# rate

### The Physics of an Inclined Treadmill

A bad day for your ego is a great day for your soul. -Jillian Michaels One of the most popular exercises at the gym is the treadmill. And why wouldn't it be? Whether you're running or walking, it's a great way to get your heart rate up, get your body moving, and for many people, a great way to burn calories. But however you use a treadmill, there's one extremely simple thing you can do to dramatically intensify your workout: incline it! If you're an outdoor walker/runner, this is the equivalent of going uphill instead of over level ground. There are many physiological differences in walking…

### Is Dark Energy the same as Acceleration?

In a comment on my last post, What is Dark Energy, Kendall asks the following, which is such a good one I think it deserves its own post: I thought the expansion was accelerating? Aren’t you saying that it is on its way down to 85% of its current rate? Sounds like expansion is slowing, but still leaves us with an open universe… People do say the expansion of the Universe is accelerating. But that doesn't mean that the expansion rate is accelerating. It means that if you take a look at any one galaxy that isn't gravitationally bound to us in the Local Group (that is, any big galaxy that isn't…

### What is Dark Energy?

You've all heard these words before. Dark Energy. But what is it, and why are we stuck with it? Let me start by telling you a story. Imagine, for a minute, that you have a candle. You know everything about this candle, including how bright it is and how far away it is from you. Like so: Now if I move this candle twice as far away, I know it's going to be one-fourth as luminous. If I move it three times as far away, I know it's going to appear one-ninth as luminous. And if I move it a thousand times farther away, I know what I see is going to be one-millionth as luminous as the original…

### The Universe is Accelerating?

Sure, there's dark energy, but what does that really mean? First off, there's the bizarre phenomenon we see: very distant objects appear dimmer than we expect in a Universe filled with just matter and space. This supernova (above) should appear much brighter for how distant it is, based on what we know about supernova. This means one of three things are going on: Supernova were intrinsically different when they were younger, and inherently fainter. Some type of dust is blocking the light from distant supernova, making them seem fainter. These supernova are actually farther away than we had…