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Why can’t I go faster than the speed of light?

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Re: Why can’t I go faster than the speed of light?

#101

Post by phkahler »

firebaze wrote: post #78
godelski wrote: post #70

Earlier quoted context omitted.

I'm pretty sure this doesn't work out because you have to slow down. So thinking about it, if you are traveling at that speed because of your inertial reference frame it is equivalent that everyone else around you is moving at (or near) the speed of light and they are moving slowly through time. This is the classic twin paradox and there is a resolution to it, which is that you can't instantaneously turn around.[0] O…

It does work out, in fact you could go arbitrarily far in space (and, mandatory, in external time) if you had infinite energy to spend. The acceleration and deceleration phase is almost negligible. Edit: the faster you go, the slower your own (inertial) time passes. That means the external time passes faster, and the factor grows to infinity the closer you get to C. In fact, subjectively there is no speed limit. As y…

But motion is all relative. Who is considered to be moving faster?

Re: Why can’t I go faster than the speed of light?

#103

Post by jeffwass »

lurquer wrote: post #72
danielsju6 wrote: post #60

Earlier quoted context omitted.

If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. The main ”paradox” found by experimention is that the speed of light is a constant, regardless of your velocity. The only way this could be true, if you do a thought experiment, is if time was dialating for you. As for the physical and mathematical “why is this ha…

> If you were watching their lives out the window of your spaceship you’d see them in fast forward vv. they’d see you in slow motion. Everything is relative. Both observers, looking at one another, would see the other moving near c. Neither would know who was ‘actually’ moving. Yet, you assume there would not be a symmetry in their respective views of the other’s passage of time. Explain why. In simpler terms, a twin…

The symmetry is broken in your twin example because the travelling twin had to accelerate to depart, accelerate to turn around, and accelerate to stop again at earth.

Re: Why can’t I go faster than the speed of light?

#104

Post by gridspy »

dhosek wrote: post #97

My favorite general relativity paradox: A runner is running with a 20m pole at a sufficient velocity so that a stationary observer sees the pole having length 10m. The runner runs through a barn which is 10m long. And two people outside shut the doors simultaneously so that the runner is completely enclosed in the barn for a moment. But from the runner's perspective, the barn has length 5m long. What does she see hap…

How do the two people at opposite ends of the barn agree on when to close the doors as a runner approaches at relativistic speeds?

Also, relevant xkcd (what-if) https://what-if.xkcd.com/1/

Most likely from the runner's perspective the world turns white as they dissolve to plasma prior to reaching the barn.

Re: Why can’t I go faster than the speed of light?

#105

Post by n3k5 »

dhosek wrote: post #97

My favorite general relativity paradox: A runner is running with a 20m pole at a sufficient velocity so that a stationary observer sees the pole having length 10m. The runner runs through a barn which is 10m long. And two people outside shut the doors simultaneously so that the runner is completely enclosed in the barn for a moment. But from the runner's perspective, the barn has length 5m long. What does she see hap…

> And two people outside shut the doors simultaneously

No, they don't. I'd phrase it differently, e.g. “each door is shut for an instant when the end of the pole is just inside the door”. (Also, make it clear that the barn is long enough to fit a 10m pole between the two shut doors.)

When you put it as “shut the doors simultaneously”, it's more troll physics than a paradox.

Meta-puzzle: figure out how to still imply that the runner is completely enclosed for an instant, without incorrectly insinuating that it is so from her perspective.

Re: Why can’t I go faster than the speed of light?

#106

Post by eesmith »

zamadatix wrote: post #44
xyzzyz wrote: post #26

Earlier quoted context omitted.

To put it another way, time travel machines are very much theoretically possible, and in fact are “only” an engineering problem (an extremely hard one, however). But, only forward travel is allowed: time travel machine could take you as far forward as its engineering would allow it, but there is no going back.

At 1G constant acceleration (both speeding up and slowing down) you can make it on a short vacation to the Andromeda galaxy and back in a lifetime (or 5 million years from the perspective or Earth).

It looks like about 57 years.

Assuming constant acceleration to the 1/2-way point, flip, deceleration, and using http://www.projectrho.com/public_html/rocket/slowerlight3.ph... :

  Time elapsed (in starship's frame of reference, "Proper time")
  T = (c/a) * ArcCosh[a*d/(c^2) + 1] (given acceleration and distance)
  year = 365.25*24*3600; c = 3E8; a=9.8; d=1.25*1_000_000*(c * year)
  from math import acosh
  T = (c/a) * acosh(a*d/(c*c) + 1)
  print(T/year)
  => 14.3 years each quarter 
  => 57 years round trip
The speed at flip would be 99.99999999993978% c - good thing intergalactic space is mostly empty.

Re: Why can’t I go faster than the speed of light?

#108

Post by [deleted] »

dhosek wrote: post #97

My favorite general relativity paradox: A runner is running with a 20m pole at a sufficient velocity so that a stationary observer sees the pole having length 10m. The runner runs through a barn which is 10m long. And two people outside shut the doors simultaneously so that the runner is completely enclosed in the barn for a moment. But from the runner's perspective, the barn has length 5m long. What does she see hap…

[deleted]

Re: Why can’t I go faster than the speed of light?

#109

Post by contravariant »

dhosek wrote: post #97

My favorite general relativity paradox: A runner is running with a 20m pole at a sufficient velocity so that a stationary observer sees the pole having length 10m. The runner runs through a barn which is 10m long. And two people outside shut the doors simultaneously so that the runner is completely enclosed in the barn for a moment. But from the runner's perspective, the barn has length 5m long. What does she see hap…

From the frame of reference of the runner the pole will first hit the door at the end of the barn (unless it opens in time), and the door at the front of the barn will only close just after the back of the pole has passed the door.

If the doors actually don't open in time then the resolution for the fact that the pole doesn't physically fit is that nothing can be rigid at relativistic speeds. So either the door or the pole or both will deform (violently) to allow the pole to fit inside the barn.

Re: Why can’t I go faster than the speed of light?

#110

Post by masa331 »

chrisoverzero wrote: post #96
masa331 wrote: post #92

Of course you can go faster than light, way faster. When it comes to physics there are no limits how fast, far or deep you can go. People constraint themselves with articifial limits and it's not necessary a bad thing. But real limits doesn't exist. I'v heard someone saying space is a big ball and outside of it is nothing. I imagine nothing as a black space but that actually is something. So there is something after…

> Of course you can go faster than light, way faster. OK. How?

I don't know
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