How do we know the universe is ever expanding? 31 views6 days ago Question31.48K June 8, 2021 3 Answers How do we know the universe is ever expanding?In: Physics LouManShoe commented June 8, 2021 When a source is moving away from a viewer the light emitted gets a slightly reddish color due to light red light moving slightly slower. If a source is moving toward a viewer, the light gets a bluish tint. We have observed a general redshift in light from other celestial bodies. There is other evidence too in quantum mechanics that has further support for this, but it’s quite complicated and I don’t fully understand it myself. Eulers_ID commented June 8, 2021 So this guy named Hubble did a whole bunch of measurements of distant stars and galaxies including how far they are form us and how fast they’re moving. Okay, that’s not exactly true, a bunch of the velocity measurements came from a guy named Slipher. When you look at the data he collected you see [this relationship](https://www.pnas.org/content/pnas/112/11/3173/F1.medium.gif). That graph shows that the further something is from us, the faster it’s moving away from us. There’s really no special magic here. It’s just a matter of measuring the data and looking at it.Also, the guy that found this out? He got a fancy telescope named after him. You’ve probably heard of it. Unfortunately, there’s not also a Slipher telescope. JimmyThePete commented June 8, 2021 Doppler effect. When the source of a wave is travelling away from you, the waves stretch out causing a shift down. That’s why the sound of a car horn changes as it drives past – the sound waves are getting longer and therefore the pitch is changing.The same thing happens with light waves – if the source is travelling away from you, the wavelength of light stretches until it drops below the visible spectrum. If this didn’t happen, then you wouldn’t see individual stars at night – the night sky would be full of stars from all over the universe. 0 AnswersActiveVotedNewestOldest Register or Login Other Questions You Might Be Interested In:Eli5: why does top water bottle companies use plastic to bottle the water?How do trees grow in width?Why do different gear ratios give different torque? Why isn't it the faster a wheel goes the more to...Do different cars have different RPMs for driving at a constant speed?How does LSD do *that* to your brain?Why can’t computers solve Mathematical proofs?