Could the original size of the Universe be the Planck length

In summary, the conversation discusses the concept of the Planck length and its relationship to the beginning of space and time. It is noted that the Planck length is just a unit of length and our current models of the universe do not have a clear understanding of how space and time began. The idea of the universe being infinite and always having been infinite is also mentioned. It is also clarified that objects that are gravitationally bound are not affected by the expansion of the universe, as they are not expanding rapidly.
  • #1
If you guys haven’t noticed through my posts so far is that I am interested in the Big Bang.

I am considering the concept of the Planck length, but I may have some confusion.

How did Space time start? Did the universe start from nothing and created units of spacetime? Could the original size of the universe be the Planck length? Space and time breaks down the closer you get to the origin, similar to the Planck length.

Anyone have any facts or clarify some confusion?
 
Space news on Phys.org
  • #2
BadgerBadger92 said:
I am considering the concept of the Planck length, but I may have some confusion.
The Planck length is just a unit of length. For various reasons we expect it to be a sensible unit to measure the sizes where some quantum effects become important, but that's all it is.
BadgerBadger92 said:
How did Space time start?
We don't know. Our models break down sometime in the very early universe. We hope thar a future theory of quantum gravity will address this.
BadgerBadger92 said:
Could the original size of the universe be the Planck length?
We currently model the universe as spatially infinite, in which case it was always infinite in size. Just very dense in the past.
BadgerBadger92 said:
Space and time breaks down the closer you get to the origin, similar to the Planck length.
Our models of spacetime almost certainly break down as we get close to the origin of the universe, yes. Don't confuse that with anything actually breaking down.
 
  • #3
Planck length is just the smallest length we could hope to measure..
It's not a physical constant.
 
  • #4
rootone said:
Planck length is just the smallest length we could hope to measure.

We don't know that this is true. It's a common, plausible speculation in quantum gravity, but it's still just a speculation, not an established fact.

rootone said:
It's not a physical constant.

This seems a bit of a quibble since its value is determined completely by the values of other things that are usually considered physical constants (##G##, ##c##, and ##\hbar##).
 
  • Like
Likes rootone
  • #5
There is an assumption that the universe is and always has been infinite. The concept that the entire universe was once very tiny is a common misconception. The observable universe was once very tiny. We have no reason to believe that beyond the visible universe things aren't exactly the same out forever. So while everything that we can see was once very very tiny, we believe that there were an infinite number of those beyond it.
 
  • #6
Aye, "as far the eye can see", this is a reasonable assumption.
 
  • #7
Wouldn't the entire universe have been gravitationally bound at the beginning of the big bang? Intuitively it would make sense for everything to be equally effected by the expansion of the universe, but what I have found that scientists say gravitationally bound objects are not effected by the expansion of the universe. I am not sure if what they mean is that the effect is just not significant or the space is not actually expanding in that part of the universe.
 
  • #8
Justin Hunt said:
Wouldn't the entire universe have been gravitationally bound at the beginning of the big bang?

No, because the universe was expanding so rapidly. Your intuitions about "gravitationally bound" are taking into account the universe's density, but implicitly assuming an object that dense which is at rest. An object that dense which is expanding rapidly is not the same.

Justin Hunt said:
scientists say gravitationally bound objects are not effected by the expansion of the universe

That is because "gravitationally bound objects" here means objects much, much smaller than the universe as a whole--objects like Earth, or the solar system, or our galaxy, or a galaxy cluster. All of these objects are more or less at rest--more precisely, all of their parts are on average at rest relative to each other. They are not expanding rapidly; if they were, they wouldn't be gravitationally bound.
 

1. Could the original size of the Universe be the Planck length?

The answer is currently unknown and is still a subject of ongoing research and debate in the scientific community.

2. What is the Planck length and why is it important?

The Planck length is the smallest possible length scale that has any physical meaning. It is important because it is a fundamental constant in physics and is used to study the behavior of particles at extremely small scales.

3. How does the Planck length relate to the size of the Universe?

The Planck length is significantly smaller than the smallest observable length scale in the Universe, which is the Planck scale. It is thought that the Universe was at this extremely small scale during the earliest stages of its expansion.

4. Are there any theories that suggest the original size of the Universe was the Planck length?

There are some theories, such as loop quantum gravity and string theory, that propose a minimum length scale in the Universe, which could potentially be the Planck length. However, these theories are still in the early stages of development and have yet to be fully tested and proven.

5. How could we potentially determine the original size of the Universe?

Scientists are currently using various methods, such as studying the cosmic microwave background radiation and observing the behavior of particles in the early Universe, to try and determine the original size of the Universe. However, due to the extreme conditions of the early Universe, it is a challenging task and the answer may continue to elude us.

Suggested for: Could the original size of the Universe be the Planck length

Replies
5
Views
1K
Replies
5
Views
1K
Replies
36
Views
4K
Replies
25
Views
1K
Replies
22
Views
1K
Replies
11
Views
1K
Replies
2
Views
1K
Back
Top