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

Show HN: What if the speed of light was 5 km/h?

rivendell.dmitrybrant.com

Post reply on HN
Print view View original

131–140 of 236 posts

Re: Show HN: What if the speed of light was 5 km/h?

#131

Post by irjustin »

buf wrote: post #121
santiagobasulto wrote: post #90

Some time ago I had the following shower thought: "the Speed of Light is pretty slow" How i got there: The closest major galaxy to the Milky Way is Andromeda, and is 2.5 million! light-years away. And this is the CLOSEST galaxy, the universe is extremely big. Of course that as you get closer to C, the traveling object will experience time dilation (relative to observer), so the time passed will be less. At 99.999% C,…

Not only that, from light's perspective, it takes no time at all. ;)

From the light's perspective: "what is this.... time you speak of?"

Re: Show HN: What if the speed of light was 5 km/h?

#132

Post by MathMonkeyMan »

rrr_oh_man wrote: post #117
marcyb5st wrote: post #106

Earlier quoted context omitted.

Yeah, it is and the math get's really counterintuitive to grasp since humans (at least me) have trouble thinking in exponential terms. If you accelerate at 1g constantly for 1y you travel 0.5 light years. You do that for 10.5 years and you reach the center of the milky way. You do that for another 4 (~14 total) years and you are in the Andromeda galaxy, and you do that for another 10 years (~24 years total) and you r…

> math get's really counterintuitive to grasp People always say that about speed of light stuff, but I don’t get it. Do you have any more examples of counterintuitive math? Because what you’re describing is basically the equivalent to compound interest in finance. (e.g. investing $100 at 10% interest over 10 years results in $260)

The proper time (that is, the time the traveler measures on a clock) goes to zero very quickly towards the end. Even with both axes plotted logarithmically, it's just a sudden drop at the end towards light speed.

- [pic](https://home.davidgoffredo.com/hackernews/proper-time-one-li...)

- [plot](https://home.davidgoffredo.com/hackernews/proper-time-one-li...)

Re: Show HN: What if the speed of light was 5 km/h?

#133

Post by lostlogin »

mjmas wrote: post #127
ExoticPearTree wrote: post #124

Earlier quoted context omitted.

> If you accelerate at 1g constantly for 1y you travel 0.5 light years Can't we accelerate past 1G constantly? Or do we expend so much energy doing it that we can't realistically do it with today's technology?

We can't necessarily survive that well when under acceleration greater than 9.81 metres per second per second for extended periods of time.

Gravity on Earth varies about .7%.

Increasing the acceleration a little bit more than that (eg to 1%) would make a difference.

https://en.wikipedia.org/wiki/Gravity_of_Earth

Re: Show HN: What if the speed of light was 5 km/h?

#134

Post by jdjfbfbdbfnf »

ExoticPearTree wrote: post #124
marcyb5st wrote: post #106

Earlier quoted context omitted.

Yeah, it is and the math get's really counterintuitive to grasp since humans (at least me) have trouble thinking in exponential terms. If you accelerate at 1g constantly for 1y you travel 0.5 light years. You do that for 10.5 years and you reach the center of the milky way. You do that for another 4 (~14 total) years and you are in the Andromeda galaxy, and you do that for another 10 years (~24 years total) and you r…

> If you accelerate at 1g constantly for 1y you travel 0.5 light years Can't we accelerate past 1G constantly? Or do we expend so much energy doing it that we can't realistically do it with today's technology?

We need a massive rocket to escape the earths gravity (1g). That takes us minutes and a crap ton of fuel. The issue is to keep doing that with fuel and oxidiser constantly for 1, 2 or 10 or 25 years is a monumental amount of energy, which is a monumental amount of weight, which is a monumental amount of volume... Also you also need the exact same amount of fuel to stop again.... So yeah ... We don't got it yet

Re: Show HN: What if the speed of light was 5 km/h?

#135

Post by alex_duf »

atlimar wrote: post #99
santiagobasulto wrote: post #90

Some time ago I had the following shower thought: "the Speed of Light is pretty slow" How i got there: The closest major galaxy to the Milky Way is Andromeda, and is 2.5 million! light-years away. And this is the CLOSEST galaxy, the universe is extremely big. Of course that as you get closer to C, the traveling object will experience time dilation (relative to observer), so the time passed will be less. At 99.999% C,…

> At 99.999% C, the traveler would take ~11,000 years if we add more 9s, is it possible to reduce that number to within a human lifespan?

You can but I don't want to see that energy bill

Re: Show HN: What if the speed of light was 5 km/h?

#136

Post by gigisfndr »

This is an awesome thought provoking question! My mind goes immediately to perhaps using this as a “time scaled” model to “observe” well known physical experiments and physical phenomenon if possible eg Young’s Experiment. Could that work / be useful? I am not a physicist but currious.

Re: Show HN: What if the speed of light was 5 km/h?

#138

Post by jeanlucas »

rrr_oh_man wrote: post #129
jeanlucas wrote: post #122

Earlier quoted context omitted.

One million seconds is 11 days, a billion seconds is 31 years.

Thanks! But same here imho: 1,000 seconds = ~0.01 days (~17 min) 1,000,000 seconds = ~11.57 days (~12 days) 1,000,000,000 seconds = ~11,574.07 days (~32 years) 1,000,000,000,000 seconds = ~11,574,074.07 days (~32k years) It all seems quite logical once you put everything into the same unit, I think. Maybe it's just our human calendar/time unit rollercoaster (60*60*24*30*12) that's playing tricks on us here.

Of course it is logical, we are not discussing the math.

But it isn't intuitive, you're not used to numbers that big or that grow that fast.

Few things go from a million to a billion, especially when related to time.

Re: Show HN: What if the speed of light was 5 km/h?

#139

Post by TheOtherHobbes »

ExoticPearTree wrote: post #124
marcyb5st wrote: post #106

Earlier quoted context omitted.

Yeah, it is and the math get's really counterintuitive to grasp since humans (at least me) have trouble thinking in exponential terms. If you accelerate at 1g constantly for 1y you travel 0.5 light years. You do that for 10.5 years and you reach the center of the milky way. You do that for another 4 (~14 total) years and you are in the Andromeda galaxy, and you do that for another 10 years (~24 years total) and you r…

> If you accelerate at 1g constantly for 1y you travel 0.5 light years Can't we accelerate past 1G constantly? Or do we expend so much energy doing it that we can't realistically do it with today's technology?

We can't do it with any rocket-like propulsive technology. By the time you get anywhere close to c the front of your spacecraft is being abraded into nothing by interstellar gas, larger particles of dust will kill you, and colliding with anything bigger creates an explosion that can be seen for light years. You need to be flying a large asteroid to even think about surviving it - you still won't for long, but you will have time to think about it - and the energy requirements are wildly impractical.

Magic warp bubble tech is the bare minimum, and we're nowhere close to inventing that.

Re: Show HN: What if the speed of light was 5 km/h?

#140

Post by Terr_ »

santiagobasulto wrote: post #90

Some time ago I had the following shower thought: "the Speed of Light is pretty slow" How i got there: The closest major galaxy to the Milky Way is Andromeda, and is 2.5 million! light-years away. And this is the CLOSEST galaxy, the universe is extremely big. Of course that as you get closer to C, the traveling object will experience time dilation (relative to observer), so the time passed will be less. At 99.999% C,…

In terms of comparisons to human lifespan, I think this one is interesting:

If you can somehow accelerate/decelerate at a constant human-acceptable 1G, time dilation means almost anywhere is reachable in a human-lifetime.

That coincidence(?) could easily become false if we are accustomed to lower accelerations or lesser lifespans.

Post reply on HN