# Silly doubt on relativity

Hello ,

I have this question in my mind from long time. There are two travelers in two trains and one observer on ground(Stationary). One train is travelling at 99.99% speed of light and another train is travelling at speed of light . My question is that the person who is at light speed train what he is going to see ? How they are all going to see each other?

(sorry my English is not very good)

Regards,
Asutosh

Integral
Staff Emeritus
Gold Member

Assume that the massive objects are travelling at c.

Integral
Staff Emeritus
Gold Member
Non physical assumptions lead to nonsense results.

bapowell
Assume that the massive objects are travelling at c.
This assumption simply cannot be made within the framework of special relativity.

Alright instead of train make it as space shuttle which can travel @ c.

bapowell
Alright instead of train make it as space shuttle which can travel @ c.
Are you serious? Aren't space shuttles massive objects?

Ryan_m_b
Staff Emeritus
Alright instead of train make it as space shuttle which can travel @ c.

Objects with mass cannot travel at c. It is physically impossible, you might as well be asking how many corners a square circle has.

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because we living in type0 civilization.

because we living in type0 civilization.

The civilization I live in makes sense, perhaps you live in a different one.

bapowell
The civilization I live in makes sense, perhaps you live in a different one.
I don't know...have you heard Rick Perry speak lately? :tongue2:

Fredrik
Staff Emeritus
Gold Member
Alright instead of train make it as space shuttle which can travel @ c.
The problem with your original question isn't that trains are much slower than space shuttles. The problem is that you asked us to make an assumption that's logically inconsistent with special relativity. The assumptions of SR don't contradict each other, but they imply that massive particles have speeds <c in inertial frames. So when you asked us to assume that a massive object moves at c, you asked us to contradict the theory we were going to use to answer the question.

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Ryan_m_b
Staff Emeritus
because we living in type0 civilization.

Unless you have a type∞ civilisation it's not going to happen it takes infinite energy or infinite time to accelerate an object with mass to c. Therefore it isn't possible.

Ok cool denge!

I have a question myself...

Why is it that responders pretend to act dumb and pretend that they don't understand the question, saying there is no answer, saying it is a non-physical assumption, does not compute... etc?

These responders know good and well that the uninitiated are asking a perfectly good question, but making a tiny error in their question's rigor when saying "going at c" rather than saying "approaching c", "almost c", "very close to c", "near c", or "99.99999998% of c"...

It only takes an additional phrase in the answer to clarify that "at c" is not possible for masses, but "as close to c as you want to get without getting there" is possible for thought experiments. Then the examination of the adjusted question may be considered physically/mathematically.

Why the snub rudeness to people that don't indicate they know the special insider way to properly phrase high speed mass questions concerning light dynamics?

If this was being done nicely to lead the questioner to the appropriate way to reform the question with alignment to rigor as in the Socratic method that would be fine, but the way people just drop the obtuse one liners and act like they don't have a clue as to what the question pertains just seems obnoxious.

When someone makes the "mass going at c" mistake, why not immediately suggest an adjustment to the thought experimental conditions to correct the lack of rigor and proceed, rather than snubbing the questioner with terse "pretended ignorance"?

Ryan_m_b
Staff Emeritus
I have a question myself...

Why is it that responders pretend to act dumb and pretend that they don't understand the question, saying there is no answer, saying it is a non-physical assumption, does not compute... etc?
You are assuming that the OPs of these questions are simply using "at c" by mistake and really want to ask about "near c". In my experience this is not the case, rather such threads are down to a misunderstanding that travelling at c for a massive object is down to what is possible and not because we simply don't know how.

bapowell
When someone makes the "mass going at c" mistake, why not immediately suggest an adjustment to the thought experimental conditions to correct the lack of rigor and proceed, rather than snubbing the questioner with terse "pretended ignorance"?
Agreed. So, why didn't you do this rather than spending your whole post lecturing the rest of us here for being dumb and insensitive to the OP?

"...travelling at c for a massive object is down to what is possible..."

That phrases has no meaning to me.

Ryan_m_b
Staff Emeritus
In my experience this is not the case, rather such threads are down to a misunderstanding that travelling at c for a massive object is down to what is possible and not because we simply don't know how.
"...travelling at c for a massive object is down to what is possible..."

That phrases has no meaning to me.
What I mean is that in my experience the OP is of the understanding that the reason science says "nothing can travel at c" is down to our not being able to figure out how to do it yet. This is a common, but incorrect, understanding hence why I said it was a misunderstanding because most of the time OPs don't realise that it is physically not possible.

Agreed. So, why didn't you do this rather than spending your whole post lecturing the rest of us here for being dumb and insensitive to the OP?

Don't you see that I did do just that? The correction is inherent within the criticism. Perhaps the OP now knows how to ask the question in a way that will attract polite and thoughtful answers? And perhaps those answering now have a nice technique with which to address questions that are flawed by lack of rigor?

ghwellsjr
Gold Member
I have a question myself...

Why is it that responders pretend to act dumb and pretend that they don't understand the question, saying there is no answer, saying it is a non-physical assumption, does not compute... etc?

These responders know good and well that the uninitiated are asking a perfectly good question, but making a tiny error in their question's rigor when saying "going at c" rather than saying "approaching c", "almost c", "very close to c", "near c", or "99.99999998% of c"...

It only takes an additional phrase in the answer to clarify that "at c" is not possible for masses, but "as close to c as you want to get without getting there" is possible for thought experiments. Then the examination of the adjusted question may be considered physically/mathematically.

Why the snub rudeness to people that don't indicate they know the special insider way to properly phrase high speed mass questions concerning light dynamics?

If this was being done nicely to lead the questioner to the appropriate way to reform the question with alignment to rigor as in the Socratic method that would be fine, but the way people just drop the obtuse one liners and act like they don't have a clue as to what the question pertains just seems obnoxious.

When someone makes the "mass going at c" mistake, why not immediately suggest an adjustment to the thought experimental conditions to correct the lack of rigor and proceed, rather than snubbing the questioner with terse "pretended ignorance"?
The problem is that no matter how fast you are "going", that is, no matter how much you have accelerated in the past, when you measure the speed of light, it is still c, not some tiny fraction of c because you are "traveling at 99.999999998%c. So the reason why most people are asking the question about traveling at c is that they already know that going a tad bit under c is relatively the same as not moving at all.

Either way, people need to learn that you don't have to accelerate at all in order to "see" what it is like to travel at almost the speed of light, they can just transform a Frame of Reference in which they are at rest into a Frame of Reference that is moving at 99.99999998%c and see what happens to them. But they cannot transform into a Frame of Reference that is moving at c because the equations for the Lorentz Transformation have a factor that results in a division by zero when v=c.

bapowell