Our first “Ask a Scientist" feature is all about the ever-growing universe.
1) The universe is ever expanding. Nothing can expand within nothing. So what is it expanding into? (from Michel Sastre, Canada)
2) Where does the universe get the energy to expand and what kind of energy is it? (from Mario C Elia, United States)
3) Does the universe have a true up and down and left and right? (from Andrea DiTommaso, United States)
I can certainly understand why such questions are being asked! Because it is really strange that cosmologists talk about an expanding universe, a “stretching" of space, a Big Bang that started it all, and the like.
The confusion starts due to the strange fact that we are inside the universe. It's hard to step out of the box when the box is all there is. From our everyday perspective, when we see something expanding, we immediately also see what's expanding into. An inflating balloon grows outwards into the space surrounding it.
We can easily picture this because we are seeing things from the outside. We see the balloon and its surface stretching outwards as air is pumped into it. This is the privileged observer's view, one where we have a detached and complete grasp of what's going on, a view “from the outside." It is very hard for us to get over this balloon-expanding image, no less because we use it all the time to explain the expansion of the universe! But the universe is no balloon.
Current measurements from European Space Agency's Planck satellite indicate that the universe has a flat (or nearly flat) geometry. For cosmology, a flat geometry means that rays of light actually travel on a straight line across space. (In a curved geometry, the rays would trace a curved path, like when you run your finger over the meridian of a globe.) A flat geometry means that the universe is probably infinite. If you'd move on a straight line, you'd never come back to where you started. (In a spherical geometry, if you move along the equator or any meridian you'd get back to your starting point.)
Even more questions
And here come the questions. How can something infinitely large be expanding? The usual follow-up question (inspired by the expanding balloon image) is, “expanding into what?" The straight answer is that the universe doesn't expand into anything. There is no space “out there" for it to expand into. What the cosmic expansion does is stretch space itself, as if space were made of some kind of stretchy rubber material. There is no physical border out there, only stretching space. I know, pretty weird. Let's work this out.
To picture this, we need to build a “view from the inside," as human observers inside the cosmos. Here is one way: Imagine a checkerboard. A checkerboard is a two-dimensional space: you can move in two directions, up-down, left-right. Real space is three-dimensional, as we can also move vertically up and down. But picturing spaces in 2D is much easier for us, so the checkerboard will do. Now imagine you put a penny at each vertex of the checkerboard—the point where two lines meet. The checkerboard is our flat universe (imagine that it extends to infinity in all directions), and the coins are galaxies. Of course, the real universe is not this orderly, but the idea is the same.
If the universe were static—that is, not expanding or contracting—the coins (galaxies) would just sit on the vertices. In an expanding checkerboard universe, the squares would stretch and grow equally in both directions and the coins would be carried along, like corks floating on a river. Here comes the “view from inside": If you were a creature sitting in one coin (galaxy), you'd see all your neighbors move away from you and would conclude that your galaxy is at the center of the expansion. But that's an illusion. Every observer in every coin would see the exact same thing, its neighbors moving away. No coin (or point in the geometry) is more important than any other point. The universe has no center. When it comes to the cosmic expansion, there is perfect space democracy. It's incorrect to picture the expansion as a bomb that exploded far in the past, with the galaxies being the debris of the explosion.
Back to the real universe, every point is a center of the expansion, and potential observers there would measure their neighbors moving away, carried by the stretching geometry. This is what the cosmic expansion means. In 1929, American astronomer Edwin Hubble measured the expansion and showed that it obeys a very simple law, where the galaxies move away from one another with velocities that grow in proportion to their distances. So, a galaxy that is twice as far away from us than a closer one moves away (or recedes) twice as fast.
We can't know for sure
There is one important point to consider. Even though the universe may very well be infinite, we can't really know for sure. All we can do is measure the geometry of the universe that we can see. By “seeing," I mean gathering information from objects that are very far away. Since the universe has a finite age of about 13.8 billion years (since the Big Bang), light could only have traveled a finite distance since then. That distance is about 47 billion light-years. (It would be 13.8 billion light-years if the universe weren't expanding. But because it is, light gets a “lift" and is carried away farther in the 13.8 billion years it had to travel.)
In other words, we are trapped in a bubble of information, called the “particle horizon." The universe probably continues beyond that—since it's probably infinite, but, like a fish within a fishbowl, we can only see a portion of it, our bubble of information.
Finally, the engine behind the expansion. That would require another whole essay. But let me just say that when you squeeze matter to very high pressures and temperatures, it doesn't like it. Just as hot steam is made of water molecules colliding and moving away from one another at high speeds, hot matter particles also move at high speeds. They don't like to be trapped in a small volume.
Now, since the universe has been expanding for 13.8 billion years, it was much smaller in the past. In the very distant past, it was much smaller, hotter, and denser: a very unstable initial state of hot particles balled up in a small volume. We don't yet know all the details of this initial state, but we do know that there was a lot of pent-up energy there, waiting to be released. In a sense, what we call the Big Bang is precisely this fast release of this pent-up energy in this initial state.
The wonderful thing about it is that when you add all kinds of energy contribution in the universe at any time, you can easily get zero! Why? Because the energy of gravitational attraction, the ruler of all things cosmic, counts as being negative.
As theoretical physicist and cosmologist Alan Guth said, the universe is the ultimate free lunch. What kinds of matter filled up this initial state we still don't know. But we do have the vague contours of the whole picture, enough for us to tell our modern cosmic story.
Once a week.
Subscribe to our weekly newsletter.
Evolution doesn't clean up after itself very well.
- An evolutionary biologist got people swapping ideas about our lingering vestigia.
- Basically, this is the stuff that served some evolutionary purpose at some point, but now is kind of, well, extra.
- Here are the six traits that inaugurated the fun.
The plica semilunaris<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NjgwMS9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTY3NDg5NTg1NX0.kdBYMvaEzvCiJjcLEPgnjII_KVtT9RMEwJFuXB68D8Q/img.png?width=980" id="59914" width="429" height="350" data-rm-shortcode-id="b11e4be64c5e1f58bf4417d8548bedc7" data-rm-shortcode-name="rebelmouse-image" />
The human eye in alarming detail. Image source: Henry Gray / Wikimedia commons<p>At the inner corner of our eyes, closest to the nasal ridge, is that little pink thing, which is probably what most of us call it, called the caruncula. Next to it is the plica semilunairs, and it's what's left of a third eyelid that used to — ready for this? — blink horizontally. It's supposed to have offered protection for our eyes, and some birds, reptiles, and fish have such a thing.</p>
Palmaris longus<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NjgwNy9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzMzQ1NjUwMn0.dVor41tO_NeLkGY9Tx46SwqhSVaA8HZQmQAp532xLxA/img.jpg?width=980" id="879be" width="1920" height="2560" data-rm-shortcode-id="4089a32ea9fbb1a0281db14332583ccd" data-rm-shortcode-name="rebelmouse-image" />
Palmaris longus muscle. Image source: Wikimedia commons<p> We don't have much need these days, at least most of us, to navigate from tree branch to tree branch. Still, about 86 percent of us still have the wrist muscle that used to help us do it. To see if you have it, place the back of you hand on a flat surface and touch your thumb to your pinkie. If you have a muscle that becomes visible in your wrist, that's the palmaris longus. If you don't, consider yourself more evolved (just joking).</p>
Darwin's tubercle<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NjgxMi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0ODUyNjA1MX0.8RuU-OSRf92wQpaPPJtvFreOVvicEwn39_jnbegiUOk/img.jpg?width=980" id="687a0" width="819" height="1072" data-rm-shortcode-id="ff5edf0a698e0681d11efde1d7872958" data-rm-shortcode-name="rebelmouse-image" />
Darwin's tubercle. Image source: Wikimedia commons<p> Yes, maybe the shell of you ear does feel like a dried apricot. Maybe not. But there's a ridge in that swirly structure that's a muscle which allowed us, at one point, to move our ears in the direction of interesting sounds. These days, we just turn our heads, but there it is.</p>
Goosebumps<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NzMxNC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNzEyNTc2Nn0.aVMa5fsKgiabW5vkr7BOvm2pmNKbLJF_50bwvd4aRo4/img.jpg?width=980" id="d8420" width="1440" height="960" data-rm-shortcode-id="8827e55511c8c3aed8c36d21b6541dbd" data-rm-shortcode-name="rebelmouse-image" />
Goosebumps. Photo credit: Tyler Olson via Shutterstock<p>It's not entirely clear what purpose made goosebumps worth retaining evolutionarily, but there are two circumstances in which they appear: fear and cold. For fear, they may have been a way of making body hair stand up so we'd appear larger to predators, much the way a cat's tail puffs up — numerous creatures exaggerate their size when threatened. In the cold, they may have trapped additional heat for warmth.</p>
Tailbone<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NzMxNi9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY3MzQwMjc3N30.nBGAfc_O9sgyK_lOUo_MHzP1vK-9kJpohLlj9ax1P8s/img.jpg?width=980" id="9a2f6" width="1440" height="1440" data-rm-shortcode-id="4fe28368d2ed6a91a4c928d4254cc02a" data-rm-shortcode-name="rebelmouse-image" />
Image source: Decade3d-anatomy online via Shutterstock<p>Way back, we had tails that probably helped us balance upright, and was useful moving through trees. We still have the stump of one when we're embryos, from 4–6 weeks, and then the body mostly dissolves it during Weeks 6–8. What's left is the coccyx.</p>
The palmar grasp reflex<img class="rm-lazyloadable-image rm-shortcode" type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA5NzMyMC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNjY0MDY5NX0.OSwReKLmNZkbAS12-AvRaxgCM7zyukjQUaG4vmhxTtM/img.jpg?width=980" id="8804c" width="1440" height="960" data-rm-shortcode-id="67542ee1c5a85807b0a7e63399e44575" data-rm-shortcode-name="rebelmouse-image" />
Palmar reflex activated! Photo credit: Raul Luna on Flickr<p> You've probably seen how non-human primate babies grab onto their parents' hands to be carried around. We used to do this, too. So still, if you touch your finger to a baby's palm, or if you touch the sole of their foot, the palmar grasp reflex will cause the hand or foot to try and close around your finger.</p>
Other people's suggestions<p>Amir's followers dove right in, offering both cool and questionable additions to her list. </p>
Fangs?<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Lower mouth plate behind your teeth. Some have protruding bone under the skin which is a throw back to large fangs. Almost like an upsidedown Sabre Tooth.</p>— neil crud (@neilcrud66) <a href="https://twitter.com/neilcrud66/status/1085606005000601600?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Hiccups<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Sure: <a href="https://t.co/DjMZB1XidG">https://t.co/DjMZB1XidG</a></p>— Stephen Roughley (@SteBobRoughley) <a href="https://twitter.com/SteBobRoughley/status/1085529239556968448?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Hypnic jerk as you fall asleep<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">What about when you “jump” just as you’re drifting off to sleep, I heard that was a reflex to prevent falling from heights.</p>— Bann face (@thebanns) <a href="https://twitter.com/thebanns/status/1085554171879788545?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script> <p> This thing, often called the "alpha jerk" as you drop into alpha sleep, is properly called the hypnic jerk,. It may actually be a carryover from our arboreal days. The <a href="https://www.livescience.com/39225-why-people-twitch-falling-asleep.html" target="_blank" data-vivaldi-spatnav-clickable="1">hypothesis</a> is that you suddenly jerk awake to avoid falling out of your tree.</p>
Nails screeching on a blackboard response?<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Everyone hate the sound of fingernails on a blackboard. It's _speculated_ that this is a vestigial wiring in our head, because the sound is similar to the shrill warning call of a chimp. <a href="https://t.co/ReyZBy6XNN">https://t.co/ReyZBy6XNN</a></p>— Pet Rock (@eclogiter) <a href="https://twitter.com/eclogiter/status/1085587006258888706?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Ear hair<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Ok what is Hair in the ears for? I think cuz as we get older it filters out the BS.</p>— Sarah21 (@mimix3) <a href="https://twitter.com/mimix3/status/1085684393593561088?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Nervous laughter<blockquote class="twitter-tweet" data-lang="en"><p lang="en" dir="ltr">You may be onto something. Tooth-bearing with the jaw clenched is generally recognized as a signal of submission or non-threatening in primates. Involuntary smiling or laughing in tense situations might have signaled that you weren’t a threat.</p>— Jager Tusk (@JagerTusk) <a href="https://twitter.com/JagerTusk/status/1085316201104912384?ref_src=twsrc%5Etfw">January 15, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Um, yipes.<blockquote class="twitter-tweet" data-conversation="none" data-lang="en"><p lang="en" dir="ltr">Sometimes it feels like my big toe should be on the side of my foot, was that ever a thing?</p>— B033? K@($ (@whimbrel17) <a href="https://twitter.com/whimbrel17/status/1085559016011563009?ref_src=twsrc%5Etfw">January 16, 2019</a></blockquote> <script async src="https://platform.twitter.com/widgets.js" charset="utf-8"></script>
Research has shown how important empathy is to relationships, but there are limits to its power.
- Empathy is a useful tool that allows humans (and other species) to connect and form mutually beneficial bonds, but knowing how and when to be empathic is just as important as having empathy.
- Filmmaker Danfung Dennis, Bill Nye, and actor Alan Alda discuss the science of empathy and the ways that the ability can be cultivated and practiced to affect meaningful change, both on a personal and community level.
- But empathy is not a cure all. Paul Bloom explains the psychological differences between empathy and compassion, and how the former can "get in the way" of some of life's crucial relationships.
Ultimately, this is a fight between a giant reptile and a giant primate.
The 2021 film “Godzilla vs. Kong" pits the two most iconic movie monsters of all time against each other. And fans are now picking sides.