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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?

#51

Post by PaulDavisThe1st »

In the 70s, I remember reading "The Quincunx of Time", which made great use of a key distinction (for the purposes of some classic 70s scifi):

It's not that nothing can move faster than the speed of light, it's that nothing can accelerate to a speed faster than the speed of light.

If you could bring particles into being that already moved faster than light, they would not violate our understanding of relativity or the rest of physics. Hence ... the tachyon. https://en.wikipedia.org/wiki/Tachyon

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

#52

Post by stareatgoats »

otterley wrote: post #21

My favorite way to think of it is that the speed of anything is measured in distance per unit time. You can’t change the constant that is the speed of light, but what if you could change what “time” means? The constant holds, but time doesn’t; it varies among observers. A second from the perspective of observer A is not identical to a second from the perspective of observer B. Freaky, but true.

I still don't get this. I simply can not accept that the speed of light is that same for all observers, irrespective of their respective speeds vs the light source. It is obviously a cornerstone of Einsteins theory (I forget which; either the special or general relativity), but to me this is simply not logical. To state that the speed of light is the same only because the relative time is variable for respective observers is unconvincing, which requires that things like blueshift/redshift to be explained by logical gymnastics, and not the straightforward reason that the speed of light for all observers is a direct function of the relative speed vs the light source. But what do I know.

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

#53

Post by nycdatasci »

yawaworht1978 wrote: post #43
redwood wrote: post #23

I think a lot of people assume that this means you couldn't go more than a few (~100) light-years in your lifetime... But this is not actually correct. Counter-intuitively you can theorically go any number of light-years (essentially) in your lifetime, as long as you are able to approach the speed of light because when you do so the distance is dilated and hence you're covering far more ground within your reference f…

I know this is true, but I never got my head around this, maybe someone can help. So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth? And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I h…

Einstein can help: https://books.google.com/books/download/Relativity.pdf?id=3H...

His book was intended to help people understand these exact questions, without getting into any complex math.

Regarding "how is this possible?": This was experimentally verified in the 70s in the Hafele–Keating Experiment. Read more here: https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experim...

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

#54

Post by unyttigfjelltol »

Looks to me like the short answer to the question posed in the headline is that matter is composed at an atomic or subatomic level of energies similar to light and so it would be quite inconvenient to try to propel the mass as a whole faster that its constituent parts can go. A similar principle may well be true for straight-line inertia, which might be caused by the same as the force that makes gyros stay on course. In general the scientific discussions seem to touch these ideas but approach theories in reverse of intuition so it's hard to know if they align.

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

#55

Post by ghayes »

rkagerer wrote: post #25
redwood wrote: post #23

I think a lot of people assume that this means you couldn't go more than a few (~100) light-years in your lifetime... But this is not actually correct. Counter-intuitively you can theorically go any number of light-years (essentially) in your lifetime, as long as you are able to approach the speed of light because when you do so the distance is dilated and hence you're covering far more ground within your reference f…

It just means you can't within the lifetimes of the people you left behind. For that you need more exotic contraptions (wormholes, warp drive, etc).

If they were to wait a year and then come find you far away, would it net out and you’d be the same age?

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

#56

Post by thriftwy »

programmer_dude wrote: post #2

Wow, this is the first time I have understood why nothing can go faster than the speed of light and why time dilation is a thing. A very easy to read article, give it a try. Also if you are curious why a moving charge creates a magnetic field watch this Veritasium video: https://www.youtube.com/watch?v=1TKSfAkWWN0

Frankly though, I not sure why they couldn't just use a simpler correction: postulate that moving charge only creates magnetic field with regard to objects moving relative to it. Which is also basically true?

This way, the stationary observer will sure notice that there's F_B, but will also know that the charge moving alongside the (also moving) rod does not experience it.

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

#57

Post by redwood »

shrimp_emoji wrote: post #39
mjburgess wrote: post #31

Earlier quoted context omitted.

If distances are dilating, why isn't that /less/ ground?

The distance doesn't dilate; time does. The distance contracts . E.g., to a photon moving at 1c, the whole universe has a contracted length of 0 meters, and it crosses the whole universe instantly. To us, observers at and the photon takes to cross the whole universe. By the time the photon's 0-second journey across the entire universe has finished (whatever that means), we're all extremely old. :D This is the time di…

Thanks for the clarification

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

#58

Post by justusthane »

yawaworht1978 wrote: post #43
redwood wrote: post #23

I think a lot of people assume that this means you couldn't go more than a few (~100) light-years in your lifetime... But this is not actually correct. Counter-intuitively you can theorically go any number of light-years (essentially) in your lifetime, as long as you are able to approach the speed of light because when you do so the distance is dilated and hence you're covering far more ground within your reference f…

I know this is true, but I never got my head around this, maybe someone can help. So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth? And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I h…

> So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth?

From the photon's perspective, it passes earth immediately. From our perspective, it takes 7 or 8 minutes.

> And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I have aged by the end of the journey?

You would have aged as much as your watch says you would have aged. Zero seconds.

>If I travelled at one percent of speed of light, same distance, i suppose 100 years would elapse for me, how much would elapse on earth?

I don't know how to do the math, but a very, very long time would have passed on earth.

> And what if I left earth at 50percent of light speed , traveled 1 light-year away and did a turn and came back to earth at same speed. For me, it would be 1 year, but if I had a twin brother who was waiting on earth, would i now be a year younger than him? And how is this possible?

Yes, you would be younger than him, and it's possible because that's just how relativity and time dilation work. It's even practically measurable in "real" life: http://www.leapsecond.com/great2005/tour/

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

#60

Post by danielsju6 »

yawaworht1978 wrote: post #43
redwood wrote: post #23

I think a lot of people assume that this means you couldn't go more than a few (~100) light-years in your lifetime... But this is not actually correct. Counter-intuitively you can theorically go any number of light-years (essentially) in your lifetime, as long as you are able to approach the speed of light because when you do so the distance is dilated and hence you're covering far more ground within your reference f…

I know this is true, but I never got my head around this, maybe someone can help. So if a photon is emitted from the sun, it's passing earth immediately? Then why does sunlight need 7 or 8 minutes to get to earth? And let's say, i travel one light-year at the speed of light, that should be instantaneous, right? The odometer would show 1 light-year, my watch would should 0 seconds and some decimals. How much would I h…

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 happening”, that’s where Einstein comes in.

It’s an exponential. At 0.5c 100 years to you would be 115 years elasped to an observer, 0.9c 229 years, 0.999c 2,236 years, etc.

Here’s an online calculator for the dilation effect https://www.omnicalculator.com/physics/time-dilation

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