<story><title>Four years on, new experiment sees no sign of ‘cosmic dawn’</title><url>https://www.quantamagazine.org/in-new-experiment-astronomers-see-no-sign-of-cosmic-dawn-20220228/</url></story><parent_chain><item><author>deanCommie</author><text>For any physicists reading, I have a question about the Big Bang: Is the standard consensus that the specific physical description is literal or just the closest approximation&amp;#x2F;visual model we have that matches the data?&lt;p&gt;I ask because I was in my 30s before I learned that Dark Matter and Dark Energy are effectively metaphors. There is something that contributes more gravity in the universe than our understanding of the it predicts. And there is something that contributes energy to accelerating the expansion of the universe, and we have no idea what. So we call them &amp;quot;matter&amp;quot; and &amp;quot;energy&amp;quot; but TECHNICALLY they don&amp;#x27;t have to be right? It could also be that something exists that is completely beyond our bounds of understanding.&lt;p&gt;I ask because this feels very much the situation with the Big Bang. Even if all the data shows the universe rapidly expanding in fractions of a second, it is incomprehensible to understand where the energy for it came from, or what happened &amp;quot;before&amp;quot;. And the answer &amp;quot;nothing happened before because that&amp;#x27;s when time started&amp;quot; feels like an acknowledgement of the limitations of our human understanding.&lt;p&gt;So here&amp;#x27;s my follow-up question: Obviously we build an understanding of the universe based on observations of the data. And sometimes the data doesn&amp;#x27;t match and we have to upgrade Newtonian Physics to Einsteinian, or introduce Quantum Mechanics, etc. So are there comparable&amp;#x2F;equivalent investigations&amp;#x2F;experiments going on today that reveal numbers&amp;#x2F;observations that are basically fundamentally unexplainable without looking beyond the realms of our understanding of the limitations of our universe?</text></item></parent_chain><comment><author>lisper</author><text>IANAP but I&amp;#x27;ve done a lot of reading about this.&lt;p&gt;&amp;gt; &amp;quot;nothing happened before because that&amp;#x27;s when time started&amp;quot; feels like an acknowledgement of the limitations of our human understanding.&lt;p&gt;&amp;quot;Nothing happened&amp;quot; is not the correct answer.  The correct answer is that we don&amp;#x27;t know what happened because before you get to the big bang, our current theories of physics stop working.  If you run the equations of general relativity backwards from current conditions you get to a singularity and at that point you can&amp;#x27;t go back any further.  That singularity is called the &amp;quot;big bang&amp;quot;.  But we know that this is (almost certainly) &lt;i&gt;not&lt;/i&gt; an accurate model of what actually happened because we know that GR is (almost certainly) just an approximation of some as-yet-undiscovered theory of quantum gravity, just as Newtonian mechanics is an approximation of GR (in the case of weak gravitational fields).&lt;p&gt;&amp;gt; So here&amp;#x27;s my follow-up question: Obviously we build an understanding of the universe based on observations of the data. And sometimes the data doesn&amp;#x27;t match and we have to upgrade Newtonian Physics to Einsteinian, or introduce Quantum Mechanics, etc. So are there comparable&amp;#x2F;equivalent investigations&amp;#x2F;experiments going on today that reveal numbers&amp;#x2F;observations that are basically fundamentally unexplainable without looking beyond the realms of our understanding of the limitations of our universe?&lt;p&gt;They&amp;#x27;re trying.  The big problem is that all of the low-lying experimental and theoretical fruit has been picked, and doing experiments that will actually advance fundamental physics (i.e. whose outcomes cannot be predicted accurately by GR and QFT) is fantastically difficult.  The math turns out to be really hairy too.  No one has been able to figure out out to quantize gravity so that GR and QFT can be combined into a single theory, let alone propose an experiment that could test such a theory.  It&amp;#x27;s a major problem, almost at the level of a crisis.  Fundamental physics essentially has made no progress since the standard model was finished 50 years ago.</text></comment>
<story><title>Four years on, new experiment sees no sign of ‘cosmic dawn’</title><url>https://www.quantamagazine.org/in-new-experiment-astronomers-see-no-sign-of-cosmic-dawn-20220228/</url></story><parent_chain><item><author>deanCommie</author><text>For any physicists reading, I have a question about the Big Bang: Is the standard consensus that the specific physical description is literal or just the closest approximation&amp;#x2F;visual model we have that matches the data?&lt;p&gt;I ask because I was in my 30s before I learned that Dark Matter and Dark Energy are effectively metaphors. There is something that contributes more gravity in the universe than our understanding of the it predicts. And there is something that contributes energy to accelerating the expansion of the universe, and we have no idea what. So we call them &amp;quot;matter&amp;quot; and &amp;quot;energy&amp;quot; but TECHNICALLY they don&amp;#x27;t have to be right? It could also be that something exists that is completely beyond our bounds of understanding.&lt;p&gt;I ask because this feels very much the situation with the Big Bang. Even if all the data shows the universe rapidly expanding in fractions of a second, it is incomprehensible to understand where the energy for it came from, or what happened &amp;quot;before&amp;quot;. And the answer &amp;quot;nothing happened before because that&amp;#x27;s when time started&amp;quot; feels like an acknowledgement of the limitations of our human understanding.&lt;p&gt;So here&amp;#x27;s my follow-up question: Obviously we build an understanding of the universe based on observations of the data. And sometimes the data doesn&amp;#x27;t match and we have to upgrade Newtonian Physics to Einsteinian, or introduce Quantum Mechanics, etc. So are there comparable&amp;#x2F;equivalent investigations&amp;#x2F;experiments going on today that reveal numbers&amp;#x2F;observations that are basically fundamentally unexplainable without looking beyond the realms of our understanding of the limitations of our universe?</text></item></parent_chain><comment><author>simonh</author><text>The idea that the universe rapidly expanded in a fraction of a second right at the beginning is called inflation theory, it&amp;#x27;s a supplemental modification of the big bang theory and not all physicists that accept the big bang theory also accept inflation theory. There are also some theories that try to explain what there might have been &amp;#x27;before&amp;#x27; the big bang, conformal cyclic cosmology for example. Then there&amp;#x27;s zero energy universe hypothesis, which suggests the universe may have arisen from a random quantum fluctuation - though a fluctuation of what is unclear.&lt;p&gt;So there are quite a few alternative variations on big bang theories. The observation that the universe is expanding seems solid, and the detection of the cosmic microwave background means something must have happened long ago that blasted out all that energy, seemingly everywhere at once. When you go beyond those though things start to get less certain.</text></comment>