Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

gravityandlevity.wordpress.com

Post reply on HN
Print view View original

71–80 of 234 posts

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

#71

Post by DangitBobby »

franciscop wrote: post #33

A bit all over the place, the author assumes "It is even less well-known that the rule “nothing moves faster than the speed of light” is a consequence of the laws of electricity and magnetism" but at the same time "This is also a well-known property of electricity and magnetism" and then drops some equations. Most people for whom this property of electricity and magnetism is well known, also know that the speed limit…

The author's assumptions were spot on for me. I am familiar enough with E&M to know the equations and roughly understand relatively but did not know where the intuition for a universal speed limit comes from.

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

#72

Post by lurquer »

danielsju6 wrote: post #60
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…

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 in a c-speed rocket could very well assume he was still and the earth was moving away. He should expect to find a younger twin when the earth ‘returned.’ Yet the examples only have the earth twin age, so to speak, and not the rocket twin.

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

#75

Post by subroutine »

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 age I want by varying my speed. Since the same 1 hour passes for me no matter the age for them I chose, it seems like I'm selecting an already existent future from a stack, not fast-forwarding the present I left.

Q2. How do black holes exist if time stops inside a black hole? That is, they continue to move through spacetime, even though spacetime is not moving within the hole? I accept that a black hole can form, and can stop time, I'm just curious how something that stops time continues to persist in the present. The way I'm visualizing this, is like a lava lamp about to bleb off some goo from the top [1]. As the object gets more and more dense, it curves and drags spacetime more and more, until eventually its density passes the Schwarzschild radius and blebs off.

[1] https://m.media-amazon.com/images/I/615deDvfDkL._AC_SS450_.j...

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

#76

Post by bambam24 »

Do you have zero mass? Otherwise just to a 150lbs person will have mass of a galaxy at 99% of the speed of light. And to go remaining %1 you will need to have a power to push entire galaxy 0.1% of speed of light. At 99.999998% of speed of light the man will need to burn all the elements in the universe. Basically a credit card or bank loan cannot buy you such energy.

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

#77

Post by DangitBobby »

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…

It's a consequence of the time dilation. You are not stationary towards the photon to an outside observer, so to them it looks like the photon moves away from them faster than it moves away from you. And from the obserer's perspective, your clock is ticking slower. That's the key. The amount that your clock is ticking slower is such that you, the one moving, would calculate the speed of the photon the same as the stationary observer, because you would do so from your own slower clock.

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

#78

Post by firebaze »

godelski wrote: post #70
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'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 you go faster, anything around you ages faster, but you yourself won't encounter any speed limit.

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

#79

Post by the_gipsy »

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?

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

#80

Post by RHSman2 »

bollu wrote: post #6
kevinventullo wrote: post #5

Earlier quoted context omitted.

Hm, but if I can make my angle orthogonal to the time axis, isn’t that like instantaneous movement?

Yes, which is why a photon experiences zero proper time.

They should make a movie called ‘Photon’ and track its life. A parody based on science.
Post reply on HN