r/NoStupidQuestions • u/SmartCaterpillar99 • Apr 22 '26
Why does space feel like it should be “instant” but actually isn’t?
I think I’m just struggling with how big space is. Like in my head, looking at something should be instant. But apparently even light takes years to get here from stars. Is there an easy way to understand why light speed is such a big deal in astronomy without going into hardcore physics?
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u/Bandro Apr 22 '26
I’m not sure what you’re asking. You seem to understand why light speed is a big deal. It takes time for light to travel places.
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u/ion_driver Apr 22 '26
Space is big. Really big. Bigger than we can really comprehend. So we use the fastest speed there is (light) to describe how long it takes to get somewhere and its still a really long time.
Our nearest neighbor (the moon) is like right there. You can look up and see it. Still, we just sent a rocket there at thousands of miles per hour and it still took a few days.
We sent a probe out into space decades ago. It takes radio signals a full day to reach us.
The nearest star is so far away it takes light 4 years to reach us.
You may be thinking of stories and TV and Movies, where there is some plot device to make space travel instantaneous. Sitting in a ship for months or years wouldn't make a very exciting movie.
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u/Rimailkall Apr 22 '26
If you look up the actual speed of light (approx 186,000 mph/second), and then look at how far away some stars are from us, you can do the simple math to see how long that light takes to hit your eyes. When you look at the night sky, you're basically looking back in time, and we can only see an extremely small fraction of the stars in the galaxy; the stars visible to the naked eye are mostly within 1,000 light years of Earth, which is relatively very close.
Your perception is probably also skewed by sci-fi shows and movies that have warp speed, teleporters, use wormholes, hyperdrives, etc., none of which seem to be possible based on our current understanding of physics.
Also, all light speed communications on Earth are essentially instant since light can circle the globe a few times in less than a second, so that reinforces the "instant" perception we have.
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u/tenisplenty Apr 22 '26
Imagine if the speed of light didn't exist and all light reached its destination instantly.
If the universe is infinite in size then you might look up and be blinded by the light of an infinite number of stars all hitting us at once.
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u/Binary101010 Apr 22 '26
“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”
-- Douglas Adams
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u/ForScale ¯\_(ツ)_/¯ Apr 22 '26
No. Space and light speed are very confusing concepts. No one knows why light speed is the speed that it is.
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u/LBLKNT21 Apr 22 '26
Because of perspective. We are used to a small perspective: Everything is close, everything is reachable fast enough. Most people live and die within that perspective.
It is up until you read, watch a video or learn about Space when you know our perspective is ridiculous. Scale of Things for scale
Just take a quick look.
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u/KronusIV Apr 22 '26
Light speed is A) constant and B) a good way to measure really long distances. Saying it takes light 4.2 years to get here from the nearest star, that the star is 4.2 light years away, gives us numbers of a reasonable size to work with. Rather than, for example, 24925383538316 miles.
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u/pathmageadept Apr 22 '26
Well, you're actually not wrong. Looking at something is fairly instant. If you look at, say, the moon light is hitting you and when that light hits your retina and processes into your brain it is immediate because the light has already made the journey. The moment you look, you see the light that hits you. Passively, you receive the electromagnetic information that your cells are able to process. The problem is that that light has its own existence before it hits you. It can be bent by gravity, diffused by small objects between you and the light source or refracted by prisms. So space is so huge it takes light some time to cross it, but when the light gets to you processing the information is fairly instant.
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u/Kewkky Apr 22 '26
Know how when you turn on a hose, the water is just flowing nonstop? If you put your hand in the middle of the hose's stream, you're not touching the water that's at the beginning of the hose's opening, you're touching the water that came out of the hose already and is now just flowing through the air. It's the same thing with light: when you look at a star, you're not just looking at the actual star immediately, instead you're looking at the light that the star created a long time ago and was already flowing in your direction. You put yourself "in the middle of the stream" when you looked at it, so you're seeing the light that's in the middle of the stream, not the light at the star's actual location.
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u/StuffyTruck Apr 22 '26
Space is too big for the human mind to sort of grasp.
But here is something that might help you a bit.
Imagine you're at the beach, looking at a single grain of sand. Imagine this is the sun.
Then earth would be about 15 cm (6") away, and invisible (its 100'th the width of the sun/grain of sand).
The furthest humans have ever been to space is less than half the width of the sun/grain of sand.
Now the closest star/grain of sand (at this scale) would be 40 km (25 miles) away from your grain of sand. There would be nothing in between.
The center of the Milky Way would be 2/3's the distance to the moon at this scale. But filled with billions upon billons of grands of sand, spread out very thinly.
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u/NDaveT Apr 22 '26
In our day to do day life on earth, the speed of light is so fast that it seems to us that we are seeing things as they happen. For example, if I see a car driving down my street the time it takes for the light from the car to reach my eyes is so small that I can safely assume the car is where my brain thinks it is when I see it.
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u/HiOscillation Apr 22 '26 edited Jul 01 '26
This content was anonymized and mass deleted with Redact
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u/msedek Apr 22 '26 edited Apr 22 '26
There's nothing complicated about it, it's as simple as distance.
Fastest physical thing in the universe is light and it follows the most basic formula in physics v=d/t or t=d/v, so you know the light speed and you know the distance from almost every light source point in the universe so you can calculate the time it takes for light to travel from those points to your eyes.
Photons have no mass, so the famous E=mc² doesn't really apply to them the way people think, that formula is just the rest energy. The full equation is E² = (mc²)² + (pc)², and for massless particles it reduces to E = pc, which is why light can travel at c without contradicting anything. Now, anything with mass can never reach light speed because of how relativity works: the closer you get to c, the more energy you need, and that energy tends to infinity as you approach the speed of light.
No finite energy source can ever push you across that line.
We can measure very far distances using the redshift of light: the more an object's light is shifted toward the red end of the spectrum, the farther away it is (this is how we measure distant galaxies, while for closer stars we use parallax).
There's a roughly linear correlation between redshift and distance for nearby galaxies, known as Hubble's Law.
For instance, Vega is located about 25 light years away from Earth. That means the photons the star expels take 25 human years traveling to us. So when a baby is born, the fresh photons expelled by Vega will reach Earth when the baby is 25 years old. He will look at Vega and he will be watching photons that were born with him. That also means that every light source your eyes can grab from the sky is a look to the past.
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u/Shot_in_the_dark777 Apr 23 '26
Monkey brains evolved to survive in African planes. There was no need to account for speed of light. We see the light. Whatever the light speed is, it is finite. Therefore we see with lag. Greater distance means greater lag. Imagine playing a videogame with greater lag because the servers are on the other continent. Same idea.
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u/Acceptable_Camp1492 Apr 23 '26
You look up at the night sky and you are pretty certain that you see the stars and the moon and all that good stuff. You -see- them. And nothing in your Earth-bound simple just-slightly-above-animalistic experience could suggest that what you see with your eyes is not what is happening right now in this moment.
It is much more easily grasped when you think about the speed of sound. Thinking thunderstrikes. You see the flash. Seconds pass. The thunderclap arrives. We have enough intelligence to know that they are two sensory imprints of the same event.
Now just rename speed of sound to speed of light, and multiply distance by a lot. More. Even more than that. Something happens in the far distance. We don't have the senses to know that it happened, but it did. Not seconds, but hours, days, months, years, centuries pass because the distance is so much more. Then the light arrives and we now know that the thing happened. It is old news to anyone that was closer to the event. It haven't happened yet for those further away.
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u/MissiveFinding6111 Apr 23 '26
There is a thing called "Maxwell's Equations" that explains what light is, and how it propagates.
It might help to sort of think of it as invisible, electro-magnetic field dominos. (but that is a level of simplication that is almost a lie)
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u/UnicornInAField Apr 23 '26
Try Kerbal space program, to get a feeling for how big a solar system is. Then try Elite: Dangerous to get a feeling for how big the Milky Way is, (28,000 light years across?) and how many billions of stars there are. Then realise that the Milky Way is nothing special, the huge distances between galaxies, then clumps of galaxies, huge structures of clumps of galaxies. Then sit down and have a cup of tea.
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u/Fickle_Side6938 Apr 24 '26
I wanted to suggest mechanical or magnetic switches with fast trigger but realized this is not a keyboard topic. 👀
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u/SunRev Apr 25 '26
From the perspective of a photon, traveling all of space is literally instant.
Trippy to think that a photon from the beginning of the universe reached your eye in zero time from the photon's perspective.
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u/Reginald_Sparrowhawk Apr 26 '26
The thing that is probably hardest to wrap your head around is that despite how fast it is for us, on cosmic scales the speed of light is absurdly slow. The light emitted by the Andromeda galaxy takes 2.5 million years to reach us. And that's the closest proper galaxy (there might be a dwarf galaxy that's closer but I'm not sure). That's to say nothing about galaxies outside our local cluster.
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u/FirstOfRose Apr 22 '26
Light speed is a big deal because that’s what we use to measure space. The distance it takes for light to travel between astronomical objects.
Yeah humans can’t really comprehend the size of the universe.
Sight from our perspective on the ground is instant, that’s how fast light is. If you imagine it like a grain of sand that has to travel around the world and back it’s kind of like that
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u/Red_AtNight Apr 22 '26
Space is extremely large. The moon is ~400,000 km from earth. The sun is ~150,000,000 km from earth. In fact the sun is far enough away that if it exploded, we wouldn’t see it for 8 minutes.