Quantum Gravity and time's arrow

In summary, the conversation discusses an article that talks about two papers utilizing the finding that space-time behaves as if it has two dimensions at small scales. The author questions why time is assumed to be the same in both directions and mentions a book by Brian Greene that posited this idea. The conversation also references Horava's gravity theory, which has been discussed in a physics forum.
  • #1
hatfarm
8
0
So, a couple weeks ago I read this article. I came here, expecting that someone would probably talk about it (I've been viewing posts here for a while, but became a member only recently). No one, that I could find, has actually talked about it, so I though it would be a good first post for me :). Here's the actual http://arstechnica.com/science/news...-everything-by-ditching-tenet-of-physics.ars" to the article which talks about two papers that utilize the recent finding of space-time behaving as if it has two dimensions at small scales. This allows space to be 1 dimension and time is the other. When you do this, space is the same along all paths, but time isn't (I don't know why, and can't read the actual papers).

This got me thinking about what I was thinking when I first read Brian Greene's "The Fabric of the Cosmos," why does anyone assume that time should be the same forward and backward? Have we ever observed it to be so? I will agree that there are times when it is possible to take a small slice of space-time and not be able to tell the difference forward or backward in time. Like watching a fan move, you wouldn't necessarily know which way time was pointing initially. But this isn't true of all of space-time, space is, but it certainly isn't the same when you put time in there. It seems to me like a way of sticking to classical physics where everything is just a bit easier.

I'm no physicist, actually really just getting started in my physics education, and I'm only going to minor in it, so I don't really know how many people assume that time should be the same both ways. That is something that Brian Greene posited in that book though, and it just struck me as odd, since science is supposed to be used to explain observations and I've never heard of anyone observing that. Perhaps I just misunderstood what he was trying to say, but I just had to ask to make sure.
 
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  • #3
Wow, can't believe I missed that... sorry. Thanks!
 

1. What is quantum gravity and how does it relate to time's arrow?

Quantum gravity is a theoretical framework that aims to unify the theories of general relativity and quantum mechanics. It attempts to describe the gravitational force at a microscopic level, where quantum effects become significant. Time's arrow refers to the asymmetry of time, where time only moves in one direction and does not flow backward. Quantum gravity attempts to explain this arrow of time and how it emerges from the fundamental laws of physics.

2. What is the current state of research on quantum gravity and time's arrow?

Quantum gravity is still a highly active area of research, and there is no complete theory that successfully unifies general relativity and quantum mechanics. Many different approaches have been proposed, such as loop quantum gravity, string theory, and causal dynamical triangulation. Some of these theories also address the issue of time's arrow, but there is no consensus on which approach is the correct one.

3. Can quantum gravity explain why time only moves forward?

There is no definitive answer to this question as quantum gravity is still a developing field. Some theories, such as loop quantum gravity, suggest that the arrow of time may arise from the discrete nature of spacetime at a microscopic level. However, more research and evidence are needed to fully understand the connection between quantum gravity and time's arrow.

4. Are there any experimental tests for quantum gravity and time's arrow?

As quantum gravity is a theoretical framework, there are currently no experimental tests that can directly confirm or refute its predictions. However, scientists are conducting experiments that could indirectly provide evidence for certain aspects of quantum gravity, such as the behavior of gravity at extremely small scales. Additionally, observations of the cosmic microwave background radiation may provide insights into the early universe when quantum gravity effects were significant.

5. How does the concept of time in quantum gravity differ from classical physics?

In classical physics, time is considered to be absolute and universal, meaning that it is the same for all observers. However, in quantum gravity, time is thought to be an emergent concept, and its behavior may vary depending on the scale and context. Additionally, quantum mechanics introduces the idea of superposition, where particles can exist in multiple states simultaneously, which challenges our traditional understanding of cause and effect and the flow of time.

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