Is all of our universe… lit? Can you be hurtling through space and accidentally fly head first into a planet because oops you didn’t have your headlights on?



Is all of our universe… lit? Can you be hurtling through space and accidentally fly head first into a planet because oops you didn’t have your headlights on?

In: Physics

No. There are large voids between galaxies of nothingness for hundreds of thousands of light years. There is also void space within galaxies.
I believe the term is “Orphan planets”; planets not attached to a star and just hurtle through space like a supermassive asteroid.

If you were hurtling through the Milky Way, you would see basically the same view as our night sky, but all around you, and with many more/brighter stars (no light pollution from the ground to obscure them.

It would be equally beautiful and terrifying, I think.

But the Milky Way is a galaxy. Most of space is the in-between nothingness outside of galaxies. If you weren’t near anything at all, the only “stars” you see would themselves be entire galaxies.

You could ram into a planet. That’s what an asteroid impact is…but in this case, you are the asteroid. If you were in a ship and had controls, I think we can also assume you will have sensors to see the planet coming. There are rogue planets that drift all alone, so sure, hypothetically we can say that if you have no sensors and are *extremely unlucky* you could randomly hit a planet. But this would also mean entering a galaxy first, and surely you would know you were at least doing that.

It is extremely unlikely for you to collide with anything in space. There is a gigantic amount nothing out there. So it’s far more likely to drift through a near empty abyss without collisions.

But in the unlikely event that you do end up heading towards a planet you don’t know about, you’d feel it’s gravity long before you hit it. So that’s a warning sign.

As for whether you can see it? Almost everything emits infrared light, so you probably have devices in your space ship that can detect that light, even if your naked eye can’t. Also if you are in a galaxy, which is where most planets are, there will be stars nearby that light it up.

>Space … is big. Really 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, but that’s just peanuts to space.
>- Douglas Adams, “The Hitchhiker’s Guide to the Galaxy”

The chances of something running into something else in space (other than the occasional hydrogen atom) is miniscule.

That said, most of interstellar space is also quite dark. In deep space, nothing’s going to be illuminated like you’d see on Earth. If anything, something large or very close by would only be visible as a silhouette against a the background star field of space (and, unless you’re inside a galaxy, that star field is going to be very very very dim.

For something the size of a planet, you might notice the gravitational pull of the planet long before you otherwise sense it (if you think to look for it). If not that, everything emits a tiny amount of radiation, so there’s a very dim and invisible-to-the-naked-eye glow to everything, if you have the instrumentation to see it.

If the object was, say, the size of a box truck, floating in deep space, you’d probably bump into it before you noticed it without with some sort of active scanning technology.

Light permeates the entire observable universe, so technically everything is “lit.” But even in our own solar system, the objects in the Kuiper belt are very faint because light is governed by the inverse square law (light dims by distance squared). So, it would depend on what type of sensors you have, but objects in interstellar space and especially intergalactic spece would be very close to perfectly dark in the visible spectrum.

It depends what you define as bright enough to be visible, and what means you’re using to detect objects around you.

There are rogue planets that travel through the galaxy, and have no star they orbit. These planets could be about the best candidate for the situation you describe, where I imagine you are wondering just how big of an object a human might not visually notice if only looking with the naked eye and no headlights.

Keep in mind however that you’d not see the planet, but you’d definitely see the silhouette it blocks out between you and the starry background. So you would have to be pretty inattentive or moving at a pretty high velocity relative to the planet to not notice it approaching, blocking out more and more of the stars in front of you.

So the candidate for what you’d run into would perhaps be much smaller. Or to run into something bigger, you’d need to find yourself located somewhere where much of the starry background is blocked by cold, dark matter. I have no idea if this is something that occurs commonly in the universe, but I wouldn’t be surprised if some condensing clouds of gas could perhaps cool off (ie emit less light) and begin to compress…?

All of this said, you’d have a very long wait ahead of you if you weren’t actively searching for something to crash into. As other posts have said, there’s a mind boggling amount of distance between objects in space. And since bright things like stars are in the parts of the universe with objects closer together, to get into your pitch black planet scenario, you’d be in a part of the universe with even more mind bogglingly large distances between objects. The chance of hitting something planet-sized is not zero, but it is vanishingly small.

All of the universe is lit by starlight to some degree (at least in open space). The degree of light may vary wildly depending on where you are, from right next to a star to an intergalactic void, but it’s all illuminated.

As to whether you could run into an object without seeing it first, that would depend on how sensitive your observations are, how reflective the object is (it’s albedo), and how well lit the area of space you’re in is. A reflective object near a star (such as our moon) will be hard to miss, but a non reflective object in intergalactic space will be much harder to see.

Mmmm. There are such things as rogue planets that don’t orbit a star. If all you had to detect things in your way were your eyes then yes. You could collide with a planet you didn’t see.

You know how in a lot of sci fi movies they pass through an asteroid field and the pilot has to maneuver the spaceship expertly to avoid colliding with the Asteroids?

In real life, you can pretty much go through the Asteroid belt between Mars and Jupiter with your eyes closed and won’t hit anything at all. In fact, you probably won’t even _see_ an Asteroid unless you look through a nice telescope.

Space is empty. _Really_ empty.

Another way to think of it this: In about 4 billion years, Andromeda and Milky Way will collide with each other. Two galaxies with 500billion – 1 trillion stars _each_. The fascinating part? Even after the galaxies collide, pretty much none of the individual stars will hit _anything at all_.

I think this was a great question. Its its interesting all the inferences In this response thread. I Inferred OP meant visible spectrum using their eyes (since they referenced headlights) others made no such inference. I also inferred they were asking for possibility not probability and others did not make those inferences. Tons of great, thoughtful, responses.

Think of it this way.

At our point in space, any light reaching us is point light from the star’s source. No “reflected” light is strong enough to reach us past a certain distance, just look how small Venus and Mars are in the sky.

We see things in deep space far away when they block light from the stars.

So to answer your question, if there is a star close enough to you, then everything is lit. If you are in deep space, then objects in space will cause dark spots as you move through. Theoretically, you could hit it if you were not paying attention.

Really good question because it requires multiple answers.

1) There’s a **LOT** of space in space. So it’s not likely to hit something except over really long periods of time (Billions of years).

[Astrophysicist Dr. Becky – Likelihood of Stars to Collide](

2) There is actually a lot of rogue planets, asteroids, dust, and other materials out there that are very dark and so would be hard to detect with our current technology until you crash into them.

[PBS Spacetime Dark Matter](

3) Technically, the vacuum of space is most likely the coldest thing in the universe at a chilly 2.73 K. So any real object made of atoms is warmer than that and so glows some light. This light can be infrared light that you might be familiar with from those glowing red heaters. You and I can’t see that light, but your skin can feel it as warmth and we have scientific sensors that can see it.

[Scishow Space Coolest Place in Outer Space](

[PBS Spacetime Cosmic Microwave Background](

4) If you had a really bright headlight in front of your spacecraft, even if you were moving really fast up to high percentages of the speed of light (like 99%). The light you emit would still head away from you at the speed of light and so would illuminate objects ahead of you. Though you may not be able to correct your course in time to stop the crash.

[VSauce Would headlights work at the speed of light?](

[PBS Spacetime Speed of Light](

Edit: Added video links

I feel like everyone who answered is hyper focused on a pretty poor understanding of what I assume your question was.

It doesn’t sound like you’re asking about the likelihood of “colliding with a planet.”

It sounds like you’re asking about whether or not you’d be able to see a planet, or asteroid, or anything else, regardless of what your interaction with it was going to be?

I don’t have the answer for you, but I’m just hoping that, if this is more of what you meant (it seems pretty obvious to me that this is what the actual question was), maybe people will be able to see this and understand the question better.