# Shape of the Universe: Flat or Curved?

• moonman
In summary, gravity is not an attractive force but rather a result of the curvature of space caused by massive objects. This is similar to how marbles resting on a flat rubber sheet create local dimples while the overall sheet remains flat. While GR claims that gravity needs curves, observations of cosmic microwave background hot spots suggest that the universe is flat. This can be explained by the small-scale curvature caused by massive objects in an otherwise flat universe.
moonman
I'm not overly familiar with GR, but I have heard that gravity is basically a result of the curvature of space. Its not an attractive force so much as its a consequence of traveling on a curved surface. But I've also read that observing cosmic microwave background hot spots leads to a flat universe. So can the universe be flat, if GR claims gravity needs curves?

moonman said:
Its not an attractive force so much as its a consequence of traveling on a curved surface.

Tomato, tomawto.

But I've also read that observing cosmic microwave background hot spots leads to a flat universe. So can the universe be flat, if GR claims gravity needs curves?

I think this was covered by someone else in another thread recently, but the basic idea is that massive objects are like little "dimples" in spacetime, despite its overall flatness. Imagine a large, flat rubber sheet with a few marbles resting on the surface. The marbles make an impression locally, but the overall sheet is flat. In the real world, the small-scale curvature due to gravitationally bound objects can be demonstrated with phenomena like gravitational lensing.

## 1. What is the shape of the universe?

The shape of the universe is a topic of ongoing research and debate among scientists. According to current scientific understanding, the universe is most likely flat, meaning that it has a Euclidean geometry and infinite extent.

## 2. How do scientists determine the shape of the universe?

Scientists determine the shape of the universe by studying the cosmic microwave background radiation, which is an afterglow of the Big Bang. By analyzing the fluctuations in this radiation, scientists can measure the curvature of space and determine if it is flat or curved.

## 3. What does it mean for the universe to be flat?

A flat universe means that the universe has a constant density and no overall curvature. This also means that parallel lines will never intersect and that the angles of a triangle will always add up to 180 degrees, just like in Euclidean geometry.

## 4. What evidence supports a flat universe?

There are several lines of evidence that support a flat universe. One is the measurements of the cosmic microwave background radiation, which indicate a flat geometry. Another is the observations of distant supernovae, which suggest that the expansion of the universe is accelerating, a characteristic of a flat universe. Additionally, the distribution of galaxies in the universe is consistent with a flat geometry.

## 5. Is there any evidence for a curved universe?

While the majority of scientific evidence points towards a flat universe, there are some theories and observations that suggest a curved universe. For example, some theories propose a hyperbolic or saddle-shaped universe. Additionally, there have been observations of anomalies in the cosmic microwave background radiation that could potentially be explained by a curved universe.

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