6 ms·

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,

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, the traveler would take ~11,000 years to arrive to Andromeda. So again, even at 99.999% C, 11K years seems like a LONG time to reach even the closest galaxy. My reasoning was: the speed of light is pretty damn slow. But then I realized: no, it's not the speed of light that is slow, is my frame of reference. For us humans, 11,000 years seems like A LONG time, but for the universe is not that long. The universe's age is estimated to be 13.8 billion years. 11,000 years is 0.0000007971 of the age of the universe. An average human lives 70 years, 0.0000007971 of that lifespan is approximately ~0.4 hours, or 29 minutes, so it's not that bad. So yeah, frame of reference matters.

atlimar 1mo ago
> 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?
- santiagobasulto 1mo ago
  Yes. Time dilation (with respect of the stationary observed) is calculated using the Lorentz factor. At 99.999% of C, the Lorentz factor is ~223.6. It grows pretty quickly as you add more 9s to the fraction. Every two additional 9s multiply the Lorentz factor by ~10. So at 0.99999999999 c, it'd be ~223,607x. 2.5M years / 223,607 is: ~11 years Of course this is all highly theoretical. https://en.wikipedia.org/wiki/Lorentz_factor https://en.wikipedia.org/wiki/Lorentz_factor
  - desterothx 1mo ago
    The speeds are theoretical (unachievable), time dilation itself is robust and proved (gps wouldn't work as precisely without accounting for it)
    - santiagobasulto 29d ago
      of course I meant that a human made object traveling at those speeds was theoretical, not time dilation itself. Never thought I'd have to clarify that :)
- ndsipa_pomu 1mo ago
  Yes. If you can manage to get arbitrarily close to the speed of light, the amount of perceived time would get arbitrarily close to zero.
- ryeights 1mo ago
  Proper time asymptotically approaches zero here right?
- deleted 1mo ago
  [deleted]
- marcyb5st 1mo ago
  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 reach what today is considered the edge of the observable universe. By the time you get there you are basically traveling at a rounding error from C.
  - rrr_oh_man 1mo ago
    > 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)
    - jeanlucas 1mo ago
      One million seconds is 11 days, a billion seconds is 31 years.
      - rrr_oh_man 1mo ago
        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.
        jeanlucas 1mo ago
        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.
- alex_duf 1mo ago
  You can but I don't want to see that energy bill
- futureshock 1mo ago
  Of course! You can arrive as quickly as you want as the traveler. You can cross the observable universe in a few hours if you add enough 9’s.
- andsoitis 29d ago
  > if we add more 9s, is it possible to reduce that number to within a human lifespan? Yes. At 99.99999999% of c it would take 35 years from the perspective of the traveler. However, an observer on earth will still see it taking 2.5m years.
buf 1mo ago
Not only that, from light's perspective, it takes no time at all. ;)
- irjustin 1mo ago
  From the light's perspective: "what is this.... time you speak of?"
  - cluckindan 1mo ago
    Also: ”Did we just go somewhere?”
    - RHSman2 1mo ago
      Does it know somewhere?
      - cluckindan 28d ago
        When it interacts with matter, it briefly becomes something else which does!
Terr_ 1mo ago
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.
- thwarted 1mo ago
  This is a really interesting video that explores this topic, pointing out that at near light speeds, the entire universe becomes accessible in a single human lifetime. The Overview Effekt: Time Dilation Visualized https://youtu.be/8FT-oz9aZU4 https://youtu.be/8FT-oz9aZU4
- sinuhe69 1mo ago
  Then I guess you will need millions tones of perfect mass to light converter like Astrophage just to get to the neighbor. The universe is simply too big to comprehend.
- no_multitudes 1mo ago
  > If you can somehow accelerate/decelerate at a constant human-acceptable 1G Well, you also need clarketech heat dissipation and collision deflection technology, if you want to get there without vaporizing.
  - Sohcahtoa82 1mo ago
    Yeah, once you reach a certain speed, even colliding with a fleck of dust can obliterate a ship. Colliding with a single 0.3 mg grain of salt at 20% of the speed of light creates an impact with 560 MJ of energy, equivalent to 130 kg of TNT, over 8 times the nuclear bomb dropped on Hiroshima. Even a tiny speck of dust, half a microgram, is equivalent to a hand grenade when hit at 20% the speed of light. You wouldn't be able to even escape the solar system before your shields were devoured. If you accelerated at 1G constantly, you'd be going 3.5% of the speed of light by the time you reached Pluto's orbit. Space dust particles are already hitting you like nuclear bombs at that speed.
  - 29d ago
mr_mitm 1mo ago
It doesn't really make a lot of sense to contextualize a velocity with a distance or a time period. You think those time periods are large because you see a lot of numbers in the units you chose, or because it is much larger than your lifespan. But in the grand scheme a galaxy is nothing but a spec of dust, 10k years a blink of an eye. There is no other natural velocity that I'm aware of that we could compare it to, but we can say that the speed of light is the fastest there is, so how can it be slow?
sh0gg0the 1mo ago
On YT there is a video of a flight through the solar system at the speed of light starting at the Sun. It's a pretty boring video. You see very little movement and change over time. After 8 minutes Earth slowly passes by. After 44 minutes you reach Jupiter and the video ends.
- shagie 1mo ago
  If The Moon Were Only 1 Pixel (A tediously accurate scale model of the solar system) https://www.joshworth.com/dev/pixelspace/pixelspace_solarsystem.html https://www.joshworth.com/dev/pixelspace/pixelspace_solarsys... has a button at the bottom right for 'C' which scrolls to the right at the speed of light on that scale. https://thinkzone.wlonk.com/SS/SolarSystemModel.php?scale=10000000&table=y&map=n&us=y&stars=y&light=y https://thinkzone.wlonk.com/SS/SolarSystemModel.php?scale=10... lets you make scale model calculations (useful if you're building one). The default model scale has the speed of light at 67.06 mi/h (107.9 km/h). This puts Earth out at 14.16 miles and Alpha Centauri at 2,581,000 miles away. I personally like the "Sun is 5 inches" scale because that puts the speed of light at 323.1 ft/h (10x garden snail speed) which is 1.46 miles/day... because that puts Alpha Centauri at 2,354 miles away... which is a conceivable distance. If you go to a scale of the sun being 500 inches (about 110000000) and the speed of light is 6 mph, Alpha Centauri is 234,600 miles away - the distance to the moon. It also lists the scale distance to the center of the Milky Way 1,327,000,000 miles) and Andromeda (137,400,000,000 miles) which are in the unconceivable range.
  - sh0gg0the 29d ago
    Does this take relativistic effects into account? The video I mentioned doesn't. Near the speed of light your surrounding looks like sped up and the distance to your target is clinched. Your own time runs slower in comparison and the distance is shorter. So theoretically you're able to reach the destination millions of LY away in your lifetime. Edit: I now watched the animation. It's exactly the same as the YT video. Speed of light is very, very slow.
  - petersumskas 28d ago
    In Australia there is a scale model of the Solar System where the sun is the main dome of Siding Springs observatory and the planets are on billboards at scale size and distance. Pluto is several hundred kilometres away (and the size of a tennis ball on the billboard) This discussion has made me wonder what it would look like to have a different scale where the distances are based on the “speed limit” (which is mostly 100km/hr)…so that earth, for example, would be 8min from the Sun. Neptune or Pluto would be 4 - 7 hours away. It would still fit in Australia but be significantly larger.
cheschire 1mo ago
I wonder what the light equivalent of a sonic boom is.
- _Microft 1mo ago
  Cherenkov light
hnlmorg 1mo ago
> the Speed of Light is pretty slow Professor Farnsworth: That's why scientists increased the speed of light in 2208.
NetOpWibby 1mo ago
Wow…that makes sense. I’ve had the initial similar thought but never investigated further, thank you for this.
nayuki 1mo ago
Pedantic note: The symbol for the speed of light constant is c (italic lowercase c). https://en.wikipedia.org/wiki/Speed_of_light https://en.wikipedia.org/wiki/Speed_of_light Roman lowercase c is the metric prefix centi-. Roman uppercase C is the metric unit coulomb. Italic uppercase C has various uses such as: a variable denoting capacitance in electrical engineering; an undetermined constant of integration in calculus.
Tepix 1mo ago
> "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. The speed of light is high. It's just that the universe has expanded into an unimaginably large area by now.
stackedinserter 1mo ago
Yeah, space exploration/colonization can be only made by species that live a million years, or can pass the same goal across many generations forward. Maybe it's the answer to Fermi paradox: aliens are all around, we're just too fast for them to communicate.
- BobaFloutist 1mo ago
  Relativity fixes that a little, you don't need to go light speed to make it all over the place within your lifetime, it's the observers who sent you off that will never reap the fruits of their effort.
davidoduk 1mo ago
So when we think we're looking at Andromeda today, we're actually seeing Andromeda as it happened 2.5 million years ago. That means someone/something? in Andromeda today, with the ability to see Earth clearly, would see some of our ancestors, like Homo habilis. I've always wondered, if we end up being able to travel faster than light, we'd technically be able to look into the past depending on how far we go. 1000 light years away and you can see your ancestors on earth.
- yellowapple 1mo ago
  A good enough lens would make it straightforward to solve murder mysteries, provided the murder happened outside on a sunny day.
- fwip 1mo ago
  In some sense yes, but I'm not sure there's enough photons coming from Earth 1000 light years away to see anything, even with a fantastically sensitive telescope. It would be very cool, though.
- deleted 29d ago
  [deleted]
IAmBroom 1mo ago
The OTHER effect of time dilation that isn't being mentioned: the rest of the universe is not accelerating with you, so it doesn't experience time dilation. Along your trip you will see stars turn red, sometimes flashing white and blinking out, but sometimes just fading away. Your civilization will without a doubt go extinct. If you are exceedingly lucky, you may see other civilizations of other species arise... but you'd need very high energy receivers in front of you, or deep infrared receivers behind, and of course be staring at the right place to see the signs. You may eventually begin to notice the revolving motion of galaxies. After that, if you continue, you'll see galaxies collide. By then your planet will have been dead for longer than it was a planet when you left it.
DoneWithAllThat 1mo ago
There’s sci fi novels that deal with it in just these terms. Like some folks with head out on a .99c acceleration ship and be like “okay we’ll be there in fifteen thousand years (original reference frame time)” and that’s just the scale at which the story unfolds. You just accept that when you leave on these trips that if you ever come back now it’s tens of thousands of years in the future there. Nbd

atlimar 1mo ago

> 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?

santiagobasulto 1mo ago
Yes. Time dilation (with respect of the stationary observed) is calculated using the Lorentz factor. At 99.999% of C, the Lorentz factor is ~223.6. It grows pretty quickly as you add more 9s to the fraction. Every two additional 9s multiply the Lorentz factor by ~10. So at 0.99999999999 c, it'd be ~223,607x. 2.5M years / 223,607 is: ~11 years Of course this is all highly theoretical. https://en.wikipedia.org/wiki/Lorentz_factor https://en.wikipedia.org/wiki/Lorentz_factor
- desterothx 1mo ago
  The speeds are theoretical (unachievable), time dilation itself is robust and proved (gps wouldn't work as precisely without accounting for it)
  - santiagobasulto 29d ago
    of course I meant that a human made object traveling at those speeds was theoretical, not time dilation itself. Never thought I'd have to clarify that :)
ndsipa_pomu 1mo ago
Yes. If you can manage to get arbitrarily close to the speed of light, the amount of perceived time would get arbitrarily close to zero.
ryeights 1mo ago
Proper time asymptotically approaches zero here right?
deleted 1mo ago
[deleted]
marcyb5st 1mo ago
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 reach what today is considered the edge of the observable universe. By the time you get there you are basically traveling at a rounding error from C.
- rrr_oh_man 1mo ago
  > 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)
  - jeanlucas 1mo ago
    One million seconds is 11 days, a billion seconds is 31 years.
    - rrr_oh_man 1mo ago
      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.
      - jeanlucas 1mo ago
        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.
alex_duf 1mo ago
You can but I don't want to see that energy bill
futureshock 1mo ago
Of course! You can arrive as quickly as you want as the traveler. You can cross the observable universe in a few hours if you add enough 9’s.
andsoitis 29d ago
> if we add more 9s, is it possible to reduce that number to within a human lifespan? Yes. At 99.99999999% of c it would take 35 years from the perspective of the traveler. However, an observer on earth will still see it taking 2.5m years.

buf 1mo ago

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

irjustin 1mo ago
From the light's perspective: "what is this.... time you speak of?"
- cluckindan 1mo ago
  Also: ”Did we just go somewhere?”
  - RHSman2 1mo ago
    Does it know somewhere?
    - cluckindan 28d ago
      When it interacts with matter, it briefly becomes something else which does!

Terr_ 1mo ago

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.

thwarted 1mo ago
This is a really interesting video that explores this topic, pointing out that at near light speeds, the entire universe becomes accessible in a single human lifetime. The Overview Effekt: Time Dilation Visualized https://youtu.be/8FT-oz9aZU4 https://youtu.be/8FT-oz9aZU4
sinuhe69 1mo ago
Then I guess you will need millions tones of perfect mass to light converter like Astrophage just to get to the neighbor. The universe is simply too big to comprehend.
no_multitudes 1mo ago
> If you can somehow accelerate/decelerate at a constant human-acceptable 1G Well, you also need clarketech heat dissipation and collision deflection technology, if you want to get there without vaporizing.
- Sohcahtoa82 1mo ago
  Yeah, once you reach a certain speed, even colliding with a fleck of dust can obliterate a ship. Colliding with a single 0.3 mg grain of salt at 20% of the speed of light creates an impact with 560 MJ of energy, equivalent to 130 kg of TNT, over 8 times the nuclear bomb dropped on Hiroshima. Even a tiny speck of dust, half a microgram, is equivalent to a hand grenade when hit at 20% the speed of light. You wouldn't be able to even escape the solar system before your shields were devoured. If you accelerated at 1G constantly, you'd be going 3.5% of the speed of light by the time you reached Pluto's orbit. Space dust particles are already hitting you like nuclear bombs at that speed.
- 29d ago

mr_mitm 1mo ago

It doesn't really make a lot of sense to contextualize a velocity with a distance or a time period. You think those time periods are large because you see a lot of numbers in the units you chose, or because it is much larger than your lifespan. But in the grand scheme a galaxy is nothing but a spec of dust, 10k years a blink of an eye. There is no other natural velocity that I'm aware of that we could compare it to, but we can say that the speed of light is the fastest there is, so how can it be slow?

sh0gg0the 1mo ago

On YT there is a video of a flight through the solar system at the speed of light starting at the Sun. It's a pretty boring video. You see very little movement and change over time. After 8 minutes Earth slowly passes by. After 44 minutes you reach Jupiter and the video ends.

shagie 1mo ago
If The Moon Were Only 1 Pixel (A tediously accurate scale model of the solar system) https://www.joshworth.com/dev/pixelspace/pixelspace_solarsystem.html https://www.joshworth.com/dev/pixelspace/pixelspace_solarsys... has a button at the bottom right for 'C' which scrolls to the right at the speed of light on that scale. https://thinkzone.wlonk.com/SS/SolarSystemModel.php?scale=10000000&table=y&map=n&us=y&stars=y&light=y https://thinkzone.wlonk.com/SS/SolarSystemModel.php?scale=10... lets you make scale model calculations (useful if you're building one). The default model scale has the speed of light at 67.06 mi/h (107.9 km/h). This puts Earth out at 14.16 miles and Alpha Centauri at 2,581,000 miles away. I personally like the "Sun is 5 inches" scale because that puts the speed of light at 323.1 ft/h (10x garden snail speed) which is 1.46 miles/day... because that puts Alpha Centauri at 2,354 miles away... which is a conceivable distance. If you go to a scale of the sun being 500 inches (about 110000000) and the speed of light is 6 mph, Alpha Centauri is 234,600 miles away - the distance to the moon. It also lists the scale distance to the center of the Milky Way 1,327,000,000 miles) and Andromeda (137,400,000,000 miles) which are in the unconceivable range.
- sh0gg0the 29d ago
  Does this take relativistic effects into account? The video I mentioned doesn't. Near the speed of light your surrounding looks like sped up and the distance to your target is clinched. Your own time runs slower in comparison and the distance is shorter. So theoretically you're able to reach the destination millions of LY away in your lifetime. Edit: I now watched the animation. It's exactly the same as the YT video. Speed of light is very, very slow.
- petersumskas 28d ago
  In Australia there is a scale model of the Solar System where the sun is the main dome of Siding Springs observatory and the planets are on billboards at scale size and distance. Pluto is several hundred kilometres away (and the size of a tennis ball on the billboard) This discussion has made me wonder what it would look like to have a different scale where the distances are based on the “speed limit” (which is mostly 100km/hr)…so that earth, for example, would be 8min from the Sun. Neptune or Pluto would be 4 - 7 hours away. It would still fit in Australia but be significantly larger.

cheschire 1mo ago

I wonder what the light equivalent of a sonic boom is.

_Microft 1mo ago
Cherenkov light

hnlmorg 1mo ago

> the Speed of Light is pretty slow Professor Farnsworth: That's why scientists increased the speed of light in 2208.

NetOpWibby 1mo ago

Wow…that makes sense. I’ve had the initial similar thought but never investigated further, thank you for this.

nayuki 1mo ago

Pedantic note: The symbol for the speed of light constant is c (italic lowercase c). https://en.wikipedia.org/wiki/Speed_of_light https://en.wikipedia.org/wiki/Speed_of_light Roman lowercase c is the metric prefix centi-. Roman uppercase C is the metric unit coulomb. Italic uppercase C has various uses such as: a variable denoting capacitance in electrical engineering; an undetermined constant of integration in calculus.

Tepix 1mo ago

> "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. The speed of light is high. It's just that the universe has expanded into an unimaginably large area by now.

stackedinserter 1mo ago

Yeah, space exploration/colonization can be only made by species that live a million years, or can pass the same goal across many generations forward. Maybe it's the answer to Fermi paradox: aliens are all around, we're just too fast for them to communicate.

BobaFloutist 1mo ago
Relativity fixes that a little, you don't need to go light speed to make it all over the place within your lifetime, it's the observers who sent you off that will never reap the fruits of their effort.

davidoduk 1mo ago

So when we think we're looking at Andromeda today, we're actually seeing Andromeda as it happened 2.5 million years ago. That means someone/something? in Andromeda today, with the ability to see Earth clearly, would see some of our ancestors, like Homo habilis. I've always wondered, if we end up being able to travel faster than light, we'd technically be able to look into the past depending on how far we go. 1000 light years away and you can see your ancestors on earth.

yellowapple 1mo ago
A good enough lens would make it straightforward to solve murder mysteries, provided the murder happened outside on a sunny day.
fwip 1mo ago
In some sense yes, but I'm not sure there's enough photons coming from Earth 1000 light years away to see anything, even with a fantastically sensitive telescope. It would be very cool, though.
deleted 29d ago
[deleted]

IAmBroom 1mo ago

The OTHER effect of time dilation that isn't being mentioned: the rest of the universe is not accelerating with you, so it doesn't experience time dilation. Along your trip you will see stars turn red, sometimes flashing white and blinking out, but sometimes just fading away. Your civilization will without a doubt go extinct. If you are exceedingly lucky, you may see other civilizations of other species arise... but you'd need very high energy receivers in front of you, or deep infrared receivers behind, and of course be staring at the right place to see the signs. You may eventually begin to notice the revolving motion of galaxies. After that, if you continue, you'll see galaxies collide. By then your planet will have been dead for longer than it was a planet when you left it.

DoneWithAllThat 1mo ago

There’s sci fi novels that deal with it in just these terms. Like some folks with head out on a .99c acceleration ship and be like “okay we’ll be there in fifteen thousand years (original reference frame time)” and that’s just the scale at which the story unfolds. You just accept that when you leave on these trips that if you ever come back now it’s tens of thousands of years in the future there. Nbd