# What happens if the sun no longer emits visible spectrum?

All of a sudden the sun only produce every wavelength of the electromagnetic radiation except visible spectrum and there are no sign of recovery, the brightest minds on Earth cannot determine the root cause much less trying to remedy the situation.

Q1: Since visible light only constitutes a tiny portion of the entire EM spectrum, it shouldn't spell the end of humanity... am I being delusional?

Q2: How long do we have left given worst case scenario? (whether I should pour all my retirement fund into doomsday insurance policy or just stock up on candles...)

• Can you explain the reason for this change? – HDE 226868 Jan 30 '16 at 13:19
• @HDE226868: here's 101 reps and you can keep the "change"... – user6760 Jan 30 '16 at 13:55
• I don't quite understand. – HDE 226868 Jan 30 '16 at 14:47
• @HDE226868: no worry despite the sun being our closest star yet we failed to diagnose the anomaly, so don't that it gets the better of you as even all the elite minds seem to be at a loss... cheer up and take a breather! – user6760 Jan 30 '16 at 15:02
• So it's going to be like a night-club, then, with fluorescent materials glowing under the UV from the sun? – sh1 Jan 30 '16 at 20:18

OK, so all the energy from the Sun is now radiated in other wavelengths. I assume it is still the same amount? If so, the temperature is not going to change. The exact nature of the radiation matters a little for this scenario, as short wavelengths of EM radiation like UV, X-rays and gamma radiation are going to fry our DNA and give everybody cancer within days.

We are not going to die because of the darkness directly, we are going to starve to death. Plants require light in the visible spectrum to do the photosynthesis, so all plant life is going to die off quickly. As a consequence, all animal life is also dying from the lack of a food source.

Oxygen is not going to be a problem in a very long time, as there is $10^{18}kg$ of the stuff, enough for 7 billion humans for 300,000 years.

For the the last month of the age of humanity, we are not going live in complete darkness, as most power-plants do still work. (except for the ones unwisely built to use renewable solar power). Some hastily built systems for growing plants in artificial light are likely to be built, so at least a few humans are going to survive.

The best things you can do to prepare for this scenario:

• Stock up with canned food in order not starve in the first months.
• Build yourself a greenhouse with plenty of crops, and install Xenon lamps in the ceiling of it. They are going to provide simulated sunlight for the plants.
• Have a backup source for electricity, in case the power grid somehow becomes messed up. After all, your life depends on it. Solar panels does not count as a backup :)
• Note that "backup source of electricity" is a real mouthful. Let's say you need 1/10 acre of greenhouse , or just about 400 square meters. At a nominal 500 w/sq meter of light and 20% emitter efficiency, you'll need a 1.25 MW generator. This will require about 90 gal/hour of diesel while running, or roughly 63,000 gallons per month. – WhatRoughBeast Jan 30 '16 at 15:55
• @WhatRoughBeast Yes, you are pretty much dead if the power-grid fails – Hohmannfan Jan 30 '16 at 15:57
• Surely oxygen is something we'll be burning through very quickly with power generation for all the artificial lighting we'll run. But it seems like a big coincidence that plants could only live on light right in our visible spectrum. Our vision is more or less centered on the wavelength that most plants reject. – sh1 Jan 30 '16 at 20:15
• Both photosynthesis and our vision evolved to use the light that reached us through the atmosphere, so yes, they're going to die. Oxygen consumption will increase as all those dead plants decompose, and CO2 levels will increase as there are no plants to pull it out. But yes, we'll probably starve to death long before anything else kills us. – chepner Jan 31 '16 at 14:20
• @chepner, I mean human wavelength boundaries aren't universal to all earthly vision; so if the notch cut out specifically for humans were to coincide exactly with what plants absorb, that would be an odd coincidence. I looked it up and they appear to take a bit more UV than we can see, but I only saw that it didn't drop to zero before going beyond of human vision. I don't know how long the curve stays above zero, and I don't know what the sun starts to emit out there once it's altered. – sh1 Feb 4 '16 at 7:56

So let's assume some alien force has decided to terraform Earth by putting some sort of filter in the upper layers of our atmosphere that blocks certain parts of the spectrum, but not all of it.

There is still energy to be had, and still ways to generate light that our vegetation needs to survive while we work on adapting to our new situation. We have the technology to help mother nature along and evolve plants that can handle the new sunlight, glasses to shift non-visible parts of the spectrum to visible (to us parts), etc..

The biggest problem as I see it is not food, it's atmosphere. If our biosphere suddenly disappeared, we'd suffocate because photosynthesis is how oxygen primarily gets into our atmosphere. Depending on how suddenly this event happened, I don't know that we could grow enough biosphere with artificial lighting, especially considering that the ocean is the major portion of the oxygen cycle. I'm not sure exactly how the atmosphere would balance out, but I'm fairly sure that the surface would be unlivable for a while until we figured out a solution.