How Do We Know The Universe Is ACCELERATING?

The universe is expanding – this we know from looking at red shifts of distant galaxies – but the acceleration of the universe's expansion is harder to measure. It requires measuring the change of recession velocity over time, and it's done by comparing Type Ia supernovas as standard candles at different distances, which is how we know the universe is accelerating!

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REFERENCES

Type Ia supernovae

Luminosity Distance

Straightforward references:
Ryan Foley talking about WFIRST & Dark Energy
Dark Energy FAQ:
Why does dark energy make the universe accelerate?
David Spergel on dark matter & WFIRST

Slightly-technical references:
Permlutter article (old article but quite well explained & goes into future directions near the end)

Technical references:
Mukhanov’s Physical Cosmology
Nobel Prize Summary
Cosmological redshift

And twitter - @minutephysics

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Created by Henry Reich

[KyleLi]

I love how that few second side note at the end of the video did better in explaining dark energy than anything else I've watched.

[thenotflatearth]

Build a wall around the universe to stop expanding

[amirrezafatahi]

this is by far the simplest explanation I have seen for accelerating expansion.
two thumbs up

[kevinfils-aime]

"Although you will probably not be able to fathom it... I will tell you one last thing.. Time will keep on accelerating."

[LazerLord]

That siren was too real for me, lol. I looked around me to see what was happening, only to realize it was in a video.

And I live in the US, where the sirens don't even sounds like that.

[aibohpex]

0:51 I was sitting in the cafeteria with my headphones, looking around for the ambulance driving by like an idiot xD

[smanni]

Great, great video. So many well explained concepts and the illustrations were spot on. Fantastic work man!

[mattroh]

"A galaxy far far away"
Good reference

[fatguyzplaytuff]

Damn you nailed it on this one. Super informative and simplified enough for everyone to understand. I mean right down to the straightforward graphs and explaining standard candles so elegantly, well done. P.s your drawings of supernovae are cool.

[taralewis]

In the past few years I have become absolutely fascinated with all things 'space' (a VERY wide field).. I love watching & learning from your videos..

[settle]

doesn't "dark" mean "I don't fucking know?" in physics?

[SpecialEDy]

Or the speed of light is slowing down, or time is speeding up? If the universe is indeed expanding, time is relatively speeding up as gravity wells move farther away from one another. You get the same effect as accelerated expansion.

[AcerbicMaelin]

I was really puzzled about this idea recently and this explained it really clearly. Thanks Henry!

[Pendoza]

This is such a good video. Little puns, good explanation, clear and fast. Thumbs up!

[tsk]

0:34 A long time ago in a galaxy far far away...

[aniruddhdeshpande]

best video ever! Thank you so much Henry!
I always wondered how do we know that the observable universe is actually accelerating. Thanks for making it clear!

[HartlandOrchard]

so awesome. you can really tell that sooo much went into this. thank you!

[williamluksha]

Hey, so I have a question. (edit: a few actually) When you look at a star, galaxy, or supernova, and see that it is redshifted, how do you know what color it should be? Because like you said in the video, you use the correct color of the object vs. the amount it's redshifted to determine its speed. What if the object is supposed to be that reddish color? For example, if you look at a star and see that it is slightly reddish, how do you know that it isn't just a larger and older star with a different color and distance from Earth than what you were expecting? Would triangulation help in determining its distance, and thus its correct color?

[DKPOWA]

Thank you for all your hard and interesting work!

[laggeryt]

And how do we know what wavelength the light should be? How do we tell a 1a Supernova from another one when it's happening so far away? This video warrants a followup, because it tells us what conclusion we can make if the observed doesn't meet expecations, but not how we get those expectations.