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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?

#81

Post by l332mn »

stareatgoats wrote: post #52
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 obs…

> To state that the speed of light is the same only because the relative time is variable for respective observers is unconvincing

Not sure what you mean by relative time?

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

#82

Post by ncallaway »

stareatgoats wrote: post #52
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 obs…

> but to me this is simply not logical.

It is not logical if you really believe that speeds add linearly (that is, if you are going 5mph past an observer and throw a ball 5mph, that the result is the ball moving 10mph).

Speeds don’t actually add linearly like that, but they come very very very very close to doing so for all speeds humans are used to dealing with.

So, we all have very deeply held gut feelings that speeds should add linearly. Once you let go of that, it becomes much easier to understand many of the things that don’t feel logical about relativity.

Ultimately, it is logical, but from a different set of axioms than most humans tend to have.

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

#83

Post by [deleted] »

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…

[deleted]

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

#84

Post by throw_away »

justusthane wrote: post #58
yawaworht1978 wrote: post #43

Earlier quoted context omitted.

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…

> > 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.

Eh, at .01c, not so much: https://www.omnicalculator.com/physics/time-dilation?c=USD&v...

(=100.005y, not even two days extra)

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

#85

Post by subroutine »

the_gipsy wrote: post #79
subroutine wrote: post #75

Q1. Does the future already exist? I realize this might be purely philosophical, but if I leave Earth, and fly through space near c kph, and return home a few hours later to find everyone aged 50 years... are they the "same" people, or are they a future-instance of the people left? To clarify, theoretically I could leave earth, and return home in exactly 1 hour (from my ref frame), and basically make people whatever…

Q1b. Are you the same person you were yesterday?

I think yes, and the answer is more concrete for "oneself", since the molecules that make-up oneself are all accelerating and decelerating with you/as you in your own reference frame.

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

#86

Post by hollander »

nycdatasci wrote: post #53
yawaworht1978 wrote: post #43

Earlier quoted context omitted.

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...

That Google link doesn't work.

https://www.gutenberg.org/ebooks/5001

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

#87

Post by [deleted] »

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…

[deleted]

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

#88

Post by chrischen »

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…

> And let's say, i travel one light-year at the speed of light, that should be instantaneous, right?

Time slows down for the faster moving particles. And by time slowing down we mean all the particles in your body equally all start to move slower and more sluggishly in sync.

This is because it takes more energy to accelerate a particle as it approaches the speed of light. So if you had a pendulum clock moving almost at the speed of slight, that velocity of the pendulum at rest would be at X m/s, but if the whole system is already moving super fast the extra X m/s would take too much energy. So since the energy is constant the relative speed of the pendulum just becomes much slower.

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

#89

Post by lovegoblin »

xondono wrote: post #64
nimish wrote: post #37

Earlier quoted context omitted.

They are only theoretically possible if you allow for negative mass and energy--not an engineering problem so much as a "need to find exotic matter" Basically people ran the EFE "backwards" to see what matter distribution makes the wanted curvature. You get either negative mass-energy or the bubble doesn't travel ftl iirc.

The Alcubierre drive “beats” the speed of light, for the effects described 0.7-0.9c are more than good enough (if slightly unpractical). We can’t do that either for now, but is way easier on the feasibility scale.

> The Alcubierre drive “beats” the speed of light

The Alcubierre drive is only a thought experiment that requires "exotic matter" (aka fairy dust) to work.

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

#90

Post by ergocoder »

hyperman1 wrote: post #63
ergocoder wrote: post #35

"Nothing can go faster than light" is just a convention and is not experimentally confirmed. IIRC there are a few things that go faster than speed of light (e.g. universe expanding). "Spooky action at a distance" is also not known very well. That could also break the speed of causality law. While Bell's theorem hints that this is not the case, there are some exceptions to Bell's theorem. Right now a lot in physics ar…

AFAIK 'nothing goes faster than c' is wrong in the 'lies to children category'. The devil is in the details. In fact, plenty of things go faster than c. As a standard example, take a wall at 1m distance and a flashlight. move the light spot at 1 m/s. If you put the wall at 2m, the same spot will now go 2 m/s. If you put it at 300 000 km, the spot will go at 300 000 km/s, slightly over light speed. The problem is more…

That is a reasonable argument.

And what you point out is actually the speed limit of causality, instead of light. It just happens that light travel really fast.

Though the article wants to discuss the speed of light as you mentioned, so I focused on speed of light.

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