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Does time dilation mean that faster than light travel is backwards time travel?
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Ok. So my question is, I've always heard it that Faster Than Light travel is supposedly backwards time travel.
However, the time dilation formula is
$$T=fracT_0sqrt1-v^2/c^2$$
And while it is true that speeds greater than $c$ turn the denominator negative, doesn't the whole thing get rendered a complex fraction, rather than negative or backwards time flow, due to the square root of a negative number being a complex one?
Wouldn't this then mean that faster than light travel does something weird, rather than backwards time travel? In other words, wouldn't what happens during faster than light travel be some sort travel in a complex plane and wouldn't that have radically different implications to backwards time travel, depending on the direction one took FTL?
special-relativity time-dilation faster-than-light time-travel
edited 4 hours ago
Qmechanic♦
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asked 5 hours ago
Guthrie Douglas Prentice
211
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up vote
4
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Ok. So my question is, I've always heard it that Faster Than Light travel is supposedly backwards time travel.
However, the time dilation formula is
$$T=fracT_0sqrt1-v^2/c^2$$
And while it is true that speeds greater than $c$ turn the denominator negative, doesn't the whole thing get rendered a complex fraction, rather than negative or backwards time flow, due to the square root of a negative number being a complex one?
Wouldn't this then mean that faster than light travel does something weird, rather than backwards time travel? In other words, wouldn't what happens during faster than light travel be some sort travel in a complex plane and wouldn't that have radically different implications to backwards time travel, depending on the direction one took FTL?
special-relativity time-dilation faster-than-light time-travel
edited 4 hours ago
Qmechanic♦
98.2k121731066
asked 5 hours ago
Guthrie Douglas Prentice
211
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
According to SR faster than light travel is impossible, so trying to draw reasonable conclusions from this equation is meaningless.
– Aaron Stevens
4 hours ago
1
Tachyons are allowed in SR, and they do also have a proper time
– Ã¡Ã¸Ã¼Ã¾Ã½ âырðý
4 hours ago
1
@áøüþýâырðý I'll delete my comment if tachyons are shown to exist.
– Aaron Stevens
1 hour ago
Imaginary time is spacelike (and vice versa), sort of. But see physics.stackexchange.com/questions/121380/… and the various links on that page.
– PM 2Ring
1 hour ago
1
@PM2Ring I see what you mean. I meant SR that we have experientially verified.
– Aaron Stevens
58 mins ago
 |Â
show 3 more comments
up vote
4
down vote
favorite
up vote
4
down vote
favorite
Ok. So my question is, I've always heard it that Faster Than Light travel is supposedly backwards time travel.
However, the time dilation formula is
$$T=fracT_0sqrt1-v^2/c^2$$
And while it is true that speeds greater than $c$ turn the denominator negative, doesn't the whole thing get rendered a complex fraction, rather than negative or backwards time flow, due to the square root of a negative number being a complex one?
Wouldn't this then mean that faster than light travel does something weird, rather than backwards time travel? In other words, wouldn't what happens during faster than light travel be some sort travel in a complex plane and wouldn't that have radically different implications to backwards time travel, depending on the direction one took FTL?
special-relativity time-dilation faster-than-light time-travel
edited 4 hours ago
Qmechanic♦
98.2k121731066
asked 5 hours ago
Guthrie Douglas Prentice
211
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Ok. So my question is, I've always heard it that Faster Than Light travel is supposedly backwards time travel.
However, the time dilation formula is
$$T=fracT_0sqrt1-v^2/c^2$$
And while it is true that speeds greater than $c$ turn the denominator negative, doesn't the whole thing get rendered a complex fraction, rather than negative or backwards time flow, due to the square root of a negative number being a complex one?
Wouldn't this then mean that faster than light travel does something weird, rather than backwards time travel? In other words, wouldn't what happens during faster than light travel be some sort travel in a complex plane and wouldn't that have radically different implications to backwards time travel, depending on the direction one took FTL?
special-relativity time-dilation faster-than-light time-travel
special-relativity time-dilation faster-than-light time-travel
edited 4 hours ago
Qmechanic♦
98.2k121731066
asked 5 hours ago
Guthrie Douglas Prentice
211
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 4 hours ago
Qmechanic♦
98.2k121731066
asked 5 hours ago
Guthrie Douglas Prentice
211
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 4 hours ago
Qmechanic♦
98.2k121731066
edited 4 hours ago
Qmechanic♦
98.2k121731066
edited 4 hours ago
Qmechanic♦
98.2k121731066
98.2k121731066
asked 5 hours ago
Guthrie Douglas Prentice
211
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 5 hours ago
Guthrie Douglas Prentice
211
asked 5 hours ago
Guthrie Douglas Prentice
211
211
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Guthrie Douglas Prentice is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
3
According to SR faster than light travel is impossible, so trying to draw reasonable conclusions from this equation is meaningless.
– Aaron Stevens
4 hours ago
1
Tachyons are allowed in SR, and they do also have a proper time
– Ã¡Ã¸Ã¼Ã¾Ã½ âырðý
4 hours ago
1
@áøüþýâырðý I'll delete my comment if tachyons are shown to exist.
– Aaron Stevens
1 hour ago
Imaginary time is spacelike (and vice versa), sort of. But see physics.stackexchange.com/questions/121380/… and the various links on that page.
– PM 2Ring
1 hour ago
1
@PM2Ring I see what you mean. I meant SR that we have experientially verified.
– Aaron Stevens
58 mins ago
 |Â
show 3 more comments
3
According to SR faster than light travel is impossible, so trying to draw reasonable conclusions from this equation is meaningless.
– Aaron Stevens
4 hours ago
1
Tachyons are allowed in SR, and they do also have a proper time
– Ã¡Ã¸Ã¼Ã¾Ã½ âырðý
4 hours ago
1
@áøüþýâырðý I'll delete my comment if tachyons are shown to exist.
– Aaron Stevens
1 hour ago
Imaginary time is spacelike (and vice versa), sort of. But see physics.stackexchange.com/questions/121380/… and the various links on that page.
– PM 2Ring
1 hour ago
1
@PM2Ring I see what you mean. I meant SR that we have experientially verified.
– Aaron Stevens
58 mins ago
3
3
According to SR faster than light travel is impossible, so trying to draw reasonable conclusions from this equation is meaningless.
– Aaron Stevens
4 hours ago
According to SR faster than light travel is impossible, so trying to draw reasonable conclusions from this equation is meaningless.
– Aaron Stevens
4 hours ago
1
1
Tachyons are allowed in SR, and they do also have a proper time
– Ã¡Ã¸Ã¼Ã¾Ã½ âырðý
4 hours ago
Tachyons are allowed in SR, and they do also have a proper time
– Ã¡Ã¸Ã¼Ã¾Ã½ âырðý
4 hours ago
1
1
@áøüþýâырðý I'll delete my comment if tachyons are shown to exist.
– Aaron Stevens
1 hour ago
@áøüþýâырðý I'll delete my comment if tachyons are shown to exist.
– Aaron Stevens
1 hour ago
Imaginary time is spacelike (and vice versa), sort of. But see physics.stackexchange.com/questions/121380/… and the various links on that page.
– PM 2Ring
1 hour ago
Imaginary time is spacelike (and vice versa), sort of. But see physics.stackexchange.com/questions/121380/… and the various links on that page.
– PM 2Ring
1 hour ago
1
1
@PM2Ring I see what you mean. I meant SR that we have experientially verified.
– Aaron Stevens
58 mins ago
@PM2Ring I see what you mean. I meant SR that we have experientially verified.
– Aaron Stevens
58 mins ago
 |Â
show 3 more comments
3 Answers
3
active
oldest
votes
up vote
2
down vote
I don't know what you mean by "some sort travel in a complex plane". Faster than light travel is by definition some object that changes position from $x_0$ to $x_1$ in such a way that $dfracx_1-x_0Delta t>c$, where $Delta t$ is the elapsed time. There is no time travel involved when this happens, but causality will take a blow if events at $x_1$ depend on events at $x_0$.
answered 4 hours ago
Cuspy Code
29115
add a comment |Â
up vote
2
down vote
When using formulas in physics it is important to keep in mind the assumptions that the formula is based on. In this case $T_0$ is the time on a clock in its rest frame. It is doubtful that tachyons exist, but if they do then they are not at rest in any inertial frame, so the time dilation formula simply does not apply.
However, the Lorentz transform does apply. So (in units where c=1) if we had a tachyon which moved at 2 c in our frame then it would have a worldline like $(t,x)=(lambda,2lambda)$ where $lambda$ is an affine parameter and the y and z coordinates are suppressed. Now, if we do a Lorentz transform to a frame moving at 0.6 c relative to our frame then the worldline would be $(t’,x’)=(-0.25lambda, 1.75lambda)$.
Note that the worldline in the primed frame has the affine parameter increasing as time decreases whereas the affine parameter increases as time increases in our frame. In that sense it is traveling backwards in time in one frame or in the other.
answered 16 mins ago
Dale
2,238415
add a comment |Â
up vote
0
down vote
In fact, faster than light travel is theoretically possible, and one argument for that goes like this:
The important thing is for T to be a real number, and here we have three cases for that to happen:
Both T0 and sqr(1-v^2/c^2) are real numbers, in this case we must have v
Both T0 and sqr(1-v^2/c^2) are pure imaginary and in this case v>c. Don't be discouraged by the fact that T0 is imaginary because these particles cannot be at rest, in fact they always move faster than the speed of light. Such hypothetical particles are called tachyons.
Both T0 and sqr(1-v^2/c^2) are zero. In this case v=c. And such particles are bound to always move in the speed of light. Such particles are called massless particles.
answered 1 hour ago
Arthur
175
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Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
1
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
add a comment |Â
3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
I don't know what you mean by "some sort travel in a complex plane". Faster than light travel is by definition some object that changes position from $x_0$ to $x_1$ in such a way that $dfracx_1-x_0Delta t>c$, where $Delta t$ is the elapsed time. There is no time travel involved when this happens, but causality will take a blow if events at $x_1$ depend on events at $x_0$.
answered 4 hours ago
Cuspy Code
29115
add a comment |Â
up vote
2
down vote
I don't know what you mean by "some sort travel in a complex plane". Faster than light travel is by definition some object that changes position from $x_0$ to $x_1$ in such a way that $dfracx_1-x_0Delta t>c$, where $Delta t$ is the elapsed time. There is no time travel involved when this happens, but causality will take a blow if events at $x_1$ depend on events at $x_0$.
answered 4 hours ago
Cuspy Code
29115
add a comment |Â
up vote
2
down vote
up vote
2
down vote
I don't know what you mean by "some sort travel in a complex plane". Faster than light travel is by definition some object that changes position from $x_0$ to $x_1$ in such a way that $dfracx_1-x_0Delta t>c$, where $Delta t$ is the elapsed time. There is no time travel involved when this happens, but causality will take a blow if events at $x_1$ depend on events at $x_0$.
answered 4 hours ago
Cuspy Code
29115
I don't know what you mean by "some sort travel in a complex plane". Faster than light travel is by definition some object that changes position from $x_0$ to $x_1$ in such a way that $dfracx_1-x_0Delta t>c$, where $Delta t$ is the elapsed time. There is no time travel involved when this happens, but causality will take a blow if events at $x_1$ depend on events at $x_0$.
answered 4 hours ago
Cuspy Code
29115
answered 4 hours ago
Cuspy Code
29115
answered 4 hours ago
Cuspy Code
29115
answered 4 hours ago
Cuspy Code
29115
29115
add a comment |Â
add a comment |Â
up vote
2
down vote
When using formulas in physics it is important to keep in mind the assumptions that the formula is based on. In this case $T_0$ is the time on a clock in its rest frame. It is doubtful that tachyons exist, but if they do then they are not at rest in any inertial frame, so the time dilation formula simply does not apply.
However, the Lorentz transform does apply. So (in units where c=1) if we had a tachyon which moved at 2 c in our frame then it would have a worldline like $(t,x)=(lambda,2lambda)$ where $lambda$ is an affine parameter and the y and z coordinates are suppressed. Now, if we do a Lorentz transform to a frame moving at 0.6 c relative to our frame then the worldline would be $(t’,x’)=(-0.25lambda, 1.75lambda)$.
Note that the worldline in the primed frame has the affine parameter increasing as time decreases whereas the affine parameter increases as time increases in our frame. In that sense it is traveling backwards in time in one frame or in the other.
answered 16 mins ago
Dale
2,238415
add a comment |Â
up vote
2
down vote
When using formulas in physics it is important to keep in mind the assumptions that the formula is based on. In this case $T_0$ is the time on a clock in its rest frame. It is doubtful that tachyons exist, but if they do then they are not at rest in any inertial frame, so the time dilation formula simply does not apply.
However, the Lorentz transform does apply. So (in units where c=1) if we had a tachyon which moved at 2 c in our frame then it would have a worldline like $(t,x)=(lambda,2lambda)$ where $lambda$ is an affine parameter and the y and z coordinates are suppressed. Now, if we do a Lorentz transform to a frame moving at 0.6 c relative to our frame then the worldline would be $(t’,x’)=(-0.25lambda, 1.75lambda)$.
Note that the worldline in the primed frame has the affine parameter increasing as time decreases whereas the affine parameter increases as time increases in our frame. In that sense it is traveling backwards in time in one frame or in the other.
answered 16 mins ago
Dale
2,238415
add a comment |Â
up vote
2
down vote
up vote
2
down vote
When using formulas in physics it is important to keep in mind the assumptions that the formula is based on. In this case $T_0$ is the time on a clock in its rest frame. It is doubtful that tachyons exist, but if they do then they are not at rest in any inertial frame, so the time dilation formula simply does not apply.
However, the Lorentz transform does apply. So (in units where c=1) if we had a tachyon which moved at 2 c in our frame then it would have a worldline like $(t,x)=(lambda,2lambda)$ where $lambda$ is an affine parameter and the y and z coordinates are suppressed. Now, if we do a Lorentz transform to a frame moving at 0.6 c relative to our frame then the worldline would be $(t’,x’)=(-0.25lambda, 1.75lambda)$.
Note that the worldline in the primed frame has the affine parameter increasing as time decreases whereas the affine parameter increases as time increases in our frame. In that sense it is traveling backwards in time in one frame or in the other.
answered 16 mins ago
Dale
2,238415
When using formulas in physics it is important to keep in mind the assumptions that the formula is based on. In this case $T_0$ is the time on a clock in its rest frame. It is doubtful that tachyons exist, but if they do then they are not at rest in any inertial frame, so the time dilation formula simply does not apply.
However, the Lorentz transform does apply. So (in units where c=1) if we had a tachyon which moved at 2 c in our frame then it would have a worldline like $(t,x)=(lambda,2lambda)$ where $lambda$ is an affine parameter and the y and z coordinates are suppressed. Now, if we do a Lorentz transform to a frame moving at 0.6 c relative to our frame then the worldline would be $(t’,x’)=(-0.25lambda, 1.75lambda)$.
Note that the worldline in the primed frame has the affine parameter increasing as time decreases whereas the affine parameter increases as time increases in our frame. In that sense it is traveling backwards in time in one frame or in the other.
answered 16 mins ago
Dale
2,238415
answered 16 mins ago
Dale
2,238415
answered 16 mins ago
Dale
2,238415
answered 16 mins ago
Dale
2,238415
2,238415
add a comment |Â
add a comment |Â
up vote
0
down vote
In fact, faster than light travel is theoretically possible, and one argument for that goes like this:
The important thing is for T to be a real number, and here we have three cases for that to happen:
Both T0 and sqr(1-v^2/c^2) are real numbers, in this case we must have v
Both T0 and sqr(1-v^2/c^2) are pure imaginary and in this case v>c. Don't be discouraged by the fact that T0 is imaginary because these particles cannot be at rest, in fact they always move faster than the speed of light. Such hypothetical particles are called tachyons.
Both T0 and sqr(1-v^2/c^2) are zero. In this case v=c. And such particles are bound to always move in the speed of light. Such particles are called massless particles.
answered 1 hour ago
Arthur
175
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
1
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
add a comment |Â
up vote
0
down vote
In fact, faster than light travel is theoretically possible, and one argument for that goes like this:
The important thing is for T to be a real number, and here we have three cases for that to happen:
Both T0 and sqr(1-v^2/c^2) are real numbers, in this case we must have v
Both T0 and sqr(1-v^2/c^2) are pure imaginary and in this case v>c. Don't be discouraged by the fact that T0 is imaginary because these particles cannot be at rest, in fact they always move faster than the speed of light. Such hypothetical particles are called tachyons.
Both T0 and sqr(1-v^2/c^2) are zero. In this case v=c. And such particles are bound to always move in the speed of light. Such particles are called massless particles.
answered 1 hour ago
Arthur
175
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
1
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
add a comment |Â
up vote
0
down vote
up vote
0
down vote
In fact, faster than light travel is theoretically possible, and one argument for that goes like this:
The important thing is for T to be a real number, and here we have three cases for that to happen:
Both T0 and sqr(1-v^2/c^2) are real numbers, in this case we must have v
Both T0 and sqr(1-v^2/c^2) are pure imaginary and in this case v>c. Don't be discouraged by the fact that T0 is imaginary because these particles cannot be at rest, in fact they always move faster than the speed of light. Such hypothetical particles are called tachyons.
Both T0 and sqr(1-v^2/c^2) are zero. In this case v=c. And such particles are bound to always move in the speed of light. Such particles are called massless particles.
answered 1 hour ago
Arthur
175
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
In fact, faster than light travel is theoretically possible, and one argument for that goes like this:
The important thing is for T to be a real number, and here we have three cases for that to happen:
Both T0 and sqr(1-v^2/c^2) are real numbers, in this case we must have v
Both T0 and sqr(1-v^2/c^2) are pure imaginary and in this case v>c. Don't be discouraged by the fact that T0 is imaginary because these particles cannot be at rest, in fact they always move faster than the speed of light. Such hypothetical particles are called tachyons.
Both T0 and sqr(1-v^2/c^2) are zero. In this case v=c. And such particles are bound to always move in the speed of light. Such particles are called massless particles.
answered 1 hour ago
Arthur
175
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 1 hour ago
answered 1 hour ago
Arthur
175
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 1 hour ago
Arthur
175
answered 1 hour ago
Arthur
175
175
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Arthur is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
1
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
add a comment |Â
1
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
1
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
1
1
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
You didn't address the issue of traveling backwards in time.
– D. Halsey
1 hour ago
1
1
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
I don't see how defining some particle to move faster than the speed of light means it is theoretically possible. Unless you have a very very lose definition of theoretically possible of "if I make a theory about it, then it must be theoretically possible." Usually theoretically possible means that we could achieve it, but there is some obstacle we currently can't overcome. Tachyons haven't been shown to exist, so there really isn't any argument to be had that it could be possible to travel faster than light.
– Aaron Stevens
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@AaronStevens it seems that we have different understandings of "theoretically possible". I use it to mean that it is not ruled out by the current laws of physics. Tachyons are of this type, although their existence will create real problems for causality.
– Arthur
1 hour ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
@D.Halsey if tachyons exist, then they travel with space-like intervals in spacetime, which makes them able to travel both forward and backwards in time.
– Arthur
59 mins ago
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Guthrie Douglas Prentice is a new contributor. Be nice, and check out our Code of Conduct.
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3
According to SR faster than light travel is impossible, so trying to draw reasonable conclusions from this equation is meaningless.
– Aaron Stevens
4 hours ago
1
Tachyons are allowed in SR, and they do also have a proper time
– Ã¡Ã¸Ã¼Ã¾Ã½ âырðý
4 hours ago
1
@áøüþýâырðý I'll delete my comment if tachyons are shown to exist.
– Aaron Stevens
1 hour ago
Imaginary time is spacelike (and vice versa), sort of. But see physics.stackexchange.com/questions/121380/… and the various links on that page.
– PM 2Ring
1 hour ago
1
@PM2Ring I see what you mean. I meant SR that we have experientially verified.
– Aaron Stevens
58 mins ago