The edge of the observable universe is actually about 46 billion light years away. I hope that doesn't hopelessly confuse things...scopehead said:I've never understood this: we measure the edge of the observable universe to be around 13 billion LY away, so we are seeing the state of things 13 billion years ago.
The CMB was emitted about 13.7 billion years ago. The matter that emitted the CMB we see was only about 42 million light years away at the time. Today, that matter is about 46 billion light years away.scopehead said:I've never understood this: we measure the edge of the observable universe to be around 13 billion LY away, so we are seeing the state of things 13 billion years ago. But 13 billion years ago, wasn't the universe much, much smaller? Did distant quasars and galaxies look like they do "now" so soon after the Big Bang?
Simple analogies would be very helpful for me here...
That farthest galaxy is seen as it was 13.1 billion years (i.e. Giga-years, or Gy) ago. It is not 13.1 billion light years (Gly) away in any sense. It was at around 3 Gly distant when it emitted that light we observe now, but due to the continuous expansion of space in the path of the light, two things happened:scopehead said:Ok, so I'm looking at an image of the furthest known galaxy, 13.1 billion LY away. So a few hundred million years after the Big Bang, our universe was at least 13.1 billion LY in radius? Probably even much bigger, right? If that's the case, it all makes sense. My mistake was in assuming the universe was still very small. I guess I didn't realize just how huge inflation was. Thanks again.
Usually when they say something is X light years away, they're using light travel time as the distance measure. So when something is 6 billion light years away, they really mean it took 6 billion years for the light to reach us. Usually other distance measures are denoted in units of either parsecs or centimeters (yes, centimeters for measuring intergalactic distances are a thing, though parsecs are more common).scopehead said:Great explanation. Thank you. But I wonder why, in all the popular media, they say that objects are x light years away, as in the example of "the furthest known galaxy?" Seems like most people are as misinformed as I am (was), even the quasi-scientific writers. But I guess that's another thread.
Sorry to resurrect an old thread, but this line of discussion has me wondering, how do you apply the concept of "now" to something 30 billion light-years away?Bandersnatch said:That farthest galaxy is seen as it was 13.1 billion years (i.e. Giga-years, or Gy) ago. It is not 13.1 billion light years (Gly) away in any sense. It was at around 3 Gly distant when it emitted that light we observe now, but due to the continuous expansion of space in the path of the light, two things happened:
- it took much longer than just 3 billion years for the light to get to us (there was more and more distance to cover as the universe grew), i.e. 13.1 Gy
- by the time the light emitted 13.1 Gy ago finally got to us, the galaxy has been carried away by the expansion, and is now at about 30 Gly.
sandy stone said:Sorry to resurrect an old thread, but this line of discussion has me wondering, how do you apply the concept of "now" to something 30 billion light-years away?
Typically what's done is to divide the universe into equal-time slices. One way of creating such a slice is saying that it comprises all points that see the CMB at a specific temperature. For example, we observe the CMB as 2.725K, so "now" on a galaxy 30 billion light years away would be the time where it also observes the CMB at 2.725K.sandy stone said:Sorry to resurrect an old thread, but this line of discussion has me wondering, how do you apply the concept of "now" to something 30 billion light-years away?
OK, that's pretty cool, thanks. (And thank you, PJ)Chalnoth said:Typically what's done is to divide the universe into equal-time slices. One way of creating such a slice is saying that it comprises all points that see the CMB at a specific temperature. For example, we observe the CMB as 2.725K, so "now" on a galaxy 30 billion light years away would be the time where it also observes the CMB at 2.725K.
The "size vs. age" paradox refers to the observation that certain species of animals or plants appear to grow larger as they age, while others do not. This paradox has been studied in biology and evolutionary theory for many years.
This paradox is considered significant because it challenges our understanding of how organisms grow and develop. It also raises questions about the mechanisms and evolutionary advantages of size increase with age.
Some examples of species that exhibit the "size vs. age" paradox include sea turtles, elephants, and trees. These organisms continue to grow in size as they age, even after reaching reproductive maturity.
No, the paradox is not observed in all species. In some species, growth stops or slows down significantly after reaching reproductive maturity. This is known as indeterminate growth.
There are several proposed explanations for this paradox, including the accumulation of resources over time, trade-offs between growth and reproduction, and selective pressure for larger size in older individuals. However, more research is needed to fully understand this phenomenon.