to the events themselves, since events are instantaneous...

 

[MeJennifer]

There is only one proper time on a given worldline that contains those events, but there are multiple possible worldlines that contain the events, and they measure different proper times between the events. Do you disagree?

Do you realize that there is only one possible worldline (or multiple in certain curved spacetimes) between events that are lightlike separated?

 

[JesseM]

Not at all, and hopefully you can see that light always travels on a particular worldline!

Sure, but the proper time along a null geodesic is always 0 (or maybe physicists don't even talk about 'proper time' for null geodesics, but in the limit as timelike geodesics get closer and closer to null geodesics the proper time should approach 0).

 

[spiffomatic64]

"Moving at 0.9c" doesn't mean anything unless you specify what it's relative to. If you're moving at 0.9c relative to Earth and you fire a photon, it will move at 1c relative to you, and also at 1c relative to the Earth, because of the way relativistic velocity addition works.

another quick question about this

If this were true, wouldn't that mean that the Earth observer sees the traveler going just .1 less than the speed as the light?

to the earth, the light would look like it was going .1c from the traveler right?

That would make it seem as though time were slowing down (from Earth's pov) for the traveler. when in fact its the opposite right? From Earth's pov, the traveler should look like he is speeding up, right?

sorry to de-rail the tangental arguments we have going :) but they are way over my head

 

[JesseM]

Do you realize that there is only one possible worldline (or multiple in certain curved spacetimes) between events that are lightlike separated?

Yes, but as I said in response to the earlier comment you edited, if it makes sense to talk about proper time on this worldline at all, the proper time would be zero. So this still doesn't help make sense of your comment that the time between light leaving Earth and arriving at Sirius B "is" 8.6 years.

 

[JesseM]

another quick question about this

If this were true, wouldn't that mean that the Earth observer sees the traveler going just .1 less than the speed as the light?

to the earth, the light would look like it was going .1c from the traveler right?

Yes, in the Earth frame the distance between the traveler and the photon is only increasing at a rate of 0.1 light-seconds per second.

That would make it seem as though time were slowing down (from Earth's pov) for the traveler. when in fact its the opposite right? From Earth's pov, the traveler should look like he is speeding up, right?

No, the Earth will measure the traveler's clocks to be slowed down rather than speeded up (and will also measure the traveler's rulers to be shrunk in the direction of motion). In relativity, any observer moving inertially (constant velocity) will measure clocks that are moving relative to themselves to be running slow.

 

[MeJennifer]

Sure, but the proper time along a null geodesic is always 0 (or maybe physicists don't even talk about 'proper time' for null geodesics, but in the limit as timelike geodesics get closer and closer to null geodesics the proper time should approach 0).

That is the proper time of the photon but alternatively we can use several affine parameters for a null geodesic.

 

[JesseM]

That is the proper time of the photon but alternatively we can use several affine parameters for a null geodesic.

But the affine parameters aren't really "time". Anyway, are you claiming that when you said the time "is" 8.6 years and the distance "is" 8.6 light-years, you were thinking in terms of affine parameters on the photon's worldline? If not, how is this relevant to what we were talking about before?